Hemp Growing

Spontaneous hybridization has, for instance, been reported in weedy populations of B. rapa growing in agricultural crops and in natural populations of B. rapa occurring near waterways. Second, flowering time has been extensively studied in B. rapa, and temporal clines in phenotypic traits have been observed. For example, time to first flowering has been shown to be positively correlated with stem height and stem diameter. Third, transgenic lines of B. napus containing a green fluorescent protein gene associated with the Bt transgene have been constructed. The presence of the Bt transgene in the offspring of weedy plants can therefore be inferred by exposing the plants to UV light.The aim of our experiment was to assess the impact of interspecific hybridization between weedy B. rapa and transgenic B. napus on the evolution of the weedy phenotype. This was done by identifying the phenotypic traits increasing hybridization opportunities for weedy individuals, searching for associations between these phenotypic traits and the transgenic trait in the offspring of weedy mothers and evaluating the relative fitness of hybridizing weeds. Our results show that weedy individuals that flowered later and for longer periods were more likely to receive transgenic pollen from crops and weed6crop hybrids. Because stem diameter is correlated with flowering time, plants with wider stems were also more likely to be pollinated by transgenic plants. Our results suggest that the transgene and maternal genes promoting late flowering, long flowering periods and stem thickening may be preferentially associated in the offspring of weedy mothers. However, growing trays although time to first flower is a heritable trait in B. rapa, our experiment did not confirm the gametic association between the transgene and genes promoting late-flowering in the offspring of hybridized weedyplants.

Indeed, given the very small numbers of Bt-GFP+ seedlings recovered from the experimental populations, we could not study the association between the transgenic trait and other phenotypic traits in weed plant offspring. We also found that the weedy plants with the highest probability of hybridization produced fewer seeds, despite producing larger numbers of flowers. The most straightforward interpretation of this result is that fecundity was reduced by hybrid crosses. Controlled crosses between the weedy and transgenic plants used in the experiment and several previous studies have indeed shown that crops and weed6crop hybrids have lower siring success than do weeds. Therefore, our experiment suggests that maternal weeds that flowered late and for long periods are less fit, because they have a higher probability of hybridizing with GM crop plants or hybrids. This may result in counter-selection against this subset of weed phenotypes, and a shorter earlier flowering period. It is noteworthy that this potential evolution in flowering time does not depend on the presence of the Bt transgene in the crop, and may even be counter-balanced by positive selection acting on the transgene if the latter was positively associated with maternal genes promoting late flowering and long flowering periods. Recent experiments indeed indicate that the Bt transgene does not induce any fitness costs in hybrids between transgenic B. napus and weedy relatives. It may therefore convey a selective advantage under insect herbivore pressure. In conclusion, our analyses show that phenological differences between weedy birdseed rape and transgenic rapeseed are likely to alter the phenotypic structure of weed populations, by promoting interspecific hybridization in only a subset of weedy plants with specific phenotypes and by altering the fitness of hybridizing weeds. Unfortunately, we could not verify the non-random association between the transgenic trait and other phenotypic traits in the offspring of weedy populations because of the very low rate of transgene introgression.

Nine populations, each composed of 15 Brassica rapa plants and 15 of one of three types of transgenic plants were sown as seeds and then grown from germination until death in a glasshouse at the University of California, Irvine. The nine populations were divided into three blocks, with each transgenic type replicated once per block. Plants were grown in individual Conetainer H pots filled with a 75/25 mixture of potting soil and sand. Before planting, seeds were vernalized on wet filter paper at 4uC for 5 days. Pots were spaced 7.6 cm apart and were watered every day until 90% stopped producing flowers. An equal amount of 10:10:10 NKP liquid fertilizer was applied to each pot on the sowing date. The three types of transgenic plants were: Bt-transgenic B. napus crop plants, Bt-transgenic B. napus 6B. rapa F1 hybrids, and first generation backcrosses . Over 20 unique seed and 20 unique pollen parents were used to produce each of the three types. B. rapa plants served as seed parents for the F1 and backcross types. B. napus were all homozygous for the Bt-GFP insertion, whereas the F1 plants were all hemizygous. The backcross generation was expected to consist of an equal mixture of hemizygotes and null homozygotes for the insertion. B. rapa seeds were obtained from over 400 mature plants in a population at Back Bay, near Irvine, California. Transgenic B. napus plants were derived from spring rapeseed lines . In addition to the Btcry1Ac gene from Bacillus thuringiensis , these lines contained a green fluorescent protein gene under the control of the cauliflower mosaic virus 35S promoter and a nopaline synthase terminator cassette. The fate of the Bt transgene could therefore be inferred by exposing the offspring to UV light. Flowering schedules were constructed for each individual plant by recording the time to first flower and the number of opened flowers on every fourth day until the end of the flowering period. The lifetime of a flower is about three days , so this procedure made it possible to estimate the total number of flowers produced by each plant over the flowering period.

The length of the flowering period was defined as the number of scoring days on which the plant had opened flowers. Every fourth day, all open flowers on all plants were hand pollinated in each of the nine experimental populations . Each experimental population was composed of 30 plants which were numbered from 1 to 30. On each pollination day, a random sequence of 30 numbers was generated for each population. For a given population, a pollination session consisted of brushing all the flowers of the first plant in the sequence, and then brushing all of the flowers of the next plant. This was continued until the brush from the 30th plant was used to transfer pollen to the first plant. Each plant was brushed up and down several times to deposit the pollen from the previous plant in the sequence and collect the maximum amount of pollen. A given plant was only brushed if it was alive and had one or more open flowers. Otherwise the next plant in the sequence was considered. Each of the nine populations had its own brush, and new brushes were used for each pollination session. This hand-pollination procedure was chosen to approximate the behaviour of a bumble bee in a patch of oilseed rape. Bumblebees tend to visit many plants successively and rarely revisit the plants. They deposit most of the pollen from a source plant on immediate neighbours.We performed all statistical analyses with SAS/STATH software. Plants that died during the experiment were excluded from the analysis and the final data set contained 117 weedy plants. We first investigated how phenological traits affected the chances of interspecific hybridization between Bt-trangenic plants and weeds. We used a mixed linear model , with transgenic type as the fixed treatment effect, phenological traits of weeds as covariates, grow tray and block and treatment6block interaction as random effects. The response variable was the proportion of flowers receiving pollen from Bt-transgenic plants . The response variable was log-transformed to increase its normality . If a factor was not significant as a single effect or in interaction with other factors, it was eliminated from the model and the analysis was rerun. We continued until there was no further improvement in residual maximum likelihood. We then investigated how morphological traits affected the chances of hybridization. A mixed linear approach was then used to determine whether the morphological traits changing with time to first flower had a significant effect on PPR. As above, transgenic type was treated as a fixed treatment effect, morphological traits were covariates and block and treatment6block interaction were treated as random effects.

We used the mixed linear approach with block and treatment x block interactions as random effects, to investigate whether the phenological and morphological traits which were found to favour hybridization of weedy mothers were transmitted to their offspring. In this model, transgenic type was treated as a fixed effect, the maternal trait as a covariate and the average offspring phenotypic trait as the response variable. The normality of the response variables was checked , and data was transformed as necessary. Finally we investigated the relationship between opportunities for hybridization and fecundity in weeds. We used the mixed linear approach with transgenic type as the fixed treatment effect, PPR as the covariate and block and treatment6 block interaction as random effects. The response variable was the total number of filled seeds. Its normality was checked with a Kolmogorov-Smirnov goodness-of-fit test . We then checked that the mother plants with the highest expected probability of receiving transgenic pollen also had the highest proportion of Bt-GFP+ seedlings. The proportion of Bt-GFP+ seedlings did not follow a normal distribution and could not be transformed. We therefore checked the effects of transgenic type, PPR and block separately, in non parametric oneway ANOVAs . The correlation between PPR and the proportion of Bt-GFP+ seedlings was assessed using Spearman’s rank correlation test .Weeds are great challenges for crop production, particularly those that are the same biological species as the crop they infest. For example, weed beets infest sugar beet fields, and weedy rice infests cultivated rice fields. The phenotypic similarity of such conspecific weeds to the related crops often frustrates visually based hand weeding. Also, genetic similarity means that the crop and the weed are so physiologically similar that herbicide must be applied on the weed with great precision to prevent application on the crop, again requiring visual discrimination . Because of their close evolutionary relationship, conspecific weeds are typically cross-compatible with the related crop species . Thus, conspecific weeds represent a unique challenge for their control in crop production because gene flow can deliver useful genes/alleles to weed populations from both their domesticated relatives as well as nearby non-weedy wild relatives . This infusion of genetic diversity can provide a substrate for rapid adaptive evolution . Crop-toweed gene flow has played a significant role in the adaptive evolution of weeds, such as weed beet , weedy rice , and California wild radish . The foregoing examples are a subset of unmanaged populations with introgressed domesticated alleles that have evolved increased weediness or invasiveness . In addition, crop-to-wild gene flow may also affect the evolutionary dynamics of wild populations, causing weed problems .The advent of genetically engineered crop species has stimulated discussion about whether crop-to-weed and crop-to-wild transgene flow might have an ecological or environmental impact . Like any other genes, transgenes should move from a GE crop to its non-GE counterparts and to wild/weedy relatives via pollen-mediated gene flow . If a weed/wild population has acquired a transgene that confers a strong selective advantage, and is exposed to a relevant selective pressure , it is likely to exhibit enhanced fitness and evolutionary potential under the natural selection, that may result in unwanted environmental consequences such as increased weediness or invasiveness . An introgressed transgene with neutral fitness impacts is expected to persist in the population; whereas a transgene with negative fitness impacts is expected to be purged from the population unless is a replenished by subsequent gene flow . Thus, a better understanding of correlates of crop transgenes in wild/weedy populations facilitates biosafety assessment of impacts caused by transgene flow. Consequently, the fitness and phenotypic correlates of crop transgene presence under field conditions have been studied in many systems; e.g. squash – wild gourd, maize – teosinte, cultivated sunflower – wild sunflower. For the world’s most important transgenic crops that have been commercialized or are nearing commercialization, the cultivated rice – weedy rice system is perhaps the best studied in that context. In China, a large number of GE rice lines with various transgenes have been developed, and some of them are under bio-safety assessment or on their way for commercialization .

Trees were manually edited with MEGA X . The DNA-A and DNA-B phylogenetic trees were rooted with the sequences of the genomic DNA of the OW monopartite begomovirus tomato yellow leaf curl virus and the DNAB component of the OW bipartite begomovirus African cassava mosaic virus , respectively.Preliminary datasets of complete sequences of 584 DNA-A and 240 DNA-B components were assembled. This included the complete nt sequences of the DNA-A and DNA-B components of: the bipartite begomoviruses from the M1-M4 samples; the TbLCuCV isolates from CU; and sequences of selected viruses retrieved from GenBank. SDT and the Recombination Detection Program version 4.0  were used to remove sequences that were identical or having nt sequence identities <70%. Final datasets of complete sequences of 488 DNA-A and 201 DNA-B components were used for recombination analyses. MSA were generated with MUSCLE within MEGA X , and the alignments were manually edited and exported as FASTA files. Detection of recombination breakpoints and identification of potential parental viruses were performed with RDP4. The recombination analysis was performed with default settings and a Bonferroni-corrected p-value cut-off of 0.05. Only recombination events detected with three or more methods coupled with significant phylogenetic support were considered bona fide events.In the phylogenetic tree generated with the complete DNA-A sequences, the TbLCuCV isolates from Hispaniola formed a strongly supported clade with the isolates from CU. Within this clade there was evidence of genetic divergence between isolates from CU and Hispaniola, grow trays consistent with geographical separation . In this tree, AbGYMV was placed on a distinct branch , which was included in a larger strongly supported clade with the TbLCuCV isolates.

This clade was part of the larger C1 clade of the AbMV lineage, which includes mostly weed-infecting begomoviruses from the Caribbean Basin , whereas the other large clade included crop- and weed-infecting begomoviruses from many countries of Latin America . The phylogenetic tree generated with the complete DNA-B sequences revealed a similar overall topology, but with some notable differences. The TbLCuCV isolates from Hispaniola and CU were placed in a strongly supported clade in the AbMV lineage . In contrast to the DNA-A tree, AbGYMV did not form a sister clade with the TbLCuCV isolates, but was placed together with the TbLCuCV isolates and other weed-infecting bipartite begomoviruses from the Caribbean Basin in the strongly supported C1 clade of the AbMV lineage . In the DNA-B tree, the C2 clade included viruses from North and Central America and the Caribbean Basin, whereas more distantly related viruses from South America were placed in a paraphyletic group . Finally, whereas the DNA-A tree clearly separates the BGYMV, Brazil, SLCuV and BoGMV lineages, these clades clustered together in a larger clade in the DNA-B tree . Taken togetherwith the SDT analysis and sequence comparisons, the results of the phylogenetic analyses are consistent with TbLCuCV and AbGYMV representing distinct but closely related species, which are most closely related to NW bipartite begomovirus species infecting weeds in the Caribbean Basin.In a preliminary experiment, N. benthamiana plants agroinoculated with the multimeric cloned DNA-A and DNA-B components of TbLCuCV-[HT:14] were stunted and newly emerged leaves showed epinasty, crumpling, deformation, mosaic and vein yellowing by 14 dpi .In the host range experiment, the infectious cloned DNA-A and DNA-B components of TbLCuCV induced stunting and golden/yellow mosaic in newly emerged leaves of all agroinoculated Malachra sp. plants by 14 dpi .

These symptoms were similar to those observed in Malachra sp. plants in the field in Hispaniola , thereby fulfilling Koch’s postulates for the golden/yellow mosaic disease of Malachra sp. TbLCuCV also induced stunting and epinasty and crumpling of newly emerged leaves of agroinoculated N. tabacum and N. glutinosa plants, and stunting and epinasty, deformation, chlorosis and mosaic of newly emerged leaves of agroinoculated common bean plants by 14 dpi . D. stramonium plants agroinoculated with TbLCuCV developed chlorotic spots in newly emerged leaves, whereas symptomless DNA-A and DNA-B infections were detected in some agroinoculated tomato plants by 14 dpi . TbLCuCV did not infect Cayenne long pepper , pumpkin and C. amaranticolor plants. N. benthamiana plants agroinoculated with the multimeric cloned DNA-A and DNA-B components of AbGYMV were stunted and developed mild symptoms of epinasty and crumpling in newly emerged leaves and no obvious mosaic or vein yellowing by 14 dpi . These symptoms became progressively milder by 21 dpi . In the host range experiment all Abutilon sp. plants agroinoculated with the infectious DNA-A and DNA-B components of AbGYMV were stunted and developed epinasty and striking golden/yellow mosaic of newly emerged leaves by 14 dpi . Moreover, these symptoms were similar to those observed in Abutilon sp. plants in the DO , thereby fulfilling Koch’s postulates for the golden/yellow mosaic disease of Abutilon sp. in the DO. In contrast, agroinoculated Malachra sp. plants developed no symptoms and only a small number of plants had DNA-A only infections . AbGYMV induced mild upward leaf curling symptoms in N. glutinosa, and very mild symptoms of leaf epinasty in common bean by 14 dpi . Symptomless DNA-A and DNA-B infections were detected in agroinoculated N. tabacum and D. stramonium plants, whereas symptomless DNA-A only infections were detected in some tomato by 14 dpi . AbGYMV did not infect Cayenne long pepper, pumpkin, C. amaranticolor and A. indicum plants.

In all these experiments, the presence of the inoculated DNA-A and DNA-B components was confirmed in newly emerged leaves of representative symptomatic and in all non-symptomatic plants by PCR tests with component-specific primers . Plants agroinoculated with the empty vector or bombarded with gold particles alone did not develop symptoms and were negative for the TbLCuCV/AbGYMV DNA-A and DNA-B components.To further investigate the relationship between TbLCuCV and AbGYMV, pseudorecombination experiments were conducted in N. benthamiana and Malachra sp. plants . In N. benthamiana, pseudorecombinants formed with the TbLCuCV DNA-A and AbGYMV DNA-B or AbGYMV DNA-A and TbLCuCV DNA-B were highly infectious and induced severe symptoms by 14 dpi. The TA + AbB PR induced epinasty, crumpling, deformation, mosaic and vein yellowing symptoms, which were more similar to those induced by the TbLCuCV parent . In contrast, the AbA + TB PR induced mostly epinasty and crumpling symptoms, which were more similar to those induced by the AbGYMV parent . Thus, the symptoms induced by these PRs were associated with the source of the DNA-A component. Furthermore, the symptoms induced by both PRs were more severe than those induced by the AbGYMV parent . Taken together, these results suggest an important role for the DNA-A component in symptom development in this host. In equivalent experiments conducted in Malachra sp., both PRs were infectious, but at lower rates than in N. benthamiana. Furthermore, the PRs differed markedly in infectivity, with the TA + AbB PR having an infection rate of 80%, whereas that of the AbA + TB was only 22%. The symptoms induced by these PRs were different compared with those induced by the parental viruses. Thus, both PRs induced more severe symptoms than those induced by the AbGYMV parent . Furthermore, the TA + AbB PR induced epinasty, crumpling and deformation, but little yellow mosaic ; whereas the AbA + TB PR induced epinasty, crumpling, deformation as well as yellow mosaic by 14 dpi . These results suggest an important role for the DNA-A component in infectivity and a role for the DNA-B component in symptom development in Malachra sp. In PCR tests with component-specific primers, the inoculated DNA components were detected in newly emerged leaves of all symptomatic plants. Together, these results established that the components of these viruses are interchangeable, consistent with the conservation of critical CR sequences and their close phylogenetic relationship . Moreover, grow systems for weed infectivity and symptoms were host-dependent, involved both components and revealed evidence of differential adaptation of these viruses.Since the advent of agriculture humans have encountered plants that have frustrated their goal to manage their environment. Today, we call the plant pests that interfere with agriculture ‘weeds’. In the last few centuries, humans have taken an increasing interest in preserving and otherwise maintaining the biodiversity of more ‘natural’ [i.e., ‘less managed’ ] communities. Here, too, plant pests frustrate human intentions. In such situations, these plants are called ‘invasives’. Weeds and invasives are problematic plants at ends of a continuum of how intensively humans manage an ecosystem, with manicured lawns and cultivated croplands at one end, through forest plantations and rangelands, to natural, deliberately lightly managed, areas at the other end. Thus, the distinction between weeds and invasives, though often clear, is occasionally fuzzy or arbitrary.

Some plants can become weeds and/or invasives with the appropriate ecological opportunity and without any genetic change. But an increasing body of research has revealed that some plants have evolved to become pests. Following the publication of the book, The Genetics of Colonizing Species , evolutionary biologists began to focus on how weeds might evolve . The idea of evolution as a potential route to invasiveness has become rapidly accepted in the last two decades, not only for plants, but also for animals and microbes . With the goal of understanding whether and how weediness and invasiveness evolve, empirical studies are accumulating that compare problematic lineages with their putative ancestral populations, in plants as well as other organisms . Some of these studies compare genetic marker variation, often identifying changes in diversity and population genetic structure. Other descriptive studies compare phenotypic or ecological differences of the invasive or weed and those of putative source populations . The latter can suggest evolutionary changes, but ‘common garden’ experiments in both the invaded and the native range are often necessary to demonstrate genetically-based phenotypic or ecological differences between problematic organisms and their presumed progenitors . A classical case is that of a variety of barnyard grass [Echinochloa crus-galli var. oryzicola P. Beauv.], a noxious weed that has evolved to mimic domesticated rice . Barrett grew seedlings of E. crus-galli var. oryzicola, its progenitor, E. crus-galli var. crus-galli, and O. sativa in a common garden experiment measuring numerous morphological characters. Multivariate analysis of 15 quantitative characters revealed that, in their vegetative phase, rice and its weedy mimic are not significantly different morphologically from each other, despite being in different genera. However, both differed significantly from E. crus-galli var. crus-galli . Morphological crop mimicry is an adaptation that is the result of continued selection by visually based human weeding. Indeed, barnyard grass individuals in Japanese rice fields that most closely resemble cultivated rice plants morphologically are less likely to be removed from rice fields by hand-weeding . Apparently, thousands of years of hand-weeding rice selected for a crop mimic that is almost vegetatively indistinguishable from rice. Similar studies have been conducted for invasives. In a common garden experiment conducted in California, Dlugosch and Parker compared invasive California populations of the shrub Canary Islands St. John’s wort with the native populations of that species, including the genetically-determined precise source population . They found that California populations had evolved an increased growth rate relative to the source population. They also found a diversification of flowering phenology of the California plants that correlated with their latitudinal origins. Such apparently adaptive evolutionary changes are not uncommon, although some authors caution that alternative explanations can account equally well for the appearance of adaptation . Only a handful of experimental studies report no evidence for adaptive evolution in invasives relative to their putative source populations . The example of Dlugosch and Parker is exceptional for invasives in that the progenitor population was precisely identified, allowing for the appropriate experimental comparison of progenitor and derived genotypes. But most often detailed information about source populations is, at best, lacking or at worst, complicated by an unknowable number of multiple introductions to multiple locations over decades with little knowledge about the time and place of initial invasion.A subset of weeds and invasives has evolved from domesticated ancestors, presenting certain advantages for study. We note that weeds and invasives can evolve from domesticate plants by two different pathways . Some, like California’s weedy rye are directly descended from a crop , though not all endoferal plant pests necessarily arise via evolutionary change. Other problematic plants, such as Europe’s weed beet , are descended from hybrids between a crop and another, usually wild, taxon .

The study site varied in weed population composition each year. Based on non-treated plots, watergrass species infestation in 2019, averaged 10% abundance compared with 28% in 2021 . Sedge and broadleaf pressure were similar in both years. Similar variations have been noted in this same field location and attributed to annual differences in temperature and management . In 2021, the study was seeded 12 days earlier than in 2019; the weather differences between the two years may have contributed to the difference in weed population .Pyraclonil applied alone or with other herbicides provided 76-96% control of watergrass species at 14 DAT . The efficacy of pyraclonil alone decreased as the season progressed, reaching 54% watergrass control at 42 DAT, which was less than pyraclonil applied with other herbicides. All tested herbicide combination treatments provided excellent seasonlong control of watergrass species. There were no differences among the pyraclonil combination treatments regarding their control of watergrass species at 14 DAT or 42 DAT; watergrass control ranged from 88-100% in treated plots by 42 DAT. Pyraclonil applied alone did not achieve season-long watergrass control and should be combined with other herbicides that express season-long activity on watergrass species. There was no difference in sprangletop control among pyraclonil treatments at 14 DAT; however, there was a non-significant trend of 100% control of sprangletop achieved with pyraclonil followed by propanil, pyraclonil followed by thiobencarb followed by propanil, grow room pyraclonil followed by bispyribac-sodium followed by propanil, pyraclonil followed by penoxsulam followed by propanil, and pyraclonil followed by florpyrauxifen-benzyl followed by propanil .

At 42 DAT, however, the herbicide programs of pyraclonil followed by propanil and pyraclonil followed by penoxsulam followed by propanil provided similarly low control of bearded sprangletop, ranging from 61-68% control. The decline in weed control from 14 DAT to 42 DAT may be attributed to the late emergence of bearded sprangletop that escaped the pyraclonil treatments . Bearded sprangletop requires 215 growing degree days to achieve 90% emergence, contributing to a later emergence compared to other common weeds such as watergrass species, which require only 124 GDD for 90% emergence . GDDs for June 2019 and June 2021 were estimated and used to establish 90% bearded sprangletop emergence in thermal time degree days . However, there was no difference in the amount of GDDs between the years that the field study was conducted. The field location received 220 GDDs by 21 days after seeding in 2019, enough to reach 90% emergence of bearded sprangletop in 2019. In 2021, the field location reached 229 GDD for 90% bearded sprangletop germination 20 days after the rice was planted. The combination of pyraclonil followed by benzobicyclon plus halosulfuron followed by propanil gave 50% control of bearded sprangletop at 14 DAT; however, at 42 DAT, no sprangletop was found in the treated plots. Benzobicyclon plus halosulfuron is applied at 1.5 rice leaf stage but exhibits long-lasting weed control through both foliar and root uptake that may account for the control of later cohorts of bearded sprangletop . Pyraclonil applied alone did not control ricefield bulrush substantially differently from the untreated plots and was insufficient for effective ricefield bulrush control; however, the pyraclonil applications followed by propanil, benzobicyclon plus halosulfuron and propanil, clomazone and propanil, thiobencarb and propanil, bispyribac-sodium and propanil, or penoxsulam and propanil achieved similar ricefield bulrush control ranging from 61-88% at 14 DAT .

Differences in ricefield bulrush control among the different herbicide combinations began to emerge at 42 DAT. The treatment of pyraclonil followed by benzobicyclon plus halosulfuron and propanil and pyraclonil followed by florpyrauxifen-benzyl and propanil controlled 97% of ricefield bulrush. These two treatments provided greater control over ricefield bulrush than pyraclonil followed by propanil, 48% control, and pyraclonil alone, 23% control. Benzobicyclon plus halosulfuron is a standard treatment to control ricefield bulrush in California, which explains the higher level of control resulting from this program . Later-season application of florpyrauxifen-benzyl at early-tiller stage may be timed toeliminate ricefield bulrush that are not controlled by the combination of pyraclonil and propanil, which may account for the high efficacy of this herbicide combination. Pyraclonil applied alone and all herbicide combinations achieved greater control of smallflower umbrellasedge at 14 DAT . Pyraclonil applied alone provided 65% control of smallflower umbrellasedge at 14 DAT. This level of control at 14 DAT was less than that of pyraclonil applied in combination with benzobicyclon plus halosulfuron followed by propanil and thiobencarb followed by propanil, ranged from 95 to 97% control, respectively. The following pyraclonil combinations provided greater smallflower umbrellasedge control compared to pyraclonil alone, which provided 48% control at 42 DAT: pyraclonil followed by benzobicyclon plus halosulfuron and propanil, pyraclonil followed by thiobencarb and propanil, pyraclonil followed by propanil and bispyribac-sodium, pyraclonil followed by penoxsulam and propanil, and pyraclonil followed by propanil and florpyrauxifen-benzyl.

All treatments provided significantly higher levels of control than the untreated plots at 42 DAT. Pyraclonil alone was insufficient for effective season-long control of small flower umbrellas edge; however, when partnered with other herbicides labelled for control or suppression of this weed, the level of control was excellent. Plots treated solely with pyraclonil maintained the lowest levels of ducksalad control of the treatments tested, ranging from 85 to 86% control throughout the season . All pyraclonil combinations had excellent control of ducksalad that ranged between 92 to 100% at 14 DAT. Ducksalad control remained high and ranged between 86% to 100% at 42 DAT for all herbicide combinations with no differences among treatments. Pyraclonil applied alone provided 86% control of redstem at 14 DAT . All pyraclonil combination treatments provided excellent control of redstem at 14 DAT.Some redstem appeared at 42 DAT in plots treated with the combinations of pyraclonil followed by propanil and pyraclonil followed by clomazone followed by propanil but there was no difference between these treatments and the other treatments tested. All herbicide treatments provided effective season-long control of redstem.Rice injury was observed as chlorosis and stunting across all treatments in both years from 7 DAT to 42 DAT. The rice injury data revealed significant year-by-treatment interaction, so the data were analyzed separately by year for both chlorosis and stunting ratings. Several treatments caused chlorosis at 14 DAT in 2019: pyraclonil , pyraclonil followed by clomazone and propanil , pyraclonil followed by thiobencarb and propanil , and pyraclonil followed by propanil and bispyribac-sodium . All other treatments had chlorosis ranging from 41 to 61%, with the exception of the herbicide combination of pyraclonil followed by propanil and florpyrauxifen-benzyl, which displayed 25% chlorosis. However, by 42 DAT in 2019, drying cannabis only pyraclonil alone exhibited chlorosis, at 4% in the treated plots . No rice chlorosis was observed in any treated plot in 2021 at 14 DAT . At 42 DAT, the herbicide combination of pyraclonil followed by thiobencarb and propanil caused 19% chlorosis, which was significantly higher than other treatments. Chlorosis gradually disappeared in the treated plots. Hakim et al. also found slight rice injury including chlorosis from herbicide applications consisting of thiobencarb and propanil in non-saline soils in Malaysia. The chlorosis ratings between 2019 and 2021 were diverse. All treated plots presented some chlorosis at 14 DAT in 2019 but recovered by 28 DAT and demonstrated negligiblephytotoxicity after 42 DAT. No chlorosis was observed in any treatment until after 21 DAT in 2021. Only the combination of pyraclonil followed by thiobencarb and propanil provided any sign of chlorosis at 19% at 42 DAT in 2021. Applying thiobencarb slightly earlier than recommended on the manufacturer’s label may have caused the early chlorosis, but the rice was able to recover from the early phytotoxicity. No stunting was observed for any treatments in 2019 at 14 DAT. The combination of pyraclonil followed by thiobencarb followed by propanil caused 24% stunting by 42 DAT, which was significantly different from the five other treatments .

Pyraclonil alone, pyraclonil followed by propanil, pyraclonil followed by benzobicyclon plus halosulfuron and propanil, pyraclonil followed by clomazone and propanil, and pyraclonil followed by propanil and florpyrauxifen-benzyl caused rates of stunting indistinguishable from the untreated plots. There was no significant stunting from any other treatments besides the combination treatment containing thiobencarb. The combination of pyraclonil followed by benzobicyclon plus halosulfuron followed by propanil caused 4% stunting in 2021 at 14 DAT, which was slightly more stunting than the other treatments, but otherwise no severe stunting was observed at that early date for any treatment . Pyraclonil applied alone and pyraclonil followed by benzobicyclon plus halosulfuron followed by propanil caused 7 and 8% stunting, respectively, at 42 DAT. These results agree with earlier research that noted that pyraclonil at rates ranging from 25 to 200 g ai ha-1 caused ≤ 8% shoot biomass reduction when applied to a commonly used rice variety in China . The herbicide program containing thiobencarb resulted in significantly greater stunting at 23% at 42 DAT compared to all other herbicide treatments . Baltazar and Smith Jr. found 30% stunting in rice treated with propanil and thiobencarband noted that yields were unaffected by this early season stunting. A possible explanation for the phytotoxicity from the herbicide combination containing thiobencarb may result from the application timing. Thiobencarb was applied at 1.5 rice leaf stage in order to coincide with 2 leaf stage of the watergrass species in the field. This application timing is slightly earlier than the recommended application timing of 2 rice leaf stage . The interaction of yield by years was significant; therefore, these data were presented separately. There were no significant differences in yield among treatments in either study year. In 2019 rice yields averaged 8,796 kg ha-1 , whereas in 2021, yields from the herbicide programs averaged 11,294 kg ha-1 . The difference between the two years’ yield may be due to the difference in planting date and weather patterns between the years this study was conducted. The difference in average yield in our study coincided with average rice yield for California. In 2019, the average yield for California rice was 8,536 kg ha-1 , whereas in 2021, California rice averaged 10,144 kg ha-1 .Rice is one of the most commonly grown agricultural commodities in the world and contributes significantly to sources of human energy across the globe . California is the second largest rice-growing state in the USA, with approximately 200,000 ha of rice acreage in California, much of which is concentrated in the Sacramento Valley. The majority of California’s rice production consists of short- and medium grain japonica varieties and a few long-grain indica varieties, including cultivars developed for both the local climate and a continuously-flooded cropping system, where rice is pre-germinated and seeded by airplane onto fields with a 10-15 cm standing flood . Decades of using this practice to suppress grass, sedge, and broadleaf weeds that would otherwise decrease yields, in addition to no crop rotation, have selected for weed species that exhibit ecological requirements and growing patterns that are similar to rice and can compete with rice resources . The flooded conditions in which most California rice is grown favor weedy grasses that are well-adapted to flooded conditions which include watergrass species Beauv. spp., bearded sprangletop [Leptochloa fusca Kunth ssp. fascicularis N. Snow] and weedy rice . Crop yields and harvest quality face the highest biological constraints due to weed infestations, and farmer inputs towards weed management are expected to increase as herbicide resistances spreads worldwide . Certain weeds and weed groups cause more yield loss than others, even at lower infestation densities . In rice systems, grasses are considered the most difficult weeds to control due to the narrow selectivity between the crop and the grass weeds . Rice yield losses can amount to79% after season-long interference from barnyardgrass [Echinochloa crus-galli Beauv.] and have been recorded as high as 59% due to season-long competition with late watergrass [Echinochloa phyllopogon . Koss] . Weedy rice is an increasingly problematic weed in rice-growing regions around the world causing yield loss and contamination due to the critical weedy traits of seed shattering and seed dormancy, which builds up a large soil seed reservoir for future years . The weedy rice infestation threshold stands at one to three plants m-2 in the USA, with higher ratios causing significant yield loss; weedy rice densities of 30 to 40 plants m-2 can reduce rice yields by 60-90%, depending on the height of the cultivar .

The percentage of DEGs involved in cellular processes and response to stimuli were higher for upregulated genes, whereas the percentage of DEGs involved in biological processes, localization, signaling, multicellular organismal and developmental processes were higher for downregulated genes. Similar relatively low percentages of DEGs were associated with metabolic and rhythmic processes and interspecies interaction. Additionally, a few upregulated genes were associated with immune system processes. In the molecular function class, the majority of DEGs were associated with binding and catalytic activities and these include up and down regulated genes. Those involved in structural molecule activity were upregulated, whereas those associated with molecular function regulator and transporter activities were downregulated . Finally, DEGs involved in molecular adaptor and molecular transducer activities were specifically upregulated. Together, these results suggest that the tomato defense response to TYLCV infection involved up and downregulated genes with similar molecular functions and biological processes. In order to validate the expression levels of these 12 selected DEGs were determined with RT-qPCR . Nine DEG were upregulated in line LA3473-R in response to TYLCV infection . Worldwide begomoviruses show a phylogeographic distribution, with most bipartite ones occurring in the New World , and most monopartite ones occurring in the Old World , and often in association with satellites DNAs that are either required for disease development or have no obvious effect on virulence . However, there are notable exception to this distribution, hydroponic rack system including the identification of indigenous NW monopartite begomoviruses infecting tomato in Peru, Ecuador and Northern Brazil .

The long distance spread and emergence of new begomoviruses has been mediated by the whitefly B. tabaci species Middle East Asia Minor 1 , which is a supervector of plant viruses . Furthermore, before the global spread of the whitefly supervector, begomovirus diseases were widely distributed in noncultivated plants in the NW and OW, with these viruses presumably spread by indigenous species of whiteflies . However, after the global spread of the polyphagous B. tabaci MEAM1 in the 1990s, indigenous begomoviruses were introduced into new cultivated and non-cultivated plant species . This has resulted in the emergence of similar diseases of crops and some weeds in different geographical regions. For example, the NW bipartite begomoviruses bean golden mosaic virus and bean golden yellow mosaic virus are different species that have independently evolved to cause beangolden mosaic disease of common bean in South America and North and Central America and the Caribbean Basin, respectively . Human activities have led to the long-distance intercontinental movement of numerous begomoviruses, which has further blurred the geographic separation of OW and NW begomoviruses, and accelerated the worldwide spread of NW bipartite economically important begomovirus diseases, e.g., introduction of NW bipartite squash leaf curl virus into the Middle East from the NW, and appearance of tomato leaf curl New Delhi virus in the Western Mediterranean Basin from the subcontinent of Asia . However, the most well documented and economically important example is the worldwide dissemination of the invasive OW monopartite begomovirus tomato yellow leaf curl virus . TYLCV was first introduced into the Dominican Republic during the early 1990s , and it has now invaded the Southern US, Mexico and the rest of the world, following the spread of the whitefly supervector .

Unfortunately, the tomato crop is highly permissive host for begomovirus infection, with ~90 tomato-infecting begomovirus species recognized by the International Committee on Taxonomy on Viruses . Tomato is one of the most consumed vegetables in the world . In Central America, tomato has become one of the most important crops in terms of area of cultivation and production . In Costa Rica , tomato is one of the most important vegetable crops, andis locally produced and sold as a fresh market crop often by small holder farmers. However, since the late 1980s, tomato production in CR has been impacted by different begomoviruses representing three examples of emergence and invasion: indigenous locally evolved, invasive from the region and exotic from a different continent. The indigenous tomato infecting begomovirus in CR is tomato yellow mottle virus , previously referred to as tomato geminivirus-Costa Rica . ToYMoV is a NW bipartite begomovirus associated with stunting and yellow mosaic/mottle of leaves . Growers first observed the tomato yellow mottle disease in the late 1980s , and ToYMoV was the predominant tomato-infecting begomovirus in CR until the introduction of the NW bipartite begomovirus tomato leaf curl Sinaloa virus in the late 1990s and the OW monopartite TYLCV in 2012 . Therefore, we consider ToYMoV to represent an indigenous, locally evolved begomovirus, ToLCSiV as an introduced virus from the region and TYLCV as an introduced virus from outside the region. Here, we utilized the tomato begomovirus situation in CR to examine their invasion biology, i.e., their interactions in terms of disease development, viral accumulation and viral genetics. To do this, we first completed the molecular and biological characterization of ToYMoV using full-length infectious DNA-A and DNA-B clones to fulfill fulfilling Koch’s postulates for the ToYMoD and to show that the virus primarily infected solanaceous species. Phylogenetic and sequence analyses indicated that ToYMoV may comprise a distinct lineage that is closely related to the squash leaf curl virus lineage of NW begomoviruses. This is consistent with the long period of local evolution in the region. Full-length infectious clones of an isolate of ToLCSiVfrom CR were generated and used to assess genetic interaction with ToYMoV.

The infectious clones of ToYMoV, ToLCSiV and TYLCV were then used to inoculate tomato plants with each virus clone and all combinations, and symptoms induced and viral DNA accumulation were determined. These findings are discussed in terms of the nature of the invasion biology of these viruses and to predict the future impact of these begomoviruses on tomato product in CR.The complete sequences of the cloned full-length DNA-A and DNA-B components of the GR1 isolate of ToYMoV collected in Grecia in 1990 and the L1 isolate of ToLCSiV collected in Liberia in 2002 were 2,574 nt and 2,547 nt , respectively, and 2,610 nt and 2,563 nt , respectively. The genome organization of these isolates is typical of NW bipartite begomoviruses, i.e., that is, a single gene on the virion -sense strand that encodes the CP, and four in the complementary -sense strand encoding the Rep, the transcriptional activator protein , the replication enhancer and the AC4 protein, respectively. Additionally, the CP and REn aa sequences of these isolates possess the N- and C-terminal motifs PWRlsAgT and AVRFATDr , respectively, which are characteristic of NW begomoviruses . The AC4 aa sequence contains the N-terminal myristoylation domain required for membrane targeting . The DNA-B components of these isolates have two ORFs, one in the v-sense strand encoding the nuclear shuttle protein , and one on the c-strand strand that encodes the movement protein . Pairwise sequence comparisons performed with SDT and the sequences of full-length DNA-A and DNA-B components of the GR1 isolate from Grecia revealed the highest identities with those of the DNA-A and DNA-B components of isolates of ToYMoV from CR . Consistent with these results, the ORFs of these components all had very high identities, i.e., all nt and aa sequence identities were ≥97%, with the exception of the AC4 aa sequence . Similar results were obtained for NTRs, including the common region and the hypervariable region of the DNA-B component . The next highest identities for the DNA-A component sequence were with NW bipartite begomoviruses from Latin America, including Sida chlorotic mottle virus from Brazil , tomato yellow leaf distortion virus from Cuba and tomato yellow vein streak virus from Chile . These results confirmed that the begomovirus infecting tomato plants with yellow mosaic/mottle symptoms in Grecia in 1990 was a variant of ToYMoV, which was named tomato yellow mottle virus-[CR:Grecia:1990] . The SDT analysis performed with the sequences of the complete DNA-A and DNA-B components of the L1 isolate from Liberia revealed the highest identities with those of the DNA-A and DNA-B components of isolates of ToLCSiV from CR and NI , cannabis vertical grow system whereas identities were lower with available partial sequences of isolates from MX. Similar results were obtained in comparisons made with nt and aa sequences of the ORFs , whereas common regionidentities ranged from ≥93 to 97% and identities for HVR of the DNA-B component ranged from ≥95 to 98% .

The next highest identities for the sequences of the DNAA component were with NW bipartite begomoviruses from Latin America, including Sida interveinal bright yellow virus from MX , Sida yellow vein virus from Honduras and chino del tomate virus from MX . The ToYMoV common region sequence contains all the cis-regulatory elements implicated in virus replication and gene expression, e.g., the conserved geminivirus stemloop structure with the nonanucleotide sequence TAATATT↓AC, the Rep high-affinity binding site and the canonical AC1 TATA box and G-box . The Rep high-affinity binding site is composed of two direct repeats of GGTGT adjacent to the AC1 TATA-box, and an upstream inverted repeat ACACC . The Rep iteron-related domain is MPPPKKFRLS , which is predicted to interact with the core iteron sequence GGTGT . Here, it is worth nothing that it has been proposed that ToYMoV may possess a unique 8 nt iteron sequence that is found in all members of the SLCuV lineage . The DNA-A and DNA-B components of ToLCSiV share a common region of 174 nt, which is 96% identical, indicating these are cognate components. The Rep high affinity binding site of ToLCSiV consists of two direct repeats of the GGGGT adjacent to the AC1 TATA-box, and one inverted ACTCC motif . The Rep IRD is MPSVKRFKVS , which is predicted to recognize the GGGGT iteron .In the phylogenetic tree generated with the sequences of the complete DNA-A components, the ToYMoV isolates from CR were placed together in a strongly supported clade , consistent with the low level of sequence divergence among these isolates collected ~22 years apart . This clade was erected as a sister group of the SLCuV lineage, which is composed primarily of cucurbit-infecting begomoviruses from the Southern US, MX and Central America. In the phylogenetic analysis performed with the complete DNA-B sequences, ToYMoV was also placed as a sister clade of the SLCuV lineage . Interestingly, in this DNA-B tree, the ToYMoV isolates were most closely related with bean leaf crumple virus from Colombia . The ToLCSiV isolates from CR form a strongly supported clade with the isolate from NI . This clade was part of the AbMV lineage, which includes crop- and weed-infecting begomoviruses from North and Central America and the Caribbean Basin, such as chino del tomate virus from MX and ToMoV from Florida . In the tree generated with the complete DNA-B sequences, the ToLCSiVisolates from CR and NI were also placed together in a strongly supported clade in the AbMV lineage .RDP4 analysis reveal a single recombination event in the DNA-A component of all four ToYMoV isolates , whereas no recombination was detected in the DNAB component nor in the DNA-A and DNA-B components of ToLCSiV. The recombination event in the ToYMoV DNA-A was 424 nt and spans nts 2056 to 2479 and includes the 5’ end of the AC1 ORF, the entire AC4 ORF and the 5´ sequence of the common region. Thus, this event was in the well-known begomovirus recombination hot-spot region . The RDP4 analysis further indicated that the recombinant region was derived from an uncharacterized minor parent, whereas the major parent was most similar to tomato chlorotic leaf distortion virus from Venezuela .The infectivity and pathogenicity of the full-length cloned DNA-A and DNA-B components of ToYMoV-[CR:Gre:90] were established by particle bombardment inoculation of N. benthamiana and tomato seedlings . By 14 dpb, all of the bombarded N. benthamiana plants were stunted and newly emerged leaves showed epinasty, crumpling, yellow mosaic/mottle and vein yellowing ; whereas tomato seedlings were stunted and newly emerged leaves had developed epinasty, crumpling and mild yellow mosaic/mottle by 14dpb . In N. benthamiana and tomato plants, symptoms in ToYMoV-infected plants became progressively milder by 21 dpb . Notably, symptoms in tomato plants following bombardment of the infectious ToYMoV clones were similar to those of the ToYMoD of tomato in the field in CR, thereby fulfilling Koch´s postulates for this disease.

Careful weed management during the season is important, but it must be followed up with off-season weed control as well. Short-season crops such as lettuce can provide opportunities for frequent cultivations and a rapid turnover of crops on the land, thus reducing some weeds’ ability to mature and set seed. Highly competitive cover crops can also smother weeds. If you carry weeds with seed out of the field for disposal, you can also significantly reduce the seed bank. Each of these techniques can help growers minimize weed problems, and that translates to lower hoeing bills.Cultivation is probably the most widely used weed control method in organic vegetable operations. Mechanical cultivation uproots or buries weeds. Burial works best on small weeds, while larger weeds are better controlled by destruction of the root-shoot connection or by slicing, cutting, or turning the soil to eliminate the root system’s contact with the soil. Cultivation is effective against almost all weeds, with the exception of certain parasitic forms such as dodder. Effective cultivation must precisely and accurately target weed growth areas, and so requires good land preparation and bed shaping. Shallow cultivation usually is best, since it brings fewer weed seeds to the surface. Level beds allow more precise depth of tillage. Cultivation requires relatively dry soil; subsequent irrigations should be delayed long enough to prevent the weeds from re-rooting. In addition, vertical farming supplies cultivations should be carried out early enough in the growth cycle to kill weeds such as burning nettle and purslane that set seed early in the growth cycle. The goal of cultivation is to cut out weeds as close to the seed row as possible without disturbing the crop. In most cases, precision cultivation can take care of the weeds on over 80 percent of the bed.

The remaining weeds must be removed from the seed row by hand or using other mechanical means. Here are some common cultivation implements: Various knives, L-shaped and crescent-shaped beet hoes, and sweeps can be used to cut and uproot weeds on bed tops within 1 to 3 inches of the crop row. These can sometimes be combined with reversed-disc hillers that cut vining weeds such as field bindweed and move soil away from the crop row. Disc hillers are often reversed as crops get larger so they will throw soil around the base of the crop plant to bury weeds. Rolling cultivators have become common cultivating implements for a number of crops. A rolling cultivator’s primary purpose is to uproot weeds, but it can also be adjusted to throw soil and bury weeds in the crop row. A new generation of cultivators has been developed to remove weeds from between the seed rows, and in some situations from the seed row itself. Spring-tine cultivators, torsion Bezzerides cultivators, Budding in-row weeders, and brush hoes all can be adjusted to take out weeds between seed rows or close to the seed row. Some of these cultivators can remove weeds from the seed row itself in fields planted to tough-stemmed crops like cotton. Computer-guided cultivators that can distinguish the crop from weeds are under development and may soon be able to remove weeds selectively from within the seed row. Cultivation implements are often mounted on sleds for accurate, close cultivation in row crops. Guide wheels, cone wheels, and other devices are also used, but in general these are less precise than sleds. Various implements can be attached to these guidance setups to remove weeds. Even the best cultivators will not eliminate all weeds, so some hand weeding is often necessary. It is easier to remove weeds by hand while they are small.

The proper timing of cultivations depends on the speed of weed growth: in spring a two- to three-week periodis about right; in the fall or winter, longer periods between cultivations may be appropriate. The practice and experience of the grower are important factors in effective cultivation. Weeds that compete with the crop early in the crop cycle may be more damaging to crop yield than weeds that establish later in the season. Late-season weeding may disturb the crop’s root system or knock off flowers or fruit, which may reduce yields. Obviously, late season cultivations to reduce weed seed production must be weighed against the potential for yield loss.Flamers are useful for weed control. Propane-fueled models are the most common. Flaming does not burn weeds to ashes; rather, the flame rapidly raises the temperature of the weeds to more than 130°F; The sudden increase in temperature causes the plants’ cell sap to expand, rupturing the cell walls. For greatest flaming efficiency, weeds must have fewer than two true leaves. Grasses are difficult to impossible to kill by flaming because the growing point is protected underground. After flaming, weeds that have been killed rapidly change from a glossy appearance to a duller appearance. Flaming can be used prior to crop emergence in slow-germinating vegetables such as peppers, carrots, onions, and parsley. In addition, flaming can be used postemergence on crops such as young onion and garlic or as a directed treatment to the base of tougher crops when they are 12 or more inches tall. Postemergence flaming does adversely impact the yield of the crop, so its use must be weighed against the potential damage the weeds might cause. Typically, flaming can be applied at a speed of 3 to 5 mph through fields, although this depends on the heat output of the unit being used. Best results are obtained under windless conditions, as winds can prevent the heat from reaching the target weeds.

The efficiency of flaming is greatly reduced if moisture from dew or rain is present on the plants. Early morning and early evening are the best times to observe the flame patterns and adjust the equipment.Soil sterilization in organic agriculture involves the use of heat or naturally generated biocides to kill weeds. Heat is applied as steam or by soil solarization. In steam sterilization, the steam is injected into the soil to kill weed seeds. The large quantities of fuel and water required by this technique make it an expensive choice, so its use is limited to small acreages of high-value horticultural crops or landscaping. Ozone is a naturally occurring biocide that is being researched for use as a soil sterilant. The ozone is generated mechanically and then injected into the soil. Ozone injection shows promise as a weed-reduction tool, but it is unclear at this time whether this technique will be considered an organically acceptable practice. Soil solarization involves placing a clear plastic mulch over a tilled, moist soil to allow the solar energy to heat the soil and kill germinating weed seeds. To be most effective, solarization should be performed during summer and fall periods of maximum solar radiation exposure. Mulching is another weed control method. A mulch blocks light, preventing weed germination and growth. The materials that can be used as mulches are varied, and include plastics and organic materials such as municipal yard waste, wood chips, straw, hay, sawdust, and newspaper. To be effective, a mulch needs to block all light to the weeds, and some mulch materials require a thicker application layer that others to accomplish this. Plastic mulches vary in thickness from 1.5 mil to about 4 mils. The most common color for weed-control plastic is black, since it completely blocks light. More recently, a clear, infrared-transmitting plastic has been introduced. The IRT plastic blocks certain wavelengths of light but allows others to pass, and that heats the soil better for early-season crop growth. Plastic mulches are generally placed on the beds and their edges covered with dirt to keep them from blowing away. Drip irrigation is needed to get moisture to the crop under the plastic mulch. Certain weeds, including nutsedge, vertical weed grow are able to penetrate the plastic and so are not completely controlled by plastic mulches. Other weeds can grow in the openings provided for crops. Further problems with plastic mulches include difficulties keeping them in place under windy conditions, disposal after the crop is harvested , and their cost . Organic mulches such as municipal yard waste, straw, hay, and wood chips must be maintained in a layer 4 or more inches thick in order to block out light.

Organic mulches break down over time, and the original thickness typically reduces by 60 percent after one year. Coarse green waste works better as a mulch. Organic mulches are mostly used for permanent crops, landscaping, and non-crop areas, although they are also very effective for transplanted vegetables. Organic mulches can be grown in place. Plants used to produce organic mulches include cereals, clovers, vetches, and fava beans. These mulches must die or be killed before or shortly after crop planting in order to avoid excessive competition with the crop. Living mulches were developed in the eastern United States, but are currently being tested on various fruiting vegetables in California .Although winter squash can be planted “on the flat” , a bedded system improves moisture retention and weed management. Perform standard tillage practices to incorporate crop or cover crop residue , break compaction, and adequately loosen soil. Then, form the planting beds using bedding shovels or a rolling cultivator. If there is no rainfall following bed formation in the spring, preirrigate with overhead irrigation to wet the root zone and germinate weeds prior to planting. This pre-irrigation further improves soil conditions and tilth by breaking down soil clods or clumps of cover crop residue, leaving the soil loose, moist, and friable. Following the pre-irrigation , eliminate newly germinated weeds with a rolling cultivator or other suitable cultivation technique. If timing is good and the moisture is uniform, such a run can work wonders. This initial cultivation breaks surface crusting and provides a “soil mulch” to slow evaporative loss of deeper soil moisture. Once crop or cover crop residue is adequately decomposed and soil temperatures are above 60ºF, use a suitable planter to push aside the drier soil on the bed tops and plant the squash seeds into the deeper moisture in the bed.In general, winter squash can be planted from mid-May through June on California’s Central Coast. Shorter-maturing varieties can be planted in early July. Planting dates are based on timing of adequate seedbed preparation , soil moisture , and optimal soil temperature . Plant late enough in spring to allow for rapid plant growth; this will help limit cucumber beetle and other herbivore damage to seedlings. Planting dates must be early enough to allow the crop to mature and adequately field cure before fall rains, heavy dew, or frost.Winter squash seed can be planted to moisture by hand with a shovel or trowel. There are also “seed stick” planters that are very effective for planting winter squash. Push planters such as the Planet Jr. are effective for garden-scale production, but require a special “deep” opening shoe to get the seed far enough into moist soil. On larger field-scale blocks , use a tractor-mounted planter such as the John Deere 71 “flexi” planter or other similar plate-type planter . Adjust planting depth with a rotating cam on the side of the planter, which changes the angle of the press wheel in relation to the disc openers. For mixed blocks of winter squash on relatively small plots, the planter hopper can be removed and the seeds hand dropped into the drop tube. This circumvents the need for multiple seed plates to match each variety. Note that it is better to plant into soil on the drier side. On many soil types, if the soil is too wet at planting, soil surface crusting can impede successful crop emergence. Squash plants that struggle to break through crusted soil may remain stunted. In cases when the soil is either too wet or too dry, you can form a “cap” of soil over the seed line to either minimize crusting or to minimize further evaporative loss . Run soil cappers behind the planter to create a loose cap of soil right over the seed line behind the planter’s pack wheel . With optimum soil conditions and planting depths, plants should emerge in 7–10 days. Uniform emergence is the best sign of optimal planting conditions and potential for a successful crop. The most critical aspect of effectively “planting to moisture” is your ability to judge soil moisture and decide on seed depth.

The third highest ranking concern of the Northern and Southern San Joaquin Valley and Low Desert regions was “water quality ”, while “regulations on water quality” was the third highest ranking concern for the Intermountain region. The third highest ranking concern of the Coastal and ierra Nevada regions was “regulations on chemical use”. The acramento alley ranked “input costs” in the top three concerns. Growers were asked about their top management challenges for the agronomic crops they grow. While several stood out, such as weed control and irrigation/water management ranking as the top challenges , there was relatively strong representation across categories. Soil management, disease control, and harvest operations ranked lowest. When broken down by the top 8 agronomic crops, the highest-ranking management challenges differed among crops . Irrigation/water management was the top management challenge for alfalfa and corn silage growers, while weed control was the top management challenge for dry beans, sunflower, and cotton growers. For rice growers, irrigation/water management and weed management were tied for first as the top management challenge. Nutrient management was the top management challenge for wheat and corn grown for grain.Slightly more than 2/3rds of responses were from California’s Central Valley which is where most of the state’s agricultural production is located . In 2017, counties with the highest total cropland were Fresno , Kern , Tulare , Merced , and San Joaquin . According to USDA NASS data from 2018, the district containing Fresno, Kern, Kings, Madera, Merced, San Joaquin, Stanislaus, and Tulare had the highest total gross value of agronomic crops in 2018 , vertical grow rack system while the district containing Butte, Colusa, Glenn, Sacramento, Solano, Sutter, Tehama, Yolo, and Yuba counties had the second highest gross value of agronomic crops in 2018 .

Therefore, since 67% of our respondents represent these two districts, the geography of our respondents appears to be representative of where much of the agronomic crop production is taking place in the state. Representation is lacking most in Imperial county, which is a large producer of agronomic crops, particularly hay crops. In 2018, Imperial county had 341,229 acres in agronomic crops, ranking second in the state for gross value of alfalfa production . However, it is important to note that the average farm size in Imperial County in 2018 is much larger than the state average of 348 acres, meaning that less people may be working larger areas of land. Therefore, looking only at acreage and economic value in agronomic crops may not be representative of how many people in our target population work in a particular region. Regarding the top three field crops grown by respondents, agriculture census data from 2017 shows that rice represented 541,000 planted acres in California, alfalfa 720,000 acres, and wheat 480,000 acres in 2016 . Grain corn represented 420,000 planted acres, silage corn 315,000 acres, cotton 218,000 acres, dry beans 50,000 acres, and sunflower 46,600 acres. Therefore, crop representation in our needs assessment survey roughly follows the area planted throughout the state. The results of our survey indicate that respondents are skewed slightly younger than the distribution of the industry population. According to the 2017 Census of Agriculture Online, the average age of California farmers is 59 years old . Nearly 60% of survey respondents were 54 years old or below, and the greatest number of respondents fell between the ages of 35-44 . This may be related to the mode of survey delivery. Online surveys may be bias towards younger respondents with higher income and education .

Additional drawbacks to online surveys include the fact that the survey presentation may vary based on browser settings and variations in hardware which may increase the likelihood of response error . In addition, the flexibility of the internet and ease with which false identities can be created can make survey results unreliable . Online surveys do have the advantage of allowing for large-scale and inexpensive data collection. With online surveys, costs per response decrease as sample size increases, while for surveys sent through postal mail, costs tend to increase significantly as sample size increases . Research comparing electronic surveys to postal surveys has confirmed that electronic survey content results may be no different than postal survey content results yet provide advantages of fast distribution . Qualtrics Survey Software allowed us to customize survey questions based on the respondent’s primary vocation. While paper surveys can also indicate that a set of questions are only for people that select a particular answer choice in a previous question, the online survey allows for a more customized experience through format and response control . Electronic surveys can also yield a significantly higher response rate than paper surveys . Because the objective of this study was to reach the broadest audience possible, an online survey that could be completed on a computer or mobile phone platform was selected.Water-related issues were clearly the most prominent in our survey responses, representing 4 out of the top 5 concerns listed by respondents. Specifically, regulations on water use and water costs were the two concerns that had the highest number of respondents expressing that they were “very concerned”.

The Sustainable Groundwater Management Act , signed into law by Governor Brown in 2014, requires groundwater-dependent regions to stop over drafting groundwater and develop plans to balance pumping and recharge . Since this is the first time groundwater use is subject to regulations in California, growers are expectedly concerned about changes that will occur as a result. Groundwater contributes % of California’s water supply in an average year, and up to % or more during dry years, while some agricultural and disadvantaged communities rely on groundwater for up to 100% of their water supply . This suggests that tensions will grow in the future as groundwater pumping regulations are enacted. Water is generally the most-limiting input for crop production, and therefore impacts on cost, availability, or quantity will limit the capacity for growers to manage this resource. California has approximately 2.8 million ha of irrigated land, which produces nearly 90% of the harvested crops in the state . A decrease in water availability because of new regulations has implications for maintaining the same area under irrigation into the future. Impacts of water decline were already being felt before SGMA was signed into law. Due to increasing incidence of prolonged drought, California saw a decline of more than 200,000 acres of irrigated land between 2004 and 2006, while nearly 250,000 acres had to be idled in 2014 alone . It is projected that an additional 500,000 to 1 million acres of land in the San Joaquin Valley alone may have to be retired due to SGMA . Uncertainty and difficulty around water resource planning and management is amplified by increasing unpredictability of weather patterns. Annual rainfall varies greatly in California – more notably than other parts of the country – which makes predicting rain fall year to year a challenge . For these reasons, it was unsurprising that irrigation and water management were ranked as a top management challenge for survey respondents.A large portion of respondents expressed that they are “very concerned” about regulations on chemical use, such as pesticides, fertilizers, and herbicides. Given new or impending bans on agrochemicals in California, vertical farming racks it makes sense that growers are concerned about finding alternatives. California’s recent ban on chlorpyrifos – an inexpensive and effective pesticide used nationwide since 1965 – highlights this issue. Chlorpyrifos exposure has been linked to harmful health effects, including neurodevelopmental disorders . In 2015, the Environmental Protection Agency proposed a federal ban for chlorpyrifos on all food crops, but soon after, the federal government under the Trump administration concluded the science was “unresolved” and removed the ban. Regardless, California, along with Hawaii and New York, decided to move forward with banning chlorpyrifos. In California users were required to stop using these products on December 31, 2020. Other states continue to use these agrochemicals, leaving California growers to feel like they are at a competitive disadvantage.

The ban on chlorpyrifos has and will likely continue to be felt where it was most heavily used. This includes Fresno, Tulare, Kern, and Kings counties, all of which have strong representation in our survey. The period between 1991-2012 saw large increases in chlorpyrifos use in these four counties . During this time, 7.2 million pounds of chlorpyrifos was used in Fresno county, 6.1 million pounds was used in Tulare county, 5.4 million pounds were used in Kern counties, and 3.2 million pounds was used in Kings county . Effects will also be felt heavily in alfalfa production since chlorpyrifos is the most popular side-spectrum insecticide for management of key alfalfa pests, such as the alfalfa weevil and aphids . In our survey, 5% of alfalfa growers and consultants said that they were “very concerned” about regulations on chemical use. There are other impending regulations on neonicotinoids in California, which are commonly used on cotton, corn, and grains. However, recent evidence has linked these chemicals to honeybee die off and declining pollinator health . Because of the high solubility of neonicotinoids in water, it has also been found that they readily leach into water bodies and can persist over multiple years, which has implications for aquatic species . In July 2018, the California Department of Pesticide Regulation announced that they will not consider applications of any new uses of neonicotinoid insecticides until re-evaluation of the chemicals are completed . An addendum was published in January 2019, and the investigation is ongoing . This prospective ban is particularly worrisome to certain stakeholders. A recent study found that in 2011 between 79-100% of maize acreage in the USA were treated with neonicotinoids . In addition to chemical bans, there are significant challenges with getting new products registered in California. California is unique in that tens of thousands of residents live near intensively farmed areas and the production is often labor-intensive. Therefore, the effect of pesticide use at the agricultural-urban boundary and the potential effect on farmworkers are key evaluation factors for product registration by the California DPR, while there is not as much emphasis on these factors at the federal level by the U.S. EPA . In addition, federal pesticide law mandates that the U.S. EPA consider the economic benefits of a pesticide when deciding whether to register it. California law does not allow consideration of economic benefits in the decision to register a pesticide unless there is no feasible alternative. Therefore, the financial advantages of using a certain pesticide cannot outweigh the health risks of use under California law. This is beneficial for communities, farmworkers, and consumers – yet, it may seem unfair to growers and input suppliers when market competitors have access to chemicals that they do not.Weed control was ranked as the top management challenges by growers and consultants. Current estimates of losses on global crop production show that weeds cause the largest losses , followed by insects , and diseases . Total weed control costs in the U.S. are more than $11 billion a year, most of which is spent on herbicides . The direct annual cost to monitor and control invasive plants in California is estimated at around $82 million . One of the most widely used herbicides is glyphosate. Although the Environmental Protection Agency has repeatedly stated that glyphosate is safe, California has led the charge in holding Monsanto accountable for Roundup’s link to cancer in humans and the death of important insects. As early as 2017, California added glyphosate to its list of carcinogens under Proposition 65 and the state has a growing number of cities and counties banning or restricting glyphosate. To date, more than 40 communities in the state of California have restricted the use of glyphosate in some capacity . Yet, weed management as a category in our survey was broad and could mean many things – new weed species, herbicide resistance, drift issues, or preventing the use of certain herbicides, Therefore, UCCE must work directly with agronomic crop producers to determine future directions of weed management research. Herbicide resistance is a growing concern in cropping systems throughout the state, particularly in rice .

Together, these rapidly expanding species cover more than 15 million acres throughout California . The phenological development of medusahead and yellow starthistle is in part what makes these invaders so successful. Medusahead, and particularly yellow starthistle, mature late in the annual growing season . These species germinate after the first fall rains, with smaller germination events sometimes occurring later in the wet season . Although germination timing is similar to that of the surrounding grassland community, medusahead does not produce seed heads until late April or May, after most naturalized annuals have completed their life cycle . Yellow starthistle commonly produces seed heads in May and June; it begins flowering in June and can continue beyond October . In fact, many of yellow starthistle’s developmental stages generally extend well into the summer dormant period distinctive to Mediterranean climates . The later development periods enable medusahead and yellow starthistle to take advantage of late spring and early summer rains when they occur. When late-season moisture is present, medusahead and yellow starthistle will continue to grow after potential competitors have stopped, allowing them to dominate and dramatically alter the vegetation structure .Prescribed livestock grazing is commonly proposed as a low-cost, if not profitable, option to manage weedy species on rangelands. Prescribed grazing is the controlled implementation of the timing, vertical grow room design frequency and intensity of grazing to achieve specific goal, such as weed control. Small-scale grazing studies have examined the effects of livestock type , grazing intensity and grazing season on individual weed species .

These studies have consistently demonstrated that properly timed and intensive grazing can reduce medusahead cover by 30% to 100% and yellow starthistle flower heads by 75% to 90% . Experimentally manipulated livestock grazing has also been shown to enhance herbaceous diversity and native plant richness in vernal pools, interior annual grasslands and coastal grassland sites . However, there is little published work examining pasture-scale implementation of prescribed grazing to manage invasive weeds.Across California, rangeland managers have reported that livestock grazing can be managed to control medusahead and yellow starthistle . These findings are experiential rather than experimental — that is, based on direct implementation, observation and site-specific fine-tuning of intensity, season and frequency of livestock grazing to achieve specific goals. A recent scientific review of conservation effectiveness of rangeland management practices highlighted a critical need for the monitoring and reporting of practice effectiveness at the pasture scale . Collaborative, on-theground management implementation and monitoring will enable managers and researchers to better assess effectiveness and practicality of conservation practices such as prescribed grazing to control invasive weeds. Our objective was to assess the effect of a “real” prescribed grazing regime implemented by ranch personnel on medusahead and yellow starthistle populations on a Bureau of Land Management grazing allotment known as the Bear Creek Unit of the Cache Creek Natural Area.The Bear Creek Unit, located in Northern California’s interior coast range in Colusa County, is an 11,090-acre BLM-managed land that consists of a patch-mosaic of annual grasslands, blue oak woodlands and serpentine chaparral plant communities. The climate is Mediterranean, with hot, dry summers and mild, wet winters. Mean annual precipitation is 24 inches, and mean annual air temperature is 61°F .

Sites examined in this study ranged from approximately 1,200 to 1,600 feet in elevation. For this study, we targeted the annual grassland and blue oak woodland plant communities, as they provided the majority of forage on the management unit, and were dominated by the target weeds. In the study area, soils were largely formed from residuum of sandstone and shale , with a small inclusion of soils formed from alluvium . Common nonnative annual grasses include soft chess , slender oat and ripgut brome . This area also supports various native forbs, including miniature lupine , Ithuriel’s spear , owl’s clover Chuang & Heckard, mariposa lily and tidytips . Native grasses are widely scattered in the area, with purple needle grass being the most prominent native perennial grass. Medusahead and yellow starthistle are common across the landscape, with an emerging population of barb goatgrass also present.Until August of 2001, the Bear Creek Unit was continuously grazed throughout the growing season under grazing leases. The BLM, which acquired the Bear Creek Unit in 1999, terminated grazing in 2001 in an attempt to enhance native plant cover. In the 4 years following cessation of grazing, BLM monitoring teams reported increased invasive weed cover and high accumulations and persistence of vegetative litter, or thatch . In fall of 2006, average residual dry matter across the unit was estimated to be 4,200 pounds per acre. In working toward invasive weed control — one of BLM’s top management priorities — the BLM collaborated with local stakeholders to reintroduce grazing on the Bear Creek Unit in 2006. To target medusahead and yellow starthistle, we implemented a moderately stocked, rotational cattle grazing system across 11 paddocks, ranging from 80 to 600 acres in size. Paddocks were generally grazed January through May using cows calving between January and March — cattle on and off dates, stocking densities and paddock rotations were made at the discretion of the site manager based on factors such as drinking water availability, forage availability and cattle conditions . From 2006 to 2011, cattle numbers ranged from 318 to 520, averaging 392 total cows during the study period.

Grazing event duration ranged from several days up to 2 weeks, with two grazing events per paddock: one grazing from late November to February to reduce weed thatch, and allow alternative species to establish ; and one grazing event from March to June to target late-flowering invasives . By October of 2009, we estimated average RDM across the unit to be 1,400 pounds per acre, or approximately one-third the RDM observed under initial ungrazed conditions.Prior to reintroduction of cattle grazing, we established permanent paired plots in each of the 11 paddocks. Permanent plots were chosen in a random stratified manner to ensure sample sites were representative for each pasture. Exclosure plots measured 8 feet by 8 feet and were livestock proof. To examine shifts in plant species cover and abundance over the course of the study, we began monitoring plant community composition in June of 2006. At each set of permanent grazed and ungrazed paired plots, we estimated percent basal cover by species within a 10-ft2 hoop. Ocular estimates of herbaceous composition were collected after peak standing crop for both grazed and ungrazed plots in June of 2006, 2009 and 2011. This resulted in a total of 22 observations for each year, and 66 total observations for the study period. To determine if grazing management at the Bear Creek Unit significantly impacted medusahead and yellow starthistle over the course of the study, we used linear mixed effects regression to examine trends in cover of these species between grazed and ungrazed treatments. The dependent variables observed were percent medusahead and yellow starthistle cover, and the independent variables were treatment , year and the interaction between treatment and year. Within each treatment, we also examined changes in cover between the baseline and final evaluations for the most commonly occurring species: medusahead, yellow starthistle, soft chess, filaree , red brome , ripgut brome, slender oat and a composite functional group composed of several thatch-loving species including red brome, ripgut brome and slender oat. We used linear and generalized linear mixed effects regression models to test for differences in percent observed species cover between 2006 and 2011. For all analyses, site identity was included as a random term to account for repeated measurements . Standard diagnostic tests were used to check assumptions of linearity, normality and constant variance. Analyses were performed using STATA/SE 13.0 statistical software . To examine changes in overall plant community composition, clone rack we used non-metric multidimensional scaling . NMDS is an ordination technique widely used to examine patterns in multidimensional data and, unlike other ordination methods, makes few assumptions about the data. Species cover values were log-transformed, and NMDS scores were calculated based on a Bray-Curtis dissimilarity matrix . Analysis was conducted in the R software environment using the metaMDS routine from the vegan package . The metaMDS function selects several random start positions to find a global solution, so that it does not become trapped at local optima. The final configuration is rotated via principal components so that the first dimension explains the greatest amount of variance. NMDS was run for 2 through 6 dimensions, with the optimal number of dimensions selected via examination of a scree plot, which displays stress versus dimensionality for each solution .

To examine whether overall plant community composition significantly differed between grazed and ungrazed treatments, we used blocked multiresponse permutation procedures . MRBP provides a non-parametric test of multivariate differences between pre-defined groups, such as “grazed” and “ungrazed” plots . Observations were blocked by plot pair identification number, and species cover data were log-transformed. Our analyses showed that prescribed grazing applied to Bear Creek Unit did not impact yellow starthistle cover. Trends in basal cover of yellow starthistle did not significantly differ between grazed and ungrazed treatments , with no significant changes in yellow starthistle cover for either treatment between baseline and final evaluations . The lack of response to grazing may be due to a mismatch in the timing of grazing and the post-bolting/pre-flowering phenological stages of yellow starthistle. Since yellow starthistle matures and produces seeds later than other species, including medusahead, grazing late in the annual growing season is particularly important for effective suppression . In addition, yellow starthistle populations commonly exhibit multiple life forms simultaneously . This diversity creates an additional obstacle to suppression, because individual plants are not all susceptible to grazing at the same time. During this study, timing of cattle removal was dictated by real management considerations such as availability of water and desirable forage for livestock, which were both limited by May in most years. As a result, cattle were likely not present during the post-bolting/pre-flowering phenological stages when grazing can reduce yellow starthistle cover and seed production .Following baseline botanical evaluations, medusahead cover within grazed treatment plots fell by roughly half in 2009. Additionally, in 2009, medusahead cover in the grazed treatment was significantly lower than that observed in the ungrazed treatment . However, by the final evaluation , medusahead cover for both grazed and ungrazed treatments converged to similar levels. As with yellow starthistle, research has shown that grazing late in the growing season is critical to successful medusahead control . However, medusahead develops earlier in the spring than yellow starthistle and does not exhibit yellow starthistle’s diversity of life forms. Medusahead’s earlier maturing phenology narrows the window for grazing to achieve suppression. Although managerial constraints in this study made it impossible to graze late enough into the season to impact yellow starthistle, medusahead populations were impacted in several years. The differential reduction of medusahead cover in the grazedtreatment between the periods 2006 through 2009 and 2009 through 2011 is potentially explained by three interacting factors: timing and amount of rainfall; timing of cattle removal each spring; and ability of medusahead to recover from grazing and produce seed. During the period 2006 through 2009, when medusahead cover was significantly reduced in the grazed treatment , late spring and/or total annual rainfall were substantially lower than reported long-term averages in 2007 and 2008. Lack of late season precipitation created dry soil moisture conditions at the end of the grazing season, which potentially diminished the ability of medusahead to recover from grazing and produce new seed heads , which is why the plant reduction created in 2008 is apparent in 2009. With the exception of 2006 and 2010, cattle were removed from the management unit between May 22 and 27. The lower late season rainfall, and resulting depleted soil moisture levels, may have created a multi-year window of opportunity in which the timing of grazing overlapped with the most susceptible phenological stages of medusahead development. In contrast, late spring rainfall during the period 2009 through 2011 was well above the reported long-term average, which potentially enhanced the ability of medusahead to respond to postgrazing conditions. Although the timing of cattle removal was similar to that of the 2006–2009 period , this late season rainfall enabled medusahead plants to recover from grazing disturbances and produce new inflorescences.

Researchers and advocates in Uganda used data on deforestation, costs and benefits of tobacco farming and other issues to develop public support for effective tobacco control policies and for the Framework Convention on Tobacco Control. In February and March 2004, researchers with the Environmental Action Network conducted a survey among farmers in Uganda focusing on deforestation and economic and health status. Researchers interviewed government officials on the same issues. Findings revealed that farmers in Uganda suffer worsening poverty and poor health associated with tobacco growing. The project is a best practice to retrieve and organize data on the social and environmental costs of tobacco growing. In the U.S., tobacco farmers and tobacco control advocates committed to reducing disease caused by tobacco and ensuring the prosperity and stability of tobacco farmers, their families and communities. Beginning in 1994, national groups such as the National Black Farmers Association and the Campaign for Tobacco-Free Kids, state groups such as the Coalition for Health and Agricultural Development in Kentucky and the North Carolina Council American Cancer Society, and regional groups such the Burley Tobacco Growers Cooperative and the New England Society of Public Health Education participated in meetings with representatives of all groups affected by tobacco, provided expertise to educate participants of similar and opposing positions, vertical farming supplies and encouraged tobacco dialogue to strengthen alliances between farmers and health advocates. Cooperation and commitment to promote tobacco farmer prosperity and public health renders false the dichotomy between policies for tobacco agriculture development and policies directed at the reduction of tobacco use.

The common ground established by farmers and health groups in the U.S. is a best practice that could be used to build partnerships for tobacco farmer welfare and tobacco control in developing countries. Conclusion Tobacco farming contributes to poverty and insufficient economic development in developing countries. Farmers under contractual obligations to tobacco companies or farm landlords are vulnerable to leaf downgrading, suppressed tobacco prices, and inflated prices for inputs. Bonded labor prevents farmers from receiving earnings to cover costs for inputs, food requirements, and health care needs. Child labor undermines children’s education and threatens their health and physical growth, pushing children into a cycle of poverty. Tobacco farming involves wood use for curing and pesticides and fertilizers that destroy forests and pollute soils and water tables. Tobacco farming erodes the lives of present and future generations of farmers, harming human and land capital, key assets for rural development, that could otherwise be devoted to healthy crops and environmentally friendly agriculture.Ecological interactions are increasingly recognized as being highly contingent on their context, shaped by forces that are both historical and contemporary as well as biotic and abiotic . For example, variation between years and sites can have profound influences on the outcomes of field experiments in community ecology . If we want the results of ecological experiments to be general, and not unique to a particular site or time, we need to better explore and understand these and other contingencies. Understanding such contingencies is also crucial for successfully restoring ecosystems. One emerging theme is the phenomenon of priority—how differences in arrival times by different species may have profound effects on the long-term trajectories of communities .

Such priority effects were the centerpiece of initial definitions ofassembly theory, and are currently being explored as potential management techniques in ecological restoration, in particular to assist the establishment of less-competitive species in communities . A number of experimental studies on perennial herbaceous plants have shown that a 1- to 3-week priority can significantly affect initial community structure . In other words, initial community structure is contingent on the relative arrival times of species. This includes research in our study system , where we have extended this concept to show that even small initial priority effects of native perennial grasses over exotic annual grasses can multiply over several years to result in substantially greater cover by the natives . Priority effects may be particularly relevant for testing the mechanisms underlying the competitive advantage of invasive annual plants over native perennials. In many western US ecosystems, these invasives have become community dominants . It has been posited that this competitive advantage is driven by the earlier germination and initially higher growth rates of the annuals . Several short-term priority experiments suggest that this is the case . Most of these studies were carried out at a single site and in a single planting year, and we do not know how the strength and consequences of this priority effect differ though space and time. The structure of communities may also be dependent on conditions in the year in which they were established . Ecologists , and restoration practitioners have noted differences in project outcomes and results from experiments initiated in different years, but these have not been subject to controlled experiments where putative drivers of year differences are manipulated. Community structure may be also contingent on site conditions, and the relative abundances of different species may change over relatively small environmental gradients .

It is likely that these differences are due to a combination of site effects, year effects or differences in restoration practices , but these different factors have rarely been examined together in controlled, replicated experiments. Here we report the results of experimental tests of how seeded native perennial grass cover is influenced by competition with exotic annual grasses, the relative timing of seed arrival , rainfall addition and geographical location . We also tested the interactions among priority, rainfall addition and site effects.Over the previous 6 months , we had collected seeds of local provenance at each of the three sites from four native perennial grasses and four exotic annual grasses . For a few of these 24 provenances for which local reproductive populations could not be located, we purchased seeds from local native seed providers. We made some adjustments at the species level to match local sites: for the annual Avena species, we collected and sowed A. fatua in Davis and the very similar A. barbata at McLaughlin and Hopland; for the annual Vulpia species, we collected and sowed V. myuros at Davis and McLaughlin, and the similar species V. bromoides at Hopland. At each site, we established five blocks, each with two replicates of the following four planting treatments: natives sown alone , natives sown together with exotics , natives sown and exotic sown 2 weeks after the next germinating rain and exotics sown alone 2 weeks after the next germinating rain . Planting treatments were implemented in an additive design . In a splitplot design, blocks were divided in half, with one half designated for rainfall manipulation . Each experimental plot was 1.25 m on a side, and each was separated from adjacent plots by 1 m. Prior to planting, all sites were tilled to control weeds, both before and 1–2 weeks after the first germinating rains in the fall. Within 1 week of the second tilling, we did the first sowing . Each plot was lightly raked, sown and then raked again to increase seed–soil contact. There was a second germinating rain on 24 November. Two weeks later, the plots designated to receive a second sowing where sown. Unusually, there had been little rain in the intervening 2 weeks, and there was no rain in the 5 weeks that followed the second sowing. Therefore, to simulate an early season rain that was more similar to a normal year, weed rack the four treatments designated for rainfall manipulation in each block were watered with the equivalent of 1.25 cm of rain immediately after the second sowing pass .

Over the following weeks, plots were weeded of volunteer forbs. Because grasses are difficult to reliably identify at the seedling stage and because there were volunteer seedlings of sown species at two of the three sites , we only weeded the obvious non-sown grass species. Nonetheless, there were significantly greater exotic grass densities in the plots deliberately sown with exotics than in those without . Surveys were carried out after the main winter rain had ceased in the spring, at the time of peak flowering. For the Davis and Hopland sites, this was 26–31 May 2012. The phenology of the grasses was delayed at the higher elevation McLaughlin site, which was surveyed 8 June 2012. The areal cover of each seeded species was visually estimated for each plot. We also recorded the cover of common non-sown exotic grasses.For each of the following analyses, linear mixed-effects models were specified with the lme function from the R software package ‘nlme’ . Block was included in all of the models as a random effect. Where necessary, variance structures were specified using the VarIdent function to address violations of homogeneity of variance . ANOVA tables were generated by calling the anova command from the ‘stats’ package . Due tothe nested nature of the design we tested the effects of each factor with sequential sums of squares.It is not surprising that the success of sown native grasses was greatly reduced when sown together with exotic annual grasses , and that in general, cover by exotic annual grasses and native perennial grasses were strongly negatively correlated . In grassland restoration projects in the Central Valley of California, the presence of exotic annuals represents perhaps the greatest challenge to successfully establishing native perennial grasses, and aggressive pre-sowing control of exotics is now considered a sine qua non for restoration. Conversely, one of the most effective means of preventing the dominance of exotic annuals is the establishment of cover by native perennial grasses . Together, these processes result in strong negative correlations between exotic and native grasses. The magnitude of the competitive suppression of natives by exotics, however, varied across the three sites. Site effects are a complex array of interacting differences, including different means and patterns of rainfall and temperatures, different intensities and identities of weed challenge, and different herbivore pressures. We can only suggest which are the important drivers, but note that in the coolest site , where native grasses achieved little cover in the first year even when planted alone , they were significantly less affected by the sown exotic annual grasses , which also had reduced cover . Although in practice weed control often seeks to greatly reduce the challenge of exotic annuals for at least the first year of native planting, our results show that even a much briefer respite can have a profound effect. When exotic annual grasses were seeded just 2 weeks after germinating rains for the natives, their ability to suppress these natives was greatly reduced . This provides experimental support for the suggestion that one of the ways the exotic annual species outcompete natives in California grasslands is their demonstrated earlier germination and faster growth . The fact that the tE treatment had nearly as much exotic cover as the NE treatment strongly suggests that the late sowing did not itself greatly reduce eventual exotic cover, but that this occurred only in the presence of natives, i.e. as a priority effect. There are also reasons to believe that these differences in community structure arising from initial differences in our experimental treatments have long-term consequences . Vannette and Fukami made several predictions about the strength of priority effects that apply in this system . In particular, they suggested that priority effects would be greater under higher resource availability . In our system, however, watering reduced the strength of priority effects. This was not because of increased resource availability perse, but rather because the watering treatment effectively reduced the duration of the priority treatment. Greater temporal priority usually results in stronger priority effects . This experiment was initiated in a year when there was a 4-week drought following a few weeks of germinating rains in November . Our watering treatment suggests that one of the reasons that the priority effect was so strong in our experiment was this early wet season drought that allowed sown natives to grow for almost a full month before exotics germinated. When this drought was partially alleviated by watering, the strength of the priority effect was significantly reduced . We would predict that in a year with more consistent fall rain, these priority effects would be milder. Indeed, in a very similar experiment carried out in 2008, this was the case .

Amaranthus palmeri decreased the yield of no. 1 and jumbo grades at all densities greater than 1 plant m−1 row when compared with weed-free sweetpotato yields . Similarly, D. sanguinalis at 1 plant m−1 row decreased the weight of sweetpotato jumbo grade when compared with the weed-free check . Digitaria sanguinalis densities greater than 2 plants m−1 row decreased no. 1 grade sweetpotato yield relative to the weed-free check, with 16 plants m−1 causing the greatest loss of no. 1 and jumbo grades. These findings further demonstrate the negative impact of A. palmeri and D. sanguinalis on sweetpotato yields at low weed densities. Interspecific competition is also reflected in biomass reduction of one or both plant species competing with each other Interactions between year, crop versus no crop, and weed density were not significant ; therefore, means pooled over years were obtained for density and crop versus no crop combinations for each weed species. Biomass per meter of row of A. palmeri and D. sanguinalis increased with increasing weed density . The presence of sweetpotato reduced overall biomass per meter of row for both weed species at densities of 1, 2, and 4 plants m−1 row. Furthermore, sweetpotato reduced the rate of bio-accumulation for D. sanguinalis, as can be seen when comparing the slopes of biomass accumulation of both weeds . We believe that this was an effect of weed height, as A. palmeri quickly establishes and reduces the light reaching the sweetpotato canopy, vertical farming racks whereas D. sanguinalis does not exceed the sweetpotato canopy height as quickly as A. palmeri and is therefore less competitive with sweetpotato for light.

The impact of A. palmeri on light interception with the sweetpotato canopy has been documented by others . Individual weed biomass of A. palmeri and D. sanguinalis was similar across weed densities when grown with sweetpotato . Individual weed biomass for A. palmeri and D. sanguinalis, however, was lower for all weed densities when grown in the presence of sweetpotato compared with weeds grown without sweetpotato. The reduced individual biomass and biomass per meter of row for both weeds, when grown with sweetpotato, indicate that interspecific interference is occurring between sweetpotato and weeds. Crop biomass reductions are generally associated with increased weed competition and yield losses . However, in this study, although weed biomass was lower when grown with sweetpotato, increased weed density did not reduce sweetpotato biomass, despite the reduction in sweetpotato yield at the same densities.Individual dry biomass of each weed species growing without sweetpotato decreased as weed density increased . In the absence of sweetpotato, individual dry biomass ofboth weeds was fit to a linear-plateau model. Individual weed biomass was greatest for both weeds at the lowest density. Amaranthus palmeri and D. sanguinalis individual plant biomass decreased 71% from 1 to 3 plants m−1 of row and 62% from 1 to 4 plants m−1 of row, respectively, and remained unchanged at densities above 4 plants m−1 row for both weeds . This finding was similar to the trend observed in peanut for A. palmeri. We believe that the reduction in individual weed biomass for A. palmeri and D. sanguinalis at lower weed densities when grown without sweetpotato is due to increasing intraspecific competition as weed density increases. At the higher densities of both weeds, the impact of intraspecific competition has limited effect on further decreasing individual weed biomass.

The established threshold is the density at which all weeds achieve maximum accumulated biomass before intraspecific competition begins. Further biomass increases would require densities resulting in weed mortality due to intraspecies competition, and such densities were not evaluated in this study. This study demonstrates that A. palmeri and D. sanguinalis have the ability to reduce yield at densities as low as 1 to 2 plants m−1 row. Sweetpotato competes with A. palmeri or D. sanguinalis, resulting in reduced weed biomass. This observation suggests that sweetpotato with rapid canopy establishment and dense growth habit may provide additional competition with weeds and reduce yield loss, as proposed by Harrison and Jackson . Future studies should establish critical weed-free periods for these weeds in sweetpotato, investigate competitiveness of resistant weed biotypes with sweetpotato, and determine weed interference with sweetpotato under varying management practices .Dittrichia graveolens Grueter, commonly known as stinkwort, is a member of the Asteraceae, or sunflower, family. This plant is native to the Mediterranean region of Europe, occurring as far east as Turkey, Afghanistan and Pakistan . Stinkwort is an erect, fall flowering annual that can grow about 2.5 feet tall. Its foliage has sticky glandular hairs covered in resin. The resin emits a strong aromatic odor that resembles the smell of tarweeds. The flower heads are 0.2 to 0.3 inch in diameter and consist of short yellow ray flowers on the outer edge and yellow to reddish disk flowers in the center. Stinkwort is closely related to fleabanes, horseweed , goldenasters and telegraph weed , but it also closely resembles the tarweeds .

From a distance, stinkwort can resemble Russian-thistle , also called tumbleweed. Because it is fairly unattractive and nondescript in appearance, stinkwort initially passed unnoticed by many botanists and weed managers, and it was not included in the 1993 edition of The Jepson Manual of California flora . In its native range and some introduced regions, stinkwort inhabits riparian woodlands, margins of tidal marshes, vernal pools and alluvial floodplains, although it has not yet invaded these wildland areas in California. In California and other introduced areas of the world, stinkwort is most often found in disturbed places, such as overgrazed rangelands, roadsides, pastures, wastelands, vineyard edges, gravel mines, levees, washes and mining sites, although in California it is seldom found in rangelands or pastures . Stinkwort grows best on well drained, sandy or gravelly soils and thrives in areas with hot, dry summers but can also do well along the margins of wetlands. In addition, this plant tolerates a variety of soil types and survives under a range of soil conditions, temperatures and precipitation regimes . When adequate moisture is available, stinkwort can even survive on serpentine or saline soils. In Europe, this plant was shown to tolerate and to possibly hyper accumulate heavy metals, including mercury, zinc and copper .While stinkwort is native to the Mediterranean region, including Egypt and other areas of North Africa, this species has also been introduced to several European countries where it is not native. Within the last two decades, this weed has been spreading rapidly along the highways of Central Europe. In summer 2008, stinkwort was detected for the first time in Slovenia and Austria . Outside of Europe, stinkwort has been reported as an invasive species in Australia and South Africa . Stinkwort is not considered as a palatable species to animals. In fact, it is reported to cause poisoning in livestock . Although livestock mortality is rare, it appears to be due to enteritis caused by the barbed pappus bristles on the seed, which can puncture the small intestine wall . Stinkwort can also cause contact allergic dermatitis in humans . However, impacts to wildlife, natural ecosystems and working landscapes have not been broadly characterized. This is likely due to its very recent introduction and expansion in California and to the lack of published information on the species elsewhere in the world.The first record of Dittrichia graveolens in California is a collection made in 1984 near Milpitas in Santa Clara County . Although the initial mechanism and time of introduction of stinkwort in the state are not documented, many of the earliest collections were made in the south and east San Francisco Bay Area . Stinkwort has since spread to numerous counties in California, and many additional herbarium collections have been made throughout the state . Using the Consortium of California Herbaria records, we determined the rate of stinkwort’s spread since the first discovery in Santa Clara County. Based on collection date and location data from herbarium records, this weed invasion appears to have had only a brief lag period and to have expanded at an exponential rate over the past 18 years .

This has caused increased concern among resource managers across the state. Although it is still uncommon in many places where it is found, stinkwort has been reported in 36 of the 58 California counties . Stinkwort seeds are likely spread by wind, on the fur and feathers of mammals and birds and on motor vehicles and equipment, thus moving along transportation corridors. While the primary expansion has moved radially from the original infestation in Santa Clara County, vertical grow rack unconnected populations have also been discovered in San Diego and Riverside counties . This is likely due to either separate introductions or long-distance movement on vehicles.Stinkwort has very high seed viability, with an average of about 90% of the seeds capable of germination at the time they disperse from the plant. There does not appear to be primary dormancy in the seeds, which is defined as a seed that is dormant at the time it disperses from the plant . These traits, combined with the small seed size, suggest that seed longevity in the soil should be relatively short, perhaps 2 to 3 years. Seeds are capable of germinating at nearly any time of year in the field, but they typically germinate throughout winter and early spring following periods of precipitation. We have shown that germination is limited by soil moisture, rather than soil temperature or low light conditions . When seeds germinate in winter, the plants remain as small rosettes until mid-May. During late spring and summer, they develop into pyramid- or sphere-shaped plants that superficially resemble Russian-thistle. What makes stinkwort’s life cycle rather unusual is that it matures muchlater in the season than most annuals, even other late-season winter annuals . For example, yellow starthistle begins to send up a flowering shoot in April, begins flowering in late June, and — like most late-winter or summer annuals — has completed its life cycle by September or October. In contrast, stinkwort begins to bolt in mid-May , grows most of its branches and leaves between June and September and flowers and produces seeds from September to December. Flowering in stinkwort appears to be controlled by photoperiod , as all plants initiate flowering at the same time regardless of when they germinated . Aside from the tarweeds, there are few other late-season winter annual species with a similar life cycle in the native California flora. Some other weedy species, such as Russian-thistle, horseweed Cronquist and yellow starthistle , have similar life history strategies, with only Russian-thistle and horse weed flowering within the same time frame as stinkwort. In contrast to stinkwort, Russian-thistle is a summer annual that germinates in spring.The environmental and economic impacts of stinkwort in California have not been fully realized and are largely unknown. Our greenhouse studies have shown that stinkwort is dramatically suppressed when grown under shaded conditions, even at 50% light . Thus, like yellow starthistle, stinkwort is not expected to be competitive in understory communities of woodland and forest ecosystems. However, stinkwort can form dense infestations along highways and in open disturbed areas. In addition, while the establishment of this weed in undisturbed wildlands and rangelands is currently very limited in California, invasion of such areas over time is likely based on the pattern of spread in Australia. We are now conducting studies comparing the below ground growth and development of stinkwort with two other common grassland annual species: yellow starthistle and virgate tarweed . Yellow starthistle is an invasive winter annual, and virgate tarweed is a native species that, like stinkwort, is a late-season winter annual. The goal is to determine whether stinkwort shares the characteristics of yellow starthistle and virgate tarweed that allow them to compete with shallow-rooted grasses. These characteristics are a rapid rate of root growth and deep soil root penetration. Initial results indicate that while stinkwort does eventually grow roots as deep as yellow starthistle and virgate tarweed, this occurs several weeks after these other grassland annuals grow their roots. Thus, it may be that stinkwort will not be a significant invasive plant of rangelands, except in years when there is significant late-season rain or when competitive winter annual species are removed by overgrazing. Nevertheless, we have observed stinkwort in open riparian systems, where water is not a limiting factor and a slow-growing shallow root system will not limit its competitive ability.

Awan et al. did observe a decrease in plant height from pendimethalin treated plots in a dry-seeded system with no recovery by the final evaluation.Pendimethalin is currently not available for water-seeded rice; however, these results support the introduction of pendimethalin in California water-seeded rice. These results indicate rice injury is reduced with a post-emergence application after the 3- to 4-leaf stage rice in a water-seeded system compared to an application at 1- to 2-leaf stage. Pendimethalin is not a stand-alone herbicide and will need to be accompanied with other available herbicides to achieve season long weed control. In general, most rice cultivars tested were relatively tolerant to pendimethalin when treated after the 3-leaf stage rice; furthermore, cultivars with lower seedling vigor scores may become more injured from a pendimethalin post-emergence application. The results provide supporting data for registration of pendimethalin in water-seeded rice and provide a base knowledge from which further work should be conducted to enhance its use in this system.The authors would like to acknowledge the California Rice Research Board and BASF for providing funding for this project, the California Rice Experiment Station for their support in field management, and the various past and present lab members who assisted with this project, in particular Saul Estrada and Dr. Alex R. Ceseski. The authors also acknowledge the D. Marlin Brandon Rice Research Fellowship by the California Rice Research Trust, the Horticulture and Agronomy Graduate Group scholarships including the Bert and Nell Krantz Fellowship and the Jack Pickett Agricultural Scholarship, and the Department of Plant Sciences, UC Davis for the award of a GSR scholarship funded by endowments, indoor weed growing accessories particularly the James Monroe McDonald Endowment, administered by UCANR, which supported the student.

Rice is a staple crop produced worldwide of cultural and economic value . The export exchange of rice has become a prominent market for many countries worldwide . In the US, the export value rice production was nearly 1.7 billion USD in 2022 . Therefore, worldwide rice production must be upheld to current or superior standards to continuously fulfill the global rice demands. There are various common rice production systems used worldwide like transplanted paddies, dry-seeded seasonally flooded and continuously flooded systems . Water-seeded rice is not common worldwide but is the primary method in some geographical areas such as the Sacramento Valley of California . Waterseeded rice is the practice of seeding pregerminated seeds onto fields with a 7- to 15-cm flood, then, typically continuously flooded for the remaining of the season. The water-seeded rice production is popular in areas with ample water for irrigation or where early flood occurrence and poor drainage lead to continuously flooded fields . The flood in water seeded rice helps to control weedy rice, weedy grasses and non-aquatic weed species . However, flood-adapted and herbicide-resistant weeds have further intensified the weed management challenges in many rice fields . Historically, there has been a limited number of herbicide modes of action available for water-seeded rice . Continuous rice cultivation is common in many growing regions because of soil types and economic limitations . Overuse of the same herbicides and continuous rice cultivation have selected for herbicide-resistant weeds which reduce weed control with the currently available herbicides. To support herbicide resistance management, additional herbicides would be beneficial for growers to practice herbicide mode of action rotations . Pendimethalin is a mitotic inhibiting pre-emergence herbicide from the dinitroaniline chemistry that halts seedling growth shortly after germination . In previous surveys and preliminary greenhouse work, pendimethalin has been successful in controlling herbicide-resistant grass populations . Therefore, pendimethalin was evaluated for rice response in water-seeded rice to understand its applicability in this system .

Results from Becerra-Alvarez and Al-Khatib, in chapter 2 of this dissertation, demonstrated rice injury from pendimethalin was reduced in a post-emergence application at the 4-leaf stage rice and in a capsule suspension formulation within 1.1 to 3.4 kg ai ha-1 . However, at the suggested rice stage timing, many grasses have already emerged and control with pendimethalin is reduced. Therefore, if applied post-emergence in herbicide mixtures to control the emerged grasses, then, greater season-long weed control can be achieved. Additionally, herbicide mode of action mixtures are important strategies for herbicide resistance management which help delay resistance development and can control herbicide-resistant populations . It is hypothesized that the residual pendimethalin soil activity when applied postemergence at 4-leaf stage water-seeded rice could assist in control of late-emerging grasses. Economically important late-emerging grasses in California rice include bearded sprangletop [Leptochloa fusca Kunth ssp. fascicularis N. Snow] and watergrass populations. Bearded sprangletop is characterized as a late-emerging grass weed when compared to barnyardgrass [E. crus-galli Beauv] . While the majority of watergrass will emerge early in the season, there are subpopulations that can emerge later and are characterized as prolonged emergence throughout the season . Populations of multiple-resistant late watergrass [E. phyllopogon Koss] have demonstrated evidence of biphasic emergence with the majority emerging early in the season followed by late-emerging cohorts within the population . There is potential benefit from a pendimethalin post-emergence application for control of late-emerging grasses in water-seeded rice. Preliminary field studies evaluating water-seeded rice response were conducted on a continuous 10-cm flood with application onto the water and demonstrated timing after the 3- to 4-leaf stage reduced injury . However, some growers lower the flood depth to encourage rice seedling establishment, or when irrigation water is limited that year.

Decreasing the flood depths can influence pre-emergence herbicide rice injury in water-seeded rice as observed with available herbicides . Therefore, knowledge of rice response as affected by pendimethalin applications at different flood depths in water-seeded rice is important to develop appropriate application methods and recommendations. The objective of the field study was to evaluate the weed control and rice response of a post-emergence application of pendimethalin alone and in mixtures with currently available herbicides. The objective of the greenhouse study aimed to characterize rice response from pendimethalin applications at two flood depths.The study was conducted at the Rice Experiment Station in Biggs, CA in 2022 and 2023. The field soil is characterized as an Esquon-Neerdobe , silty clay, made up of 27% sand, 39% silt, and 34% clay, with a pH of 5.1, and 2.8% organic matter. During the off-season months, the field stubble was burned in spring 2022 prior to a pass with a single offset stubble disc. Field preparation for both years consisted of one pass with a chisel plow to dry the upper soil surface and then two passes with a single offset disc, followed by a land plane to smooth the soil surface. A granule fertilizer starter mixture application of ammonium sulfate and potassium sulfate was applied at 336 kg ha-1 . Then, a corrugated roller was used to pack the soil and eliminate large clods on the soil surface. Individual 3-m wide by 6-m long plots surrounded by 2.2-m wide shared levees were made after fertilizing and prior to flooding to prevent contamination from adjacent treatments in a replication. Seeds of the rice cultivar ‘M-209’ were pregerminated in water. For disease control, a 5% sodium hypochlorite solution was used for the first hour, then drained and refilled with only water for the remaining 24 hours. The seed was then drained until dry up to 12 hours, and seeded at 170 kg ha-1 both years onto the field with a 10-cm standing flood. The flood was maintained the whole season with the exception of a temporary lowering for the post-emergence herbicide treatments but was reflooded back to 10 cm 48 hours after the application. Copper sulfate crystals were applied by plane at 17 kg ha-1 three days after seeding for control of algae. Standard agronomic and pest management practices were followed based on the University of California rice production guidelines . Seeding dates were May 23, 2022 and May 31, 2023. The herbicides and adjuvants used in the field study are outlined in Table 1. Pendimethalin with 0.4 kg L-1 of active ingredient, vertical grow rack system was applied alone and in mixture with foliar active herbicides at the four-leaf stage rice. The pendimethalin application rates were 1.1, 2.3 and 4.6 kg ai ha-1 . The selection of these rates was based on preliminary studies on pendimethalin rates and timings, where 1.1 and 2.3 kg ha-1 were most appropriate rates for water-seeded rice as a post-emergence application . The 4.4 kg ha-1 rate was included in this study to provide rice response data at 2X of the proposed rate for waterseeded rice. The treatment herbicide mixtures with each pendimethalin rate were propanil, cyhalofop-butyl , and bispyribac-sodium . The applications were carried out with a CO2 backpack sprayer calibrated to deliver 187 L ha-1 at 206 kPa traveling at 4.8 km h-1 . The sprayer boom was 3-m wide equipped with six flat-fan 8003VS tips . At time of herbicide applications, the flood water was lowered 24 hours before treatment and reflooded back to 10 cm 48 hours after the treatment. A non-treated control and a grower standard treatment of clomazone applied at day of rice seeding were included for comparison . The treatments were arranged in a randomized complete block design with four replications both years. A follow-up herbicide application of propanil plus triclopyr was applied for sedge and broadleaf control at the midway of full tiller formation rice stage on all treatments except the non-treated . The treatments with pendimethalin alone had a follow-up treatment of cyhalofop plus florpyrauxifen-benzyl at the mid-tiller stage to control all remaining weeds after the initial assessment date . The metabolites have not been labeled of environmental concern and for the most part the pendimethalin parent molecule remains intact when bound to organic matter . In plants, metabolites are also not common and the majority remain as pendimethalin parent molecule when absorbed . The metabolites are also not documented as of concern to the environment by the US EPA ; however, quantifying metabolites helps in understanding the partitioning behavior of an herbicide in an agricultural or environmental system.Visual weed control was recorded for Echinochloa spp., bearded sprangletop, ricefield bulrush [Schoenoplectus. mucronatus Palla], smallflower umbrella sedge , ducksalad , water hyssop and redstem on 14, 24 and 56 days after pendimethalin treatment , on a scale of 0 to 100, where 0=no control and 100=complete control. Weed density counts for Echinochloa spp., sedges and broadleaves were conducted 30 DAT by sampling twice in each plot with a 30-cm by 30-cm quadrat and data scaled to a meter squared area for presentation. Bearded sprangletop counts were conducted for the whole plot after heading of the grass due to a relatively low population density in the field. Visual rice injury assessments were conducted at 20 DAT and 40 DAT by observing present symptomology, which included chlorosis and stunting on a scale of 0 to 100, where 0=no injury and 100=plant death. Rice tiller counts were conducted at 75 days after seeding by sampling twice in each plot with a 30-cm by 30-cm quadrat and data scaled to a meter squared area for presentation. Plant height was recorded at 100 DAS. Rice grain yield was collected both years and adjusted to 14% moisture. The rice grain was harvested from a 2-m by 6-m area in the plots with a small-plot combine on November 2, 2022 and October 30, 2023 .A greenhouse study was conducted at the Rice Experiment Station in Biggs, CA to characterize rice growth as affected by two flood depths after a pendimethalin application. The greenhouse study allowed more accurate management of flood depths than feasible in the field study and direct side by side treatment comparison. Plastic containers with 34-cm by 20-cm by 12-cm dimensions, with openings for drainage were filled with soil from the field study and placed inside larger 58-cm by 41-cm by 31-cm plastic containers, with no drain holes. ‘M-206’ rice seeds were pregerminated by placing the seeds inside cloth bags, and submerging in five gallon buckets for 24 hr. Then, the seeds were air-dried and ten seeds were placed on the soil surface of each smaller container, which would later be thinned to five evenly spaced plants per plot.