Hemp Growing

A key finding is that overnight charging currently has the lowest absolute level of CO2 emissions and a relatively low variance compared to other times of charging. This may not imply that an EV solution is categorically preferred on the grounds of net CO2 emissions compared to a baseline HEV, although the research does permit such quantitative comparisons. And it does convey actionable information given the vast temporal optionality currently allowed for charging. Going forward, we can envision a means of aggregating the impacts of individual analyses, meaning that these events will be weighted based on their likelihood and current behaviors. We can furthermore consider behaviors will evolve as time goes by and as larger shares of EVs are realized. However, within a transition period where EV growth and grid dynamics adapt iteratively, this study conducted novel simulations of the primary grid-vehicle scenarios which are reflective of current EV behavior and grid characteristics in recent years. The study’s consultations with experts, literature review, and data analysis revealed that about ¾ of events occur at home, with 50% on a level two charger and 25% on a level one charger. This would suggest, for the near and intermediate term, that EVs will act as a kind of aggregated demand in the evening/overnight hours and that as a block , EVs are more likely to require marginal resources because they act together to force demand projections out of the expected regime. The good news is that, for the foreseeable future, these are, on balance, curing cannabis hours that are moderately lower in terms of marginal resource carbon intensity, since they can be met by intermediate resources . Whereas workplace charging is substantially less common, perhaps the marginal mix or the hourly estimation is reasonable for the effective CO2 signatures.

As one thinks about the scale, and a situation where of EV reach double-digit shares of the fleet, it’s very likely that all the modes and locations of charging will eventually be subject to conditions where marginal assumptions prevail. How the transition period is defined and how the system boundaries between EV growth and grid resources are balanced are important, but open questions. Another essential unknown that will impact effective CO2 emissions from EVs are how predictable EV charging events become, with an emphasis on the high power, coincident peak events. More research into this question can help inform more accurate methods and models for simulating the environmental impacts of EVs. The present framework sets up an approach that will be valuable in estimating future impacts under such conditions. While additional focus and scope lie beyond this study, it is clear that a more complete understanding of popular EV charging profiles and EV driving behaviors will be essential inputs to better decision-making and resource planning. As EV use and charging habits become more predictable and well-known, the relevant data and insights can be critically valuable to utilities. For instance, foreknowledge of EV charging events will be needed at an aggregate level and could be beneficial to grid operators. The reason is that they can better plan and iterate their learning for those types of loads and events for which currently they lack visibility.In the last 40 years, 30 percent of the world’s arable land has become unproductive and 10 million hectares are lost each year due to erosion.1 Additionally, accelerated erosion diminishes soil quality, thereby reducing the productivity of natural, agricultural and forest ecosystems. Given that it takes about 500 years to form an inch of topsoil, this alarming rate of erosion in modern times is cause for concern for the future of agriculture.

This supplement explores the major causes of soil erosion and the social impacts it has on communities, underscoring the importance of agricultural practices that prevent or minimize erosion. Anthropogenic causes of accelerated soil erosion are numerous and vary globally. Industrial agriculture, along with overgrazing, has been the most significant contributor, with deforestation and urban development not far behind.2, 3, 4 Heavy tillage, fallow rotations, monocultures, and marginal-land production are all hallmarks of conventional agriculture as it is variably practiced around the world and significantly encourage accelerated soil erosion. Repeated tillage with heavy machinery destroys soil structure, pulverizing soil particles into dust that iseasily swept up by wind or water runoff. Fallow rotations, common with cash crops around the world and subsidized in bio-fuel production in the U.S., leave land vulnerable to the full force of wind gusts and raindrops. Monocultures tend to be planted in rows, exposing the soil between to erosion, and are commonly associated with fallow rotations. More and more marginal land, land that is steep and particularly susceptible to water erosion, is being planted by farmers either attracted by higher crop prices or forced by loss of productivity on flatter, but already eroded lands. In an increasingly complex global food web, seemingly separate causes of erosion begin to influence each other, magnifying their effects. For example, deforestation of tropical forests in Brazil clears the way for industrial soybean production and animal grazing to feed sprawling urban populations in the U.S. All the while, fertile topsoil is carried away by wind and water at alarming rates. Environmental harms resulting from accelerated erosion are well documented. Decreased soil fertility and quality, chemical-laden runoff and groundwater pollution, and increased flooding are just a few of these detrimental effects. There are, in addition, disproportionate social harms resulting from high rates of erosion that are less obvious, but no less directly linked. Hunger, debt, and disease are serious problems in mostly poor, rural communities around the world that are exacerbated by accelerated erosion.

As global agricultural development and trade have accelerated in the last half-century, mainly via the “green revolution” and the formation of the World Trade Organization , increasing trade pressures have raised export crop production in less developed countries. As a result, farmers mainly in Asia, Latin America, and sub-Saharan Africa are increasingly abandoning traditional farming techniques and locally significant crops in favor of adopting the industrial practices mentioned above that lead to high rates of erosion.5 While development institutions and governments proclaim concerns for the rural environment, agricultural policy supporting high commodity prices and limited credit access continually pushes farmers to intensify land use. Coupled with the fact that the total area of arable land in cultivation in these parts of the world is already very high , land degradation by soil erosion threatens food security by removing from cultivation land sorely needed for domestic food production. The majority of the world’s 868 million undernourished people live in Eastern and Southern Asia and sub-Saharan Africa. One of the international responses to soil degradation in the developing world has been to promote soil conserving tillage practices known as minimumor no-till agriculture. No-till agriculture protects soil by leaving crop residue on the field to decompose instead of plowing it into the ground before planting the next crop. Weed management is addressed with heavy herbicide use to make up for the loss of weed control from tillage. The practice, extensively adopted in the U.S., weed dryer has been popular in Brazil and Argentina, and much effort is being expended to expand no-till to Asia and Africa. There are, however, costs associated with no-till agriculture, both economic and social. First, no-till agriculture is expensive to adopt. Herbicides, seed drills, fertilizers, and other equipment require a high initial investment not possible for poor farmers without incurring significant debt. Second, heavier herbicide use increases human exposure to chemicals and contributes to water and air pollution. Third, weed pressures can change in unexpected ways as reliance on a handful of herbicides breeds resistance. Weed resistance to the popular herbicide, glyphosate, is an increasing concern in conventional agriculture and is leading to development of more harmful herbicides to compensate for glyphosate’s reduced effectiveness. Lastly, no-till agriculture also promotes monoculture cropping systems that, as described above, have a deleterious effect on soil quality. The techniques illustrated in this manual emphasize long-term soil stewardship using an integrated approach to soil health and management. For example, cover crops hold soil aggregates together in the wet season, protecting soil from the erosive effects of rain. Properly timed tillage limits its destructive effects on soil particles and soil structure. Compost promotes a healthy soil ecosystem, improving soil’s structure and its ability to more successfully withstand wind and water erosion. In addition to environmental benefits, agroecological systems are often based on traditional farming practices that promote soil-conserving techniques and varietal choices adapted to the particular region, stemming the tide of land consolidation and commodity crop production. Food security is enhanced and debt risk reduced by way of diverse cropping systems and labor-intensive, rather than input intensive, production methods. And there are public health benefits from eliminating exposure to harmful pesticides and herbicides. In sum, the serious challenge presented by accelerated soil erosion coupled with the uncertainty about whether no-till agriculture’s benefits outweigh its harms underscores the importance of employing an agroecological approach to farming that prevents soil erosion on farms.On vegetable farms in the Salinas Valley, a shrinking farm labor pool and rising minimum wages are driving innovation and adoption of machinery that can automate manual labor tasks — thinning, weeding and, for some crops, harvest. The technology is evolving quickly, led mainly by small engineering firms collaborating with large growers. Automation promises a number of benefits. Foremost, of course, is a reduced dependence on manual labor. But it could help in other ways too — for instance, automated weeding could remedy the declining effectiveness of some herbicides. UC researchers and advisors are helping to advance the basic technologies involved, and also serving as key evaluators of the technology . But the drive to automate also raises decades-old concerns about UC contributions to new technologies that are likely to primarily benefit only large-scale growers, at least in the short term.The automation of thinning and weeding involves two main steps: identifying each plant to be removed and then directing the killing of the undesired plant with a blade or a small dose of herbicide. It replaces work that would otherwise be done by hand with hoes. Figures on the acreage being thinned by machine aren’t available, but the use of automated thinners in some crops, notably lettuce, has been expanding in the Salinas Valley since its introduction in 2012 . The two in widest use in the Salinas Valley, according to several researchers and equipment suppliers, are made by two small northern European firms, Denmark-based F. Poulsen Engineering and Netherlands-based Steketee. Long-running concerns about farm labor cost and availability in Europe have driven automation innovation, and the technology has been more widely adopted there than in the United States, said Richard Smith, a UC Cooperative Extension farm advisor in Monterey County. While the weeding machines are costly — roughly $150,000 to $200,000 — their use appears to be limited more by availability than by price, according to equipment suppliers and UCCE staff. Poulsen and Steketee are small operations with limited production capacity. Britton Wilson of Pacific Ag Rentals, an equipment supplier to Salinas Valley farms, estimated that there are 15 to 20 Poulsen weeders in the United States, a figure Poulsen corroborated. “I’d love to get my hands on more” to meet local demand, he said.A crop like lettuce or broccoli represents a comparatively small market for major farm equipment makers like John Deere and Case IH. About 300,000 acres of lettuce are grown in the United States, for instance, compared with 12 million acres of cotton or 90 million acres of soybeans. As a result, vegetable crop automation is being led by small engineering and fabrication firms as well as growers themselves, often in close collaboration, said Mark Siemens, an associate specialist and associate professor of agricultural and biosystems engineering at the University of Arizona. Because the technology is somewhat modular, it’s possible to address the needs of a particular crop or grower by combining or modifying existing technologies and equipment. An example: Harvest Moon Automation, a four employee engineering firm with several clients in the Salinas Valley, recently received a patent on a modified version of a leafy greens harvester developed in partnership with two Salinas Valley growers. Steve Jens, Harvest Moon’s president, said the new machine uses a camera and pattern-recognition technology to spot foreign objects and diseased or damaged plants as the harvester moves across a field.

The intensification experiment was implemented in an established walnut orchard at the Plant Sciences Field Facility in Davis, CA, USA . The orchard was planted in the spring of 2015 with ‘Chandler’ walnuts. The entire orchard was 0.7 ha in area consisting primarily of Yolo silt loam soils . Orchard management included microsprinkler irrigation and weed-free tree strips maintained with preemergent herbicides. Experimental plots included the orchard alley between seven pairs of trees, approximately 6 m by 40 m. Cover crop programs were based on cereal rye, since it is known to be a competitive, weed-suppressing species that has desirable termination characteristics . Furthermore, this species thrives under various cultural management conditions and has cultivars that are well-adapted to grow as a winter cover crop in Central California. We used ‘Merced’ rye, which is a relatively tall cultivar. The whole experiment was conducted in one orchard over two growing seasons. Cover crops were established in the fall of each year, on November 11, 2019 and November 9, 2020, and terminated in the spring of each study year, on April 24, 2020 and April 9, 2021. Each plot received the same cover crop management program in both years of the experiment. Except for the forage treatment described below, rye was direct-planted with a seed drill at 22.5 kg planted ha-1 , drying rack and cover crop termination was performed with a flail mower. Planting and termination operations were planned to minimize equipment traffic in the orchard, and only one tractor pass was made across each orchard alley at each planting and termination date.

Flail mowers are practical for cover crop termination in California, since these implements are more common than other cover crop termination tools and they minimize crop residue ahead of nut harvest. We had five treatments which represented a range of different cover crop management intensities. The ‘sprayed’ treatment was used as our non-treated control, and the rye planted in these plots was terminated with a glyphosate application when rye plants reached 5 to 10 cm in height. These burn down applications occurred on January 13, 2020 and January 12, 2021, and included a broadcast application of Roundup Weather MAX at 1.607 L ha-1 with a carbon dioxide-propelled backpack sprayer. This treatment mimics a relatively intense commercial management system where orchard alleys are kept weed free. The ‘standard’ treatment included rye with no other cover crop management until termination. The ‘multi-species’ treatment included the base planting of rye and several additional cover crop species. The other cover crop species in the mix were common vetch 4.5 kg planted ha-1 , ‘PK’ berseem clover at 4.5 kg planted ha-1 , daikon radish at 2.25 kg planted ha-1 , and ‘Braco’ white mustard at 2.25 kg planted ha-1 . These seeds were broadcast spread immediately before rye was planted. We used these methods to establish the sprayed and multi-species treatments to minimize logistical challenges and orchard traffic, while also relying on the tractor and seed drill to enhance seed-to-soil contact of our additional cover crop species in the multi-species treatment. The multi-species treatment in this experiment has the same species and approximate planting rates as the multi-species mix in the planting date experiment described below.The ‘boosted’ treatment included a 45 kg ha-1 N top dress with granular urea after rye tillering which were made on February 25, 2020 and February 26, 2021.

The ‘forage’ treatment was managed as a rye hay intercrop. This treatment was planted at a rate of 45 kg planted ha-1 . At planting, we fertilized with 40 kg ha-1 N and 28 kg ha -1 P as granular urea and monoammonium phosphate at planting. We also top dressed with 45 kg ha-1 N after rye tillering. On the same day as topdressing, we broadcast-applied carfentrazone at 73 mL ha-1 with a backpack sprayer as a post emergent herbicide application for broadleaf weed control. The top dress and herbicide applications were applied on February 25, 2020 and February 26, 2021. The forage treatment was terminated with a swather, and the crop material was subsequently baled and removed. Immediately before cover crop termination, we destructively sampled cover crop and weed biomass. We collected biomass samples from two 0.25 m2 quadrat subsamples in each plot. Cover crops and weeds were separated before being dried in forced air drying ovens. Finally, we weighed dry plant biomass. Summer weed emergence was assessed after cover crop termination using point intercept transects. One transect was placed diagonally across the alley in each plot. Transects were 25 m long with 25 points spaced evenly along the transect. Plants were identified visually at each point. These summer weed transects were performed on June 17, 2020 and May 21, 2021, when summer weed emergence and potential cover crop regrowth might be scouted by a grower planning summer weed management. Planting date experiment. The planting date experiment was implemented in a non-bearing almond orchard at the Wolfskill Experimental Orchard near Winters, CA, USA . The orchard was established in the fall of 2017 with alternating rows of‘Nonpareil’ and ‘Aldrich’ almonds.

The entire site was about 1.1 ha in area with primarily Yolo loam soils . Orchard management included microsprinkler irrigation and weed-free tree strips treated with preemergent herbicides. The experiment was laid out as a randomized complete block design with five repetitions. Experimental plots were roughly 25 m long and 12 m wide, comprising five trees in length and two orchard alleys in width. We had five treatments, including a non-treated control and two multi-species cover crop mixes each planted at two different planting dates. The non-treated control had commercial standard vegetation management practices, which included several glyphosate applications throughout the winter months. We used cover crop mixes in this experiment because of their existing use by California orchard growers . Orchard growers frequently choose among cover crop mixes that support a variety of ecosystem services aside from vegetation management, such as pollinator health or improved soil structure, and multi-species cover crops can support some of these multifunctionality goals. Additionally, using different cover crop mixes allowed us to evaluate cover crops with different germination timings and a range of emergence phenologies. The two cover crop mixes used in this study were a ‘multi-species’ mix and a ‘brassica’ mix. The multi-species mix used the same species as the multi-species treatment in the intensification study, and it included a common combination of cover crop functional groups including a small grain, legumes, and mustards . The mix consisted of 10% ‘Braco’ white mustard, 10% daikon radish, 30% ‘Merced’ rye, 20% ‘PK’ berseem clover, and 30% common vetch planted at 56 kg planted ha-1 . Each of the cover crop mixes was planted at a relatively early planting date and a late planting date. These dates were chosen to represent a timely cover crop planting soon after nut harvest and coincidental with the onset of winter rains as well as a later cover crop planting coincidental with nut pruning, sanitation, and other winter management activities. This experiment was conducted in one orchard over three growing seasons. The early planting date occurred on October 15, 2018, October 24, 2019, and November 9, 2020. The late planting date occurred on January 31, 2019, February 10, 2020, and January 21, 2021. Cover crops were direct-seeded with a conventional grain drill. Ground preparation occurred before each planting date. Before the early planting date, the whole orchard received light tillage immediately before a glyphosate burndown. Before the late planting date, cannabis curing late planted plots and the non-treated control received an additional glyphosate burndown but no additional soil disturbance. Cover crops were terminated with a flail mower on April 19, 2019, April 27, 2020, and April 22, 2021. Weed emergence was monitored throughout the cover crop growing season using permanent point intercept transects. Each plot had one transect placed diagonally across one orchard alley. Each transect was 10 m long with 10 points along the transect. Plants were identified at each point along the transect, and monitoring took place weekly while cover crops were growing. This experiment did not have different residue management treatments, so summer weeds were not evaluated. Immediately before cover crop termination, we sampled cover crop and weed biomass using the methodology described above, including two 0.25 m2 quadrat subsamples in each plot.Data analysis. Analyses were performed in R 3.0.3 .

For biomass data from both experiments, we used ANOVA and performed multiple comparisons with Fisher’s LSD. ANOVA was performed by specifying a model with lm and entering it into Anova from the car package . The models we used had treatment, replicate, and their interaction as predictors and either weed biomass or cover crop biomass as a response variable. We inspected ANOVA assumptions visually using plot. Subsequently, weed biomass from the intensification experiment was analyzed with one outlier removed and a square root transformed response variable due to leptokurtosis. However, unabridged and non-transformed data are displayed in the figures. Finally, we performed Fischer’s LSD with LSD.test from agricolae using a significance level of P<0.05 . Summer weed emergence data were analyzed in the same manner but using cover crop regrowth and summer weed emergence as response variables. Weekly transect surveys were analyzed with multiple linear regression. We compared the slope of each regression line in to evaluate the relative rates of weed and cover crop emergence after each plant date. Cover crop emergence was represented as the change in ground cover as observed in weekly observations throughout the first ten weeks following the respective planting date of each treatment. There was only one non-treated plot in each repetition, and we evaluated ground cover following both the early and late planting dates in the same non-treated plots. Weed and cover crop emergence were modeled as functions of treatment, weeks after respective planting, and their interaction. These linear models were created using lm. We created additional linear models using other possible combinations of predictor variables and compared these various models using anova. However, we determined the model described above to be the most parsimonious. Parameter estimates for the slope of each line were compared with Tukey’s HSD using lstrends from the emmeans package . All figures were made with ggplot2 .In the intensification experiment, cover crop biomass varied with management treatment . While year was not a significant predictor of cover crop biomass , we detected an interaction between year and treatment . Furthermore, multiple comparison testing led to different conclusions from each year of the intensification experiment. With data pooled across years, the forage and boosted treatments resulted in higher cover crop biomass than multi-species or standard treatments. Within each year, the boosted treatment alone resulted in the highest cover crop biomass in 2020, while the forage treatment did so in 2021. Cover crop treatment and year both predicted weed biomass. The interaction term was also important . In general, the four cover crop programs resulted in less weed biomass compared to the sprayed treatment and similar weed biomass compared to each other. This conclusion was supported in both years of the study, but we observed less weed biomass overall in 2021. Intensified cover crop programs can increase cover crop biomass, but all of the cover crop programs we tested were similarly effective at reducing weed biomass. Less rainfall in 2021 could have contributed to differences between study years, and we attribute some decrease in boosted cover crop biomass to dry conditions after top dress fertilizer application which likely caused a reduction in plant-available nutrients from the applied fertilizer. Some cumulative effect of two years of cover cropping could have also contributed to these results.In the planting date experiment, cover crop biomass varied with cover crop treatment . Year was not significant , but the interaction between treatment and year was . In 2019 and 2020, the early planting treatments resulted in higher cover crop biomass than the late planting treatments. Differences between cover crop treatments were greatest in 2020, and the multi-species mix also resulted in greater cover crop biomass compared to the brassica mix in this year. There were no differences in cover crop biomass between treatments in 2021. Year , treatment , and their interaction all contributed to weed biomass. While we observed a lot of year-to-year variation, the late-planted multi-species treatment was consistently in the lowest statistical group for weed biomass, and the early-planted brassica treatment was consistently in the highest group.

In California, field bindweed survives in both irrigated and dryland environments, and it grows through much of the year in annual and perennial cropping systems as well as non-crop areas like roadsides . This species causes yield loss, reduces water use efficiency, disrupts irrigation infrastructure, impedes crop harvest, and creates multiple flushes of growth each growing season . These factors contribute to ongoing problems in California orchard systems. Field bindweed has a reproductive biology that includes sexual reproduction with large flowers and hard-coated seeds as well as asexual reproduction with an extensive root system, and this biology has helped it thwart many common weed management programs across California orchard systems . Because it is difficult to control, orchard weed managers often use several weed management operations against field bindweed each year, especially repeated application of systemic herbicides like glyphosate in mature orchards . Repeated applications of contact herbicides like glufosinate, paraquat, or PPO inhibitors are also common in young orchards where crop safety is a larger concern when using systemic herbicides. In fact, repeated herbicide applications are common in a variety of cropping systems . Systemic herbicides offer the apparent benefit of translocation to the extensive root system of field bindweed . However, translocation of some herbicides to field bindweed roots can be limited, and repeated herbicide applications have the potential to select for herbicide resistance . Furthermore, vertical farm equipment field bindweed frequently demonstrates capacity for regrowth following systemic herbicide applications, even when factors such as application timing, herbicide mixtures, or spray adjuvants are optimized .

Mechanical management practices that disturb the soil and underground tissues could likewise be more efficacious against field bindweed relative to mechanical practices that only affect above ground tissues . These practices, however, frequently allow regrowth from root cuttings, adventitious roots, or perennial buds . The light environment in young orchards compared to shady, mature orchards is more conducive to field bindweed . However, many young orchard trees are susceptible to injury from the systemic herbicides and intensive mechanical management practices that are commonly used against field bindweed . The compounded challenges of managing field bindweed in young orchards necessitate deeper understanding of how this species persists and can be managed in unique orchard environments. This knowledge could then inform more sustainable integrated pest management strategies with greater efficacy while reducing reliance on glyphosate and other systemic herbicides and increasing the number of management practices that are known to be safe for young trees . Integrated pest management relies, in part, on information about pest life cycles and phenology and how they relate to cropping system context. The development of integrated management programs for field bindweed necessitates greater understanding of this species’ population ecology, particularly within the context of current cropping system practices and limitations . Current management programs react to the presence of field bindweed vegetation, but integrated management programs could better account for the specific ways that this species reproduces and create site-specific management that targets the most susceptible life cycle stages . Recent advances in soil seed bank management highlight the importance of understanding all kinds of plant propagules and how these propagules differentially contribute to weed populations .

Given its relatively complex life history, field bindweed could be a useful study system for understanding perennial weed reproduction and its importance to integrated pest management. This species reproduces with both sexual and asexual propagules, creating a persistent seed bank as well as perennial roots and buds . Perfect, self-incompatible flowers bear hard, dormant seeds that maintain genetic diversity within the soil seed bank . Significant resources are also allocated towards prolific root systems, and individual plants can create underground systems that are several meters in diameter . The morphology and biomass of these root systems are influenced by light, cultivation, and other cropping system cultural factors . However, field bindweed exhibits varying degrees of phenotypic plasticity despite its morphological diversity . Integrated management programs could be strengthened by improved knowledge of how this diversity contributes to field bindweed survival in the face of varied management. Despite the importance of reproductive allocation and diversity, direct quantification of field bindweed reproduction remains challenging due to the inaccessibility of root structures and dehiscence of mature seeds .There is a need for research that addresses these challenges to help us answer questions about field bindweed reproduction in ways that contribute to commercially-relevant management. We are particularly interested in how weed management practices in orchards differentially affect above ground and below ground tissues in order to better understand how each contributes to field bindweed persistence in orchard cropping systems . Additionally, we focus on time to first flowering as a practically important reproductive trait, because it can help determine when to schedule sequential weed management treatments and how species adapt to changing environmental conditions .

California orchards are unique cropping systems that require dedicated development of integrated management programs, especially given the distinctive biology of field bindweed and the specific challenges of weed management in young orchards. Our overall aim is to use information about the reproductive biology of field bindweed to support improved ecological management of this species with practices that are feasible in California orchards. The experiments described in this study evaluated field bindweed flowering and biomass production using field and potted plant experiments. Our approach was to determine how a variety of common and prospective weed management practices in young orchards affect field bindweed reproductive resource allocation. In the field experiment, we tested various chemical and mechanical weed management practices to identify effects on field bindweed flowering timing and aboveground biomass production at timings relevant for commercial orchard production. In the potted plant experiment, we evaluated different mechanical disturbance treatments on field bindweed collected from different source populations to describe responses in flowering timing or root:shoot biomass ratios. Together, these experiments were designed to provide insight into how the distinctive reproductive morphology of field bindweed behaves and responds to orchard weed management programs.A field plot experiment was designed to evaluate how in situ field bindweed alters its reproductive response to various commercial management practices. A potted plant experiment was designed to create a common environment for testing field bindweed from a variety of source environments, as well as to provide opportunity for detailed assessment of root biomass. Together, these complementary experiments allowed us to use a broader array of methods for observing the reproductive response of field bindweed to management. Field experiment. The field experiment was a small plot study arranged in a randomized complete block design with four repetitions in each replicate. Various management programs were applied to 4.6 by 6.1 m rectangular plots in fallow fields with endemic field bindweed infestations. The whole experiment was replicated three times in time, each with a different experimental timing that coincides with different management periods for California orchard growers. Each of the replicates took place in separate fallow fields at the Plant Sciences Field Facility at UC Davis in Davis, CA . These fields consist of Yolo silt loam and had a history of orchards, agronomic crops, and field bindweed infestation before being fallowed. Field bindweed grows nearly year-round in central California, commercial indoor growing systems with a period of senescence in the winter months only; these replicate timings were chosen to mimic some of the primary periods where agricultural weed management practices already occur within that window. The first replicate was performed in the fall of 2020, to coincide with post harvest weed management timing in nut orchards . The second replicate was performed in early summer 2021, coincidental with weed management that targets summer weed emergence in orchards, especially in young orchards where there may be a greater need to manage small weeds and prevent weed establishment given a relative lack of registered herbicide options. Finally, the third replicate was performed in the mid-summer of 2021, at the timing of preharvest weed management in orchards. Management programs tested in this experiment involved sequential management steps, as is often necessary for growers dealing with field bindweed. Each of the treatments received discing and culti-packing as the first management step in order to eliminate emerged bindweed vegetation, as well as to create a uniform soil surface for treatment application. This tillage step occurred on August 19, 2020, March 25, 2021, and May 4, 2021 at each of the three replicates, respectively. The fields were subsequently monitored for bindweed reemergence, and mechanical and chemical treatments were applied to the replicates when stem regrowth reached approximately 10-15 cm in length, approximately when sequential weed management would be applied commercially.

Treatments were applied on September 15, 2020, April 20, 2021, and June 3, 2021. There were seven treatments, including one non-treated control, three herbicide treatments, and three mechanical treatments. The three herbicide treatments were broadcast glyphosate, strip-applied glyphosate, and glufosinate. Both herbicides are widely used for field bindweed management in California, but they have contrasting systemic or contact actions. The broadcast glyphosate was applied at a rate of 2.8 L ha-1 across the entire plot. The strips were applied at a rate of 5.6 L treated ha-1 in two 1.15 m-wide strips in the plot, leaving two 1.15 m-wide non-treated strips in the same plot. The glyphosate strips treatment usedthe same total amount of herbicide as the broadcast treatment, and this treatment was designed to evaluate potential impacts of glyphosate translocation when applied in strips as is common in orchards. The glufosinate treatment used 3.9 L ha-1 of Rely 280 . Each of the herbicide treatments was applied using a CO2 propelled backpack sprayer equipped with a three-nozzle boom and 80015XRVS nozzles and calibrated to apply 187 L ha-1 spray volume, based on 3.2 km hr-1 ground speed and 50.8 cm nozzle spacing. The three mechanical treatments were rototilling, flail mowing, and string trimming. These three treatments were chosen because they affect field bindweed roots and shoots differently, with rototilling representing deeper disturbance compared to string trimming and flail mowing. Each plot was monitored weekly for 10 weeks following treatment application. The first five plants to emerge in each plot were marked with stakes. In the glyphosate strip plots only, these first-to-emerge plants were in the non-treated strips within each plot. Individual plant subsamples were evaluated throughout the experiment. We used flower counts to determine average time to first flowering in each plot. No flowering was observed in the first replicate, likely since it was relatively late in the 2020 growing season, and we did not include that replicate in flower timing analysis. At the end of the 10-week observation period, we collected the above ground portion of the marked plants, dried them in a forced air oven, and weighed the dry biomass. Pot experiment. The potted plant experiment involved propagating field bindweed plants from several source populations into pots and subjecting them to different mechanical disturbance treatments. The plants were propagated vegetatively from annual crop, perennial crop, and non-agricultural home environments. The experiment used a factorial design with three disturbance treatments, including non-treated, clipping, and simulated tillage, and four field bindweed populations. Plants were collected in late 2020 from an almond orchard near Corning, California , an almond orchard in the Wolfskill Experimental Orchard near Winters, California , an annual crop field in Davis, California , and a vacant lot in Davis, California . Several dozen plants cuttings, each including both root and shoot tissue, were collected at each site and transplanted into greenhouse pots. Plant populations were maintained in the greenhouse and re-transplanted twice into new pots over a six-month period. Re-transplanting included shoot trimming to minimize powdery mildew pressure, ensure uniform plant size, and control for any legacy effects from respective environmental conditions at the time of collection. After growing in the greenhouse, we transplanted plants into 12 L pots on outdoor benches. Each pot was filled with greenhouse soil . Plants were uniformly trimmed to have 10 cm of root and 10 cm of shoot length, and only one plant was transplanted per pot. Pots were watered daily with drip irrigation. We replicated the experiment twice, and there were six repetitions of each population-treatment combination in each replicate. Transplanting occurred on April 29, 2021 for the first replicate and on May 26, 2021 for the second replicate.

However, competitive suppression of native seedlings by exotics eclipsed the feedback effect, highlighting the need for weed control in the restoration process.Understanding long-term plant community dynamics has been a key challenge in ecology , made even more challenging by the increased firequency of plant invasion and novel environmental conditions. A number of studies have demonstrated that new climatic extremes, such as severe and prolonged drought, may have long term legacies on plant communities by affecting resource availability and altering dominant species . In systems dominated by long-lived perennial plants, novel disturbances can disrupt generally predictable successional change . Understanding the impacts of novel disturbances on vegetation dynamics is even more challenging in annual-dominated plant communities, where composition can reset each year . Annual systems have high turnover in species composition due to multiple biotic and abiotic drivers with high inter-annual variability . Drivers such as the timing and amount of precipitation and temperature , fungal pathogens , and herbivores act on seed production, seed survival and germination, seedlings, and mature plants . In addition, vegetation can be influenced by the quantity of litter from the previous season . Thus, species composition in annual systems is difficult to predict and manage . These controlling variables are often strongly impacted by previous species composition, and thus predicting community changes in annual systems may benefit from considering priority effects. Priority effects are when the timing and order of species arrival during assembly determines which species can later establish in the community, leading to alternative stable states, vertical grow rack alternative transient states, or compositional cycles . Priority effects have been observed to affect composition and diversity in multiple systems .

In perennial systems, a long-lived species can physically hold space against competitors over time, occupying this niche to the exclusion of later arrivals . In fact, planting of perennial grasses is firequently used as a way to suppress annual weeds . Among annual plants, priority effects may occur through mechanisms such as litter build up, seed production and faster germination, and plant-soil feedbacks related to changes in pathogen and symbiont communities . Priority effects are stronger among species with high overlap in resource use, resulting in greater niche co-option and exclusion of later arrivals of similar function and phenology . Assessing vegetation community dynamics in California’s annual grasslands may thus benefit from defining functional groups in terms of phenology , which dictates when California grasses compete for the limited resource of soil moisture. California’s grasslands are dominated by early-season exotic annual species that are now so entrenched in the landscape they are considered naturalized; they generally outcompete native grass and forb seedlings, as they germinate and grow faster, depleting shallow soil moisture and creating light limitation . Several priority experiments have shown that native perennial grasses in this system benefit from a two-week head start over naturalized exotic species . A newer set of invading exotic annual species, including the grasses Elymus caputmedusae and Aegilops triuncialis, are classified as noxious weeds and are of particular concern because they produce thick layers of thatch that is slow to decompose and prevents germination of other species . These noxious weeds germinate at the same time as the early-season exotics, but their above-ground growth primarily occurs after rains have ended and the earlier season grasses have senesced .

In drier years, early-season naturalized exotic growth can limit noxious weeds by utilizing all soil moisture, but cannot prevent noxious weed growth if late-season moisture is present . Native perennial grasses, which are active during the late-season, may compete with noxious weeds for the dwindling late-season soil moisture. However, how long priority effects last on all three functional groups is unknown. We established field plots consisting of early-phenology naturalized exotic annual species, late-phenology annual noxious weeds, and native species commonly used in restoration mixes . Each group was seeded alone or simultaneously in mixtures with other groups to compare to assess the importance of being seeded without initial competition. All plots were then allowed to be naturally colonized by non-seeded species in the experiment, but with a subset of plots receiving a one-year weeding treatment to provide additional priority. We assessed composition over a twelve-year period that included an extreme multi-year drought followed by a historic wet year, and then another severe drought year. Such extreme weather events in other systems have been shown to disrupt plant community dynamics, reducing cover of resident species and increasing invasion . This experiment is particularly valuable because the majority of priority effect studies take place in the greenhouse and for less than a year in duration, and it is widely recognized that more field and long-term experiments are needed to determine the strength of priority effects in varying conditions . Of the few long-term studies, the current literature has shown both that priority effects either persist or disappear depending on the system and the species involved .

We hypothesized that all three functional groups of species, when seeded alone, will: have greater cover than when grown in competition, and limit recruitment of another naturally colonizing functional group. We also predict that the multi-year drought will weaken priority effects during and beyond the drought in favor of the early-season naturalized exotics, as they have will have first access to soil moisture.Plots were located in UC Davis Campbell Tract Experimental Site in Davis, CA . Prior to plot establishment, the land was used for agricultural purposes and then lay fallow for twenty-two years. The site was primarily on Reiff series soil, with a sandier lens of Brentwood soil series on 25% of the site . Under a Mediterranean climate, the site experienced hot, dry summers and wet, cold winters that correspond with the growing season of cool season grasses.Rainfall has high inter- and intra-annual variability, with mean annual precipitation of 445 mm . During the experiment, California experienced a historic drought between the 2012-2014 water years , followed by 2 years with precipitation levels that were substantially closer to the 30-year precipitation average, and then followed by one of the wettest years on record in 2017, then a dry year, followed by another historic wet year . Prior to initial seeding at the start of the experiment in fall 2007, the seed bank and resident vegetation were minimized by disking the soil, irrigating to germinate the seedbank, and spraying germinating seedlings with herbicide . Irrigation and herbicide treatments were performed twice before planting. Plots were seeded with one of the following vegetation treatments in a randomized block design : native perennial grasses and annual forbs, exotic annual noxious grasses, naturalized exotic annual grasses and forbs, and all possible combinations of these three groups , at a rate of 139 g seed/plot. Plots were 1.5 x 1.5 m with a 1m buffer between them . For each single functional group mix, equal proportion of seeds of each species were added. For functional group mixes, an equal proportion of each functional group seed was added, commercial vertical hydroponic systems with equal proportion of individual species within each functional group. Given that the common design of seeding equivalent weights across all treatments design results in the multi-group treatments having less seed per species group , short-term conclusions may be influenced by seed limitation as well as priority effects. However, the effects of seed limitation should be short-lived given the annual species in this experiment are highly prolific and able to rebound from extremely low to high cover from one year to the next, as well as naturally self-thinning . While natives are seed limited, low density can still result in high cover , and so changes in native cover can be attributed to changes in individual size as well as population response. Percent cover of each species present was assessed visually with a modified Daubenmire bin method of the inner 1m x 1m core.

Composition was measured twice each season annually from 2008 to 2019 to capture peak flowering species with different phenologies . The highest cover value across the two sample points each year for each species was used for analysis.There were multiple levels of priority in this experimental design. For a given functional group, the seeding treatment in which they were seeded alone in monotype is the highest level, as they accessed the space first with no competition from other functional groups. The seeding treatments in which that functional group were seeded simultaneously with another group are a secondary level of priority, as they shared first access to the space. The remaining seeding treatments are those in which the functional group in question was not seeded, thus they had no priority at all. If present later in the experiment, they recruited into the space after initial colonization by the planted functional group, and thus faced high competition for resources from established residents or high propagule pressure . Given the spatial distribution of the experimental plots, every plot was close to a seed source of another functional group from neighboring plots and the unplanted walkways between plots and blocks became quickly colonized, indicating that the species were dispersing throughout the site quickly. Superimposed on the above listed priority levels was a weeding treatment to determine the difference between one vs two years of priority. Natural colonization was either allowe dimmediately or postponed an extra year due to hand-weeding after the first year to maintain the initial species compositions of the seeding treatments . Since then, all plots were occasionally weeded for agricultural weeds that were not part of the study but species that self-recruited and are typical species in California grasslands were not weeded.Priority effects can be the outcome of the seeded species having both higher propagule pressure and biotically resisting the recruiting species and we are interested in the long-term trajectory of the initially planted communities and the extent to which they are naturally colonized by functional groups that have been planted nearby. To test our hypothesis, we performed two comparisons. First, for each year, we compared cover of the recruiting functional group in its monotypic seeding treatment, which presumably represents the best conditions for performance as it has the highest level of priority, to the three seeding treatments in which the functional group was not planted . If the recruiting functional group cover is higher in its own monotypic treatment, then it would suggest that the functional groups originally planted are providing some level of resistance. Second, we compared the recruiting functional group’s cover as it changed over time within each seeding treatment it was not planted into, such as whether recruiting species cover stays consistently low or increases with time. This took into consideration potential annual population fluctuations due to environmental conditions and provides detail on resistance not captured by the first comparison. Both comparisons are necessary to determine whether low presence of a recruiting functional group is due to bioticresistance or poor environmental conditions. We also compared cover between the one- and twoyear priority weeding treatments. Both comparisons were assessed with the same linear mixed effect model but differed in how we performed the post-hoc analysis. First, we fit linear mixed effect models with percent cover of each recruiting functional group as the dependent variable, specifying seeding treatment, priority length , year , and their 3-way interaction as fixed effects and plot and block as random effects. Significance was tested with analysis of variance . Both comparisons were assessed with post-hoc multiple comparison tests using estimated marginal means on the interaction of seeding treatment and year when significant in the ANOVA but differed in the order of terms used. The first compared cover across the different seeding treatments within each year while the second compared over across the 12 years within each seeding treatment. All statistical analyses were conducted in R 4.0.3 . Linear mixed effect model fitting was performed using “lme4” and “lmerTest” . Multiple comparison tests were conducted using “emmeans” .Our study assessed the role of priority effects in determining long-term community composition in a system that experienced high annual variability in weather, including a multiyear drought event followed by one of the wettest years on record, and then another historic dry year, and another historic wet year .

Wild fungus gardens contained similar peptaibols, indicating their ecological relevance, consistent with peptaibol-producing Trichoderma being an opportunistic pathogen of T. septentrionalis fungus gardens . In our laboratory experiments, two of the Trichoderma fractions with the highest abundance of peptaibols, fractions D and E, induced some of the strongest T. septentrionalis weeding responses , and purified peptaibols also induced a weeding response similar to that of theTrichoderma extract . Given that the Trichoderma fractions and purified peptaibols were derived from different strains and represent a diversity in peptaibol composition, the similarities in the observed ant behavioral activity are thus likely to be unrelated to specific peptaibols but rather generally attributable to the peptaibol class of metabolites. Furthermore, the presence of peptaibols in environmental fungus gardens lends credence to their ecological relevance and together with the experimental data parallels the logic of Koch’s postulates, suggesting that peptaibols are likely produced during Trichoderma infections of ant fungus gardens and induce ant defensive behaviors in response. Peptaibols are produced by fungi in the order Hypocreales, especially by members of the mycoparasitic family Hypocreaceae, which contains both Trichoderma and Escovopsis, a specialized ant fungus garden pathogen . Peptaibols have been hypothesized to be important for mycoparasitism , which we show here can include infections of ant fungus gardens. Interestingly, the genes needed to synthesize peptaibols are encoded within the genome of Escovopsis , vertical farming systems for sale and Escovopsis has been shown to induce a strong ant weeding response in tropical leafcutting fungus-growing ants , similar to the T. septentrionalis weeding behaviors that we observed in response to Trichoderma and its peptaibols.

We therefore hypothesize that peptaibolinduced weeding behaviors are conserved among diverse fungus-growing ants and may reflect an ancient means of pathogen detection and defense. Future work should test if ant weeding intensity is directly correlated with pathogen load, virulence, peptaibol production, or other contributing environmental factors, and also compare the behavioral responses of diverse fungus-growing ant species to diverse fungal pathogens with varying levels of virulence and specialization toward ant fungus gardens, e.g., as in ref. 58. This study demonstrates how T. septentrionalis ants protect their cultivar mutualist from opportunistic Trichoderma pathogens by sensing and responding to peptaibols as specific molecular cues that induce an ant weeding response. These cues included two previously undescribed bioactive peptaibol metabolites that we identified in this study. Future research will investigate whether ants directly sense peptaibols or indirectly respond to an intermediate signal produced by the cultivar in response to peptaibols, in addition to characterizing other potential signaling molecules that are unlikely to be present in our Trichoderma extracts . In contrast to the canonical logic of host immune responses, in which hosts directly respond to infections, T. septentrionalis responses to peptaibol signaling molecules comprise an extended defense response whereby T. septentrionalis ants respond to infections of their cultivar mutualist. Such extended defense responses may be a widespread but poorly recognized mechanism that increases host health indirectly by preventing harm to their beneficial symbionts.Vineyard-fl oor management strategies, such as weed control and cover-cropping, have wide-ranging impacts both inside the vineyard, in terms of crop management and productivity, and outside the vineyard, in terms of runoff and sediment movement into streams and rivers.

The increasing importance of water-quality issues statewide, including in Monterey County where the Salinas River drains into the Monterey Bay National Marine Sanctuary, highlights the need for management strategies that limit environmental impacts. Growers are interested in alternative weed-control practices and cover crops, but they need information in order to balance benefits with the economic realities of wine-grape production. We established a 5-year experiment in a commercial vineyard in Monterey County with the intent of identifying effective practices that can be integrated into the cropping system without negatively affecting winegrape production. The vineyard floor consists of two zones: the rows, a 2- to 4-foot-wide swath underneath the vines, which are managed primarily to control weeds by herbicide applications or cultural practices ; and the middles, interspersed between the rows, which are vegetated by cover crops or resident vegetation in the dormant season, and are tilled or left untilled in spring. Growers manage weeds in rows to reduce competition for water, nutrients and light , and to prevent tall-statured weeds such as horse weed from growing or climbing into the canopy, where they interfere with harvest. Growers transitioning to more sustainable production systems need information on how management practices affect the physical properties, health, organic matter and water retention of soil. We monitored soil microbial activity for arbuscular mycorrhizal fungi and soil microbial biomass, since weed control and cover-cropping can affect populations of beneficial soil microbes in annual crops . Dormant-season cover crops in the middles minimize runoff from winter rains . Many California growers are also willing to plant cover crops because they protect soil from nutrient and sediment loss in winter storms , suppress weeds , harbor beneficial arthropods , enhance vine mineral nutrition and increase soil organic matter .

Competition between vines and cover crops for soil moisture in spring, when both are actively growing, can lead to severe water stress and reduce grape production . However, wine-grape production is distinct from other cropping systems because water stress may be imposed to enhance wine composition ; this practice has been studied mostly in high-rainfall regions of California. The vineyard production region of Monterey County, in contrast, has low rainfall , and growers must weigh the benefits of cover crops with the possible need to replace their water use with irrigation. In addition, growers must decide on the type of vegetation to utilize in the middles. Resident vegetation is cheap and generally easy to manage. Cover crops can provide specific benefits such as nitrogen fixation or high biomass production and vigorous roots . There are many choices for cover crops in vineyard systems, ranging from perennial and annual grasses, to legumes . Each species has strengths and weaknesses, as well as associated seed and management costs.Row weed control treatments were: cultivation, post-emergence weed control only and pre-emergence herbicide , followed by post-emergence herbicide applications . Cultivations and herbicide applications were timed according to grower practices and label rates. Cultivations were carried out every 4 to 6 weeks during the growing season using a Radius Weeder cultivator . The cultivator used a metal knife that ran 2 to 6 inches below the soil surface cutting weeds off in the vine row; it had a sensor that caused it to swing around vines. Pre-emergence herbicides were applied in winter with a standard weed sprayer, and postemergence herbicides were applied in spring through fall as needed with a Patchen Weedseeker light-activated sprayer . An early and late-maturing cereal were chosen for the cover-crop treatments; legumes were not considered due to aggravated gopher and weed problems. Cover-crop treatments in the middles were: no cover crop , earlier maturing ‘Merced’ rye and later maturing ‘Trios 102’ triticale . Cover crops were planted with a vineyard seed drill in a 32-inch-wide strip in the middle of 8-foot-wide rows just before the start of the rainy season in November 2000 to 2004 . They were mowed in spring to protect vines from frost, and both cover-crop species senesced by summer. Prior to planting cover crops each November, vertical farming equipment row middles were disked to incorporate the previous year’s cover crop and stubble and prepare a seedbed. Weed control and cover-crop treatments were arranged in a 3 x 3 splitblock design with three replicate blocks covering a total of 23 vineyard rows . Each block contained six vine rows and six adjacent middles. Weed control treatments were applied along the entire length of each vine row ; cover-crop treatments were established along one-third of each middle and were continuous across the main plot treatments in each block.

Each replicate main plot-by-subplot treatment combination included 100 vines.Soil compaction. Soil compaction was measured in the vine row in November or December 2003, 2004 and 2005 with a Field Scout Soil SC-900 compaction meter . Ten sites in each plot were sampled to a depth of 15 inches. Soil moisture. Soil water storage was evaluated from volumetric soil moisture measurements taken in-row and adjacent middles to a depth of 3.5 feet at 1-foot intervals using a neutron probe. The neutron probe readings were calibrated with volumetric moisture measured from undisturbed soil cores collected at the site. Rainfall and runoff. A tipping bucket rain gauge with an 8-inch-diameter collector was used to monitor daily and cumulative rainfall at the field site. Runoff was collected at the lower end of the plots into sumps measuring 16 inches in diameter by 5 feet deep. Each sump was equipped with a device constructed from a marine bilge pump, a float switch and flow meter, to automatically record the runoff volume from the plots during storm events. During the second and third years the sampling devices were modified to collect water samples for sediment and nutrient analysis. Vine mineral nutrition. One-hundred whole leaves opposite a fruit cluster were collected from each plot at flowering in May 2003, 2004 and 2005. Petioles were separated from leaf blades, and tissue was immediately dried at 140°F for 48 hours and then sent to the ANR Analytical Laboratory for nutrient analyses. Petiole and leaf-blade tissue samples were analyzed for nitrate , ammonium , nitrogen , phosphorus , potassium , sulfur , calcium , magnesium , boron , zinc , manganese , iron and copper . Soil mineral nutrition. Composited samples from 10 soil cores taken to a depth of 1 foot were collected from the vine rows and middles at flowering as described above. Samples were air dried and sent to the ANR Analytical Laboratory for analyses. Soil samples were analyzed for pH, organic matter, cation exchange capacity , nitrate, Olsen-phosphorus, potassium, calcium, magnesium, sodium , chloride , boron and zinc. Soil microbial biomass. Due to the limited capacity of the laboratory, microbial biomass assays were conducted on selected treatments. Ten soil cores were collected to a depth of 1 foot and then composite samples were made from each replicate of the pre-emergence and cultivation weed-control treatments and the adjacent middles of the ‘Merced’ rye and bare treatments. Samples were collected about four times each year from November 2001 to November 2005 for a total of 14 sets of samples. Soil samples were immediately placed on ice and taken to the laboratory for soil microbial biomass carbon analysis according Vance et al. . Mycorrhizae. Roots were collected, stained and examined as previously reported on April 16, 2003, May 3, 2004, and June 2, 2005. Grape yield, fruit quality and vine growth. Fruit weight and cluster number were determined by individually harvesting 20 vines per subplot. Prior to harvest a 200-berry sample was collected from each subplot for berry weight and fruit composition. Berries were macerated in a blender and the filtered juice analyzed for soluble solids as Brix using a hand-held, temperature compensating refractometer. Juice pH was measured by pH meter and titratable acidity by titration with a 0.133 normal sodium hydroxide to an 8.20 pH endpoint. At dormancy, shoot number and pruning weights were measured from the same 20 vines. Statistical analysis. Analyses of variance were used to test the effects of cover crop, weed control and year on the vine, soil and microbial parameters, according to a split-block ANOVA model in SAS . Cover crop, weed control, year and their interactions were treated as fixed effects. The main and interactive effects of block were treated as random effects. Year was treated as a repeated measure. When necessary, data were log-transformed to meet the assumption of normality for ANOVA, although untransformed or reversetransformed means are presented. Changes in soil moisture among treatments during the winter and the irrigation seasons were determined from significant treatment-date interactions.We conducted evaluations with a penetrometer each fall to determine the impact of weed-control treatments on soil compaction. Soil compaction was not significantly different at any depth in 2003 . However, in 2004 and 2005 soil compaction began to increase in the cultivation treatment compared to the other two weed-control treatments. In 2004, soil compaction at the 4- to 7-inch depth was significantly greater in the cultivation treatment compared to the standard treatment , but not more so than in the post-emergence treatment . In 2005, the cultivation treatment had significantly greater soil compaction at the 4- to 7-inch depth than both the post emergence and standard weed-control treatments . At the 8- to 11-inch depth, soil compaction was significantly greater than the standard treatment , but not greater than in the post-emergence treatment .

There are several methods to make pollen grains functionally deficient and thereby reduce seed set . The most commonly used is ionizing irradiation with X-rays or gamma rays due to their ease of use, effective penetration, consistent results, and minimal disposal issues . Irradiated pollen grains can be physiologically alive, depending on the irradiation dosage, but are infertile. Irradiated grains can germinate on the stigma and even produce pollen tubes but cannot fertilize egg cells to produce embryos . Further, when sterile pollen grains are deposited on a stigma through artificial pollination, they can interfere with fertile pollen in the process of fertilization and disrupt seed production, as has been shown in apple , pear , citrus , cacao , and melon . The use of sterile pollen to reduce weed seed production is similar to the insect sterile technique , an environmentally-friendly and biologically-based method for controlling insect pest. This technique involves sterilizing male insects by irradiation and subsequently releasing the sterile males to mate with wild females , resulting in infertile eggs and reduced insect pest population sizes. Pollinating the female plants of Palmer amaranth with sterile pollen resulted in 40% reduction in the number of newly formed seeds . However, the sterile pollen technique has been rarely used as a weed control technique but could potentially be effective on dioecious weedy species because female and male flowers are in separate plants and pollen grains can be collected from male plants, sterilized and then released on female plants. The summer annual dioecious weed A. palmeri is one of the most devastating weeds in the US. It was ranked as the worst weed in US corn fields in a survey by the Weed Science Society of America . Furthermore, industrial drying rack it has evolved resistance to nine herbicide classes used and is able to produce up to one million seeds per plant .

This weed is a particularly suitable candidate for exploration of the sterilepollen technique for weed control. Being a dioecious species with separate male and female plants, it relies on cross-pollination for successful seed production. This makes it feasible to collect pollen grains from male plants, sterilize them, and subsequently release them onto female plants. The primary goal of this research was to examine the effectiveness of sterile pollen technique, SPT, as a means of disrupting seed production in A. palmeri. To this end, it was necessary to determine the optimal irradiation dose for pollen sterilization as excessively high doses may kill the pollen entirely, thereby eliminating their preventative effects on fertile pollen, while low doses may allow the treated pollen to maintain its fertility. Accordingly, a broad range of irradiance doses was tested in combination with an extensive array of artificial pollination treatments to fully explore the potential effects of the SPT on seed production in A. palmeri. Our hypothesis is that pollinating with sterile pollen, irradiated at an optimal dose, could reduce seed production in this weed. Furthermore, we speculated that the maximum reduction in seed output could be achieved when pollination with sterile pollen precedes open pollination.Seeds of A. palmeri collected from Kansas were planted in May 2020 into 3-L pots filled with UC Davis potting medium containing in a greenhouse set at a 24/32 ℃ night/day temperature regime and extended photoperiod . Fertilizers were applied as 80 ml of a general-purpose fertilizer solution weekly at 350 ppm N starting from the 2-true leaf plant stage with drip irrigation applied at 65 mL/min for two minutes twice per day. Once plants reached the flowering stage, 50 male and 50 female plants were isolated and grown in separate greenhouses .

Pollen collections were made from male plants by gentle tapping or shaking of the inflorescence. Pollen grains from all male plants were pooled and released onto aluminum foil held beneath the inflorescence. The collected pollen was then sieved through 250-mm mesh to remove large floral materials. Pollen was placed in Petri dishes covered with parafilm and then irradiated immediately with gamma rays from Cesium-137 at six dosages of 0 , 100, 200, 300, 400 and 500 Gray  at the UC Davis Center for Health & the Environment . Irradiated and untreated pollen were immediately used for pollen viability tests and hand -pollination experiments as described below.Pollen viability was assessed immediately after irradiation by using a test solution consisting of a 1% concentration of the substrate 2,5-diphenyl tetrazolium bromide in 5% sucrose. The MTT assay measures cellular metabolic activity as an indicator of cell viability and cytotoxicity . In this assay, viable pollen appears dark violet and non-viable pollen did not stain at all . Viability of 100 pollen grains for each dose at each irradiation dose was assessed by analyzing the brightness of the resulting tetrazolium stain using a digital camera and ImageJ software Version 1.46r . Grey values were used to indicate the brightness of a pixel. Because the range for grey values is 0- 255, grey value percentages were calculated by dividing the recorded grey values by 255 and multiplying by 100. Higher grey value percentages indicated lower pollen viability. Theeffects of irradiation dosage on grey value percentages were analyzed using ANOVA with Dunnett’s test.In the 2020 experiment, six lateral inflorescences of similar size from each female plant were selected to receive the following treatments: hand pollination with 1) non-irradiated pollen only, 2) irradiated pollen only, 3) non-irradiated pollen followed by irradiated pollen, 4) irradiated pollen followed by non-irradiated pollen, 5) no pollination, or 6) open pollination .

Each inflorescence was meticulously dusted with 1 ml of pollen, ensuring even and gentle distribution using a paintbrush. Thereafter, the inflorescence was immediately enclosed in a paper bag with the exception of inflorescences receiving the open pollination treatment. Hand pollination was conducted through a one-time application. About 6 weeks after pollination, inflorescences were harvested. Flower and seed numbers were measured on the above mentioned six inflorescences for each of five plants at each irradiation dosage. For each replicate, six 1-cm sections of plant branches were dissected and measured for flower and seed numbers. Two categories of seeds were identified and recorded: abnormal seeds and normal full seeds. Seed set was calculated by using the number of viable and full seeds divided by the number of flowers and expressed as percentage. To more closely simulate field conditions, this experiment was repeated in 2021 with three additional treatments: 1) hand pollination with irradiated pollen followed by open pollination , 2) open pollination for two weeks followed by hand pollination with irradiated pollen , and 3) open pollination for two weeks followed by hand pollination with irradiated pollen with no bagging, i.e., open pollination. These treatments began simultaneously when nine lateral inflorescences of similar size from five female plants reached full anthesis. As with 2020 experiment, the hand pollination was performed as a single, one-time application. Data from each year of study was analyzed separately because hand -pollination treatments differed slightly across the two years of experiment. Prior to ANOVA, in order to reduce heteroscedasticity of the residuals, seed set values were transformed using a square root transformation. Two factors, irradiation dose and pollination treatment, were firstly combined into a single factor and a one-way ANOVA was performed on seed set measurements by using aov functions in R . To better explore the interaction between the two factors, drying rack for cannabis the non-crossed treatments were removed to obtain a full-factorial design for a two-way ANOVA. The two-way factorial ANOVA was conducted using lm function followed by slicing each level of irradiation doses, with SLICE function in sasLM package , to perform the F-test for the effect of hand-pollination on seed set at each level of irradiation dose. Lastly, seed set data was back-transformed using the re_grid function in the emmeans package and confidence intervals were constructed using confint function in R .Pollen irradiated at the lowest dose exhibited the lowest grey value percentage while pollen irradiated at 500 Gy had the highest grey value .

The mean grey value of pollen irradiated at 500 Gy was significantly different from the other doses, which indicates this highest irradiation dose reduced pollen viability to a greater degree than the other doses . Under this high irradiation dose, pollen will likely be unable to produce a pollen tube and disrupt the process of double fertilization since it has lost its viability as determined by MTT staining.The viability of pollen is affected by factors such as genotype, pollen maturity, growth media composition , and environmental variables such as air temperature and humidity . Gamma ray irradiation can decrease water content in pollen, reducing the ability to transfer carbohydrate reserves, leading to changes in the cytoplasmic water, abnormal meiosis, irregular gamete formation, and ultimately decreased viability, which has been supported in studies on apples , pumpkins and winter squash , and citrus . The effect of radiation dose on pollen viability is species dependent. In some species irradiation effect is limited. For example, melon pollen can tolerate gammairradiation doses up to 3,600 Gy whereas in winter squash a 300 Gy dose reduced pollen viability by almost 80% . We found significantly reduced viability of A. palmeri pollen irradiated at 500 Gy compared with non-irradiated pollen, which indicates that seed production in this weed is sensitive to ionizing irradiation. However, our goal in the practice of irradiation is not the complete loss of viability. For effective implementation of SPT, it is essential to have semi-functional pollen that can outcompete and displace wild pollen while remaining incapable of fertilizing the ovule. Understanding the sexual reproduction process is important to gain insight about how to increase the competitiveness of irradiated pollen. When the pollen tube enters the female reproductive tissue, intensive communication occurs between the pollen tube and one synergid cell. After the contact of pollen tube and synergid cell, the receptive synergid degenerates . Following release of the two sperm cells from the pollen tube, they interact and fuse with the egg cell nucleus and the central cell nuclei, forming the major seed components embryo and endosperm, respectively. Any of the steps involved in double fertilization or a subsequent event could trigger the block of attraction of multiple pollen tubes to a single ovule . If fusion fails, one synergid can persist and continue to attract multiple pollen tubes until fertile sperm are delivered or the synergid senesces. The recovery of fertilization is limited to the second pollen tube, indicating that there is no third chance for fertilization in two synergid celled plants. The optimal irradiation dosage to sterilize pollen should maintain the function of the vegetative cell but induce failure in cell fusion. If the irradiated pollen can disrupt fertilization twice, there is no third chance for this ovule to produce a seed , thereby reducing overall seed production.Both in 2020 and 2021, the combined effect of irradiation dose and application treatment had a significantly different effect on seed set . Additionally, the effect of different irradiation doses, application treatments, and their interaction on seed set was significant in both years . Female plants that received no pollination did not produce seed in either year so this treatment will not be discussed further in the results. However, in contrast to this observation, a study has proposed apomixis as a potential mechanism for seed production in isolated female plants . In both years, regardless of the irradiation dose, all pollination treatments involving irradiated pollen consistently resulted in lower seed sets compared to open pollination . The mean seed set obtained from pollination treatments involving irradiated pollen never exceeded 35% and decreased to nearly 0% when using only irradiated pollen at doses of 300, 400, and 500 Gy . Seed set decreased with increasing irradiation dose up to 300 Gy in all pollination treatments with irradiated pollen. However, there was an increase in seed set beyond the 300 Gy dose when pollination with irradiated pollen followed by hand pollination with non-irradiated pollen. This suggests that pollen irradiated at 100 Gy and 200 Gy maintained some ability to fertilize egg cells and produce seeds, while pollen irradiated at the higher doses of 300 Gy to 500 Gy were functionally deficient and unable to complete sexual reproduction. The 300 Gy dose seems to be the optimal dose for disrupting seed production inA. palmeri as it produced the lowest seed set when interfering with non-irradiated pollen . Irradiation of pollen has also decreased seed production and seed set in other species.

Chlopyralid is especially effective for control of legumes and composites such as Canada thistle , and yellow starthistle. Because it does not control many common broad leaf weeds such as mustards, it must be tank-mixed for complete control of the wide range of broad leaf weeds found in small grains. On wheat, clopyralid should be applied from the 3-leaf stage to early boot stage, complimenting the timing of 2,4-D and MCPA. Carfentrazone is a contact herbicide that controls weeds by disrupting cell membranes. It is effective at very low application rates on coast fiddleneck, little mallow, burning nettle, and other weeds that are difficult to control with other herbicides. Adding surfactants to carfentrazone often causes temporary crop burn. Tank mixing with UN-32 may enhance weed control. Tank-mixing carfentrazone with dicamba provides good control of common chickweed. Combining carfentrazone with phenoxy herbicides broadens the weed spectrum controlled, lowers herbicide application rates, and can reduce the risk of weeds building up herbicide resistance.Preemergent herbicides are not commonly used in small grains in California, but they can be effective in certain situations. Trifluralin is a preemergent herbicide used for wild oat and canarygrass control in wheat and barley. It is applied before or after sowing and must be incorporated no deeper than 2 inches . A double incorporation is more effective than a single incorporation. Small grains must be planted below the 2-inch herbicide zone . Results can be erratic if the zone of treatment does not have adequate moisture. Crop safety is marginal.Diclofop controls wild oat, canarygrass, and Italian ryegrass in wheat and barley.

Diclofop controls wild oat and ryegrass in the 1 to 4 leaf stage and canary grass in the 1 to 2 leaf stage. Avoid applications under saturated soil conditions or cold weather. Fenoxaprop ethyl controls canarygrass, wild oat, rolling benches for growing and several foxtails, including yellow foxtail and green foxtail . It also suppresses mustards. It has a wide window of application, providing effective control when applied between the 1 to 6 leaf stage of grasses. For best control of wild oat, delay application until most wild oat plants have emerged. A tank mixture with bromoxynil allows for a wide range of weed control at an early timing. Fenoxaprop cannot be tank-mixed with phenoxy herbicides since reduced grass control often results when such tank mixtures are used. Mesosulfuron controls most grassy weeds and many broad leaf weeds in wheat. It is especially effective on Italian ryegrass, wild oat, little seed and hood canary grass, and annual bluegrass. It controls ripgut brome and other brome species, depending on weed size at application. Most California wheat cultivars have good tolerance to the herbicide. However, wheat plants will turn a lighter green color for a couple of weeks following application. If soil nitrogen levels are low, this symptom will persist longer, and supplemental nitrogen should be applied. When treated beyond the 1 tiller stage, temporary growth suppression and shortening of the wheat plant will occur. The crop will recover more quickly from these symptoms under good growing conditions. Mesosulfuron is effective on certain broad leaf weeds, including common chickweed, wild radish, and mustards. It also provides partial control of many other broadleaf weeds, including common groundsel , little malva, coast fiddleneck, yellow starthistle, and blessed milkthistle. Mesosulfuron can be tank-mixed with bromoxynil and MCPA and may be applied from the 1 leaf to 1 tiller wheat stage and up to the 2 tiller stage of grasses.

A methylated seed oil or a nonionic surfactant is required; adding ammonium sulfate or low rates of UN-32 enhances weed control on difficult-to-control weeds. Restrictions on crop rotations are greater than with fenoxaprop.Weeds that have germinated can be chemically removed using paraquat and glyphosate before cereal planting or emergence. These non-selective herbicides have no soil-residual effects on germinating small grain plants as long as they are applied before plants emerge through the soil. If the herbicide comes into contact with wheat or barley plants, severe injury will occur. Glyphosate can also suppress perennial weeds such as johnsongrass, nutsedge , bermudagrass , and dandelion when they are growing before grains are planted or emerge.The presence of green weeds late in the season can cause harvest and post harvest problems. Green weeds can slow the progress of combines, raise the moisture content of the harvested crop, and discolor or even cause off-flavors of the harvested grain. Weeds that often cause problems at harvest include field bindweed, Russian thistle, five hook bassia , kochia, common lambs quarters, knot weed, swamp smart weed, and johnson grass. Problems with green weeds at harvest can be avoided by using a preharvest herbicide application or by swathing the crop before combining. In both cases the green weeds should be allowed to dry before the crop is combined. Soil temperature results gathered after steam application in the field were similar to other mobile steamer applicator studies . The premise of this research was to evaluate the pest control efficiency of steam applied in a band prior to planting. We found that weeds, pathogens, and hand weeding times were reduced in steam-treated plots, and yields improved in some cases. In trial 3, for 176 min, steam temperatures were above 70oC were obtained with the Steamy applicator, which used a rototiller as it was incorporating steam on flat ground.

Agitating the soil as the steam was incorporated allowed for better steam penetration targeting soil aggregates compared with trials 4 and 5 done by the Yuma Steamer. The Yuma steamer kept a steam temperature above 70oC for 98-105 minutes. The temperature duration time above 70oC for the Yuma steamer was not as long as the temperature duration in the Steamy applicator trial. The Yuma steamer has a bed shaper attached to it to ensure the bed tops stay firm after application and is faster than the Steamy.The results from the weed analysis indicate that steam disinfestation does an excellent job controlling weeds, especially on hairy nightshade, goosefoot, sheperd’s-purse, burning nettle, and common purslane. Another objective in this study was to evaluate steam + hydrogen peroxide applied as a band to determine whether this product improves the pest control efficacy of steam by raising the temperature. Hydrogen peroxide did not have a significant effect on weed and pathogen control, hand weeding time, and yields compared with the steam treatments. Because the trials used soils naturally infested with Pythium spp. and S. minor, we had varying levels of disease in the field trials. Steam + hydrogen peroxide did not significantly reduce the amount of Pythium spp. colonies or S. minor sclerotia compared with steam alone. In trial 2, upon steam application, temperatures stayed above 70 oC for a shorter amount of time compared to the other trials . The steam treatment had a significant effect on reducing S. minor sclerotia by 94% when compared with the control using the Steamy in trial 3, similar to findings in other studies . The steam treatment reduced Pythium spp. colonies by 99% when compared with the control using the Yuma steamer in trial 4, similar to another study that was done . Out of all the trials, trial 4 had the most diseased lettuce plants and the best reduction of Pythium spp. colonies. The lettuce plant size for the steam-treated lettuce was significantly larger with an increase in yield when comparing with the control in trial 4 and 2, cannabis dry racks suggesting pathogen suppression. Gross revenues for the lettuce trials in this research showed the potential steam has to increase lettuce yields. A steam study done in strawberry production by Michuda et al., suggested a maximum soil temperature of 62-63oC should be a standard for growers at a duration of 41-44 mins to maximize net returns and increase fruit yield. In our lettuce steam study we surpassed that reaching temperatures above 70oC which increased yield and gross revenue peracre. Better disease control likely resulted in greater lettuce growth with a gross organic revenue of $5,624 an acre for the steam treated lettuce vs. 4,042 an acre for the non-treated control lettuce. The difference was $1,582 an acre. For the gross conventional revenue, it was 5,066 an acre for the steam treated lettuce vs. $3,640 an acre for the non-treated control lettuce. The difference was $1,426. The cost of field application per acre is $971, which suggests steam treatment maybe economically feasible to use commercially in-field given the great gross revenues per acre, but we believe that there is room for improvement in this cost. Machine operator and worker wage will increase the operating costs of this field applicator as the cost of minimum wage increases in the future, so more research needs to be done to drive the costs of the applicator down.

Research and development should focus on the implementation of a rototiller to agitate the soil to target soil aggregates for better steam penetration. Improvements might include making the machine lighter so that there is less compaction. Ideally, machine development and construction should be done in the United States to reduce the overall price of the applicator. It is important to increase the speed of application, but it needs to be done in a way that the machine still heats the soil and makes adequate dwell time. Currently, it takes 9.07 hours to steam an acre, so if the time of application can be reduced, then the amount of fuel costs can be reduced as well. It will be of great benefit to work with a known industry leader like, TriCal Inc. because they specialize in developing new effective technologies and build products to control soil pests in California. Steam applicator development can be maximized with the help of contractors who have the capabilities of building a steam applicator who can lease out to farmers. Steam is also an option for organic farmers to make an applicator in house that can be of great benefit given the need for non-chemical ways of controlling soil pests.Nevertheless, my results indicate that with a greater reduction of pathogen inoculum and weed seeds in the soil using steam, this will allow more opportunity for the crop to thrive with less pest competition. Even though the hydrogen peroxide treatment was evaluated only in two of five trials, there was no significant advantage when compared to the steam treatment alone. Hydrogen peroxide still has potential to create an exothermic effect in the soil steaming process. As a recommendation for future studies if hydrogen peroxide is more thoroughly incorporated into the soil and the trial is pre-inoculated with soil pathogens, there may be a yield benefit. This work further shows the true potential of band steaming for weed and pathogen control in the field .Surface mulches are widely used in the production of strawberries and certain high value vegetable crops. Polyethylene mulch is used on virtually all tomato and strawberry production in Florida and is also widely used in the production of other crops such as peppers, eggplant, and melons throughout much of the southern United States. Researchers at the University of Florida estimate that more than 100,000 acres of vegetable crops in that state currently use plastic mulches annually, making Florida the national leader in this production system . In California, the majority of strawberry and staked tomato production uses polyethylene mulch. Peppers, eggplant, and melons also use mulches in certain situations, especially when earliness is desired. Field management and research related to plastic mulches in these production regions is now quite developed. Potential benefits as well as drawbacks of polyethylene mulches for vegetable crop production are given in table 1. The use of intercrop cover crop residues as surface mulches is a more recent and far less widely used production practice. It has recently gained considerable interest in a number of commercial vegetable crop production regions in the United States. Potential advantages and disadvantages of this vegetable crop production technique are summarized in table 2. Reflective plastic and some cover crop mulches share similar features relative to crop production: insect and disease management, weed management, fertilizer availability, and water conservation. In order for production practices using either polyethylene or cover crop mulches to be successfully adopted in California, specific production goals must be carefully matched with specialized management know how and experience.Plastic mulches have been commonly used for commercial vegetable crop production for more than 30years.

Few California soils in sunflower growing areas have shown yield limiting K deficiencies; sandy soils are the most likely to show K fertilizer responses.Sulfur deficiency, though rarely observed in sunflowers, is characterized by slow growth and overall uniform light green color of the plant. It is generally only observed once every 5 to 7 years, and may occur only after high rainfall, prolonged wet soil conditions, and cooler soil temperatures from January to March, especially in wheat. In the Sacramento Valley, some soils may show temporary deficiency of S, and most irrigation water contains little or no sulfur. Fertilizers such as ammonium sulfate, a common source of S in the past, are no longer being used as commonly as non-S-bearing aqua ammonia and other high-analysis fertilizers and therefore S deficiencies might occasionally occur. Broadcast and incorporate elemental S into S-deficient soils at a rate of 50 to 100 pounds of S per acre to provide a correction that will last several years. Elemental S is best applied in the fall when the fields are bedded up to allow time for oxidation to sulfate-S, the form used by plants. The time necessary to oxidize elemental S depends on soil temperature and moisture, as well as on the size of the particles applied. Particle size may cause the timeline to change from a few weeks to several months before the applied elemental S becomes effective. Other materials such as gypsum , which is about 17% S, provide the readily available sulfate form of S and can also be used. These materials should be applied at a rate that supplies about 25 to 50 pounds of S per acre and should be incorporated into the top 2 to 3 inches of soil to be most effective.Although soil moisture can be assessed by using the “look and feel” method, rolling benches for growing soil moisture sensors can provide more accurate information. There are many sensor options available to growers, including tensiometers and gypsum blocks, that are accurate and relatively easy to use and inexpensive.

Tensiometers indicate soil moisture levels by measuring the soil moisture tension, or how strongly water is held onto soil particles. Therefore, low soil moisture tension indicates moist soil, and high soil moisture tension indicates dry soil. Gypsum blocks buried in the soil measure the electrical resistance of water, which can be converted into a soil moisture tension value. Soil moisture tension is usually expressed in centibars . Soil moisture sensors must be installed in areas that are representative of the field; that is, the site must have a soil type that is typical of the field and needs to receive full irrigation coverage. Sensors should be installed to the depth of the active root water uptake zone, which for sunflowers would be 4 feet. Monitor soil moisture at 1 foot, 2 feet, 3 feet, and 4-feet deep to determine when to irrigate and to ascertain the depth or adequacy of an irrigation. It may also be useful to monitor at 5 feet to determine whether excess irrigation water is being applied, causing water to percolate past the sunflowers’ 4- to 5-foot rooting depth. The threshold level for soil moisture in the root zone for sunflowers and irrigation needs depend on soil type, irrigation system , growth stage, and amount of deep moisture in the soil profile. General guidelines for soil moisture monitoring can be given based on limited experience with sunflower production in clay loam soils in the low desert of California. For heavy soils, the upper limit for soil moisture depletion in the top 2 feet of the root zone is 90 to 120 cb. Irrigation should be applied when soil moisture content reaches this threshold level. If soil moisture is depleted beyond this level, the crop will be under stress.

However, roots can extend beyond 4 feet and this threshold could be reached and the crop may not show signs of stress if there is moisture in the deeper soil profile or a shallow water table available up to 6 to 8 feet below the soil surface. In experiments conducted at the UC Desert Research and Extension Center from 2016 to 2018, sunflower plots that were subjected to 60 percent deficit irrigation practices showed no stress and yields were not affected by the reduced water applications due to the presence of a shallow water table 6 to 8 feet below the soil surface.In some years, soil pests that live at or below the soil line, such as variegated cutworm , wire worms , and seed corn maggot , can seriously damage seedlings and cause significant stand losses. These pests tend to be sporadic in time and space; they tend to be more troublesome in wet years when weed vegetation is heavy, and they have a patchy distribution in fields. They are often problematic in the same field year after year, so monitoring and being familiar with the history of the field is important for managing these pests in crop rotations. Use of insecticide seed treatments, such as Cruiser 5FS will help control early-season soil-dwelling pests. Sunflower Moth Sunflower moth, also known as sunflower head moth , is the most serious pest of sunflower in California and other U.S. sunflower growing states. The adult sunflower moth is grayish, ⅜ inches long, and rests with wings clasped tightly to the body, giving it a slender cigar shape . Eggs are difficult to find because they are usually laid at the base of florets in the flower head. The newly hatched larvae are pale yellow but darken to shades of brown with longitudinal white stripes and a light-brown head capsule. Insect excrement and tangled mats of webbing on the flower heads indicate larval activity . Mature larvae drop to the ground on a strand of silk, crawl into cracks in the soil, spin cocoons, pupate, and later emerge as adults.

There can be 3 generations of head moth per year. In California, the sunflower moth likely overwinters as a larva in the cocoon stage in the soil. In colder climates, such as Midwestern states, the moth is migratory. In the Sacramento Valley, the moths begin to emerge in June and are generally most troublesome in July and August. Early-planted fields sometimes escape moth damage, as moths seem to build up on early planted fields and disperse into later planted fields when they reach greater numbers. In the Imperial Valley, plantings are generally early enough that they escape head moth flights, but if one occurs, it would be in May. Significant outbreaks of sunflower moth can occur, with yield losses of 30 to 60 percent and occasionally 100 percent in fields where the moths are not controlled. The only way to effectively and economically manage this pest is through insecticide treatments. There are no effective cultural practices, and bio-control cannot be relied on because the primary brachonid parasitoid wasp in sunflowers cannot readily reach the head moth larvae deep in the florets with its ovipositor or break through the seed shell to reach the larvae and sting them. Sunflower moths can be monitored using Pherocon IIB pheromone traps baited with sunflower moth pheromone lures. Two traps are generally placed along the north and south side edges of fields, taking advantage of the prevailing winds to maximize trap catches. Traps should be monitored weekly, and more often during bloom when sunflowers are most sensitive to damage by the moths. When trap thresholds reach 4 or more moths per night, especially with July and later-blooming fields, the field should be treated with an insecticide to prevent damage and crop losses, cannabis dry racks especially from secondary pathogens. When using insecticides during bloom, it is critically important to protect honey bees to promote bee activity and crop pollination. If an insecticide treatment is needed, spray before hives are brought into fields prior to bloom or early in the morning before bees are visiting flowers. Insecticides that control head moth include Coragen , Warrior or Asana , and XenTari . Coragen does not control adult moths but gives good caterpillar control with recommendations to apply twice, once at the late flower bud stage and again at the very beginning of bloom , to ensure good coverage and protection. Coragen is relatively safe for bees, but applications should be made early in the morning when bees are less active to protect them from harmful effects of sprays.Lygus bugs are small plant bugs with a very distinctive yellow V on their back . They are serious pests of numerous crops, including strawberries, beans, and cotton. In confectionary type sunflowers, feeding damage causes brown spots known as kernel brown spot , reducing the quality of the seed for the snack food industry. However, the impact of Lygus on hybrid seed production is unclear. Lygus feeding damage may reduce sunflower seed germination, a focus of current UC ANR research. Western Flower Thrips Western flower thrips are tiny, slender, light-yellowish insects.

The nymphs are wingless, while adults have clear, slender wings . When they feed, they generally cause leaves to be deformed, but they also leave behind silver patches on the lower side of leaves with tiny black fecal pellets. Plants usually outgrow the problem, just as they outgrow severe leaf tattering from wind damage. However, high numbers of thrips and heavy feeding damage can injure seedling stands if temperatures are high and plants are water stressed, and they may require a pesticide treatment for control to prevent stand loss.Two-spotted Spider Mite Two-spotted spider mites are found in sunflowers, particularly later in the season as the plants senesce. Mites are small, pinhead-sized, oblong, and yellowish with two dark pigmented spots, and they have eight legs . The eggs of spider mites are whitish and spherical and can be seen with a hand lens. Spider mites are usually found on the underside of leaves, with colonies beginning on the lower leaves and moving upward on the plant. Spider mite feeding damage first appears as stippling on leaves. As numbers increase, spider mites spin fine webbing and move rapidly around the plant on the webbed area. Damage in heavily infested plants includes leaf desiccation with a whitish-gray cast and stunted plants. Infestations are usually associated with mature plants, dust along field edges from dirt roads, water stress, and natural senescence and control is generally not needed. Postharvest Storage Pests Sunflower seeds destined for export must be examined to ensure that they are free of stored product insect pests. These include dermestid beetles ; weevils ; lesser grain borer ; sawtoothed grain beetle ; red and confused flour beetles ; and slender and broad horned flour beetles . More information on stored product pests and their control can be found in the pantry pests notes and in Residential, Industrial, and Institutional Pest Control by O’Connor-Marer .California’s dry climate, and rich, irrigated soils provide excellent conditions for growing strong, healthy sunflowers that experience fewer diseases with less severity than sunflowers grown in the main oil-production areas of the Midwest under summer rainfall. Very few of these diseases lead to yield losses in California growing conditions, but many are of quarantine significance and thus would preclude seed from being exported to foreign countries. This could cause serious economic impacts, so it is important to monitor for diseases. The fungal diseases in California sunflower production classified as quarantine status by many foreign countries include downy mildew , rust , and Sclerotinia head and stalk rot . Fortunately, these diseases are very rare in California due to our hot, dry summers. In a 15-year study by Gulya et al. , only three quarantine-type diseases were found in sunflower in California, including rust in 4% of fields, Sclerotinia rot in 2.6% of fields, and downy mildew in 0.4% of fields. Each importing country has different pathogens that are excluded. Since U. S. companies may not know in advance where the seed will be exported, it is imperative to ensure fields are free from as many diseases as possible. If the pathogen involved is soilborne, rotate to a nonsusceptible crop to reduce the disease inoculum in the field. Downy mildew and rust are sunflower-specific diseases, so any crop is suitable to rotate for controlling them. However, for pathogens with a broad host range like Sclerotinia spp., nonhost monocots must be rotated to help reduce the sclerotia soil inoculum. For diseases such as Rhizopus head rot, rotation offers nohelp since the fungus is ubiquitous and persists as a saprophyte on any organic matter.

These two weevils are the most widely used biological control agents of water hyacinth, Eichhornia crassipes , a floating aquatic plant native to South America. Classical biological control of water hyacinth has been implemented across the globe, with some introductions resulting in significant reduction in water hyacinth cover and/or bio‐ mass, including parts of Australia, China, East Africa, the U.S. Gulf Coast, India, Mexico , and the lower elevation regions of South Africa . Releases of N. bruchi and N. eichhorniae from the native range began in the early 1970s, with initial and subsequent releases in 30 and 32 countries, respectively. These weevils have contributed substantially to the control of water hyacinth in at least 13 countries . Through their use as biological control agents, these two weevil species have often undergone multiple and serial introductions . For example, in the United States, weevils of N. eichhorniae released into northern California underwent four sequential importation steps from the original Argentinian population in the native South American region. Native Argentinian weevils were re‐ leased into USA: Florida in the 1970s, and the weevils in USA: Florida were used to found a population in USA: Louisiana, which were then used to found populations in USA: Texas. This USA: Texas population was the source for the northern California population released in the early 1980s . Similarly, in South Africa, there were multiple introductions of each N. bruchi and N. eichhorniae with each new release being sourced from a different location to which they had been introduced for biological control , cannabis drying racks rather than directly from the native range. These multiple introductions from the non‐native range represent serial bottlenecks in population size that could potentially reduce genetic diversity and limit adaptive potential.

Alternatively, these multiple introductions from different source populations could increase genetic diversity through genetic admixture of the different source populations . The latter may occur particularly if each source population had sufficient time to diverge or adapt to the region of introduction, resulting in increased genetic differentiation from its source population. Based on the importation history and documented releases of these two biological control agents, we proposed several hypotheses addressing our five study questions in turn. We hypothesized that hybrids of these two species would occur, as they have frequently been co‐introduced to the same geographic regions and individuals with morphological characteristics of both species have been found . We hypothesized that genetic diversity would be the highest in the native range compared to regions where the weevils were introduced as biological control agents. Similarly, we hypothesized that the populations from the native range would have more rare alleles than the introduced regions. We hypothesized that allelic richness would reflect the number of individuals released . Specifically, as the initial propagule size of N. bruchi was greater than that of N. eichhorniae in USA: Florida, we ex‐ pected that populations of N. bruchi in USA: Florida would be less likely than populations of N. eichhorniae to lose rare alleles and exhibit reduced allelic richness in the introduced range compared to the native range. In cases where multiple introductions were prominent, particularly regarding the introduced populations of N. eichhorniae in South Africa, we hypothesized that the geneticad mixture would increase genetic diversity and buffer against the negative effects of serial bottlenecks. On a global scale, regarding the number of serial introductions, we hypothesized that populations with more introduction steps away from the native range would harbor lower genetic diversity than those with fewer steps. As the initial releases occurred over 40 years ago, we hypothesized that despite originating from the same initial populations that most introduced populations would have diverged genetically from the native range and each other.Importation and release history were obtained from peer‐reviewed literature, government reports , shipment letters , unpublished quarantine records , and published quarantine records .

However, there were many gaps, as details in the importation and release history of biological control agents are often missing or not easily accessible to the public including the number of adults surviving shipments, the number used for mass‐rearing after quarantine inspection, the number ultimately released, the localities of the releases, and whether multiple releases occurred. From the shipment letters and quarantine reports pertaining to the initial exports from Argentina to USA: Florida , it appears that samples from at least two populations of N. bruchi and N. eichhorniae were collected from Argentina and released in USA: Florida. Initial shipments of N. bruchi received in 1974 to the USA: Florida quarantine consisted of 156 and 1,050 surviving adult weevils from collections in Campana Lagoon and Dique Lujan, Buenos Aires, Argentina, respectively. However, it is unclear whether or not individuals from Campana were used for mass rearing, based on notes about possible infections by nematodes. Additional shipments from these collection sites appear to have occurred around this same time, but it cannot be confirmed whether they were used for augmenting the populations that were eventually released. Samples from two populations of N. eichhorniae were collected and shipped in 1971, with the number of surviving adults arriving in the quarantine in USA: Florida documented as 10 from Campana Lagoon and 156 from Santa Fe, Argentina, with these collection sites c. 300 miles apart. An additional third population of N. eichhorniae may have been received, containing a mixture of 219 weevils from Campana and Dique Lujan Buenos Aires and arriving in 1975 . However, these reports indicated potential nematode and fungal infestation in this later shipment, and again it was not clear whether or not offspring from these weevils were included in augmentation of laboratory colonies or released. In 1980, following the quarantine and mass‐rearing periods in USA: Florida, 50 N. bruchi adults were released from USA: Florida in Wallisville Reservoir, Texas, USA . N. eichhorniae were found in this same reservoir as a consequence of westward migration from a biological control site in Louisiana .

In 1981, 500 adults of N. eichhorniae were imported from Louisiana populations and released in Wallisville, Texas . A total of 7,500 N. eichhorniae and 2,823 N. bruchi from the populations in Wallisville Texas were then released across four locations in the Sacramento–San Joaquin River Delta in California . All other importation data pertinent to this study are summa‐ rized in Figure 1 and further detailed in the Supporting Information Appendix S1.Potential microsatellite loci for N. bruchi and N. eichhorniae were identified using a Perl script, PAL_FINDER_v0.02.03 , and Primer3 to analyze 150‐bp paired‐end Illumina sequences from extracted DNA enriched for mi‐ crosatellite loci at the Savannah River Ecology Laboratory . From this, primers were designed for 48 loci, using only those with tri‐ and tetranucleotides and those with at least six repeats. For each species, the final loci for analysis were tested on DNA extractions from 24 adult weevils ranging across several collection sites. A set of 10 and 11 microsatellite loci for N. bruchi and N. eichhorniae, respectively, met the criteria of selection, that is, purerepeat, polymorphism, and amplification by PCR. Following amplifi‐ cation by PCR, eight and 10 loci, respectively , were kept for the statistical analysis due to the high occurrence of null alleles in two loci for N. bruchi and one locus in N. eichhorniae. After the initial screening, weed growing rack primers were combined in three multiplex reactions per individual for each species. For each 96‐well plate, we included a negative control and an internal control of aliquoted DNA from an individual weevil that was used on every plate for the respective species. PCR multiplex reactions were run separately for the two species to avoid cross‐contamination. Pig‐tails were added to the 5′ end of each reverse primer, and one of four different universal tails was added to the 5′ end of each forward primer . The system of universal tailed primers was used to introduce a fluorescent dye during the PCR according to Blacket et al., and Culley et al. . Initial single plex and subsequent multiplex PCRs were in a final volume of 10 μl containing 50–70 ng of DNA, 5 μl of Qiagen Multiplex PCR Master Mix, 0.2 μM of reverse primer, 0.05 μM of for‐ ward primer, and 0.2 μM of the corresponding fluorescent primer using fluorescence‐labeled oligos , and the addition of 2 μl of Qiagen Multiplex Q‐solution for several of the multiplex reactions . PCR was performed at the following conditions: 95°C for 15 min; 35 cycles of 94°C for 30 s, the optimum annealing temperature of each primer for 1.5 min, 72°C for 1 min, and a final extension of 30 min at 60°C. Following successful amplification, 0.5 μl of the amplified prod‐ uct was added to 11 μl of solution containing 10.5 μl Hi‐Di formamide and 0.5 μl Liz size standard. Fragment lengths were measured in comparison with the GeneScan™ LIZ® 600 Size Standard v. 2.0 and genotyped on an Applied Biosystems 3730XL DNA Analyzer at the DNA Sequencing Facility at the University of California Berkeley. Fragment lengths were manually scored and binned using the Microsatellite Plug‐in for Geneious Pro v. 5.6.2 . We re‐ran multiplex reactions and subsequently re‐genotyped samples if clear peaks were not obtained in the first run. Genotype scores were checked with the program MICRO‐ CHECKER v. 2.2.3 to identify possible null alleles and genotyping errors due to stuttering and large allele dropout .We re‐examined the relevant raw genotype data and either corrected the peak calls, or removed individuals that had poor quality peaks based on the recommenda‐ tions of MICRO‐CHECKER. Genotype scores from the two wee‐ vil species were divided into two datasets for each species as the microsatellite markers did not overlap for weevils with diagnostic morphological characteristics for N. bruchi and N. eichhorniae. The dataset for N. bruchi consisted of genotype scores for 171 weevils from eight independent collection sites among five countries. The second dataset for N. eichhorniae consisted of genotype scores for 267 weevils from 11 independent collection sites among seven countries . Final genotype scores for each individual, species, and collection site are in the Supporting Information Appendix S4. We used the program GenAlex and the R packages, “poppr” v. 2.5.0 and “adegenet” to convert genotyping results into formats suitable for analysis in R . We calculated the null allele frequency from the final datasets in the R package “pop‐ genreport” . As some statistical tests assume linkage equilibrium and Hardy–Weinberg equilibrium , we assessed deviations from LE with “poppr” and deviations from HWE across all sites for each locus with the package “pegas” . We constructed genotype accumulation curves with the R packages “poppr” and “vegan” to test whether sufficient sampling had been performed for each species and collection site.To evaluate whether co‐introduction of these two related weevils species resulted in hybridization, we first identified individuals for each species that had ambiguous markings on the elytra that contrasted the typical morphological characteristics for that species . Then, we tested both sets of species‐specific microsatel‐ lite markers on 12 weevils with ambiguous morphological characteristics, as well as on weevils that had the typical species‐specific morphological characteristics for comparison. Hybridization is inferred from at least two of the species‐specific markers from each species amplifying in the same individual .As bottlenecks in population size can reduce genetic heterozygosity through processes of genetic drift and inbreeding, we estimated the average observed and expected heterozygosity, deviations from HWE , and the average “inbreeding coefficient” for each collection site across all loci with the R package “diveRsity” . Here, we use FIS to estimate increases in ho‐ mozygosity due to genetic drift caused by a larger population being separated into sub‐populations, rather than due to consanguineous mating . Thus, we used “g2” to test for inbreeding within populations of each weevil species by using 1,000 permutations in the R package “InbreedR”. In populations with inbreeding, g2 is significantly greater than zero, indicating correlated heterozygosity among pairs of loci . We compared total and aver‐ age allelic richness and the number of private alleles among collection sites . To compare genetic diversity among the introduced and native populations, we tested for the effects of population on genetic diversity by fitting linear mixed models with the lmerfunction in the lme4 package . Implementing an LMM accounts for the variability of the mi‐ crosatellite loci by modeling locus as a random effect, and collection site as a fixed effect with allelic richness or expected heterozygosity as the response variables in separate models.

Twenty-seven weedy rice plants were chosen for genotyping along with 12 accessions of temperate japonica varieties that are cultivated in California. Leaf tissue from the outdoor grown plants was excised and desiccated for shipment to Clemson University for DNA extraction. DNA was extracted from desiccated leaf tissue using the Macherey-Nagel NucleoSpin 96 Plant DNA extraction kit . Purified genomic DNA was diluted 2:1 in nuclease-free water for polymerase chain reactions . PCR was carried out using standard conditions to amplify 48 gene fragments selected by [21] from 111 sequenced tagged sites developed by [38]. PCR products were checked by gel electrophoresis and cleaned up using Exonuclease and Antarctic phosphatase treatment following the method described in [39]. Direct sequencing in both the forward and reverse directions was carried out by the Clemson University Genomics and Computational Biology Laboratory. Sequences were assembled into contiguously aligned sequence ‘contigs’ and assigned quality scores using Phred and Phrap. Contigs were aligned and inspected visually for quality and heterozygous sites in BioLign version 4.0.6.2 . Heterozygous base calls were randomly assigned to two pseudo-haplotypes, which were then phased using PHASE version 2.1. Due to low levels of heterozygosity in the data set, haplotypes were inferred with very high probabilities and consistency across five runs. All sequences have been submitted to NCBI GenBank . Phased haplotypes were aligned with sequences obtained from [21]. These additional sequences consist of the same 48 STS loci for a broad range of AA genome Oryza species including 58 weedy rice accessions sampled over a 30 year period from Arkansas, Louisiana, Mississippi, Missouri, and Texas. Also included in this dataset are sequences from the major cultivated groups from Asia and Africa , vertical racking as well as wild species sampled from Asia , Africa , Central America , and Australia.

Genetic structure and divergence. Summary statistics for each STS locusincluding nucleotide diversity at silent sites using the Juke’s Cantor correction, Watterson’s θ at silent sites, number of segregating sites S, and Tajima’s D were calculated in DnaSP version 5.0 . Arlequin version 3.5 was used to calculate pairwise FST and ФST estimates with 10,000 permutations to assess significance.Bonferroni corrections were used to determine Pvalue cutoffs. Recombination break points in each locus were determined using the four gamete test in SITEs. The population-mutation parameter FST is an estimate of genetic divergence within and between groups and was used to test for the extent of genetic differentiation. To better estimate divergence betweenCaliforniaweedy rice and other rice groups, the population mutation parameter ФST was used, which is similar to FST but uses distances between haplotypes, not just haplotype frequencies. Genetic diversity was measured by computing the average nucleotide diversity , total number of segregating sites, and Watterson’s θw within each field as well as within all fields combined. Population structure was inferred using InStruct, which was designed to allow for inbreeding by not assuming Hardy-Weinberg equilibrium within populations. Using STRUCTURE for inbreeding populations results in inappropriately higher rates of inferred splitting between populations . Five permutations for each number of populations were set from 1 to 22 with 500,000 steps and a burn-in period of 100,000 steps. In Structruns were completed on the Clemson University Condor computing cluster. Log likelihoods for each run were compared to determine the best fit K value. Distruct version 1.1 was used to create the graphical display from the results obtained with InStruct. Isolation with Migration modeling was used to test for best fit models of isolation-migration and simultaneously estimate effective population sizes , migration between populations , ancestral population size and time since divergence .

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

Qualitative descriptors were transformed using the PRINQUAL procedure of SAS with the OPSCORE option for optimal scoring and MONOTONE option for monotonic preservation of order. Principal Components Analysis with maximum total variance was performed on the combined quantitative and transformed qualitative descriptors. The variables describing cultivars were reduced by eliminating any that did not vary by descriptive statistics and then using both random and a priori sampling to preserve group partitioning while identifying the eigenvectors which most clearly separated groups. UPGMA hierarchical clustering using the CLUSTER procedure of SAS was performed to confirm separation of clusters on PCs and to generate a dendrogram using average Euclidean distances. Qualitative transformations, PCAs, and MANOVAs were executed in SAS1 Version 9.3 . Average estimates of genetic differentiation between weedy rice in California rice fields are very low, ranging from 0 to 0.0026 . There are no significant differences in FST estimates for any of the 48 loci. The highest FST estimate was 0.077, betweenCRR1 and CRR4 at STS085. These low values indicate no population structure and no divergence of weedy rice in the fields sampled, which supports the appropriateness of a genetic diversity assessment for California weedy rice . Measures of genetic diversity for California weedy rice within each field as well as for weedy rice within all fields combined are also very low , rolling benches consistent with a recent founder event, or strong population bottleneck. These values are a full order of magnitude lower than what was calculated for strawhull and blackhull weedy rice ecotypes collected from the southern US. Due to the lack of population substructure and low genetic diversity, we placed all California weedy rice into one group for the remaining analyses. Values for average population differentiation estimates across all 48 loci indicate high divergence between California weedy rice and all other sampled groups. The lowest mean value is with O. rufipogon collected from Southeast Asia . Taking the median values across the 48 loci allows better understanding of the patterns across all loci. The lowest divergence was between California SHA weedy rice and BHA and SH; median ФST values indicated that for at least half of the loci tested divergence was an order of magnitude lower than the mean estimates . This indicates that the mean ФST is high due to divergence at a few loci, and that California weedy rice does share some similarity to weedy rice from the southern US at several loci.The most recent divergence of California weedy rice from other Oryzasis from California rice cultivars , which was estimated at about 118 generations ago . The other divergence estimates were over an order of magnitude older . Interestingly, both SH and BHA weedy rice from the southern US have very old divergence estimates: approximately 30,000 and 17,000 , respectively.

These numbers are likely inflated compared to the reported origin of domesticated rice approximately 10,000 generations ago due to interactions among other closely related genotypes. This follows work examining model testing performance of IMa under several scenarios,which showed that divergence estimates inflate when gene flow from other populations is included in the model. A model of relative divergence times shows a shallow, recent coalescence of California weedy rice and California crop rice alleles, whereas SH and BHA southern US weedy rice and Chinese O. rufipogon show a much older divergence from California weedy rice . Migration estimates between California weedy rice and all other groups were quite low, with higher estimates of migration into California weedy rice in all cases. Indeed, these data should not be interpreted as absolute numbers but instead as relative values. Any overestimation of the generation values could otherwise indicate that the divergence actually happened even more recently. The effective population size for California weedy rice is very small in all cases,supporting a recent founder event or bottleneck.California weedy rice differs morphologically from other southern US weedy rice ecotypes. California weedy rice has a straw-colored hull with long awns , whereas only 7%of SH weedy rice in the southern US has awns. Nevertheless, California weedy rice shares important weedy traits with those of southern US weedy rice including high seed shattering and a red-colored pericarp in addition to tall stature and high tillering habit.Principal components analysis reduced the set of observed variables for California weedy and cultivated rice by loading them on orthogonal lines of fit based on contributions tovariance. No variation was observed amongst weedy and cultivated rice for leaf texture and angle, ligule shape, ligule color, ligule pubescence, auricle color, node color, or panicle secondary branching, so these traits were excluded from the analysis. When multiple traits represented the same metric, we chose the variable with the highest eigenvector value to represent each group or suite of highly correlated traits, although each group member or variable has an impact when describing the underlying mechanism responsible for phenotypic selection differences between the cultivar and weedy rice in California. Importantly, pericarp color clearly distinguishes weedy from cultivated rice in California , but is not highlighted in the dimension-reducing PCA because it was scored as a qualitative trait following International Rice Research Institute descriptor guidelines. The remaining phenotypic traits included vegetative growth habit characters, reproductive morphologies, and yield metrics related to grain morphology. Principal components analysis was conducted on these informative traits, excluding highly correlated variables . A second PCA was performed on a reduced dataset, which included the five traits with highest eigenvector values for each principal component in the initial analysis . Principal Components 1 , 2 , and 3 together account for 45.18% of the total cumulative variance in cultivated and weedy rice in the first PCA . Traits most greatly discriminating California weedy from cultivated rice include panicle type, leaf width ,flowering , awn color, and culm length ; lemma pubescence, texture of the panicle axis, length of the first leaf below the flag leaf, length/width ratio of grain, and width of flag leaf ; 100-grain weight of the field-collected mother plant, awn length of the field-collected and offspring plants, spikelet fertility , and grains per panicle described most of the variation along PC3. Because we were interested in the contribution of suites of traits describing each statistically significant orthogonal vector, the 15 traits contributing most to variance along the first three PCs in PCA 1 were subjected to a second analysis. In PCA 2 of “key discriminating traits,” principal components 1 , 2 , 3 , and 4 account for 74.91% of the cumulative variance in the phenotype of California weedy rice . Since components or dimensions with an eigenvalue greater than one are statistically relevant to the result , we report four principal components for this second PCA.