Hemp Growing

Restriction digestion of the target region-specific PCR product from lines 1, 2, 5 and 11 revealed that lines 1 and 5 were fully resistant to BsrI digestion, whereas line 11 showed partial digestion. However, line 2 showed complete digestion of the PCR product, similar to the wild type . Sequencing analysis of the target region PCR product from T0 lines 1, 2, 5 and 11 revealed the presence of different kinds of mutations in each line. Line 1 had a 1-nt deletion and line 2 had a 3-nt deletion; the 3-nt deletion in line 2 regenerated the BsrI restriction site, resulting in BsrI digestion of the PCR product in this line. In addition, these lines showed a single peak in the Sanger sequencing chromatogram, suggesting that they represent homozygous mutants for the CCD8Cas9 locus . However, lines 5 and 11 showed multiple peaks in the sequencing chromatogram, suggesting that they are either biallelic or chimeric mutants . Purified non-digested CCD8Cas9 target regionPCR fragments from lines 5 and 11 were cloned into a TA cloning vector. Sanger sequence analysis revealed that lines 5 and 11 are biallelic and contain four types of mutations: a 6-, 5- or 4-nt deletion, or an A insertion. Interestingly, in line 5, both alleles lost the BsrI restriction site whereas in line 11, one of the alleles restored the BsrI cut site after Cas9-mediated editing of the target . T0 transgenic tomato lines were grown to maturity and self-pollinated to generate T1 progeny. T1 progeny from lines 1, 2, 5 and 11 were designated with a small letter next to the line number . Genomic DNA was extracted from the T1 progeny and the target region of CCD8Cas9 was amplified using PCR primers fanking the target.

When this analysis was performed on T1 lines, results were similar to those with the T0 lines: lines 2a and 2b were completely digested, vertical racking indicating that the BsrI site was preserved; however, lines 1a, 1b, 5a, 5b, 5c and 11a gave PCR fragments that were resistant to BsrI digestion, indicating that the CRISPR-generated mutations in these lines were inherited from the T0 lines . Sanger sequencing of the non-BsrI-cut fragments showed deletion mutations of various lengths upstream of the PAM sequence, similar to T0. Lines 1a and 1b each contained the same 1-nt deletion and lines 2a and 2b each had the same 3-nt deletion. Moreover, biallelic mutations were detected in lines 5a, 5b, a 4-nt deletion was observed in line 5c, and a 6-nt deletion was found in line 11a . At least 15 plants from each of the T1 lines were examined for genotype at the target site using Sanger sequencing of target-site PCR products. All T1 plants from two T0 homozygous lines were homozygous for the same mutations. In contrast, the biallelic T0 lines of the Cas9-generated mutants were segregated in the T1 generation according to classic Mendelian genetics, and the ratios between the two mutations in a biallele were close to 1:2:1 as reported previously. The existence of the same mutations in sibling progeny suggested that the CRISPR mutation event occurred prior to meiosis in T0. Inheritance of the mutations in homozygous and biallelic T0 plants by T1 plants suggested that most, if not all, of the mutations resulting from genome editing activity are highly stable in nature and can be inherited in subsequent generations. Moreover, examination of transgenic region in some of the T1 generation plants suggest that 35% of line 2 and 25% of line 5, T1 plants were detected to be transgene free . The results indicated that CCD8Cas9 targeted mutations inherited to next generation in transgene free plants. The putative of-target sites associated with CCD8sgRNA were evaluated by CRISPR-P program using the CCD8sgRNA sequence against the tomato genome.

We analyzed three potential of-targets sites with high scores, which occurred in the intergenic and CDS regions of the tomato genome. Two plants from each line were selected from the T1 generations of CCD8Cas9-edited tomato plants. Sequencing of PCR products from these regions revealed no changes in the putative of-target sites in the CCD8Cas9–mutant lines .Previous studies on SL biosynthesis using rice dwarf mutants have reported that SLs regulate plant growth and morphological architecture. Furthermore, ccd8 a SL-deficient mutant of pea is known to exhibitincrease in shoot branching, lateral roots and overall dwarfing. We also observed similar phenotypic profile in CCD8Cas9 mutated lines such as highly branched shoots, increased lateral roots, decreased shoot heights and reduced fruit sizes as compared to the wild type plants . Although, morphologically, all CCD8Cas9 mutant lines showed highly branched shoots irrespective to the type of mutation but no significant differences were found in the root mass between CCD8Cas9 mutated and control plants . Interestingly, CCD8Cas9 mutated tomato lines produced considerable more number of fruits with reduced sizes as compared to the non-mutated wild-type plants . To analyze whether the CRISPR/Cas9-generated mutations in the CCD8 gene confer resistance to P. aegyptiaca, independent transgenic tomato plants from T1 lines representing the CCD8Cas9 knockout phenotypes, were triggered with P. aegyptiaca seeds. Randomly chosen T1 progeny of each lines, irrespective of their zygosity were transplanted into small pots containing soil infested with P. aegyptiaca seeds and grown for 3 months in a greenhouse. Two separate experiments with four replicates per treatment were conducted. To measure the resistance of the CCD8Cas9 mutated lines, we counted only fresh and viable parasite tubercles which are larger than 2 mm in diameter from each plant. The numbers of attached parasitictubercles and shoots were significantly reduced in the CCD8Cas9 mutated lines relative to the wild-type plants. However, the decrease in P. aegyptiaca in some of the line 11 mutants was less pronounced relative to the wild-type plants than that observed for lines 1, 2 and 5 .The tomato host plant produces different kinds of SLs—mainly orobanchol, didehydroorobanchol isomer 1 and 2, and the aromatic SL solanacols, including the recently identifed orobanchyl acetate, 7-hydroxyorobanchol isomers 1 and 2, and 7-oxoorobanchol. However, Orobanche preferentially utilizes orobanchol as the most active germination stimulant , whereas solanacol and 7-oxoorobanchol are weak stimulants.

To explore the connection between SL biosynthesis in the CCD8Cas9 mutants and their resistance to P. aegyptiaca infection, we analyzed the total orobanchol content in the roots of wild-type and CCD8Cas9 mutated T1 lines by LC–MS/MS. Orobanchol levels were significantly decreased in the CCD8Cas9 mutated lines 1b, 2a, and 11b compared to the wild type, whereas orobanchol was not detectable in lines 1a, 2b, 5a, or 5c . This is consistent with line 5 showing the highest resistance to P. aegyptiaca. In addition, although CCD8 was modified in line 11a, and the plant exhibited the typical dwarfing and shoot-branching phenotypes of reduced SL, its orobanchol content was higher than in the other modified lines. The higher orobanchol content was consistent with its lower resistance to P. aegyptiaca. To assess the higher orobanchol content in line 11a, we analyzed the DNA mutations and resulting amino acid sequences in all CCD8Cas9 mutated lines that were sampled for LC–MS/MS analysis after PCR products ligated to the TA cloning vector . The type of DNA mutation and the amino acid sequence in line 11a demonstrated that only 2 amino acids, His- 243 and Pro-244, were deleted due to Cas9 editing in the target CCD8 gene, while the rest of the coding sequence was similar to the wild-type protein .Carotenoid biosynthetic pathway derivatives all trans β- carotenoid leads to production of SL. Since CCD8 catalyze a key step in SL biosynthesis from carotenoids; hence, we are interested to discover whether CCD8Cas9 mutation affects carotenoid content and its upstream biosynthetic pathway. A simplified scheme of the correlation between carotenoid and SL biosynthesis pathways and furidone target site is illustrated in Fig. 6a. First, rolling benches to explore whether CCD8Cas9 mutation affect the carotenoid content, the content and type of carotenoid present in the root of wild type and CCD8Cas9 mutated lines were analyzed by HPLC method. Interestingly, CCD8Cas9 mutation altered the profile of differenttypes of carotenoids and its derivative, such as total carotenoids, lutein; β-carotene were substantially altered from the wild type . To further gain insight into the above results, we analyzed the expression of prominent gene Phytoene desaturase-1 and Lycopene cyclase 1-β , involved in the carotenoid biosynthetic pathway which acts upstream of CCD8. Results obtained using quantitative real-time PCR demonstrated that expression of PDS1, LCY-β and CCD8 was upregulated in CCD8Cas9 edited T1 lines as compared to the wild type .These results demonstrate that a decrease in SL content in the root of CCD8Cas9 mutants, affect the carotenoid profile by modulating expression of the gene involved in carotenoid pathway.Biotic stresses induced great economic challenges for farming and food production worldwide. Broomrapes that affect the roots of many economically important agriculture crops throughout the semiarid regions of the world especially the Mediterranean and Middle East, are regarded as some of the most serious pests in vegetable and feld crops. Efective means to control parasitic weeds are scarce and lack of novel sources of resistance limits our ability to manage newly developed, more virulent broomrape races. Therefore, an innovative solution to the problem is greatly needed.Recent work utilized the power of CRISPR/Cas9 to engineer the rice plant architecture through genomic editing of OsCCD7 gene, having decreased SL and reduced Striga hermonthica germination. Utilizing similar CRISPR/Cas9 genome-editing strategy, we have developed non-transgenic tomato mutant plants with no “foreign-DNA” that exhibits resistance to P. aegyptiaca. We designed a CCD8sgRNA construct to target the second exon of the tomato CCD8 gene to disrupt SL biosynthesis.

Several independent T0 transgenic tomato lines—1, 2, 5 and 11—were generated, of which lines 1 and 2 were homozygous mutants whereas lines 5 and 11 were biallelic in nature. In general, T0 mutants presented somatic mutations; to avoid this, T0 plants were self-pollinated to generate T1 homozygous plants. In the T1 generation, we found homozygous deletions and insertions in the target gene that were biallelic in the T0 plants without any new mutation detected. T1 lines 1, 2, 5 and 11 were selected for further analysis because of their stable genetic modification. Te different types of mutations observed in the different lines may be due to the differential activity of Cas9, depending on the transgene insertion site, as shown previously in tomato. In addition, Sanger sequencing of potential of-target sites with mismatches of less than 4nt with CCD8sgRNA did not identify any mutations. Te CRISPR/ Cas9 system has emerged as a powerful gene-editing tool and has been successful in more than 20 crop species to date. The heritability of the mutated genes and the generation of transgene-free plants are of major concern when using the CRISPR/Cas9 system. To follow heritability, the gene PDS1 was used to demonstrate the inheritance of mutations induced in Solanum lycopersicum. Tose authors showed that the CRISPR/Cas9 can efficiently induce heritable mutations in tomato plants from the T0 to T2 generation, and that homozygous and biallelic mutants are generated, in the first generation. In our study, we also showed that the CCD8Cas9 mutations induced in T0 lines are inherited by the T1 generation. Previous reports on the morphology of tomato SlCCD8 knock down plants by gene silencing have shown an increase in shoot branching, altered lateral adventitious root growth and decrease in plant height. Similarly another studies on SL bio-synthetic gene SlCCD7, demonstrates the SlCCD7 anti-sense tomato lines also display increased branching, reduced SL content and significantly decreased germination rate of O. ramosa, however no changes in carotenoid content in the roots were observed. Our results were partially consistent with the previous studies, we observed similar phenomenon in the CCD8Cas9 tomato plants. Mutated-plants displayed a dwarf phenotype, an increased number of shoot branches, and an increased number of adventitious roots compared to the wild-type plants. In contrast to the previous report, here we discovered that CCD8Cas9 mutants have altered carotenoid content and differential expression of genes involved in carotenoid bio-synthetic pathway. An explanation for the contradictory results could be due to the differences between mechanisms of siRNA and CRISPR/ Cas9 systems. We hypothesize that absence of CCD8 gene followed by mutation in tomato plants using CRISPR system, will not restore feedback regulation. However, a small percentage of functional CCD8 gene that could escape gene-silencing system will provide feedback regulation and restore the carotenoid level upstream in the carotenoid pathway.

Recombination was only detected in O. rufipogon, so the longest nonrecombining blocks were only utilized in the comparisons including O. rufipogon. Each comparison was run in M-mode with wide value cutoffs for all parameters to determine where posterior probability distributions ranged. After the initial run, three runs were conducted with different random number seeds and smaller cutoff values that were based on the distribution of parameter values from the first run.All runs had 100,000,000 MCMC steps after a burn-in of 100,000 steps. Each run had 10 chains with a mixing rate of five chain swaps per step. All three M-mode outputs were checked for convergence and L-mode runs were conducted on the tree files to test nested models. The maximum likelihood estimates were scaled into demographic values based on a mutation rate of 1 × 10−8 and a generation time of one year, as done with previous work, based on. All IMa runs were computed on the Condor cluster at Clemson University using primarily an extensive web-enabled system to simultaneously manage and monitor performances of each set of input priors. Use of a cluster allowed for more than 28 simultaneous runs, where priors could be checked and adjusted as needed.The goal of these phenotypic analyses was to elucidate genotype-phenotype relationships between California Oryza cultivar and weedy rice ecotypes. Thus, we determined the most influential phenotypic footprints of rapid divergence in domestic and wild-like traits of rice and its conspecific weed within the California floristic province. To characterize trait variability and by extension morphological relationships among domesticated and weedy rice ecotypesin infested fields, grow rack we quantified phenotypic diversity by first describing the variance partitioning of weedy populations and comparing the adaptive traits which characterized weedy rice to those that defined cultivars.

To more accurately characterize dimensionality in weedy or feral rice morphology, a subset of unique gourmet varieties were added to the medium-grain cultivars in the rice dataset for the phenotypic diversity analyses. Qualitative descriptors were transformed using the PRINQUAL procedure of SAS with the OPSCORE option for optimal scoring and MONOTONE option for monotonic preservation of order. Principal Components Analysis with maximum total variance was performed on the combined quantitative and transformed qualitative descriptors. The variables describing cultivars were reduced by eliminating any that did not vary by descriptive statistics and then using both random and a priori sampling to preserve group partitioning while identifying the eigenvectors which most clearly separated groups. UPGMA hierarchical clustering using the CLUSTER procedure of SAS was performed to confirm separation of clusters on PCs and to generate a dendrogram using average Euclidean distances.Average estimates of genetic differentiation between weedy rice in California rice fields are very low, ranging from 0 to 0.0026 . There are no significant differences in FST estimates for any of the 48 loci. The highest FST estimate was 0.077, betweenCRR1 and CRR4 at STS085. These low values indicate no population structure and no divergence of weedy rice in the fields sampled, which supports the appropriateness of a genetic diversity assessment for California weedy rice . Measures of genetic diversity for California weedy rice within each field as well as for weedy rice within all fields combined are also very low , consistent with a recent founder event, or strong population bottleneck.

These values are a full order of magnitude lower than what was calculated for strawhull and blackhull weedy rice ecotypes collected from the southern US. Due to the lack of population substructure and low genetic diversity, we placed all California weedy rice into one group for the remaining analyses. Values for average population differentiation estimates across all 48 loci indicate high divergence between California weedy rice and all other sampled groups. The lowest mean value is with O. rufipogon collected from Southeast Asia . Taking the median values across the 48 loci allows better understanding of the patterns across all loci. The lowest divergence was between California SHA weedy rice and BHA and SH; median ФST values indicated that for at least half of the loci tested divergence was an order of magnitude lower than the mean estimates . This indicates that the mean ФST is high due to divergence at a few loci, and that California weedy rice does share some similarity to weedy rice from the southern US at several loci. The most recent divergence of California weedy rice from other Oryzasis from California rice cultivars , which was estimated at about 118 generations ago . The other divergence estimates were over an order of magnitude older . Interestingly, both SH and BHA weedy rice from the southern US have very old divergence estimates: approximately 30,000 and 17,000 , respectively. These numbers are likely inflated compared to the reported origin of domesticated rice approximately 10,000 generations ago due to interactions among other closely related genotypes. This follows work examining model testing performance of IMa under several scenarios,which showed that divergence estimates inflate when gene flow from other populations is included in the model. A model of relative divergence times shows a shallow, recent coalescence of California weedy rice and California crop rice alleles, whereas SH and BHA southern US weedy rice and Chinese O. rufipogon show a much older divergence from California weedy rice .

Migration estimates between California weedy rice and all other groups were quite low, with higher estimates of migration into California weedy rice in all cases. Indeed, these data should not be interpreted as absolute numbers but instead as relative values. Any overestimation of the generation values could otherwise indicate that the divergence actually happened even more recently. The effective population size for California weedy rice is very small in all cases,supporting a recent founder event or bottleneck. California weedy rice has a straw-colored hull with long awns , whereas only 7%of SH weedy rice in the southern US has awns. Nevertheless, California weedy rice shares important weedy traits with those of southern US weedy rice including high seed shattering and a red-colored pericarp in addition to tall stature and high tillering habit.Principal components analysis reduced the set of observed variables for California weedy and cultivated rice by loading them on orthogonal lines of fit based on contributions to variance. No variation was observed amongst weedy and cultivated rice for leaf texture and angle, ligule shape, ligule color, ligule pubescence, auricle color, node color, or panicle secondary branching, so these traits were excluded from the analysis. When multiple traits represented the same metric, we chose the variable with the highest eigenvector value to represent each group or suite of highly correlated traits, although each group member or variable has an impact when describing the underlying mechanism responsible for phenotypic selection differences between the cultivar and weedy rice in California. Importantly, pericarp color clearly distinguishes weedy from cultivated rice in California , but is not highlighted in the dimension-reducing PCA because it was scored as a qualitative trait following International Rice Research Institute descriptor guidelines. The remaining phenotypic traits included vegetative growth habit characters, reproductive morphologies, and yield metrics related to grain morphology. Principal components analysis was conducted on these informative traits, excluding highly correlated variables . A second PCA was performed on a reduced dataset, which included the five traits with highest eigenvector values for each principal component in the initial analysis . Principal Components 1 , 2 , and 3 together account for 45.18% of the total cumulative variance in cultivated and weedy rice in the first PCA . Traits most greatly discriminating California weedy from cultivated rice include panicle type, leaf width ,flowering , awn color, and culm length ; lemma pubescence, texture of the panicle axis, length of the first leaf below the flag leaf, length/width ratio of grain, and width of flag leaf ; 100-grain weight of the field-collected mother plant, awn length of the field-collected and offspring plants, spikelet fertility , and grains per panicle described most of the variation along PC3. Becausewe were interested in the contribution of suites of traits describing each statistically significant orthogonal vector, vertical racks the 15 traits contributing most to variance along the first three PCs in PCA 1 were subjected to a second analysis. In PCA 2 of “key discriminating traits,” principal components 1 , 2 , 3 , and 4 account for 74.91% of the cumulative variance in the phenotype of California weedy rice . Since components or dimensions with an eigenvalue greater than one are statistically relevant to the result , we report four principal components for this second PCA.Traits in Californiaweedy rice plants that mimic both medium-grain and gourmet specialty cultivars include erect leaf angles, cleft ligule shape, culm strength , green node color, panicle exertion , and ligule pubescence .

Crop traits in weedy rice specific to co-occurring medium-grain cultivars include basal leaf sheath color and hull color . Crop traits grouping weedy rice with gourmet specialty varieties include intermediate tillering or spreading growth habit . These crop-like traits are presumably carried by the immediate progenitors of the weedy rice, the crop, and have not been lost by the crop. When shared between weedy and cultivated rice, some of these traits could reinforce weed persistence and adaptation to cultivation by visually disguising the weed, thus preventing detection.Wild-like traits in California weedy rice traits exhibit high variance and differentiate this nascent feral population from both medium-grain cultivated varieties M-104, M-202, M-204, and M-205 as well as gourmet varieties in several ways. Compared with medium-grain cultivars, California weedy rice has a purple pericarp, long fully developed awns, lower seed set but with more grains per panicle, open panicles with scabrous texture, more tillers and panicles, spreading growth habit, long culm with gold internodes and delayed and extended flowering period . The medium-grain cultivars in California have brown pericarp; short awns, , high seed set, less tillers and panicles than weedy rice, have compact panicles, are less than 100 cm tall, flower earlier than weedy rice, and have erect culms. Distinct clusters within the California weedy rice population can be resolved by a multivariate analysis of variance . UPGMA cluster analysis confirmed morphogroups based on the key partitioned traits identified through PCA . The number of clusters N was given as three for several clustering methods. More clusters could be resolved amongst the weedy rice, but an additional split did not offer more information when co-occurring rice cultivars were included .Weedy rice in California is a newly established and distinct group in the USA. Isolation with migration modeling suggests that California SHA weedy rice diverged from California rice cultivars approximately 118 generations ago. The relatively recent divergence, distinct morphology, and small genetic relatedness with other US weedy rice indicate that this unique population has evolved separately from a cultivated ancestor. The recent origin of California weedy rice suggests that the population has differentiated since the establishment of rice cultivation in California and is in the early stages of segregating weedy traits, such as more tillers, extended flowering, and pigmented pericarp. Across all loci, we find no haplotypes in California cultivated rice that are not present in other japonicas . Further, there are no additional shared polymorphisms between California weedy rice and other japonicas that are not shared between California weedy and California crop rice. California weedy rice either diverged from japonicas outside of the US and was brought in to California after becoming weedy or diverged from California japonica cultivated in California. The former argument that this weed was brought in is highly unlikely due to strict laws in rice seed import into California. Regardless, California weedy rice is distinct from the other US weedy rices and our coalescent IM estimates point to a recent de-domestication from the California japonica line. Indeed, while the generation values may be inflated , this does not necessarily mean that the estimate is greater than it should be. The relative values are indicative of the relatively recent divergence, which was our objective with this analysis. This result does not demonstrate definitively that time since divergence between California cultivated and weedy rice is different from that between BHA and California weedy rice; however, it is clear that California cultivated rice and California weedy rice have different origins, and more importantly, that the divergence of California weedy rice is more recently from cultivated rice in the same area than that from all other Oryza groups investigated.

As required for layer stacks, the imagery was resampled to a single scale using cubic convolution. The increase in pixel size brought the grain of the images and that of the field evaluations of vegetation composition to a similar scale, and one that was appropriate for the degree of geopositional error in our measurements .To develop and test the classification methods examined in this study, we used ground-truth points that represented locations with known geographic coordinates in patches in which vegetation was nearly pure weeds or forage. These points were extracted according to specific criteria from a broader multi-year database of vegetation points that included points collected both randomly and to represent particular vegetation types or features across a large watershed. The measures at each georeferenced point included cover of key vegetation groups within 1-m radius circle, as well as individual species of interest. Cover estimates were made using Daubenmire classes: < 5%, 5.1–25%, 25.1–50%, 50.1–75%, 75.1– 95% and 95.1–100%. To create and ground truth the image classifications for our study area, we selected all data points from our vegetation database that were in our study area and for which the vegetation composition was strongly dominated either by invasive weedy or by annual grass forage species, as represented by Daubenmire cover classes of 5 or 6, or equivalent, with no other species present in substantial amounts. In effect, weed drying rack these “pure” points represent the purest patches of each vegetation group we could locate and thus provide the clearest characterization of vegetation properties. Such dense near-monospecific patches are also important targets of weed control efforts.

We identified 98 such points for the 2008 analysis , and 119 for 2009 . For each year, each set of “pure” points was then stratified by ranch property and half of the points within each of the three properties were randomly assigned to a single combined training data point set to support initial vegetation classification, or to a similar test set for later evaluation of classification effectiveness. This stratified approach ensured that training and test ground truth sets shared similar geographic distributions.The success of phenological-based mapping depends on the identification of phenological differences in the spectral properties of target vegetation groups. This study was motivated by field observations indicating that the invasive weedy grass species generally remain green a little longer than the forage grasses at the end of the growing season ,although this window of difference can be very short. To characterize and differentiate the weedy grasses’ phenological signature, we compared NDVI values from the imagery at locations of known weed and forage patches in peak spring and at the end of the season in both study years. To test whether the signal from weed-dominated vegetation was distinct, we used repeated measures MANOVA with NDVI values in March and May as the time-repeated response variables with between-subject factors of year, vegetation type, property, and year x vegetation type and within-subject factors of month, month x year, month x vegetation type, month x property, and month x year x vegetation type. In the primary analysis, we compared values using the mid-May image for 2009 , which was most similar to the date of image acquisition in May 2008. However, because weed senescence may occur quickly in May, we also evaluated how NDVI values differed between two dates in May 2009 . Finally, in addition to considering the March and May NDVI characteristics of the vegetation types, we also considered the March—May NDVI differences.

After characterizing the phenological signature of weed-dominated vegetation, the next step was to determine whether a phenological-based approach could perform consistently enough over time to serve as a reliable tool for multi-year detection of weed persistence, expansion or contraction. Our first questions centered on the choice of imagery inputs. Could a single NDVI image provide enough classification power? If so, which month for image acquisition would be best: March , when vegetation is most likely to be green? Or May , when weed-dominated patches are most visible to a field observer? Alternatively, would using two images improve classification accuracy enough to merit the extra costs and processing time? If so, was it most effective to stack the two images and evaluate the two-layer set simultaneously as two bands of a single image? Or rather was it more effective to create a difference image that would highlight the phenological changes in which we were most interested? ΔNDVI contains less information than stacked NDVI , but that information focuses specifically on temporal NDVI changes relevant to a phenology-based analysis. To test these questions, we compared the robustness of classifications that used these four different types of imagery inputs, all used after conversion to NDVI-analogues: March NDVI alone ; May NDVI alone ; a two-layer stack of March and May NDVI, classified together as two bands of a single image ; and ΔNDVI, a single-band difference image made, as previously described, by subtracting May NDVI from March NDVI . With these four types of inputs, we tested both unsupervised and supervised classification methods to delineate vegetation types. For simplicity, all classifications relied solely on NDVI imagery and ground truth data; none utilized additional information . Throughout, the same mask was used to remove water, trees, roads, and structures from the classification.

To conduct a supervised classification on raster data, the operator must provide the software with information necessary to determine the vegetation type represented by each pixel, often by providing georeferenced “training” sites that exemplify the properties of the target vegetation to be identified. We conducted parallelepiped supervised classifications on all image sets using the training set of weed- and forage-dominated “pure” ground truth points previously described . Iterative testing indicated that the most effective classifications were produced when we used a standard deviation of 2.0 for the weed classes and 1.0 for the forage classes, although a small number of pixels fell outside the standard deviation constraints and were unclassified. We conducted additional supervised classifications in ENVI using maximum likelihood classification, which required at least two image layers per analysis; the maximum likelihood classification was thus conducted only with the two-layer stacked NDVI image inputs . Results were not strongly sensitive to threshold choice; we used 70% for consistency with the unsupervised approach . Unsupervised classification. Unsupervised classification is easier than supervised classification for the operator to initiate, as the computer simply generates the specified number of map classes from imagery inputs using one of several algorithms. However, then the operator must determine which, if any, of the computer-generated map classes best represents the target vegetation type. Here we conducted unsupervised isodata classifications in ENVI 4.7 on all image sets. Each classification was run for 40 iterations with a pixel change threshold of 2.0% to create 8 classes, as previously determined in iterative tests to be effective. After the unsupervised classifications were produced, rolling bench we assigned vegetation types to the computer generated map classes by comparing the distribution of the classes to the same training set of “pure” ground truth points used to produce the supervised classifications. A map class was designated as weed-dominated if at least 70% of the “pure” ground truth points falling within its extent were weed-dominated points. All other classes were designated “Non-Weeds,” which included both forage-dominated pixels and heterogeneous weed-forage mixes. In a few cases, unsupervised classification produced a map class that did not contain any ground-truth points, in which case that class was assigned the identity of the majority class surrounding it. Metrics for comparison of classification accuracies. To quantify classification accuracy, we compared the weed maps produced for each combination of imagery and classification approach with the “test” or “validation” set of ground-truth data points that were distinct from the training points used to produce the classification. Following the classic methods of Congalton, we used an error matrix to calculate four metrics, based on the distribution of weed and non-weed class pixels and ground truth points: Overall accuracy and the Kappa statistic describe the general accuracy of a classification. Overall accuracy is the percentage of test points for which map classes and field data agree, across all map classes. The Kappa statistic adjusts overall accuracy to take into account agreement that might occur solely by chance. It is calculated as: /, where Observed = Overall Accuracy. Expected is calculated as the product matrix divided by the cumulative sum of the product matrix . In the Kappa analysis, we used the Z-test to determine if each classification was better than random at α = 0.05. For the Kappa statistic, values above 0.60 indicate good to excellent agreement between the classification and the ground truth data. Producer’s accuracy measures the percentage of a specific target vegetation on the ground that the map properly describes .

It is calculated as the percentage of ground-truth points correctly identified as the target vegetation out of the total set of ground-truth points for that vegetation type. For example, if there are 100 ground-truth points on the ground that represent weed-dominated vegetation and only 80 of them fall within the map’s weed class, then the producer’s accuracy for the weed class in that map is 80% and the map has missed 20% . User’s accuracy describes the purity of a specific map class. For example, if the map says that a particular area is best classified as weed-dominated, how true is this in the field? What percentage of the vegetation in the field area corresponding to the map class “Weeds” is in fact weed-dominated? User’s accuracy for a target vegetation type is calculated as the percentage of all ground-truth points within the field area corresponding to a map class that correctly match the map class type. For example, if within the field area delineated by the map’s weed-dominated class there are 80 ground-truth points representing weed-dominated vegetation, but also 40 ground-truth points representing vegetation dominated by other species or by vegetation mixes, then the user’s accuracy for weed-dominated cover is 80/ or 66.7%. To identify which mapping approaches were most robust to changing environmental conditions, we calculated the accuracy metrics for each classification method x NDVI image input type combination for each of the two years and the two May dates . For each combination, we then calculated the mean and coefficient of variation of the accuracy metrics that resulted from using imagery inputs from these different dates. In our judgement, the best mapping approach would combine high accuracy with strong consistency , which would support its application in study of cover changes over time.After determining which mapping approach had the greatest and most consistent accuracy, we used this approach to compare weed distributions in 2008 and 2009 across the study site. We evaluated the percentages of the landscape that were dominated by weeds in each year and how much gain or loss of weed-dominated area occurred between years. We then analyzed cover distributions by management unit. The study site included four separate management units that represented a serendipitous pre-existing gradient of grazing intensity from west to east. At the time of imagery acquisition, the westernmost management unit was used for turkey hunting and for more than five years had experienced no grazing, except by an occasional animal that broke through a neighboring fence. A second central management unit on a separate property had likewise been set aside for most of the preceding five years, and had only been grazed briefly on a few occasions by a small number of sheep. In contrast, another unit on that same property had been moderately grazed by sheep and cattle on a regular basis; and the eastern unit had been moderately to intensely grazed for more than 8 years by sheep, cattle, and goats, largely with managed intensive rotational grazing. For M3 and M4, the estimated mean stocking rates were 0.4–1.3 animal units ha-1; short term stocking rates in sub-areas of M4 were higher during rotations. As a case study to evaluate application, we used the most effective mapping approach to compare the extent of weed-dominated cover in the largely ungrazed management units with that in the regularly grazed units . While the units we studied were not established with experimental research in mind and replication was limited, each grazing category spanned similar soils and topography and included management units from two different properties. Moreover, the study site offered an opportunity for realistic application: the management units were large and part of independent working ranches managed for diverse commercial purposes.

When dealing with fast maturing crops, the grower can prevent weeds from dispersing seeds . Since weeds adapt to continuous use of the same tools, implementations of other integrated management plans are crucial .Using more than one management strategy increases the probability of weed control success like implementing a form of physical control like hand weeding integrated with herbicides can control weeds . In the produce industry 42% of total weed control expense is due to labor costs . Organic vegetable farmers are extremely limited in the choice of registered herbicides they can use, making it necessary for growers to explore more options to manage weeds . California passed legislation in 2016 that increased the minimum wage by a $1.00/hr. per year until it reaches $15.00/hr. in 2022 . With this change in place, the agricultural industry will face higher labor costs . Costs associated with hand weeding, in general, are between $300-$700 per hectare, which has continued to increase in prices as much as 64% in the last ten years . Because there are few herbicides for lettuce production, hand weeding labor costs will get even higher . Tillage and cultivation Tillage combined with herbicides can be an effective integrated treatment method . Seedbeds that are firequently cultivated will generally have higher weed populations, leading to more weed outbreaks . When dealing with soil that is cloddy the weeds are protected by the clods of dirt and need to be broken down further when prepping a field for crop seeding . Using a mechanical weed cultivator in a high-density spinach field can cause crop injury, cannabis dryer which is why spinach must be hand-weeded . There are drawbacks when it comes to mechanical cultivation . Studies have shown that even the more advanced weeding machines have a hard time removing weeds close to crop plants . 

Intelligent robotic weeders are another method currently being implemented, but these can be challenging to use in high density crops and wet conditions . Even with more advanced machines available, these robotic weeders are expensive and only the larger growers can adapt to the technology and afford high fixed costs while small growers struggle to invest . Some cultivators can only control small weeds, but it is challenging to take out older, deep-rooted weeds in lettuce production . In conclusion, cultural, physical, and chemical control methods cannot be separated and work best when used together in an integrated pest management plan.Organic agriculture is a sustainable production system that considers long-term effects involving preserving biodiversity, soil health, and the environment. There is a growing demand for organic vegetable crops for consumers who don’t want to be exposed to pesticide residues, especially on food for children . While the demand for organic produce continues to increase, it’s challenging to find effective ways to manage soil pathogens and weeds with few good pest control tools. Some challenges include high weeding costs because there are few organic-compliant herbicides, and effective management of soil pathogens is difficult. Research in weed and pathogen management for organic systems is not a high priority for many researchers and does not receive much attention, especially in production dealing with high yielding produce crops in an ever-growing marketplace . There is constant worry about persistent weed infestations in organic agriculture due to many weed escapes . In organic leafy crop production, there is a couple strategies they can use to control persistent weed infestations, one way to reduce surface seed bank is by deep burial.

This method is called plowing, which involves incorporating weed seeds into the ground, which prevents weed seeds from germinating . Plowing can create a problem because it involves burying weed seeds deep into the soil and will eventually be brought back to the soil surface during future field cultivations, so other organic production methods should be incorporated . The timing and depth of cultivation can have an effect on different weeds in a seedbank . Some weeds depend on light in order to germinate and is why weed seeds can be viable for so many years when buried deep into the soil where they are not exposed to light . Farmers have adapted to increased food production using intensive land cultivation during the green revolution and saw how productive and efficient it was to produce crops . Yet, extensive land cultivation can create more problems if not planned accordingly, so farmers learned how efficient it was to grow crops in rotation after harvest as another strategy to control pathogen inoculum and weed seeds in the soil as a common practice in organic production . Some organic practices that are used in lettuce production in coastal areas of California are crop rotations with mustard family species, into their integrated pest management program to help enhance soil fertility in an area of extreme soil disruption . Rotational crops are planned months before planting, and farmers need to have high returns to offset land and high production costs with greater risk of aphids and diseases in organic production .In spinach production, the most common herbicides used are phenmedipham and cycloate . These herbicides control grasses and broad leaf weeds, but they only control 2 out of 5 important weeds . Phenmedipham canbe used at the three true leaf stage of spinach but often cause crop injury for a short period and is labeled for processed spinach in California .

Therefore, growers need to know their weed seed bank to determine what methods would work best in their weed management plan. For preplant fumigation, which involves applying a product such as Metam sodium before the spinach is planted . However, Metam sodium is not preferred because it is restricted and has a 14-day wait before planting . Cycloate is the main preemergent herbicide used after seeding but before emergence and can also be pre-plant incorporated into the soil . In lettuce production, herbicides like Benefin is also used as a preplant herbicide applied with the help of machine incorporation on the tops of lettuce beds . Using this herbicide comes with precautions because it can persist in the soil for months and can affect rotational crops like spinach, onion, corn, and sugar beets . Incorporating the herbicide too deep can result in poor weed control . Bensulide is an important lettuce preemergence herbicide that controls annual grasses but is weak on pigweed . Pronamide is the most common preemergence herbicide for lettuce organically registered in 1969 . The herbicide does not need to be incorporated into the ground . Kerb provides excellent control of grasses and weeds in the mustard family . In addition, Kerb partially controls goosefoot and purslane in the nightshade family, malva and pigweed does not control weeds in the sunflower family like common sowhistle and common groundsel . Many growers have trouble with Kerb, especially in Yuma, Arizona because it leaches too deep in the soil profile when lettuce is irrigated, causing poor weed control . In addition, Kerb is a possible human carcinogen and has been found in groundwater . In today’s herbicide market, herbicides have been regulated and banned, leaving those that are more than 40 years old and subject to cancellation in the future . Cycloate and Dual Magnum are the only pre-application products in the market that can be used in spinach production, but Dual Magnum is not used much . Lati stated Cycloate controls broadleaf weeds well but can be difficult to control weeds in warm conditions due to increased volatility and loss. Growers continue to use herbicides because it benefits them by reducing the number of weeds in the field. Therefore, it requires less labor to hand weed in leafy crop production. Dual Magnum, an herbicide that was registered in 1977 and has a pre harvest interval timing of 50 days and is too long because spinach can be harvested in as little as 25 days . In addition, Fennimore argues that weeds like purslane can be problematic and thrive under heavily cultivated soils and in Salinas Valley’s Mediterranean climate. When herbicides like Pronamide and Bensulide were introduced in the late 1960s, there was an improvement in control . However, cannabis growing systems growers continue to have problems where reoccurring purslane infestations are persistent . Developing a new herbicide can be very difficult and expensive. The process takes 9 years and involves studying the environmental impacts of the chemical and proper development and rigorous field trials before it can be registered to be used. Sometimes chemicals going through this process do not make it successfully. Other alternatives to control weeds include using biotechnology to make herbicide-tolerant lettuce. Fennimore found that using glyphosate tolerance lettuce could control weeds better than Bensulide and Pronamide. In general, it can becostly to take this type of biotechnology to a commercial scale, but the lettuce industry soundly rejected roundup ready lettuce before it was introduced.Steam application to the soil is a method to disinfest soils by killing pathogens and weed seed in the soil. The concept of heating the soil started in greenhouse flower production dating back to the 1800s and even as far as ancient times .

Steam disinfestation first came into use in the United States in 1893 to treat greenhouse pots and eventually, as technology started evolving, different types of machine steamers were created . For example, mobile steamers come in tractor-towed or self-propelled models. Several different types of steaming techniques have been developed and evaluated in terms of costs and pathogen and weed suppression . The average cost of steaming was $4,883.24 an acre compared to the cost to use chemicals like methyl bromide or 1,3 chloropicrin application that would cost $7,324.86 per acre . Extensive research on the efficacy of steam opened new opportunities for improved steaming techniques in greenhouse production . Steam was used widely in the 1950s and 1960s, but in the 1970s, high fuel costs made steam more expensive than fumigants and so greenhouses switched to fumigants like hot gas methyl bromide . With increased chemical use regulations in greenhouse and field settings and the loss of methyl bromide, growers have renewed interest in steam. Chemical fumigants came into use in the 1960s when farmers soon found fumigants to be a cheaper and more efficient way of killing weeds and soil pests than steam . However today, it is difficult and expensive to use chemical fumigants in California agriculture due to strict regulation. Steam on the other hand, provides an alternative and is not regulated. Many argue steam is a viable alternative to methyl bromide, but better steam application methods and applicators are needed . One concern about using steam disinfestation is overheating the soil, killing beneficial microbes key in soil nitrification . Wherever steam is used, steam needs to reach a temperature of 60-70 °C for 20-30 mins dwell time to control soil pathogens and weeds effectively . Because romaine lettuce and spinach are shallow-rooted crops grown in rows, the depth of steam injection application using a banded steam technique is set to 19 cm or shallower in depth .Studies done by Baker and Van Loenen et al., evaluated the effects of various temperatures and exposure times on soil pathogens by soil type using dry steam. Dry steam is created by generating steam with one pass through the boiler followed by a second pass so that the temperature is higher and there are no water droplets . Baker found that when steaming soil in pots that were dry at a lower temperature, it took longer to reach the appropriate temperature to kill soil pathogens. In contrast, Baker also observed that when potted containers were moist just before steam application and steamed at a higher lethal temperature dose for 30 mins he observed higher kill rates of soil pathogens.Sheet steaming is one of the oldest methods of steam application and is still used in greenhouse production . The downfall of this technique is that the steam process takes 8 hours, and the performance of steam is better in clay soils, according to a study done in Italy by Gay et al. . To heat the deeper layers of the soil takes long to reach the appropriate temperature to kill soil pathogens but gave the best results in steaming the top 15 cm of the soil . Sandy soils were the most challenging soil type to steam with this method .

The effect of depth on 1,3,-D concentration was most evident in water seals and bare soil plots. HDPE and VIF plots had more uniform distribution of the fumigant through the soil profile than the water seals plots, especially 48 hours after treatment. However, 1,3-D concentration under the VIF tarp was markedly higher than in all other treatments, which suggests that there could also be differences in the top 5 centimeters of soil. These results imply that the use of a highly impermeable tarp can lead to a more uniform distribution of fumigants in the soil profile and may allow satisfactory pest control with reduced application rates . Soilborne pest control. Pest control data from the 2007 KAC emissions trial and a related 2008 emissions trial were reported previously and are not shown here. In general, however, there were few differences in pest control attributed to the fumigant application shanks used in the trial. Pythium species populations were lower in all treatments than in the untreated control, but no statistical differences were noted in Fusarium species populations among treatments. The high 1,3-D rates and well-prepared soils resulted in complete control of citrus nematodes in the bioassay bags in all treatments and depths. Weed populations were variable among treatments but tended to be lowest in methyl bromide plots and 1,3-D plots sealed with VIF and highest in the water seals and dual 1,3-D application Treatments.Nematodes and soilborne pathogens. All treatments of 1,3-D or methyl bromide effectively controlled citrus nematodes in bio-assay bags buried at 12-, 24- and 36-inch depths in each plot. However, these results, ebb and flow system which were obtained in well-prepared sandy soils with low pest and pathogen populations, may not apply to more challenging field conditions .

Applications of 1,3-D sealed with HDPE or VIF and dual application 1,3-D treatments reduced Fusarium and Pythium species propagules in the soil compared with the untreated plots . These treatments were comparable to methyl bromide in controlling Fusarium and Pythium species. Soil pathogen control with 1,3-D followed by metam sodium and 1,3-D with intermittent water seals was inconsistent between the two experiments, which suggests that specific micro- and macro-level differences in environmental and field conditions may contribute to greater treatment variability and risk to growers. Weed density. When 1,3-D was sealed with HDPE and VIF, broad leaf weed density was reduced to less than 6 weeds per square meter, which was comparable to methyl bromide . These results are similar to a previous nursery study that indicated 1,3-D or 1,3-D plus chloropicrin sealed with HDPE or VIF resulted in weed seed viability and hand-weeding time comparable to methyl bromide . Generally, intermittent water seals after a 1,3-D application resulted in broad leaf weed density similar to the untreated control. Most weeds germinate near the soil surface, thus techniques such as intermittent water seals that limit upward fumigant movement into surface soils can adversely affect weed control. The other surface treatments 1,3-D dual application and 1,3-D followed by metam sodium had intermediate broad leaf weed densities compared to untreated plots and methyl bromide. All fumigation treatments reduced grass weed populations compared to the control plots; however, the greatest reductions were observed in plots treated with methyl bromide, 1,3-D sealed with HDPE or VIF, and 1,3-D followed by metam sodium. It was clear in this study that effective surface treatments can greatly increase weed control with 1,3-D; however, even the best treatments will likely require supplemental weed control to meet grower expectations. Stock vigor and performance. Effects of surface seal treatments and 1,3-D soil fumigation on nursery stock vigor and performance in two nursery trials were evaluated in 2007 to 2010 . In the rose nursery trial, all treatments had similar rootstock vigor and number of marketable plants except when 1,3-D was followed by metam sodium.

During the 2008 growing season, roses grown in plots treated with 1,3-D followed by metam sodium had lower vigor than the other treatments; however, by harvest at the end of the second year, no differences in marketable plants were observed. In the tree nursery trial, tree rootstock vigor was reduced in plots treated with 1,3-D followed by metam sodium and1,3-D with intermittent water seals compared with the other fumigation treatments, but rootstock caliper at the end of the first growing season did not differ among treatments.Compared with some other fumigation-dependent industries, perennial fruit and nut nursery stock production systems face a more difficult transition to methyl bromide alternatives . Despite several years of research, the following significant challenges to widespread adoption of alternatives in the perennial crop nursery industry remain: National and international market expectations for nematode-firee nursery stock limit nursery stock producers to alternatives with very high nematode efficacy at significant depths in the soil. To meet California nursery certification requirements, producers are required to use approved fumigant treatments or conduct a post production inspection. A failed inspection may result in an essentially nonsalable crop. Most alternative treatment schedules are based on the use of 1,3-D , a fumigant that faces its own serious and evolving regulatory issues in California. No currently available alternative fumigant can be used in California to meet certification requirements in nurseries with fine-textured soil at registered rates. Methyl iodide, the alternative fumigant with performance most similar to methyl bromide, is not currently registered in the United States due to a voluntary withdrawal by the manufacturer. Concerns over control of weeds and fungal and bacterial pathogens in the short and long term may further limit adoption of alternatives with a narrower pest control spectrum. Containerized nursery stock production systems are being used in some parts of the industry, but the production costs, market acceptance and long-term viability of this system have not been addressed at the required scale. Adoption of methyl bromide alternatives, where they exist, in the perennial crop nursery industry will ultimately be driven by state and federal regulations and economics. Although it’s heavily regulated, 1,3-D is a viable alternative for growers with coarse-textured soil, but if 1,3-D becomes more difficult to use due to shortages or increasingly stringent regulations, it may be only a short-term solution. No viable fumigant alternatives exist for California nurseries with fine-textured soil, and some of them may be unable to produce certified nursery stock in the absence of methyl bromide. The cost of producing perennial nursery stock using more expensive, laborious or economically risky production methods will ultimately be passed on to customers and could have long-term impacts on the nursery, orchard, vineyard and ornamental industries.Weedy plants can be tolerant of herbicides due to a variety of temporal, spatial, or physiological mechanisms. For instance, a weed may avoid control efforts if it emerges after a burn down herbicide is applied or completes its lifecycle before a postemergence herbicide is applied. Similarly, large-seeded or perennial weeds can emerge from deeper in the soil and may avoid germinating in soil treated with a preemergenceherbicide. Other weedy species have physiological mechanisms of tolerance and avoid control through reduced herbicide uptake or translocation, rapid detoxification, or insensitive target sites. Regardless of the mechanism of tolerance, repeated use of an herbicide can lead to weed shifts in which weed populations become dominated by species that are not affected by the weed control measures used. A classic example of a weed shift in response to herbicides is the change from primarily broad leaf weeds to grass weeds in cereal production after the introduction of the broad leaf herbicide 2,4-D. Weed shifts can also occur following overuse of non-chemical weed control techniques, such as flame weeding or mowing, flood and drain hydroponics that tend to favor populations of grass weeds.Herbicide resistance in weeds is an evolutionary process and is due in large part to selection with repeated use of the same herbicide or products with the same mode of action. Herbicides do not cause resistance; instead, they select for naturally occurring resistance traits. On a population level, organisms occasionally have slight natural mutations in their genetics; some of these are lethal to the individual, some are beneficial, and some are neutral. Occasionally, one of these chance mutations affects the target site of an herbicide such that the herbicide does not affect the new bio-type. Similarly, mutations can affect other plant processes in a way that reduces the plant’s exposure to the herbicide due to reduced uptake or translocation or through more rapid detoxification.

Whatever the cause, under continued selection pressure with the herbicide, resistant plants are not controlled and their progeny can build up in the population . Depending on the initial firequency of the resistance gene in the population, the reproductive ability of the weed, and the competition, it may take several generations until the resistance problem becomes apparent.Two general types of mechanisms confer resistance to herbicides in weeds. Some mechanisms are related to the specific site of action of the herbicide in the plant, and others involve processes not related to the mechanism by which herbicides kill plants; these two types are known as target-site and non-target-site mechanisms, respectively. A certain weed bio-type may be resistant to more than one herbicide. Herbicide cross-resistance occurs when an individual plant is resistant to two different herbicides via the same mechanism of resistance. In this case, resistance is endowed by a single physiological process operating in common for all the herbicides involved. Multiple resistance results from selection by the simultaneous or sequential use of different herbicides, such that resistance to each herbicide is endowed by a different mechanism.Herbicides usually affect plants by disrupting the activity of a specific protein that plays a key role in plant biochemical process. Target-site resistance occurs when the target enzyme becomes less sensitive or insensitive to the herbicide. The loss of sensitivity is usually associated with a mutation in the gene coding for the protein and can lead to conformational changes in the protein’s structure. These physical changes can impair the ability of one or more herbicides to attach to the specific binding site on the enzyme, thus reducing or eliminating herbicidal activity. Although changes in protein structure occasionally result in reduced biological functionality of the enzyme and a related “fitness cost” , many target-site mutations do not have an observable fitness cost. Certain herbicide groups are particularly vulnerable to developing target-site resistance, because resistance can be endowed by several mutations, thus increasing the probability of finding resistant mutants in weed populations— even in those not previously exposed to that herbicide group. For example, specific mutations resulting in seven different amino acid substitutions in the acetolactate synthase gene are known to confer resistance to ALS-inhibiting herbicides in weed bio-types selected under field conditions. Something similar occurs with the grass herbicides that inhibit the enzyme acetyl coenzyme A carboxylase . In these cases, at least five point mutations are associated with cross-resistance patterns. These can be observed at the whole plant level and involve four classes of ACCase-inhibiting herbicides. The existence of so many mutations conferring resistance is the reason that resistance to these herbicides is firequently found and can evolve rapidly. Several mechanisms confer resistance to herbicides without involving the active site of the herbicide in the plant. Of these, the best known is the case of metabolic resistance due to an enhanced ability to metabolically degrade the herbicide. Non-target-site herbicide resistance has been well demonstrated for several gene families associated with cytochrome P450 monoxidases, glutathione transferases, and glycosyltransferases. Most of these non-target site resistance mechanisms are also present in cultivated plants and are the reason that many herbicides can be used selectively without injuring crops. Non-target-site resistance can evolve from the intensive use of diverse and unrelated selective herbicides that are similarly effective on a certain weed species and share a detoxification pathway or a mechanism precluding their accumulation at the target site that is relatively common in plants. The management of non-targetsite herbicide resistance often represents a greater challenge than management of target-site resistance, because a simple change in herbicide mode of action may not alleviate the problem. Reduced herbicide absorption or translocation can contribute to resistance in certain bio-types. These have generally been accessory mechanisms that contribute toward resistance in addition to major resistance mechanisms. However, recent evidence suggests that changes in absorption or translocation contribute importantly to glyphosate resistance in several weed bio-types.

If growers are to adopt alternative irrigation systems, understanding potential shifts in weed species’ composition will be critical to weed management. It is well documented that weed community composition can affect yields. The critical period of watergrass competition for rice in California is the first 30 d after planting, and yields can be reduced by as much as 59% when watergrass is uncontrolled . However, critical periods of competition for other weed species are not known, and differences in composition between early- and late-season weed communities and the impacts of late-season competition on rice yields remain to be seen. Using two alternative irrigation systems adapted for California rice, the primary objectives of this research were: to determine weed community composition in rice under different irrigation systems; to determine whether there are differences between early and late weed communities within a system; and to quantify differences in yields between irrigation systems in both the presence and absence of weed competition.Field preparation was standard for the California rice growing region and consisted of chiseling twice, followed by disking twice, to prepare a level seedbed . In the water-seeded alternate wet and dry and water-seeded control conditions, fertilizer was banded in by drill in strips before seeding. Fertilizer applications in the drill-seeded alternate wet and dry treatment were broadcast approximately 1 mo after planting . In all years, ebb flow tray nitrogen was applied at a rate of 171 kg ha−1 . Drilled nitrogen was applied as urea , and broadcast N was applied as ammonium sulfate .

Phosphorous was applied as triple superphosphate at a rate of 86 kg ha−1 in 2012 and at a rate of 45 kg ha−1 in 2013 and 2014. Potassium was applied as potassium chloride at a rate of 25 kg ha−1 in 2013 and 2014 only. The WS-AWD and WS-Control fields were broadcast seeded onto dry soil at a seeding rate of 168 kg ha−1 . The DS-AWD field was seeded to a depth of 2 cm at a rate of 112 kg ha−1 into dry soil. Rice seed for all treatments was pretreated with a 1 h soak in 2.5% NaClO solution to prevent infection with Bakanae disease [Gibberella fujikuroi Wollenw.]. Plots in all irrigation treatments across all years were seeded with M-206, a Calrose medium-grain rice variety widely grown in the region. The three main plot irrigation treatments were the DS-AWD, WS-AWD, and WS-Control. The DS-AWD treatment was initially flush irrigated for rice emergence and then flush irrigated once more when soil volumetric water content reached 35% .Immediately after the N fertilizer application at approximately 1 mo after planting, the DS-AWD was flooded to 10 cm above the soil surface, and water was held at that level to allow for N uptake. The WS-AWD and WS-Control plots were flooded to 10 cm above the soil surface within 24 h of broadcast seeding. The WS-AWD plot remained flooded until canopy closure of the rice, at which point water flowing into the system was shut off, and the standing water was allowed to recede into the soil. Canopy closure of the rice was determined to be when photosynthetic photon flux density reached or fell below 800 μmol m−2 s −1 , which is approximately where subcanopy PPFD stabilized. PPFD was measured every other day using a line quantum sensor at 15.2 cm above the soil surface, which was below the rice canopy.

Canopy closure was determined to be at 47, 49, and 54 d after seeding in 2012, 2013, and 2014, respectively. After being drained at canopy closure, both the WS-AWD and the DS-AWD treatment plots were flush irrigated again when soil VWC reached 35% . The WS-Control plot remained flooded until 1 mo before harvest, when it was drained to allow harvesting equipment onto the field . Soil VWC for irrigation purposes was measured at hourly intervals in each plot using EM5B data loggers and 10HS soil moisture sensors . The 35% VWC was determined using the average of the three replicates for each treatment. Further management details can be found in LaHue et al. .In 2012 there were only minor differences between irrigation systems in the weed counts taken at 20, 40, and 60 DAS. There were no significant differences in population densities of watergrass species, small flower umbrella sedge, and rice field bulrush between irrigation systems across all counts. Our results confirm previous research that showed watergrass plasticity and ability to germinate and emerge under both aerobic and anaerobic soil environments . There were three weed species with differences among irrigation treatments: redstem, ducksalad, and sprangletop. For redstem, there was an interaction between irrigation systems and count timing . Redstem was not present in any system at 20 DAS, but at both 40 and 60 DAS, the redstem density was greater in the WS-AWD than in the other two irrigation systems . Density was greater in the WS-Control system than in the DS-AWD system. The high redstem population in the water-seeded systems is consistent with earlier research showing redstem emergence under water-seeded but not under dry-seeded systems . Ducksalad density was greatest in the WS-Control and WS-AWD systems, irrespective of count timing . Sprangletop density was greatest in the DS-AWD system across all counts , though the difference was only significantly greater than the density in the WS-AWD system. These results are not surprising, since sprangletop emergence is reported to occur only under aerobic conditions in California .

Since it emerged in both the WS-AWD and WS-Control systems, further investigation of the species is warranted to elucidate whether water depth may affect emergence under flooded conditions, allowing the species to emerge under a shallow flood. Both species of sprangletop found in California, bearded sprangletop and Mexican sprangletop [Leptochloa fusca Kunth ssp. uninervia N. Snow], emerged from rice flooded to depths of 5 cm in Valencia, Spain . In Turkey, bearded sprangletop emerges at greater numbers and at a faster rate under flooded conditions than under dry conditions . Differences between weed counts at 20, 40, and 60 DAS indicate that certain species are emerging at different timings throughout the rice-growing season. Redstem did not emerge until 40 DAS across all irrigation systems. Sprangletop emerged by 20 DAS in the DS-AWD system, but did not emerge in the two water-seeded systems until 40 DAS. All other weed species emerged in significant numbers by 20 DAS, and then plant density was reduced by 40 and 60 DAS, presumably through competition for light as the canopy closed . RC and RDW. There were no significant interactions between irrigation system and years for either RC at canopy closure or RDW at harvest for all weed species and rice; therefore, only main effects are presented . RC of small flower umbrella sedge, flood drain tray watergrass species, and ricefield bulrush increased across systems from 2013 to 2014 , though the increase in rice field bulrush was not highly significant . The RC of rice also increased across all systems from 2013 to 2014. This increase may be due to the decrease in RC of ducksalad in 2014, since all other weed species increased in RC in 2014. In water-seeded Arkansas rice, ducksalad decreased yields by about 21% when germinating with rice . The decrease in RC of ducksalad in 2014 may be due to competition with other weed species, particularly watergrass, which had the greatest increase in RC of all weed species. There was a negative correlation between watergrass RC and ducksalad RC in 2013, but the relationship did not hold in 2014 . Thus, it is difficult to say with certainty why ducksalad cover decreased in 2014. Redstem and sprangletop RC were the same across years. At canopy closure the WS-Control and WS-AWD were dominated primarily by ducksalad and watergrass species, but both sedges were also present in small quantities . Sprangletop and redstem were present, but differences between systems were not significant . The only difference in weed composition between the two water-seeded systems at canopy closure was in the small flower umbrella sedge cover, which was significantly greater in the WS-AWD compared with the WS-Control. The weed species composition of the DS-AWD at canopy closure was significantly different from the composition of the water-seeded systems. It was dominated by watergrass species, and the only other species present was sprangletop . RDW of all weed species did not vary across years. There were only two species that were significantly different across irrigation systems: small flower umbrella sedge and watergrass species .

The RDW of small flower umbrella sedge was greatest in the WS-AWD, which was consistent with its RC at canopy closure. Ducksalad was not present at harvest, presumably because it had completed its life cycle and decomposed, although no information on longevity of this species is recorded in the literature. In Arkansas wet-seeded rice, Smith found that ducksalad matured by approximately 8 wk after seeding. In the DS-AWD system at harvest, the RDW of rice was 3% . In comparison, the WS-Control and WS-AWD systems had rice RDW measures of 72 and 77%, respectively. The differences in firequencies of weed species in the DS-AWD and the water-seeded systems corresponded to the differences in RC and RDW . Frequency of small flower umbrella sedge varied between WS-AWD and WSControl . The percentage contribution of small flower umbrella sedge to the dissimilarity between the irrigation systems was the greatest of all weed species at every measurement point, except at canopy closure assessment in 2013. Analysis of the two systems over time showed that although the firequency of small flower umbrella sedge was similar in the WS-AWD and WS-Control at canopy closure in 2013, the firequency of the species was consistently greater in the WS-AWD at all other assessment points . Small flower umbrella sedge cover was greatest in the WS-AWD treatment , and the relativecover of small flower increased in 2014 over 2013 . The relative dry weight of small flower umbrella sedge was greater in the WS-AWD than in the other treatments in both 2013 and 2014. Both the initial germinable seedbank assessment in 2012 and the plant density counts at 20 DAS in 2012 indicate similar germinable populations of small flower umbrella sedge in the WS-Control and WS-AWD irrigation systems. The increased density in the WS-AWD system at 40 and 60 DAS and the increased cover and biomass in both 2013 and 2014 may indicate that the drain at canopy closure affects small flower umbrella sedge germination or competitive ability. Small flower umbrella sedge germination is best under flooded conditions, though it appears to germinate well under saturated soil conditions as well . Preliminary evidence suggests that small flower umbrella sedge has a biphasic emergence pattern , and the relative growth rate of plants emerging under the second germination flush may be greater under the drier conditions of the WS-AWD. The irrigation system was shut off and the water was allowed to recede into the soil beginning at 47 DAS in the WS-AWD system in 2012. In 2013 and 2014 this occurred at 49 DAS and 54 DAS, respectively. Weed density counts were taken 1 wk before the irrigation shutoff in 2012, and weed relative cover ratings were taken 1 d before irrigation shutoff in both 2013 and 2014. Thus, it is possible that the increase in small flower umbrella sedge in the WS-AWD system may be unrelated to the irrigation system and was an artifact of greater population density in 2012. This could be related to the lower ducksalad density in the WS-AWD system that same year. Ducksalad may have a suppressive effect on small flower umbrella sedge, given that it quickly covers the canopy, blocking out light, which small flower umbrella sedge requires for germination . The two weeds had a similar density at the beginning of the experiment but small flower increased as the experiment continued .Rice relative cover increased from 2013 to 2014 over all treatments, yet the increase in 2014 at canopy closure did not correlate with an increase in rice biomass at harvest in 2014. This response confirms earlier research in California that showed competition with late watergrass after the critical period of competition further decreased rice yields . It is significant to note that despite statistically similar initial populations of watergrass species in all fields , rice cover and biomass were lowest in the DS-AWD compared with the water-seeded treatments, either indicating that the watergrass species are more competitive against rice under anaerobic conditions or confirming that rice is less competitive with weeds under anaerobic environments .

Baker highlighted high competitive ability as a characteristic of invasive species, although his focus was on competition through “special means” such as allelopathy and choking growth . In practice, invasive plant species may coexist with and outcompete natives through a variety of mechanisms. Niche differentiation, where species possess different strategies of resource use, may allow for coexistence of native and non-native invasive species . In this case, invasive species are functionally different than the natives, either by possessing novel traits or by using resources in different ways or at different times . For example, in many Mediterranean climate systems, invasive annual species display different phenology and function compared to the largely perennial or woody native communities . Alternatively, invasive species may succeed by possessing highly competitive traits . As an example, functional similarity did not predict competitive outcomes between native species and a focal invader in a California grassland; instead, competitive natives possessed trait values consistent with high rates of below ground resource acquisition and allocation to above ground tissue . Other studies have found that both niche and fitness differences operate within a given community . For example, Fried et al. found that native species with flowering phenology similar to a focal invader were adversely impacted by the presence of the invader . At the same time, native species with larger seeds and higher rates of resource acquisition were more competitive with the invader. As the relative importance of competition mechanisms is likely to change at fine scales across resource gradients , ebb and flood table experiments that manipulate resource availability and directly measure competition outcomes are likely to elucidate the mechanisms by which non-native invasive species can coexist with or competitively exclude native species.

Baker hypothesized that species possessing more ‘ideal weed’ traits would be more invasive: “probably no existing plant has them all; if such a plant should evolve it would be a formidable weed, indeed” . Trade-ofs likely limit the capacity for any species to possess all ‘ideal weed’ traits , but particular trait combinations may act synergistically . Thus, focusing on a single trait or a small handful of traits may not accurately characterize invasiveness; rather, exploring multidimensional functional differences between invasive and non-invasive species may yield greater insight into mechanisms of invasion . Traits may act in non-additive ways, as certain combinations of traits lead to success in particular conditions. For example, species with high rates of resource uptake and poorly defended tissues have the most to gain from enemy escape . Finally, different traits can result in similar fitness highlighting the need to consider multiple traits. For example, prostrate plants with strong lateral spread may shade out native plants just as effectively as tall plants . Thus, a multi-trait approach that accurately characterizes light use would be more meaningful than comparisons of mean height among invasive and non-invasive species. Many researchers have emphasized that traits or suites of traits interact with other processes, such as habitat suitability and socioeconomic factors, to influence invasion. In an effort to identify patterns of species-ecosystem interactions leading to invasion, Kuefer et al. coined the term ‘invasion syndrome’ which Novoa et al. redefined as ‘‘a combination of pathways, alien species traits, and characteristics of the recipient ecosystem which collectively result in predictable dynamics and impacts, and that can be managed effectively using specific policy and management actions’’. This synthetic approach involves an iterative process of identifying similar invasion events and their associated syndromes .

As an example, Novoa et al. point to invasive plant species in high elevation areas, which tend to share a broad environmental tolerance and a similar pathway of introduction along transportation corridors from low and mid elevation areas. Thus, managing for invasive plant species in high elevation areas entails limiting the spread of introduced species along corridors. However, as our review highlights, traits and species interactions within communities are dynamic, so an invasion syndrome approach would have to be flexible, potentially weakening the value of this framework.Phenotypic plasticity, or the ability of a plant to adjust its phenotype in response to environmental variation, was a defining feature of Baker’s ‘ideal weed’ . First, Baker and others hypothesized that plasticity could lead to success in a wide range of novel environments . Consistent with this hypothesis, plasticity is associated with increased species range size . Second, plasticity could lead to high success in certain environments . For example, invaders may be particularly adept at capitalizing on high resource conditions , opening ‘invasion windows’ when resources become abundant that allow for explosive population growth . Third, as we discuss in “Evolutionary considerations” section, plasticity can facilitate rapid evolution. Empirical evidence for the role of plasticity in invasions is mixed, however. While several large multi-species studies or meta-analyses find that invaders are more plastic than natives or non-invasive non-natives , others find that on average invasive and non-invasive species do not differ in plasticity . Interestingly, heightened plasticity is only adaptive and helps maintain fitness in a subset of species and only in response to resource increases; non-invasive plant taxa were better able to maintain fitness homeostasis in low resource conditions .

One possibility for these conflicting empirical observations is that plasticity, like other traits, may only be advantageous during certain invasion stages . A large, phylogenetically-controlled study investigating phenological plasticity in response to warming found that on average invasive species show strong phenological shifts in response to warming, while native species do not . These phenological shifts were strongest for species characterized as invasive and much weaker for non-invasive non-native species, and phenological plasticity was stronger for species that had invaded long ago, suggesting that phenological plasticity may be most important during the spread and impact stages and may increase over time through evolution .Baker and G. Ledyard Stebbins brought together evolutionary biologists and ecologists to consider the problem of invasive species and, in doing so, inserted an evolutionary perspective into the field of invasion biology . Evolutionary studies of invasive species were relatively slow to take of compared to the rapid increase in ecological works following Elton’s seminal work and the SCOPE series that followed several decades later . However, we now recognize that prior adaptation and rapid evolution during or post invasion can allow for establishment and promote the spread of invasive species. Evolutionary history reflects challenges a population has experienced in the past, and overcoming particular challenges may make it more likely for a species to be transported to, establish in, and successfully invade new areas. Post-introduction, rapid evolutionary responses to novel aspects of the invaded environment may be necessary for the invasive species to establish and spread. Because a population’s evolutionary history determines its traits, incorporating evolution into invasion biology may help explain why certain bio-geographic regions produce so many invasive species . Using quantitative genetics approaches that link traits to fitness may help inform which traits promote success in particular environments. Such studies could help explain the context dependency so firequently observed in ecological studies linking traits to invasions. Interestingly, only a few of Baker’s traits have been well investigated from an evolutionary perspective . One study explicitly focusing on Baker’s ‘ideal weed’ traits found evidence for genetic variation in traits related to competitive ability and seed production, indicating that such traits have the potential to evolve pre- or post-introduction, but growth rate exhibited little genetic variation . Furthermore, grow racks these traits were often genetically correlated, although not always in the same direction across the two populations studied, suggesting that genetic constraints may sometimes limit and other times accelerate the evolution of ‘ideal weed’ traits.The idea that evolutionary history determines invasion success has a long, but relatively sparse, history going back to at least Darwin’s seminal works.

Much of this work has investigated Darwin’s Naturalization Hypothesis which proposes that species lacking close relatives in the community are more likely to invade . This hypothesis assumes that because close relatives are likely to be functionally similar, competition may strongly limit closely related invaders compared to more distantly related invaders . The counter argument is that closely related species may have similar environmental tolerances and species interactions leading to increased likelihood of invasion by close relatives in the introduced range . Support for these competing hypotheses is decidedly mixed, but Ma et al. suggest that this may result from different processes acting across scales and invasion stages . For example, Darwin’s Naturalization Hypothesis specifically invoked competition, which occurs at very local scales. In contrast, the Pre-Adaptation Hypothesis more likely applies to the climatic factors more prevalent at regional scales. Across invasion stages, Darwin’s Naturalization Hypothesis most likely applies to the species interactions that come into play at later invasion stages post-establishment , while the Pre-Adaptation Hypothesis is more likely to pertain to the filtering processes that occur earlier in invasion . Darwin’s Naturalization Hypothesis and the Pre-Adaptation Hypothesis are both less focused on a general role for specific traits and more on the match between traits and the invaded environment. More recently, Fridley and Sax proposed the Evolutionary Imbalance Hypothesis, predicting that species from richer biotas with more stable environments and larger habitat sizes are more likely to be ecologically optimized with better solutions to ecological challenges. Essentially, these biogeographic regions have had a larger number of ‘evolutionary experiments.’ Because ecological conditions repeat across the world, better solutions in the native range are likely to lead to better solutions elsewhere too. In support of this hypothesis, phylogenetic diversity in the native range predicts invasiveness . While this hypothesis does not focus on particular traits underlying this success, it does point to a strong role for traits promoting competitive ability, like allelopathy and other mechanisms highlighted by Baker, and suggests that the traits that have evolved in the native range determine success in the invaded range. Evolutionary responses to human-modifed environments also have the potential to promote invasion. The Anthropogenically Induced Adaptation to Invade hypothesis posits that prior adaptation to human-disturbed environments in the native range facilitates invasion into similarly disturbed environments across the globe because human-disturbed environments share many similarities regardless of location . Adaptation to disturbed environments will also lead to increased abundance in areas firequented by humans, potentially contributing to increased dispersal. In this way, adaptation to disturbed environments increases the likelihood of transport and the probability of establishment once transported . While this hypothesis does not strongly focus on specific traits, instead generally focusing on adaptation to a particular environment, many traits highlighted by Baker are also thought to be adaptive in disturbed environments, including rapid growth rates, a propensity for selfng or vegetative reproduction, and high and continuous seed production. While challenging to definitively test, three types of evidence support the hypothesis. First, European taxa associated with human altered environments are much more likely to invade other continents than taxa found only in natural habitats, although it is less clear whether this advantage results from adaptation to those disturbed environments, from species sorting , or from increased likelihood of transport given their abundance in human-visited habitats . Second, in animal systems, association with human-altered habitats appears to allow for expansion of the climatic niche in the invaded range, suggesting that adaptation to human-disturbance may facilitate invasion and range expansion . Finally, laboratory studies suggest that pre-adaptation to novel environments rivals the effects of propagule pressure on introduction success . While the Anthropogenically Induced Adaptation to Invade hypothesis focuses more on adaptation to cultivated habitats, invasive species are also adapting to urban environments. This urban adaptation could lead to further trait-matching and colonization of geographically distant but environmentally similar habitats, particularly given the high abundance of invasives in cities and the high likelihood of human transport . Interestingly, some traits favored by urban environmental conditions may further facilitate invasiveness in other areas ; for example, the reduced pollinator abundance in urban ecosystem is predicted to select for increased selfing and clonality , two traits characterizing Baker’s ‘ideal weed’. However, urban conditions also have the potential to select for traits that inhibit invasion. For example, increased fragmentation in city landscapes can select for reduced dispersal that is likely to reduce the spread of invasive species at larger spatial scales .Over the past three decades, increasing evidence suggests that many invaders rapidly adapt to the novel environments they encounter post-introduction .

These standards have less meaning with the production of a new crop type, and thus create uncertainty and potential for conflict between tenants, landlords, and end-users seeking control over the production process. Landowners may want to ensure the crops or the producers’ cultural practices will not cause long term harm to the land, creating another moral hazard problem and requiring landowners to increase control or monitor producer behavior. One possible solution could be the establishment of bonding requirements for remediation, similar to those imposed on biomass plantings in Florida larger than two acres. Bonding provisions could be incorporated into both the rental lease and the biomass production contract.If producers, in spite of these concerns, are able to secure leases for an extended length of time, they remain highly exposed to termination or default by the landlord; if the landlord defaults, the producer remains bound to a biomass production contract without sufficient land upon which to grow the crops. On the other hand, if a producer desires to exit the biomass industry, or becomes unable to continue production for any reason, he faces the risk of being locked into an undesirable long term lease. Likewise, landowners, due to high asset specificity and the nascent character of the bio-energy industry, face a relatively higher risk of default by both tenants and end-users. The issues discussed above illustrate the importance of specifically considering land tenure within the biomass supply contract and linking the provisions to specially tailored farmland leases for biomass production. Moreover, biomass supply contract duration should align with crop life cycles, which should align with land lease terms.Access to land, 4×8 flood tray while the most important consideration in negotiating biomass supply contracts, is not the only issue warranting attention.

Control of germplasm, whether conventionally bred or through advanced genetic engineering technologies, is an essential element of intellectual property rights protection. Contractual agreements embedded within intellectual property licenses can impose restrictions on the grower. Many of these restrictions currently used in the agrobiotech industry go far beyond mere protection of intellectual property rights and dictate specific agronomic practices of the farmer. The use of germplasm contracts could be structured to specify inputs , farming and harvesting practices , post-harvest disposition , and post-contract actions . From the producer’s perspective, growers may wish to expand their own production by harvesting rhizomes from their fields. This practice especially is likely in the early stages of industry maturity when rhizomes or specialized seeds may be hard to procure. Biomass supply contracts, therefore, should specifically address intellectual property rights in germplasm and ensure compatibility with germplasm agreements. A second ancillary issue relates to the positive externalities derived from certain agronomic practices associated with perennial biomass cultivation. Planting Miscanthus or other bio-energy crops may control erosion, improve water quality, sequester carbon, and increase wildlife habitat. In the future, ecosystem service markets may reward these practices. Accordingly, the biomass supply contract and, if applicable, the farmland lease should specify which party may participate, and thus receive the benefits, in ecosystem service markets.The duration of the biomass production contract has serious consequences for producers, but will likely be driven from the end-user’s perspective. This is because end-users must secure a stable biomass supply for the duration of the investment cycle of the conversion facility, likely at least 20 years. 

Offering contracts for less than the optimal investment cycle creates supply risk for the end-user and potential holdup issues. Longterm contracts are somewhat less critical for producers, as dedicated energy crops can be destroyed and the land returned to traditional cropping methods with comparatively lower cost. Nonetheless, in electing to produce perennial crops, producers also make long-term commitments by establishing a crop with a production cycle that could reach 15 years. Moreover, producers may wish to renew contracts, particularly if the life cycle of the established crop outlasts the initial contract term. To address these concerns, contract length should correspond with crop life-cycle to ensure producers can recover establishment costs and obtain adequate return on investment. Shorter durations, due to asset specificity, give rise to holdup risks. In situations in which the life-cycle of the crop outlasts the duration of the contract, the producer can reduce the risk of holdup by negotiating renewal options. As the end-user’s primary concern is securing a stable supply of biomass, incorporating assignment clauses in the initial agreement can provide a seamless escape hatch for farmers no longer interested in producing biomass as part of a long-term contract. Assignment clauses may minimize potential supply disruptions and serve as a “next best” strategy compared to attaching production contracts to land title. However, due to the vertically coordinated nature of the bio-energy industry, the extent to which individual producers may negotiate the contract provisions discussed in this section remains to be seen. Nonetheless, the authors recommend that end-users seeking a stable, long-term biomass supply chain at a low overall cost should consider the issues identified above, as biomass production agreements that incorporate the sociocompatibility perspective, along with risk- and cost minimization, are more likely to result in more secure supply chain relationships.

Incorporating a combination of the solutions detailed above into biomass production contracts will substantially address the costs, risks, and sociological concerns of producers and endusers. This should improve contract negotiation processes and improve supply chain stability. Moreover, as the biomass industry matures and follow-on issues arise, the proposed Biomass Contracting Framework can serve as an important point of departure in obtaining negotiated solutions. In addition to the framework described above, the development of sustainability standards tailored to the biomass industry, such as the Council on Sustainable Biomass Production 277 or Round table on Sustainable bio-fuels , can provide further support to improved biomass contract design. By focusing on long-term sustainability, these standards can use market forces to provide additional incentives for end-users to approach contractual relationships beyond the archetypal cost- and risk-minimization perspectives. For example, the RSB’s socioeconomic principle requires skill training that is culturally sensitive and respective of existing social structures. Although the intent of this provision is to apply within the context of impoverished regions, most likely in the developing world, the underlying sustainability benefits of cultural sensitivity in skills training certainly would hold true in domestic biomass contracts between end-users and producers. In the current climate of adhesion-type contracts presented by biomass end-users, producers could reference the internationally accepted RSB standards within their limited contract negotiations as support for professional development, formation of peer groups, and even feedback mechanisms, such as fieldmen services. Sustainability standards for environmental criteria, such as biomass residue removal, compaction, erosion, soil carbon maintenance, and restrictions on introduction of potentially invasive energy crops, also may have positive cross-over effects on biomass contract design. Incorporating environmentally-based sustainability standards into biomass contracts sends a signal to the producer of the perceived environmental credibility of the practice, and lessens producer concerns regarding land stewardship and conversion from familiar cropping systems. Moreover, many of the producer autonomy concerns and cultural risk management practices identified in the social compatibility discussion in Part I.A, find resonance within these environmental standards. On the other hand, unduly restrictive practices embedded in a sustainability standard could discourage producer acceptance, if these criteria sacrifice traditional agricultural risk management practices, such as pesticide application. Nonetheless, 4×4 flood tray the incorporation of sustainability standards within the biomass contract may provide a novel means to bring together divergent views of risk management, cost-minimization, and social compatibility to create a more stable, and ultimately profitable, biomass supply chain. In the future, end-users may be able to use contractual mechanisms to coordinate efforts within its “fuel shed” to achieve greater economic and environmental sustainability.Biomass crops in the United States are projected to yield 136 billion liters of biomass-derived liquid fuels by 2022 . The expectation is that this will require cultivation of between 54 and 150 million acres of bio-energy crops. Furthermore, state and federal greenhouse-gas reduction initiatives have incentivized widespread cultivation of bio-fuel crops. Of the crops under consideration, perennial nonfood grasses are the leading candidates. To be successful in this role, these bio-energy grasses will need to possess many agronomically desirable traits, including broad climatic tolerance, rapid growth rates, high yields, few natural enemies and resistance to periodic or seasonal soil moisture stress .

One of the leading candidates among bio-energy grasses is switch grass . Switch grass is a perennial warm-season bunch grass native to most of North America east of the Rocky Mountains, where it was historically a major component of the tall grass prairie. It was included in the initial screening for bio-fuel crops in the United States in the 1970s and was determined to be the model bio-energy species by the Department of Energy . This was primarily due to its broad adaptability and genetic variability . Over the past three decades, breeding efforts have developed several cultivars, many of which produce dense stands, tolerate infertile soils and readily regenerate from vegetative fragments . These cultivars are often separated into upland ecotypes and lowland ecotypes . Switch grass is not native to California and was, in fact, included for a brief time on the California Department of Food and Agriculture Noxious Weed List due to concerns about its potential invasiveness. Although there was one documented report of an escape of switch grass from cultivation in Orange County, California , there are no known records of its escaping elsewhere or causing any ecological or economic damage, despite its long-time use as a forage and conservation species . Since its removal from the CDFA Noxious Weed List, it has been the focus of yield trials throughout California . Because of the state’s Mediterranean climate, the yield potential is high; however, the crop will require significant water and nitrogen inputs.In an ideal system, bio-fuel crops should be cultivated in a highly managed agricultural setting similar to that of most major food crops, such that the crop could not survive outside of cultivation. Under such conditions, the likelihood of escape and invasion into other managed or natural systems would be very small. Unlike bio-fuel species, most food crops have been selected for high harvestable fruit or grain yield. This nearly always results in a loss of competitive ability, typically accompanied by an increase in the addition of nutrients and often pesticides. When a bio-fuel crop is grown for cellulose-based energy, the harvestable product is the entire above ground biomass. To be economically competitive, such perennial crops should be highly competitive with other plant species, harbor few pests and diseases, grow and establish rapidly, produce large annual yields and have a broad range of environmental tolerance, while also requiring few inputs per unit area of water, nutrients, pesticides and fossil fuels . Few species fit these requirements better than rhizomatous perennial grasses, primarily nonnative species . However, these qualities and traits are nearly identical to those found in harmful invasive species . For example, species such as johnsongrass Pers and kudzu were introduced as livestock forage or for horticultural use but have escaped cultivation to become serious weeds in many areas of the United States. In selecting bio-fuel crops, a balance must be struck between high productivity with minimal inputs, on the one hand, and risk of establishment and survival outside the cultivated environment on the other. Johnsongrass, like switch grass, was first cultivated as forage, but it subsequently escaped and has become one of the world’s most expensive weeds in terms of control costs . It is currently listed as a noxious weed in 19 U.S. states. When comparing switch grass to johnsongrass and to corn, a typical agronomic grass crop, it is clear that switch grass possesses many growth traits similar to those of weedy johnsongrass and only a few similar to those of corn . While this is not direct evidence that switch grass will be a significant invasive or weedy species, it does suggest that the risk may be greater than for more typical agronomic crops. Although cultivation of switch grass and other bio-fuel crop species may ultimately prove a net benefit to society, the environmental risks associated with their potential escape into natural and managed systems should be assessed before the crops are commercialized and introduced into new regions.

Moreover, field men visits can provide a source of information and a familiar contact through which producers could “negotiate contract terms, share technical information, estimate expected yields, and maintain a presence to ensure that the contract will be renewed” The use of field men to monitor also allows for more flexibility over time, and creates “shared understanding of what constitutes standards of good professional practice” Thus, working in a cooperative spirit allows for expectation adjustments without costly negotiations or conflicts. It must be mentioned, however, that although the field men monitoring model has many benefits, several costs are involved, including the cost of hiring, training, and employing a staff of specialists to serve in this role. The previous discussion of adverse selection problems stemming from information asymmetry and the moral hazard problems associated with unobserved action offers several potential contract based solutions, including rationing, screening, signaling, and auctioning, as well as measurement and monitoring strategies. But, much of the economic contract theory discussed above assumes that parties are able and willing to write “complete” contracts— contracts that specify each party’s obligations for possible contingencies. In practice, however, parties often are unable or unwilling to write and enforce complete contracts. Accordingly, in the following section, we introduce a second important transaction cost—contract incompleteness, and remedial strategies in the biomass supply chain context.Consider the situation where the end-user and producer negotiate and execute ex ante a biomass production agreement that specifies a time and amount for delivery , but fails to specify a delivery location in the contract.

Assume the end-user has two facilities,one ten miles from the producer and another, larger facility, vertical grow system one hundred miles from the producer. The lack of a specified delivery location is a source of incompleteness in the contract. Contracts literature contains several theories for explaining why parties sign incomplete contracts. In extreme cases, complete contracts may not be necessary, such as in a transaction in an environment where all contingencies and variables are observable and verifiable, allowing perfect information to eliminate the risk of adverse selection or moral hazard. But this is a rare situation. Parties may end up signing incomplete contracts because of the bounded rationality of the parties, the presence of uncertainty in the transaction, or the inability of the parties to objectively measure and evaluate relevant variables. A third explanation, closely related to the bounded rationality of the parties, is based on Williamson’s transaction cost theory. Williamson argues that complete contracts are unattainable because the transaction costs of writing and enforcing outweighs the benefits of obtaining perfection. The marginal cost of additional completeness increases, while the marginal benefit of completeness decreases; thus, parties choose to write contracts with an optimal level of incompleteness where the marginal cost is equal to the marginal benefit of additional completeness. As a bottom line, the general consensus is that contracts are necessarily incomplete; it is impossible to cover every possible contingency sufficiently well such that neither party will be able to take advantage of a loophole or ambiguity and act opportunistically. Thus, incompleteness gives rise to the risk of ex post opportunistic behavior, which in turn creates transaction costs. 

In the complete contract literature, renegotiation serves as an ex ante constraint, incentivizing the parties to remain with the original contract, but incompleteness creates the need for ex post renegotiation. Renegotiation can be a beneficial tool where a contingency occurs that leaves both parties worse off under the terms of the original contract; this flexibility allows the parties to adjust to changes in their environment. This flexibility may even make incomplete contracts preferable to complete contracts in some scenarios. However, when certain transacting environments are present , renegotiation may be detrimental to one party, as it reduces commitment and may lead to strategic behavior. Accordingly, a party may take advantage of any ambiguity or contingency not explicitly addressed in the contract to improve ex post payoff through renegotiation. When incompleteness exists, the future returns on a party’s ex ante investment will depend on the bargaining position of the party ex post . Within incomplete contracts, economic contract literature has identified at least two factors in a transaction that influence a party’s exposure to ex post opportunistic behavior: asset specificity and allocation of property rights. Both of these factors may create holdup, a form of opportunism. Williamson defines the condition of asset specificity as “investments in which the full productive values are realized only in the context of an ongoing relation between the original parties to a transaction such assets cannot be transferred to alternative uses or users without loss of productive value.” Legal scholars refer to specific assets as reliance investments. Asset specificity creates a bilateral dependence between the parties and a quasi-rent or “surplus over opportunity cost that increases the potential for opportunistic behavior.” 

Several types of asset specificity have been defined other than physical asset specificity, including “value-added specificity” , time specificity , and site specificity . When a party makes ex ante investments with high asset specificity, the seller is especially vulnerable in renegotiation, as the buyer knows that the next best value for the seller is substantially lower. In renegotiation contexts, the buyer will offer to pay only just above the next best offer, leaving the seller with no rents. This opportunistic behavior on behalf of the buyer is called the “hold-up problem.” The party who considers ex ante whether or not to make an investment with high asset specificity can perceive the threat of holdup. He realizes he has no incentive to invest as he will receive no rents, and therefore, will under invest. This inefficient level of investment creates transaction costs and barriers to entry. Again, consider our example of the biomass production contract. The biomass producer may choose ex ante to produce a crop of Miscanthus, and make a corresponding investment. Upon harvest the parties must determine the delivery location. The harvested crop of Miscanthus has a high level of asset specificity; because the farmer has no alternative market for the energy crop, the next highest value is near zero. The biomass conversion facility understands this and, consequently, has significant bargaining power. The end-user may assert that delivery was meant to be at the larger, more efficient plant 100 miles away. The level of asset specificity puts the farmer in a weak ex post bargaining position, as he is dependent on the contract with the end-user and must satisfy the end-user to obtain revenue. Thus the farmer, even though he will incur higher transportation costs, would rather accept the added costs of transportation to a distant market than forego contract payments. In addition to this holdup, other producers who observe this scenario may refuse to invest, perceiving uncertainty and weaker incentives. Thus, one can see that asset specificity may create risk of opportunism and holdup. Several fields of literature have identified different strategies of addressing holdup, which we discuss below. However, the theoretical strategies—when placed within the context of biomass production for renewable energy products—may conflict, indoor weed growing accessories requiring a balancing approach as well as careful analysis of specific issues to determine optimal strategies.The preceding deconstruction of the sociological, risk minimizing, and cost-minimizing perspectives yields several theoretical insights for an optimal biomass contracting framework, including key elements of contract design and opportunities for trade-offs in the negotiation process. From the sociological perspective, sensitivity to non-economic factors tends to dominate decision making in the innovation context. The ability to maintain existing agricultural practices and social networks throughout the education, field trial, and commercial production stages minimizes farmer disincentives to enter into production contracts for novel biomass crops. Trialibility, information sharing, and education also have strong influences on the sociological-compatibility perspective of contracts. The risk minimizing framework shares with the sociological perspective elements of information sharing, educational experience, and use of existing agricultural risk management tools, but also incorporates the concept of risk-incentive tradeoffs and minimization of common risk.

Likewise, the cost-minimizing perspective incorporates aspects of the risk-incentive framework. But, cost-minimizing also includes unique attributes of controlling for moral hazards and adverse selection, as well as intentional design of incomplete contracts to incorporate renegotiation opportunities. Table 1, below, summarizes these results.Accordingly, a trans-disciplinary approach to optimal biomass contract design would incorporate, to the extent possible, each of the contract attributes identified in Table 1. As discussed below, where perspectives overlap, contract design should be able to accommodate the differing frameworks, or at the least identify specific issues for negotiated bargaining. The more difficult proposition is when these principles are in conflict. For example, information sharing is a fundamental aspect of the sociological compatibility perspective , but is absent, or even discouraged from the cost-minimization perspective. The following section, therefore, analyzes the tools and implications of a Biomass Contracting Framework from a trans-disciplinary perspective.Economic contract theory posits that parties to a contract must optimize the tradeoff between costs and risk, such that both parties’ aversion to risk is equal to the additional cost of minimizing that risk. As producers have different levels of risk tolerance, the appropriate amount of risk minimization will differ; risk adverse producers will be more costly to incentivize to participate than their risk neutral colleagues. Moreover,identifying and addressing the risk tolerance of producers can be a key factor in adverse selection problems. On the other hand, perhaps the most exacting lesson from the sociological literature is that producers have multiple and varied non-economic goals and barriers that must be addressed in order to facilitate adoption of energy crops. What the sociology perspective implies, however, is that many of these non-economic goals cannot be adequately compensated by greater monetary incentives ; in order to overcome these constraints, contracting parties must incorporate other strategies to align the goals and incentives of the contract with non-economic considerations, such as the impact on producer autonomy, lifestyle, current farming operation, and core values. At first glance, the absence of monetary incentives complements the cost-minimization perspective, but upon careful consideration it creates unique problems due to information asymmetry. Determining the underlying non-economic goals and barriers can be costly, especially for entities without extensive experience in the agricultural sector. For example, where a multinational oil company seeks entry to the bio-fuels market as the result of the RFS2 blending mandate, or where an electric utility previously reliant on coal and natural gas seeks a biomass supply for co-firing a power plant to comply with a state renewable portfolio standard, both actors may lack the institutional capacity to identify fundamental, non-economic barriers to farmer adoption. The adverse selection problem discussed in the context of cost minimization is made more complex as the end-user cannot confine information seeking activities to the differentiation of true high- and low-cost producers, as the end-user must also consider producers with divergent and variable non-economicgoals not satisfied merely through financial means. As a result, theoretical methods of eliminating information asymmetry through rationing, screening, and auctions may not produce the desired results. On the other hand, the process of signaling can enable end-users to identify particular non-economic barriers, along with the traditional high or low production cost structure. Moreover, cooperation and information sharing requirements embedded within a contract can enhance education and training elements, while also reducing information asymmetry. The problem of information asymmetry and moral hazard is illustrative. As discussed above, one method for the Principal to manage moral hazard is via monitoring, and one potential model is the creation of a network of fieldmen to periodically visit producers. Fieldmen can identify opportunistic or suboptimal behavior, while also providing a source of information among networked producers regarding not only technical production practices, but also financial information to lower future transaction costs. The use of monitoring strategies also implicates the risk-minimization perspective. Although incentives provide one method to allocate endogenous risk of opportunistic behavior,202 incentive payments alone cannot differentiate between the endogenous risk of lack of producer effort from exogenous factors, such as poor weather. Moreover, incentive payments may not provide adequate compensation for the non-economic considerations described in the sociological compatibility perspective. Alternative policing mechanisms, such as monitoring and collaboration through fieldmen, however, could address the endogenous moral hazard problems and minimize risk premiums. Similarly, relative performance contracts, such as tournament contracts, incorporate producer performance incentives relative to similar producers, rather than absolute measures that depend on common risks . 

It will be crucial to see if the benefits of NURTURE that I saw evidence for in my interviews carry over now that NURTURE is a module within Global G.A.P., or whether the character of those interactions and the high quality environmental and food safety “license to operate” that they helped to shape are significantly changed under Global G.A.P. management. It will also be interesting to see how this merger of standards affects market penetration of the Global G.A.P. standard. Global G.A.P. certifications active between 2014 and 2015 were not followed exclusively by any farmer interviewed during my study, but did show up as an additional standard followed concurrently by several farmers in my sample. If the merger with NURTURE allows Global G.A.P. to extend its market impact over a larger number of suppliers without fundamentally changing the structure of the NURTURE standard or its potential for positive landscape-level impacts, this merger could be one sign of positive evolution within harmonization of international food safety standards.Since I began this research, the FDA Food Safety Modernization Act in the United States has gone from a proposed rule making, to a final rule awaiting implementation, to the early stages of implementation within the US agricultural economy. Collection of the California data examined in this dissertation began while the proposed rule making was undergoing public comment, and concluded soon after initial publication of the final rule. At the time of publication of this dissertation, the Produce Rule is in effect. The first inspections called for under the FSMA Produce Rule were delayed in the beginning of 2018 by budget concerns for training new FDA inspectors, pruning cannabis issues around feasibility and definitions of certain requirements, and the complexities of developing state-level inspection protocols for the new rule.

Although the new requirements 11 are now in full effect as of September 2018 for all food businesses at all levels, FDA has reported that requirements for some types of produce farms will see a delay in enforcement reaching into 2019, or even 2020 . For many larger farms, changes have amounted to only minor refinements to existing food safety measures, because these producers already adhere to the most stringent rules in production due to their articulation with international trade networks and their deeper financial capacity to pay for audits and absorb additional costs. Conversely, for small and medium sized farms without large financial resources and for alternative producers following ecological farming methods that fit less readily into current HACCP risk-assessment frameworks without necessarily being less safe, the enforcement of FSMA’s newest provisions will present significant hurdles for day-to-day operations. Small farmers commented during the initial notice and comment cycle for FSMA that the new rules would likely put some smaller and alternative producers out of business due to the high cost of additional adaptation measures and inspections. The two iterations of the new USDA Harmonized GAP standard that I included in my analysis prior to their full implementation have also now gone into effect and have been adjusted for the enforcement of FSMA. This standard in its two iterative versions formed my category 2 Prescriptive Safety Plus, reflecting their attempts to incorporate clauses with a broader view of combined environmental and food safety concerns, and process-oriented controls in addition to prescriptive clauses. With my results from the previous chapter in mind, entry onto the state regulatory stage of standards with even a slight additional inclusion of these elements that I saw positively correlated with environmentally friendly farming practices and improved farmer experience could be a positive sign for the regulatory landscape. However, it will be necessary to see whether harmonization efforts are durable over the longer term, or if the landscape of standards remains subject to fragmentation. Hybrid food safety controls in the United States have also changed to accommodate new requirements at the national level. According to the LGMA board, as of August 2017, the LGMA standards applicable in both California and Arizona have been updated to reflect the new regulatory baseline represented by the FSMA Produce Rule.

This update was responsible for 12 the increase in prescriptive safety controls I observed in my comparison of standards, which saw the 2018 LGMA standard move back into my category 1: Prescriptive Safety. In comparison, the previous 2015 LGMA revision had contained enough process-oriented controls to place it within my category 3: Flexible Safety, representing a significant transition toward process-oriented controls that has now been reversed as private standards have intersected with changing public regulation. Producers entering into or maintaining certification to the LGMA in 2018 and beyond are now considered to be in full regulatory compliance with FSMA through the audits they already undergo. With the ability to signal full compliance through an already established public private partnership with USDA backing, the LGMA standard appears to have enhanced value and durability in a post-FSMA leafy greens market. This may complicate harmonization efforts,while also demonstrating an important back-tracking of the prior trend toward greater reliance on process-oriented food safety controls.On June 23 , 2016, residents of the United Kingdom voted in a historic referendum over rd the future of their membership in the European Union. The campaign to leave the EU won the vote by a margin of 51.9% to 48.1%, providing the popular basis for initiating the political process of exiting from the EU’s economic and political partnership represented by the EU. Under the terms of Article 50 of the Treaty on European Union, the UK has until March 29 , th 2019 to officially leave the EU with a negotiated agreement and its mutual parliamentary ratification. As of the time of writing, negotiations over the agreement are still underway, and although agreement has been reached on many specifics, the full terms have not yet been permanently established. Among many pressing economic questions for the nation, questions remain over what the UK’s exit will do to build upon or alter the functioning of the existing food safety and environment regulatory landscape in which fresh produce is currently grown. No matter what the precise terms of the final agreement, the UK’s exit will almost certainly change the face of British agriculture. The current UK leafy greens market benefits from a high degree of migrant labor drawn from other member countries within the EU under free migration rules.

If it becomes significantly harder for migrant laborers to gain access to the UK to work in agriculture, the UK produce sector could face steep competition from nearby EU countries where low-wage field labor is more easily attainable. Additionally, current environmental requirements and income support programs that some UK farmers presently enjoy under the EU’s Common Agricultural Policy will end by claim year 2020 under the terms 13 currently provisionally agreed by EU and UK negotiators as of November 14 , 2018 th . These direct payments and the regulatory mechanisms and requirements that underlie them provide the basis for UK environmental regulation in the farming sector, ensuring minimum standards of environmental protection and stewardship . Direct income support payments to farmers are slated to continue in the form of internal payments from the UK treasury until the next Parliamentary elections, due in 2022. Commentary from the UK parliament cites reasons that this exit and reorganization could be favorable for UK farmers, including relief from the more onerous parts of EU bureaucratic control and standardization of farming methods, record keeping, and crop timing . The UK’s DEFRA has announced plans to replace the direct payments with a new system designed to fix certain problems within the CAP payments, which some UK critics say do too much to reward large landholdings and too little to support real environmental stewardship. In a speech given to the Oxford Farming Conference in January 2018, Michael Gove, drying room current UK Secretary of State for Environment, Food and Rural Affairs, explained that DEFRA plans to move the nation away from CAP and its “resource-inefficient” methods of production, moving from “subsidies for inefficiency to public money for public goods” such as natural capital and environmental land stewardship. Such statements contain important clues 14 for basic framings of the values of food and farming which will soon decide which paths are considered by policy makers. Public expressions such as these pay service to the goals of environmental conservation and public goods such as food safety, but with uncertain guarantees during this ongoing time of negotiation. In February of 2018, ahead of major EU-UK negotiations, Britain’s National Farmers Union released a collaborative statement from 37 organizations representing the UK food and farming industries, in which they detailed their shared vision for what a successful British exit from the EU should aim to establish. Among other trade related goals, the statement calls on UK policy makers to ensure that new UK agricultural standards after the separation continue existing commitments to high environmental, health and animal welfare standards. However, recent evidence from the ongoing Brexit negotiations suggests that food standards may not be on track to ensure ideal outcomes for public health. With the announcement of a new program titled “Regulating Our Future” the UK Food Standards Agency has announced that its plans for food standards after Brexit will strongly favor private regulation over public regulation. This has some industry watchers worried that the future may hold a return to the scandals and failures of food industry self-regulation that plagued UK food production in the 1980s and 90s. Critics have warned that the new program undermines the publicly accountable enforcement provisions of the UK’s 1990 Food Safety Act by placing responsibility for food inspections on private commercial assurance providers instead of local and central government. Those wary of such a shift warn that this would be a misstep because private assurance firms would have a commercial incentive to serve their food industry clients over the interests of the public . Moreover, critics point out that regulatory over-influencing by corporate food actors was exactly the problem that the FSA, as a central independent watchdog agency, was famously created to solve. Non-state and hybrid standards can be effective tools for ensuring desired outcomes for food safety and the environment , but are most effective when paired with strong state regulation.First and foremost, I suggest that ensuring optimal outcomes for food safety and environmental management will require additional efforts to combat the division of food safety and environmental concerns into separate administrative and industry silos. Currently, my data show that these goals are being pursued separately by public and private standards in the United States, and through imperfect overlapping agencies within the UK government. In many cases, private standards push the frontier of regulation farther than public mechanisms, and form the most immediate point of contact uniting regulatory goals with buyer requirements and farmer practice. Currently, private standards in both nations are facing changes and updates in the wake of fluctuating regulatory climates, leaving private standards in a state of uncertainty and flux. I suggest that it is now especially important for private food safety standards in both nations to explicitly consider environmental goals alongside food safety goals. My results indicate that more balanced standards of this nature are correlated with more positive farmer experience, improved attitudes toward the natural environment, and higher use of conservation-oriented practices, goals which should be among those established during the current reorganization of regulatory priorities at public and private levels. Private standards are increasingly becoming international or global in scope, extending the reach of private regulation far beyond that of public regulation. Delivering effective food safety guarantees in global supply chains will require a shift toward more complete, internationally bench marked or otherwise harmonized standards, and nimble governance frameworks with a view of safety that does not ignore sustainability. However, market forces are currently still encouraging standards to proliferate and stay focused on food safety to the exclusion of other concerns. Additionally, regime transitions in both UK and US government make it less likely that the most balanced food safety standards currently available will be able to maintain their environmental completeness and broad conception of food safety going forward. It will be important for areas of the developed world that have rigorous and effective standards to maintain them in the face of incentives to race to the bottom, converging around standards which aim to deliver safety instead of other goods, rather than in addition.