Hemp Growing

Three crop safety studies and two supplemental dose-response evaluations were conducted in 2019 and 2020 to evaluate the crop safety of the Israeli-developed PICKIT decision support system on California processing tomatoes. These studies were conducted at the UC Davis Plant Sciences Field Research Facility near Davis, California . The soil composition at this site was 41% sand, 34% silt, and 25% clay with 2.1% OM, 6.98 pH, and estimated CEC of 18.2 cmolc/kg of soil. The site did not contain broomrape; this protocol focused on crop safety of 1X and 2X rates of herbicides used in the PICKIT system that are not currently registered for use in tomato in the United States. Plots were 12 m long on 1.5 m beds with one plant line in the center of the bed. Cultivar ‘Heinz 1662’ processing tomato transplants were planted at 30.5 cm spacing. Each bed had two 15.9 mm drip lines buried at 30.5 cm with 0.6 L/hr emitters spaced every 30.5 cm; one line ran the full length of the beds and was used for crop irrigation and fertigation, the second line was terminated at the end of each plot and connected to an above-ground manifold system which was used to apply the experimental chemigation herbicide treatments. Plots were arranged in a randomized complete block design with four replications per treatment. In 2019, two experiments were conducted to represent twoplanting dates, April 25 and May 30; a single experiment was conducted in 2020 with an April 22 planting date. Pre-plant incorporated applications of sulfosulfuron were made one day before transplanting on April 24 and May 29, 2019 in the early- and late-planted experiments respectively, and on the day of planting, April 22, 2020 . PPI herbicides were applied using a backpack sprayer and three-nozzle boom delivering 280.5 L/ha with AIXR 11003 nozzles at 28 pounds per square inch .

PPI treatments were mechanically incorporated to 7.6 cm after application, commercial grow racks after which tomatoes were mechanically transplanted with a three-row transplanter on April 25, 2019 , May 30, 2019 , and April 22, 2020. The PICKIT system’s thermal time model is based on growing degree days , with applications at 400, 500, 600, 700, and 800 GDD after transplanting depending on treatment regimes . The PICKIT program has various regimes depending on level of infestation, with each calling for different application types and total number of applications . In 2019, chemigation applications were made through the terminated irrigation line using a 20.8 L/min 12-volt electric pump and 113.5 L tank. Treatments were applied to four plots at once, with a total carrier volume of 96.1 L per treatment resulting in approximately 15.9 L per plot . In 2020, chemigation applications were made using CO2 to inject a chemigation mix into a distribution manifold with valved connections at each plot . Treatments were applied to two replicate plots at once with separate injection ports for replicates 1 and 2 and replicates 3 and 4 to reduce the system volume receiving herbicide treated water. Herbicides were diluted in 11 L of water and this solution was injected into the already-running irrigation system over approximately 15 minutes, followed by 20 minutes ofwater to flush the distribution lines. Foliar imazapic treatments were made on July 16, 2019, August 15, 2019, and June 12, 2020 and approximately 21 days later with a backpack sprayer and two-nozzle boom delivering 280.5 L/ha with AIXR 11005 nozzles at 20 PSI. These applications were made at estimated broomrape emergence and approximately 21 days later, as these studies occurred in uninfested fields. Phytotoxicity was recorded in all three studies and representative plant height was recorded in the 2020 study. All fruit from one-meter square sections of row were harvested on September 4, 2019, September 19, 2019, and September 3, 2020 at commercial maturity and fresh weights were recorded .

Phytotoxicity, height, and yield data were analyzed using a one-way analysis of variance followed by a Tukey-HSD test using the agricolae package in R version 1.2.5033 . Two supplemental crop safety trials were conducted to evaluate increasing rates of foliar applied imazapic, which is not currently registered on processing tomatoes in California. These studies were conducted at the UC Davis Plant Sciences Field Facility near Davis, CA, . Cultivar ‘Heinz 1662’ tomatoes were transplanted on April 22, 2020 in a single plant line on a 1.5 m bed with 30.5 cm spacing. Imazapic was applied late in the growing season to simulate a rescue application in a PICKIT program. Applications were made on July 7, 2020, 73 days after transplant in the first experiment and on July 21, 2020, 87 days after transplant in the second experiment at 280.5 L/ha using a two-nozzle boom with AIXR 11003 nozzles at 28 PSI. Five rates were applied in a dose response style experiment with a 0.25% v/v nonionic surfactant . Applications were made at full fruit set . Each treatment was replicated four times in a single guard row of an existing processing tomato experiment. Visual crop injury ratings were taken 3, 7, and 14 days after treatment . Phytotoxicity means were analyzed using a one-way analysis of variance followed by a Tukey-HSD test using the agricolae package in R version 1.2.5033 .A two-year study was conducted from spring 2019 to fall 2020 to evaluate rotational crop-safety of the Israeli-developed PICKIT decision support system. This field experiment included a 2019 tomato crop treated with PICKIT herbicides followed by a planting of six common rotational crops in 2020. The study was conducted at the UC Davis Department of Plant Sciences Field Research Facility near Davis, California . The site did not contain broomrape; this experiment focused on crop safety of sulfosulfuron, imazapic, and 2X rates of imazamox, imazapyr, and imazethapyr, none of which are currently registered for use in tomato in the United States.

The 2019 tomato main plots were 54.8 m long on 1.5 m beds with one plant line in the center of the bed. Each bed had one 15.9 mm drip line at a depth of 30.5 cm with 0.6 L/hr emitters spaced every 30.5 cm. This drip line was used for crop irrigation and fertigation as well as chemigation of PICKIT treatments. For the 2019 tomato crop, main plots were arranged as whole rows in a randomized complete block design with four replications. PPI applications of sulfosulfuron were made on May 29, 2019 one day before transplanting tomatoes. PPI herbicides were applied using a backpack sprayer and three-nozzle boom delivering 280.5 L/ha with AIXR 11003 nozzles at 28 PSI. PPI treatments were mechanically incorporated to 7.6 cm after application. Tomato cultivar ‘DRI 319’ transplants were planted at a 30.5 cm spacing with a three-row transplanter on May 30, 2019. At each growing degree day target chemigation applications were made through the drip line using a Venturi-style injection system attached to a cone tank over the course of 45 minutes, with treatments applied to four replicate plots at once . A single one-meter square section of each plot was harvested on September 19, 2019 and total weight of all fruit were recorded . Following the tomato harvest in 2019, the tomato crop was destroyed in place with a flail mower. After the crop residue dried, beds were lightly cultivated to reshape beds but minimize soil mixing. The 54.9 m long tomato main plots were split into six 9.1 m subplots for the 2020 rotational crops in a split plot design. The six rotational crops including wheat, corn, safflower, sunflower, beans and melons were randomly assigned to a subplot such that the 2020 experimental design was a randomized split plot with four replications. On November 22, 2019, wheat subplots were planted with a grain drill. Visual wheat injury measurements were recorded during the winter of 2019 and spring of 2020. In mid-April 2020, vertical grow weed all beds were treated with glyphosate to terminate the wheat and control winter weeds in all plots and lightly cultivated to prepare a seedbed. On April 17, 2020, corn , safflower , sunflower , beans , and melons were planted using an Earthway precision garden seeder .

Plant height and fresh weight biomass were recorded nine weeks after planting on June 23, 2020; the experiment was subsequently terminated without being taken to maturity. Height and fresh biomass data were analyzed using a one-way analysis of variance followed by a Tukey-HSD test with the agricolae package in R version 1.2.5033 .A study was conducted in a commercial tomato field in Yolo County, CA, that had been reported as infested with branched broomrape in 2019 and a portion of the crop was destroyed under CDFA quarantine provisions. The infested area was prepared for planting by the grower and used for a 2020 experiment to test the efficacy of the PICKIT protocol on branched broomrape in California tomato systems. The soil composition at this site was 25% sand, 42% silt, and 33% clay with 2.7% OM, 7.2 pH, and estimated CEC of 23.6 . Plots were 30.5 m long on 1.5 m beds with two drip lines: one 22.2 mm drip line buried at 25.4 cm and one 25.4 mm drip line buried at 30.5 cm in the center of the bed. The 22.2 mm drip line was terminated at the ends of each plot serving as the dedicated chemigation line with 0.6 L/hr emitters at 30.5 cm spacing. The 25.4 mm line was used for crop irrigation and fertigation of the entire experimental area. Plots were arranged in a randomized complete block design with four replications. PPI applications of sulfosulfuron were made on March 27, 2020 . Sulfosulfuron was applied using a backpack sprayer and three-nozzle boom delivering 280.5 L/ha with AIXR 11003 nozzles at 28 PSI. PPI treatments were mechanically incorporated to 7.6 cm after application on the same day. In addition to the experimental treatments, the entire plot area was treated with the grower’s preplant incorporated tank mix, which consisted of S-metolachlor , pendimethalin , metribuzin , and diazinon on March 27, 2020. Cultivar ‘BQ271’were mechanically transplanted using a two-row transplanter on March 30, 2020 with two plant lines in each row with plants spaced 30.5 cm apart within and between lines. A routine foliar application of 7.2 g ai/ha rimsulfuron was made by the grower to the entire experimental area after transplanting.Chemigation applications were made using CO2 to inject the chemigation mix into 50.8 mm lay flat hose connected to valved 22.2 mm chemigation lines in each plot . Treatments were applied to two replicate plots at once; plots of the same treatment in replications 1 and 2 and replications 3 and 4 were treated together. Herbicide treatments were mixed in 11 L of solution which was injected into the already-running irrigation system over approximately 15 minutes, followed by 20 minutes of water to flush the lines. Chemigation applications were made according to a modified version of the PICKIT protocol . Foliar imazapic treatments were made with a 2-nozzle backpack sprayer delivering 280.5 L/ha with AIXR 11003 nozzles at 28 PSI. Broomrape scouting was done 3 times weekly for seven weeks, followed by 1 time per week for 3 weeks starting on June 1, 2020. At each rating, individual clusters of shoots were marked with wire construction flags, with different colors representing each week’s emergence . Broomrape shoot clusters were counted and recorded weekly. Total broomrape cluster numbers were analyzed using a one-way analysis of variance followed by a Tukey-HSD test in the agricolae package in R . Broomrape emergence over time was analyzed with a 3-parameter log-logistic function in the drc package in R version 1.2.5033 . Before the trial was terminated and after the final broomrape cluster count, locations of individual clusters marked by flags were recorded with a GPS device . A Trimble Handheld GPS device was placed at each flag, the coordinate was recorded in the FarmWorksMobile application , and the color of the corresponding flag was recorded. This data was entered into ArcGIS online , and a color coordinated map was created .After two field seasons and three studies, crop safety for the imidazolinone and sulfonylurea herbicides utilized in the PICKIT system appears acceptable at both the proposed rate structure and two times the proposed rate structure in California processing tomato. These results confirm the crop safety reported for the PICKIT program in Israel.

M-209 T50 was affected by planting depth in 2019, at 79 DAP and 80 DAP for 3 cm and 6 cm planting depths, respectively. Full-season plant heights were not affected by PPB treatment, cultivar or planting depth either year .In 2018 there were no harvestable panicles or yield component analysis in UTC plots. Rice yield components in weed-free plots were significantly affected by cultivar in 2018 ; all measured yield components were greater for M-209 at either planting depth. M-209 averaged 26 more florets per panicle , and 19 more filled grains than M-206 in 2018. Percent unfilled grains was 1.6-fold greater in M-209 . Although not significant, panicle yield, 1000-grain weight, total florets per panicle, and filled florets per panicle were generally greater for rice seeded at the 6 cm planting depth for both cultivars in 2018. In 2019 yield components were significantly reduced in UTC plots. Averaged across planting depth and cultivar, panicle grain yield, florets per panicle, filled grains per panicle, and 1000-grain weight decreased 47%, 31%, 37%, and 15%, respectively . M-209 planted at the 6 cm depth had the greatest reductions in yield components in 2019 UTC plots, with nearly 30% lower 1000-grain weight and 50% blanking when seeded to that depth. In 2019 weed-free plots, cultivar differences in yield components varied. Averaged across planting depths, M-206 had greater panicle grain yield and 1000-grain weight , vertical grow racks while M-209 had greater florets per panicle . M-209 blanking percentage averaged 1.7-fold greater than M-206 in 2019.Weed group composition in untreated plots did not vary between years, however weed group densities varied greatly.

Aquatic broad leaves and algae were not observed in either year, which is in agreement with previous research on DS rice using early-season flush irrigation, orfull-season alternate wetting and drying . As aquatic weeds and algae can inhibit rice growth via shading and physical barrier in water-seeded systems, the potential suppressive benefit of early-season flushing in DS rice is clear. This can be a useful component of the stale-drill method as a measure for herbicide resistance management, as algae and broad leaf suppression can occur without any additional resistance selection pressure. Grass densities were high in both study years, however Echinochloa densities were lower in 2019, allowing L. fusca and sedges to become more competitive. It is interesting that all three major weed groups were present in roughly equal numbers early in 2019 , yet Echinochloa and sedge densities decreased dramatically by 45 DAP, while L. fusca densities increased. In 2018, extreme relative density allowed Echinochloa grasses to easily out-compete other weeds and rice in UTC plots, whereas in 2019 reduced Echinochloa density allowed L. fusca to out-compete other weeds. Emergence of L. fusca is discontinuous throughout the season , and the lack of suppressive competition -particularly from Echinochloa spp.- appeared to allow later-emerging L. fusca to freely establish.Drilling rice seed at 3cm and 6 cm depths delayed rice emergence and successfully permitted the use of a postplant burndown herbicide treatment just as rice was beginning to emerge. Using flush-irrigation to prime weed seed resulted in timed emergence of the majority of observed grasses, and glyphosate use alone reduced combined grasses by more than 50% in both study years .

Although L. fusca emergence appeared to continue after PPB treatment, this was not observed with Echinochloa or sedges. Echinochloa spp. emergence is also known to be discontinuous in rice systems , however our results suggest that shallow flushing may have inhibited Echinochloa emergence from heavy soil as it dried and crusted over. Previous research showed a weed control benefit to applying pendimethalin at rice emergence, as a part of a PPB treatment . As there were no differences in further weed control between the subsequent treatments in the present study , it appears that there were no added late-season benefits of applying pendimethalin or clomazone at the 3-leaf stage. Using the stale-drill method with PPB can achieve the dual cultural-chemical effects suppressing aquatic species and shifting the weed spectrum, as well as allowing novel modes of action to be used to control grasses and sedges. Both of these effects could reduce the spread of herbicide resistance, if stale-drill is used in rotation with other rice establishment methods.Previous research found that M-206 emergence in the field was delayed by up to three extra days by planting to 5.1 cm, compared to 1.3 cm . However, emergence in that study was likely slowed by unseasonably cool temperatures immediately following planting. A related greenhouse study comparing the relative vigor four California cultivars found that M-206 planted to 5.1 cm and 6.4 cm had time to 50% emergence of 9.4 and 14.0 days, respectively. In contrast, M-209 had T50 of 8.3 and 9.4 days at the same respective planting depths . Based on these prior findings, we expected shallower-sown rice to emerge earlier, and expected M-209 to emerge before M-206. However, although there were minor differences in emerged seedling length, we found no differences in emergence date between cultivars or planting depths. The soil at the study site is a Vertisol, characterized by shrinking and cracking as it dries .

We observed that soil cracking in hot weather after the initial flushing event followed the lines of furrows left by the seeding drill. This cracking likely exposed elongating seedlings to light and oxygen, hastening emergence . Taken together, our findings support the hypothesis that California cultivars have sufficient vigor to emerge rapidly and evenly from these depths, however the increased vigor of M-209 may provide an emergence advantage if planted in cooler than normal conditions. The stand reductions at 6 cm planting depth observed in 2018 were not repeated in 2019. It is possible that physical or allelopathic effects of the much higher weed density that year inhibited some rice from establishing. The relative competitiveness of rice and Echinochloa spp. is well documented, and recent research suggests that root exudates from E. crus-galli and E. colona may have inhibitory effects on rice germination and emergence. Alternatively, growing degree day accumulation was more rapid in 2019 due to the later planting date, which may have minimized stand reductions due to deeper seeding. Nevertheless, increased tillering in M-206 compensated for stand reductions in 2018. In a related study we found increased tillering with increasing soil crown depth in these cultivars , although the opposite has been observed previously in small-seeded cereals . In addition, M-209 planted at a depth of 6 cm reached heading later than the more shallow seeding in 2019, which resulted in fewer filled grains at time of harvest.Applying glyphosate to just-emerged rice resulted in tip die-back, but no other symptoms developed. Glyphosate is a systemic herbicide, and needs to be translocated to the crown of a graminid species in order to fatally inhibit the 5-enolpyruvlyshikimate-3-phosphate synthase enzyme . Although the emerged rice seedlings were green at the time of PPB application, the lack of secondary symptoms could be evidence that seedlings were not yet translocating, and therefore still using seed reserves for growth. In addition, glyphosate in solution is anionic, and readily binds to clay soil particles, especially in lower pH soils such as found in rice systems . It is also possible that soil particles attached to the coleoptile below the emerged leaf may have protected the rice somehwat by binding glyphosate molecules. Al-Khatib et al. found that foliar uptake of glyphosate bound to particles of silt loam with 6.6 pH was less than 1% each in alfalfa and pea , and 3% in grape , compared to roughly 50% uptake of aqueous glyphosate in the same species. Grains with starchy reserves such as rice tend to tolerate anaerobic environments well , and this fact is certainly a major factor in the ability of rice organs to elongate vigorously through heavy soils or floodwaters. Alpi and Beevers found that a vigorous japonica cultivar was able to continue coleoptile elongation for up to two weeks before exhausting seed reserves. The cellular machinery in rice that is optimized for fermentative anaerobiosis also appears to provide an emergence benefit for rice grown aerobically in deep soil. Rapid and even stand emergence is key to timing a PPB treatment in deep-sown rice, and good field scouting is essential to determining emergence.

Although application of a non-selective herbicide directly to emerged rice seedlings would not be recommended, growing tables the continued reliance of just-emerged seedlings on seed reserves can provide a fail-safe against application of a normally-lethal herbicide as a burndown treatment.Differential cultivar responses to seasonal variability were apparent in this study. Trials were planted later in 2019, for a 129-day growing season versus 139 days in 2018. Although both cultivars have nominal season durations of about 140 days , M-209 is slower to mature than M-206, reaching 50% heading about six days later in traditional WS rice culture. M- 209 reached 50% heading eight days later than M-206 in 2018, but only 3-4 days later in 2019, reflecting a T50 shift of 3-4 DAP in 2019 . As the rice was planted later in the summer, growing degree day accumulation would be expected to be greater early in the season, resulting in panicle initiation occurring earlier than expected in M-209. This possibility, along with the shortened season duration, may explain why M-209 appeared to have higher sensitivity to seasonal fluctuations than M-206.We find that the present study serves as a successful proof-of-concept for the stale-drill method as a new strategy for rice production and weed management. This work agrees with previous studies that suggested that California semidwarf rice cultivars possessed suitable vigor to emerge evenly from seeding depths up to 6 cm, and that a PPB application of a non-selective herbicide could be safely administered to emerging rice without causing sustained crop injury. Aquatic weeds were suppressed by water management, and the PPB treatment reduced overall weed density by more than 50% in both years, regardless of planting depth or cultivar used. Variability in observed effects of deeper planting on rice growth and development do not support planting rice deeper than 3 cm, however. Although the two cultivars used in this study have varying levels of observed responses to seasonal variability, adequate field preparation, irrigation management, variety selection, and scouting can help to ensure healthy and economically competitive stands. In order to validate our confidence in this method, field-scale trials analyzing the logistical and economic parameters of implementing this program across soil and climate types are necessary. In addition, further refinements to herbicide programs emphasizing reduced input costs, and the potential of reducing seedbanks of weedy rice and herbicide-resistant weeds, would help to more adequately assess the flexibility and potential utility of this method.Glyphosate-resistant crops, also known as “Roundup Ready” , have become an important part of cropping systems in the United States. In 2004, approximately 13 percent of corn, 85 percent of soybean, and 60 percent of cotton acreage was occupied by RR varieties. Alfalfa is the nation’s third most important crop in economic value, and it occupies more than 22 million acres in the United States . It is considered the premier forage crop. It is the primary feed for dairy production, and is commonly fed to beef cattle, sheep, and horses. Alfalfa is also used for green chop and silage in many areas. California is the leading producer of alfalfa hay in the United States, followed by Wisconsin, South Dakota, Minnesota, and Idaho. Roundup Ready technology has been successfully incorporated into alfalfa and is scheduled for commercial release in 2005. This publication reviews the important attributes and issues pertaining to RR technology as applied to alfalfa and the potential impacts of this technology on production systems and markets.Roundup is a broad-spectrum herbicide that kills a wide range of plants. It is not normally applied directly to crops. The RR technology incorporates genetic resistance to glyphosate into crop plants by inserting a single bacterial gene that modifies 5-enolpyruvylshikimate-3-phosphate synthase, an enzyme essential for plant growth. Monsanto has used this technology to develop several RR crops . Specifically, these new varieties will allow glyphosate to be applied over the top of the entire crop to control a wide spectrum of annual and perennial weeds commonly found in alfalfa. Several of these weeds, especially perennials, are difficult to control using conventional herbicides or non-herbicide weed control methods.

The effects of herbicide application timing on Echinochloa densities in 2016 were only significant for T5; however, Echinochloa density was generally greater in plots with deeper-seeded rice. In 2017, Glyphosate alone reduced Echinochloa density by 30%, 31%, and 73% in 1.3 cm, 2.5 cm, and 5.1 cm planting depths, respectively, while glyphosate f.b. pendimethalin reduced Echinochloa density by 58%, 66%, and 80%, across the same depths. All other treatments reduced Echinochloa density by 87% or more. Treatment timing only effected Echinochloa density in T3 and T4 in 2017. L. fusca densities were lower than those of Echinochloa in either year . Treatment effects on L. fusca density were only apparent at 1.3 cm rice planting depth either year, with T4 having the highest density of 37 L. fusca plants m-2 in 2016, and 48 plants m-2 in 2017. T4 was also the only treatment with significant timing effects on L. fusca density, with lower density at greater rice planting depth either year. Sedge densities in 2016 were affected by herbicide treatment at each rice planting depth. Glyphosate alone reduced sedge density from UTC by 40%, 23%, and 86% in 1.3 cm, 2.5 cm, and 5.1 cm rice plantings, respectively, while glyphosate f.b. pendimethalin reduced sedge density by 74%, 45%, and 86% over the same planting depths. Treatments with POST herbicides reduced sedge density the most at any rice planting depth, with an average 95% reduction.Maximum air temperature at seeding was 21.8°C in 2016, and increased to greater than 30°C by the time of rice emergence . In 2017, the maximum air temperature at day of seeding was27.5°, however, the following day saw 15.2 mm of rainfall, growing rack and maximum temperature fell to 19.4°C, remaining below 25°C for several days. Rice began to emerge from 1.3 cm planting depths seven days after planting in 2016, and 8 DAP in 2017 .

Planting rice deeper than 1.3 cm delayed stand emergence similarly in both years; emergence for rice planted to 2.5 cm and 5.1 cm was delayed by three and four days, respectively. Time to 50% heading was also delayed by 1-2 days for rice planted to 2.5 and 5.1 cm. Applying glyphosate just as rice was beginning to emerge did not result in any observable crop injury in either year. In 2016, overall rice stand establishment was not affected by herbicide treatment or planting depth, although stands generally decreased with planting depth, averaging 178, 119, and 101 plants m-2 at 1.3 cm, 2.5 cm, and 5.1 cm depth, respectively, averaged across herbicide treatments. Untreated plots in 2017 were exceptionally weedy; therefore, the rice stand was impossible to estimate for UTC plots at 2.5 cm and 5.1 cm planting depths. Nevertheless, there were no stand differences among treated plots at any given seeding depth in 2017. Planting depth did affect rice stands in 2017, however. Stands in treated plots decreased by an average 89% and 96%, at 2.5 cm and 5.1 cm depths, respectively. Rice tiller density was significantly affected by herbicide treatment and planting depth in both years . Across planting depths in 2016, tiller density was 1.6 times greater than in UTC for glyphosate alone and glyphosate f.b. pendimethalin , increasing to 2.4 times greater than UTC with T5. Tillering in 2016 decreased by an average of 19% in deeper plantings. In 2017 tiller density was greatest with T5 at 1.3 cm depth, and lowest in UTC plots at 5.1 cm depth. Compared to 1.3 cm planting depth, tiller density in treated plots decreased by 60% and 56% at 2.5 cm and 5.1 cm depths, respectively in 2017.Rice plant heights were affected by herbicide treatment in both years , however, no planting depth effects were observed in 2016. In 2016, plant height was generally higher in T3, T4, and T5, averaging 95 cm, whereas plants in UTC, T1, and T2 averaged 87 cm.

In 2017 rice heights decreased as planting depth increased. Plant heights in 2017 were greatest in T3, T4, and T5, averaging a combined 93 cm, 91 cm, and 85 cm at 1.3 cm, 2.5 cm, and 5.1 cm planting depths, respectively. Yield components were largely unaffected by herbicide treatment or planting depth in 2016 , however, in 2017 differences in panicle grain yield, number of florets, and unfilled florets were apparent. In 2017 there were no harvestable panicles in UTC plots seeded at 2.5 cm and 5.1 cm planting depths, or in T1 plots seeded at the 5.1 cm depth. In either year, panicle grain yields were generally higher in less-weedy plots, particularly in plots with POST herbicides . Planting depth effects on panicle yield were likewise only apparent in weedier plots . Thousand-grain weights were lower UTC plots either year, although there were no differences among treated plots or planting depths. In both years, florets per panicle were greater in less-weedy plots, particularly with T3, T4, and T5. Florets per panicle in less-weedy plots also increased as planting depth increased. Floret filling appeared to be little affected by plot weediness or planting depth either year, and observed differences in unfilled florets were inconsistent. Both florets per panicle and unfilled florets were generally greater in 2017 than in 2016. Rice yield was significantly affected by herbicide treatment in both years , but was less influenced by planting depth in 2016 than in 2017. In either year, yields were generally greater in less-weedy plots. In 2016, yields in plots treated with glyphosate alone were 2.4-fold, 3.6- fold, and 1.7-fold greater than UTC in 1.3 cm, 2.5 cm, and 5.1 cm plantings, respectively, while yields in plots treated with glyphosate f.b. pendimethalin increased 2.9-fold, 4.4-fold, and2.6-fold over UTC, at the same planting depths.

In 2017, yields were generally higher in plots that received POST herbicides , though yields decreased as planting depth increased. Additionally, in 2017 yields in plots planted to 2.5 cm and 5.1 cm depths, and treated with T3, T4, and T5 decreased from those at the 1.3 cm planting depth by 48%, 28%, and 24%, and by 67%, 72%, and 54%, respectively.The aim of this study was to assess the feasibility of combining a stale seedbed with deep rice seeding depth, as a means to accommodate a non-selective weed burndown treatment without delaying planting. If implemented correctly, this post plant-burndown method may provide a novel cultural tool for combatting herbicide resistance in rice. Deep-seeding of rice sufficiently delayed stand emergence to allow a PPB of glyphosate without injuring rice stands. However, burn down timing effects on weed density varied by year. In 2016, Echinochloa control with glyphosate PPB alone was reduced at deeper rice plantings. Given that PPB treatments were timed to rice emergence, we expected to see greater Echinochloa control as PPB application was delayed in deeper-seeded plots. However, in 2017 delaying PPB by 5 days in the 5.1 cm planting depth plots did reduce Echinochloa density considerably, even though Echinochloa pressure was far greater that year. It is possible that the added PPB treatment delay in 2017 afforded more time for grasses to emerge and be controlled with the treatment. As Echinochloa plants were not reduced 100% by glyphosate PPB alone in any depth or year, it is evident that Echinochloa emergence is nonsynchronous at the study site, which is in agreement with previous studies . Nonsynchronous emergence may provide some insight into the inconsistent effects of PPB treatment delay with greater rice planting depth. It is also interesting that in both years, Echinochloa densities in T3 through T5 were higher with increasing rice planting depth. It is likely that reduced rice stands in these plots resulted in concomitant reduced competition from rice, potentially allowing more Echinochloa seedlings to establish . In addition, delayed flooding at 2.5 cm and 5.1 cm planting depths may also have allowed later-emerging weeds to avoid flooding suppression. Echinochloa pressure was considerably higher in 2017 than in 2016, which had significant effects on the relative competitiveness of L. fusca and sedges. Grasses in general are the most competitive weeds in DS rice , hydroponic rack system but Echinochloa tend to emerge earlier and more vigorously than sedges and L. fusca , and can easily dominate fields where control measures are inadequate.

In either year, high Echinochloa densities in UTC, T1, and T2 plots effectively suppressed L. fusca, accounting for discrepancies between visual control estimates at 20 DAP, and weed density counts at 60 DAP. However, L. fusca was more competitive in T3 and T4 at 1.3 cm planting depth, reflecting reduced Echinochloa density, and the lack of an effective POST herbicide for L. fusca in those treatments. L. fusca can become a dominant species when Echinochloa and sedges are suppressed in DS rice systems . Delaying PPB application at 2.5 and 5.1 cm depths in T3 and T4 appeared to enhance L. fusca control, however, therefore PPB treatments afforded by planting rice deeper can aid in L. fusca management efforts, particularly in fields where L. fusca resistance to cyhalofop may a problem . Planting rice deeper than 1.3 cm delayed stand emergence by several days, although the differences between 2.5 cm and 5.1 cm planting depths were minor. This is not surprising, as rice seedlings elongate quickly in soil once seed reserves are mobilized . In a related study of California rice cultivars, below-soil seedling elongation for the most vigorous cultivars increased markedly after 6 DAP , resulting in reduced emergence delays as planting depth increased. In either year, stand establishment tended to decrease with greater planting depth, however, stand establishment with deeper seeding was much lower in 2017, as several days of cooler weather coincided with planting in 2017. Colder temperatures can reduce seedling vigor and slow elongation in heavy soil. A related study found that lower-vigor California rice cultivars continued to emerge at low rates after 21 DAP . It is therefore possible that cool weather just after planting in 2017 slowed emergence of deeper-seeded rice, resulting in final rice stands somewhat larger than those measured at 20 DAP. In WS systems, rice is typically seeded at 170 – 200 kg ha-1 to overcome seed loss due to wind or predation. Drilling seed at a higher rate may likewise overcome stand and tillering loss from deeper planting in staledrill systems. In either year, rice tiller density was reduced by a lesser degree than stand density, by either treatment or depth. Tillers per plant would be expected to increase as stand density decreases , reaching up to 5-6 tillers per plant with California cultivars. However, comparing tiller and stand densities for deeper plantings in 2017 suggests up to ten tillers per plant by 60 DAP, which seems unlikely and further suggests a weather-induced delay of rice emergence, as noted above. Ultimately, although tiller density in treated plots decreased at depths greater than 1.3 cm, planting-depth effects seem to diminish between 2.5 cm and 5.1 cm depths, in accordance with a related study on depth effects on California rice .Glyphosate alone and glyphosate f.b. pendimethalin provided sufficient weed control to limit yield reductions due to weed competition to 23 – 65% in 2016, however, in 2017 yield reductions in those treatments were up to 100%. Planting rice deeper than 1.3 cm did not have an effect on yields in 2016, but yields were reduced with increased planting depth in 2017. Yield decreases in 2017 were greater than tillering decreases, suggesting that tiller die-off in deeper plantings reduced final panicle density that year. As panicle yields and 1000-grain weights were consistent across years for the less-weedy plots, it is apparent that planting depth does not affect grain quantity or 1000-grain weight. It is interesting that both florets per panicle and unfilled florets were both higher overall in 2017, resulting in similar filled grains per panicle in both years. Higher temperatures can play a role in increasing florets per panicle , while cooler nighttime weather during anthesis can cause sterility in rice , yet there were no such phenomena in 2017 to explain the elevated florets per panicle or percentage of unfilled florets.Rice [Oryza sativa L.] is grown on about 200 000 ha in northern California . Due to its hot, dry summer climate, the CA rice environment is especially conducive to competitive grass weeds, particularly Echinochloa species. For this reason, CA rice is predominantly water-seeded, in order to suppress the growth and emergence of grasses . In water-seeding, pregerminated rice seed is broadcast by aircraft into permanently flooded basins, where the seed settles on the soil surface and pegs-down roots.

The four almond kernels that were tumbled directly in the [14C]- herbicide treated soil were rinsed with 20 mL of water. The rinsate was collected into glass scintillation vials and evaporated to near dryness using vacuum evaporation. 10 mL of Ultima Gold™ was added to the scintillation vial and analyzed using the liquid scintillation counter. The rinsed kernels were homogenized and combusted; the combustion product was mixed with scintillant and analyzed using the liquid scintillation counter.To examine the glyphosate and glufosinate residues in almonds at different pre-harvest intervals a field study was conducted in a mature almond orchard at The Nickels Soil Laboratory located near Arbuckle, California, United States. The orchard included full rows of nonpareil almonds alternating with rows of several pollinizer varieties; trees were planted 4.9 m apart within the rows and rows were 6.7 m apart. The experiment was conducted in the nonpareil rows and treatments were organized into a randomized complete block design with four replicates. Herbicide treatments included a single herbicide mix applied at timings that correspond to PHIs of 35, 21, 14, 7, and 3 days before shaking. Each plot was 19.6 m long by 4 m wide and contained four almond trees; the width of each herbicide plot started from one side of the tree trunk and extended 4 m, nearly to the nexttree row . The herbicide treatment for all plots was a tank mix of commercial glyphosate at 1,681 g ae ha-1 , harvest drying rack commercial glufosinate at 1,681 g ai ha- 1 , nonionic surfactant at 0.25% v/v , and AMS at 1% v/v .

Applications were made using a CO2 pressurized backpack sprayer with a 2 m boom equipped with four air induction extended range nozzles calibrated to deliver 187 L ha-1 at a pressure of 207 kPa. At each application date, previously fallen almonds were counted in two 1 sq m areas in each plot. On the day of harvest, the middle two almond trees of each plot were hand shaken using mallets and poles, then the nuts were left on the orchard floor to dry. Approximately 100 g of surface soil was collected from each plot at this time for herbicide analysis prior to sweeping. Three days after shaking, the nuts were swept into a windrow between tree rows in approximately the center of the herbicide-treated plots using a commercial self-propelled mechanical sweeper. Four days later approximately 500 g of nuts were collected from each plot windrow, separated by hand from the soil and other debris, and stored frozen until further analysis. This timeline corresponds to typical commercial harvest practices. At almond sampling, approximately 100 g of surface soil from each plot was also collected for herbicide analysis post sweeping.A summary of the glyphosate residues is presented in Table 2. Total glyphosate concentration is presented as the sum of glyphosate, AMPA, N-acetyl-glyphosate, and N-acetylAMPA. There were no statistically significant differences in concentration of glyphosate or total glyphosate found in the hull and shell samples. N-acetyl-AMPA was found only in almond hull samples. The almond hulls had the highest detection of glyphosate and its metabolites, averaging 0.174 mg kg-1 , while still being well below the US MRL. The almond shell samples were above the EU almond kernel residue limit of 0.1 mg kg-1 however, in practice, in shell almonds are shelled before residue analysis.

PHI within the tested range did not have a statistically significant effect on glyphosate residues in hull and shell samples. A summary of the glufosinate residue data is presented in Table 3. Total glufosinate concentration is presented as the sum of glufosinate, N-acetyl-glufosinate, and MPP. There were no significant differences in residues found in hulls, shells, or kernels and these samples were all below the US MRL for total glufosinate. The EU total glufosinate MRL was exceeded in almond shells in at least some replicate plots at 3-, 14-, 21-, and 35-day PHIs. MPP was the only compound detected in almond kernels at PHIs of 3, 14, 21, and 35 days. Although the three- and seven-day PHIs were off-label applications of glufosinate, there were no significant differences in glufosinate residues among the PHI treatments. Glyphosate and glufosinate are generally considered to have moderate and short soil halflife, respectively and the almond orchard soil samples collected from the orchard floor support that degradation pattern. Total glyphosate concentrations remained consistent, apart from an anomalous 7-day pre-sweep value, across all PHIs and pre- and postsweep samples; the range of total glyphosate in samples taken prior to sweeping was 2.331 to2.575 mg kg-1 and the range in samples taken after sweeping was 1.536 to 3.554 mg kg-1 . The half-life of glyphosate in soil ranges between seven and 60 days depending on soil properties and given samples were taken from the soil surface that was dry due to preharvest management practices it is expected the half-life would be closer to the high end of the given range. Total glufosinate concentration in the soil followed a decreasing trend from the PHI of three to 35 days with the majority of the total glufosinate concentration being attributed to MPP . Total glufosinate decreased from 5.339 to 0.210 mg kg-1 in the pre-sweep samples and from 7.687 mg kg-1 to less than the detection limit in the post-sweep samples .

Glufosinate is rapidly degraded by soil bacteria and has a half-life between three and seven days; the main degradation product is MPP . The 7-day pre-sweep sample appears anomalous and likely from a sample processing error in the unreplicated sample since there was no correspondingly high values in the almond samples from those plots . The current labels state the minimum PHI for glyphosate and glufosinate is three and 14 days, respectively. The field results showed that increasing the PHI up to 35 days before shaking did not appear to substantially reduce the amount of glyphosate or glufosinate in the samples. Total glyphosate residues in kernels from almonds sampled in the windrow were below the limit of detection at every PHI tested . At the minimum 14-day PHI total glufosinate residues in kernels from almonds sampled in the windrow were 0.037 mg kg-1 while the 35-day PHI residues were 0.089 mg kg-1 ; these data were not statistically different . Based on these data we conclude increasing the PHI of the herbicides within a range of utility for preharvest operations is unlikely to significantly contribute to lower residue levels.Prior to conducting these experiments, one almond industry concern was windfall nuts that are directly sprayed with herbicide contaminating the whole batch. Windfall nuts typically account for zero to 1% of the total harvest and nuts that fall greater than four weeks prior to harvest are usually of poor quality because of immaturity or degradation processes. The number of potentially directly-treated almonds was relatively low in this study and the earliest falling and mostly likely to be directly treated would likely be removed from the batch during processing based on the United States Department of Agriculture grading standards for size, damage, and color . The almond-to-almond transfer experiment in the lab suggested low transfer of glyphosate or glufosinate from treated to untreated nuts; therefore, the small portion of directly sprayed windfall nuts that make it through the processing facility are unlikely to have high enough residues to elevate the batch residues above the MRL. Almond hulls, shells, and kernels were below the United States MRLs for both glyphosate and glufosinate as well as their metabolites. If the EU reduces the MRL further based on new hazard and risk assessments, this will pose a challenge to California growers when choosing preharvest herbicides. It is worth noting the almonds in both the field and lab experiments presented here were not commercially processed and, thus were not subjected to mechanical and pneumatic cleaning and sorting operations to remove soil and debris; these steps likely would have more effectively removed the soil particles and soil-associated herbicides compared to these research samples.

It is also recognized that the limits of detection of the analytical instrumentation methods used are higher than the recommended new MRLs for glyphosate and its metabolites. Future research will focus on pesticide residues at the later points in almond processing and include sampling almonds and soil particles at various points within a commercial hulling and shelling facility.California produces 80% of the world’s almonds, vertical growing racks and the crop is the most valued export commodity from the state, generating $4.9 billion in export revenue in 2019 . Currently there are more than 500,000 ha of bearing almond trees in California producing over 1.3 billion kilograms of almonds annually . Almonds are mechanically harvested by shaking the trees, sweeping the nuts into windrows, and finally picking up the nuts from the orchard floor. Weeds on the orchard floor can reduce harvest efficiency by interfering with harvest equipment, so many growers utilize relatively intensive herbicide programs to maintain bare ground prior to harvest . Glyphosate and glufosinate are two commonly used herbicides for preharvest programs because of their broad-spectrum weed control and relatively short preharvest intervals , three and 14 days respectively . In 2018, over one million kg of glyphosate and nearly 300,000 kg of glufosinate-ammonium were applied in California almond orchards . Because of the harvest methods there is ample opportunity for whole almonds to come into contact with herbicide-treated soil. After almonds are collected from the field, they are usually stockpiled under plastic covers before being transported to a processing facility for hulling and possibly shelling. At the huller/sheller, almonds are processed in large batches through rollers and gravity tables as well as pneumatic and sieve separatory equipment to remove dirt, debris, and hulls. These processes produce inshell almonds or include further steps to also remove shells to produce shelled almonds . Contact with contaminated processing equipment, almonds, and debris could provide another avenue for pesticide residue contamination.California exports about two-thirds of its almond production annually , with most of the product shipping as shelled almonds . Historically, the European Union has been the largest importer of California almonds with over 50% of the shelled product going to the EU whereas the largest importer of in shell almonds is Asia . Exported shipments of almonds are subject to pesticide residue testing by the importing country’s food safety authority, and residues must be at or below the maximum allowable concentration. The maximum residue limit , commonly called tolerances in the United States , is defined by the Food and Agriculture Organization of the United Nations as the maximum allowable concentration of pesticide residue to be legally permitted in food commodities and animal feed . In the US, glyphosate and glufosinate MRLs are defined to include the parent compounds and the primary metabolites . For clarity, these MRLs will be referred to as “total glyphosate” or “total glufosinate” if the concentrations of the metabolites are to be summed with the concentration of the parent compound. The US MRL for total glyphosate in almond hulls is 25 mg kg-1 and 1 mg kg-1 for kernels. There is not a separate US MRL for in shell almonds because the residue in in shell almonds is determined by shelling the almonds and measuring the residue in only the kernels. The US MRL for total glufosinate in both almond hulls and kernels is 0.5 mg kg-1 . In the EU, the MRL for glyphosate is 0.1 mg kg-1- in almond kernels but there are not established MRLs for glyphosate metabolites. The EU MRL for glufosinate includes its metabolites N-acetyl glufosinate and 3-propionic acid ; the MRL for total glufosinate is 0.1 mg kg-1 .Glyphosate is registered in the EU until 2022 . A review completed by the European Food Safety Authority recommended that the MRL for parent glyphosate be reduced to 0.05 mg kg-1 and an optional total glyphosate MRL for the summation of glyphosate and its primary metabolites, a-amino-3-hydroxy-5-methyl-4- isoxazolepropionic acid and N-acetyl-glyphosate, set to 0.2 mg kg-1 . It is anticipated that in upcoming years glyphosate MRLs will be reduced, and it is a possibility that the chemical may not be re-registered. If at any time the safety of a current MRL is reconsidered, the MRL can be reduced to the lowest limit of analytical detection which currently is 0.01 mg kg-1 , according to European statute .

It was hypothesized that, as the water treatment pH increased, there would be greater removal of herbicide from the soil in the rinsate. As pH of the solution increased, the equilibrium of the weak acid herbicide would be pushed towards the anionic herbicide form resulting in lower sorption to the soil and greater removal in the rinsate. However, the opposite trend occurred for two of the herbicides . As water treatment pH increased, the concentration of saflufenacil and penoxsulam decreased in the aqueous solution extracted from the soil. Saflufenacil removal in the rinsate was greatest at pH 5 with about 78% and lowest at pH 8 with about 64%. At pH 5, about 35% of the penoxsulam was removal from soil and this decreased to about 22% removal at pH 8 . Indaziflam was below the detection limit of the instrumentation in all rinsate samples, regardless of pH.The results of the EC water treatments show that, as EC increased, herbicide removal decreased slightly . The effect of ionic strength on ionizable pesticide adsorption to soil has been well documented12; the common trend is that as ionic strength increases, the pesticide adsorption also increases . These data support that trend as well. The greatest amount of saflufenacil and penoxsulam was removed from soil in the 0.5 dS m-1 water solution rinse; about 70% of saflufenacil was removed from soil and about 25% of penoxsulam was removed. Meanwhile, weed dry rack in the 1.5 dS m-1 and 3.5 dS m-1 solutions, approximately 65% of saflufenacil and 22% of penoxsulam was removed . Indaziflam was below the detection limit of the instrumentation in all rinsate samples regardless of ionic strength of the rinse solution.

Indaziflam was below the detection limit in all samples; however, it is not clear if this is due to strong sorption to soil or to degradation processes. While indaziflam is considered moderately mobile to mobile in soil14, it does have a higher Koc range than saflufenacil or penoxsulam23 meaning indaziflam would be more strongly sorbed to soil than the other herbicides in this study. Indaziflam has been reported to undergo photolysis in aqueous solutions rather quickly 14; samples were stored in the dark for much of the duration of the experiment. A brief follow-up experiment confirmed the laboratory lights did not cause photolysis of the chemical in aqueous solution under the conditions of the experiments . Saflufenacil dissipates relatively quickly in the environment23. The herbicide has biotic and abiotic degradation pathways but the most relevant pathway to this study would be hydrolysis in alkaline water13. The data set shows a significant decrease in herbicide removal from soil from pH 5 to pH 6 and 8 . The pH 7 data point was not statistically different from the other pH water treatments. There have been differing reports on penoxsulam hydrolysis. The Environmental Protection Agency states that penoxsulam is stable under hydrolysis conditions15 while Jabusch and Tjeerdema report triazolopyrimidine sulfonamide herbicides do undergo hydrolysis and the rate is dependent on pH24. There have been studies completed on two other herbicides in the TSA class which support pH dependent hydrolysis rates25-26. Given that the experimental samples were held at field capacity for seven days in this study, pH dependent hydrolysis could explain why penoxsulam concentrations were decreasing from 34% removal from soil at pH 5 to 22% removal at pH 8 .Adsorption mechanisms of pesticides are difficult to define because of the complex interactions between the soil surface, soil solution, and pesticide. Additionally, it is likely more than one adsorption mechanism occurs.

There are several mechanisms by which weak acid pesticide adsorption could be positively influenced by ionic strength – cations could displace hydrogen atoms from the soil surface resulting in a slight pH decrease that would favor a neutral pesticide form, more cations could be available to bridge the anionic form of the pesticide to the negatively charged soil surface, or cations could bond with the anionic pesticide resulting in a neutral form. A recent study on the adsorption-desorption properties of penoxsulam narrowed down the possible sorption mechanisms to H-bonding, cation bridging, and surface complexation with transition metals. The data set presented here supports the cation bridging mechanism. As ionic strength of the water treatment was increased, cation concentration increased resulting in the greater likelihood to bridge the anionic form of penoxsulam to the negatively charged soil surface. Figure 1.3 shows no statistical significance between ECw 1.5 dS m-1 and ECw 3.5 dS m-1 , this likely indicates most of the available binding sites of the soil were occupied close to ECw value 1.5 dS m-1 . Due to the similarity in size and ionizable functional group to penoxsulam, it is likely that saflufenacil is undergoing the same phenomena. The water treatments representing different irrigation water quality parameters did have a slight effect on saflufenacil and penoxsulam sorption to soil. The pH treatments indicated that both herbicides likely experience pH-dependent hydrolysis; saflufenacil and penoxsulam showed a decreasing trend in herbicide removal with increasing pH, the opposite of what the hypothesized pH effect would be. This indicates that even if irrigation water has relatively high pH, it is unlikely to substantially change the availability or movement of saflufenacil orpenoxsulam in California orchard soils.

Results from the ECw treatments showed that flushing soil with a solution with moderate ionic strength could help saflufenacil and penoxsulam bind to soil versus low ionic strength. While there were statistically significant differences between water treatments, the overall effect on herbicide dissipation was minimal; the observed difference between the highest and lowest ECw treatment was only about 10% for each herbicide.In the United States almonds are a $6 billion commodity grown solely in California making almonds the second highest grossing commodity in the state behind only dairy products . As of 2020 there were more than 500,000 bearing hectares of almond trees planted in California which produced 1.3 billion kilograms of almonds . Almonds are harvested by mechanically shaking the trees, sweeping the almonds into windrows, and picking the nuts up from the orchard floor. Preharvest herbicide programs and mowing are used to control vegetation that would otherwise reduce harvest efficiency . Glyphosate has been registered in almonds since the early 1990s and glufosinate has been registered since the early 2000s ; these are commonly used herbicides for preharvest orchard preparations because of their broad spectrum weed control and relatively short preharvest interval , three and 14 days, respectively. In 2018, over one million kilograms of glyphosate and nearly 300,000 kilograms of glufosinate-ammonium were applied in almond orchards . Because of the harvesting process, there is ample opportunity for the almond hulls, shells, and kernels to be in close contact with herbicide-treated soil. The majority of California’s almond crop, about two-thirds, drying rack weed is exported and generated more than $4.9 billion in 2019 . Of the exports, 22% were shipped in shell and 78% were shipped shelled . Asia is the largest aggregate market for in shell almonds while the majority of shelled almond shipments go to European markets . Exported shipments of almonds are subject to pesticide residue testing and must be at or below a maximum concentration set by the region’s food safety authority.The maximum residue limit for glyphosate and glufosinate in almonds differ by definition as well as concentration between the European Union and the US. In the United States, both glyphosate and glufosinate MRLs, which are commonly called tolerances, are defined to include the parent compound as well as its primary metabolites .

For clarity these MRLs will be referred to as “total glyphosate” or “total glufosinate” if the concentrations of the metabolites are to be summed with the concentration of the parent compound. The US MRL for glyphosate in almond hulls is 25 mg kg-1 and 1 mg kg-1 for kernels. There is not a separate US MRL for in shell almonds because the residue in inshell almonds is determined by shelling the almonds and measuring the residue in only the kernels. The US MRL for total glufosinate in almond hulls and kernels is 0.5 mg kg-1 . In the European Union, the MRL for glyphosate is 0.1 mg kg-1 in almond kernels . The EU MRL for glufosinate includes its metabolites; the MRL for total glufosinate is 0.1 mg kg-1 . Glyphosate is registered in the EU until 2022 . A recent review completed by the European Food Safety Authority recommended that the MRL for glyphosate be reduced to 0.05 mg kg-1 and an optional total glyphosate MRL for the summation of glyphosate and its primary metabolites, AMPA and N-acetyl-glyphosate, set to 0.2 mg kg-1 . Hence, it is anticipated that in upcoming years glyphosate MRLs will be reduced, and it is a possibility that the chemical may not be re-registered. According to statute, if at any time thesafety of a current MRL is reconsidered, the MRL can be reduced to the lowest limit of analytical detection which is 0.01 mg kg-1 . Because of the importance of the European markets to the California almond industry and the importance of glyphosate and glufosinate to preharvest preparations, lab and field studies were conducted to evaluate the herbicide transfer from soil to almonds during harvest. The objectives were to determine if glyphosate and glufosinate residues can transfer to almonds from soil particles or directly sprayed almonds, whether increasing the PHI could substantially reduce the risk of herbicide in or on almond fractions and quantify the concentration of soil-bound herbicide in almond samples.This experiment was conducted to determine glyphosate transfer from directly-treated almonds to non-treated almonds. This was intended to mimic a situation where a small number of almonds fall to the ground very early and could conceivably be directly sprayed with preharvest treatments and then contaminate the later-harvested crop during harvest and handling steps. Two almonds were directly treated with 0.8325 MBq [14C]-glyphosate by using a microsyringe to dot the stock solution over the entire almond including the inside of the split hull and exposed shell. The two treated almonds were tumbled with nine non-treated almonds using the apparatus and methods described earlier. The almonds were tumbled using a rock tumbler for 15 minutes and let rest for 15 minutes. Before analysis the treated almonds were removed from the bottle, and the untreated almonds were dissected and analyzed for [14C]- glyphosate. This experiment was replicated four times.The whole almonds from each replicate from both soil transfer experiments and the almond-to-almond transfer experiment were separated for three different analyses: whole almond rinse, herbicide adsorption to almond fractions, and a surface swipe after a post-harvest mimicking process. All samples were analyzed using a liquid scintillation counter . The data were corrected for the background levels of radiation in the scintillation counter. The rinsate of whole almonds was used to determine how much [14C]-herbicide was loosely associated with the surface of the almonds. Three whole almonds were rinsed with water using gentle inverted shaking. The rinsate was collected into glass scintillation vials and evaporated using a vacuum evaporation system at 30°C . Once the samples were evaporated to near dryness, 10 mL of Ultima Gold™ was added to each vial. The samples were analyzed using the liquid scintillation counter. To determine how much herbicide was adsorbed to the almond fractions, three almonds were dissected into their hull, shell, and kernel components. Each component was homogenized using a mortar and pestle and liquid nitrogen. Approximately 500 mg of each homogenized almond fraction was collected into a combustion cone and combusted using a sample oxidizer . The combustion product, [14CO2], was collected in 20 mL of scintillation cocktail composed of 10 mL CarboSorb E® and 10 mL Permafluor® . Glass scintillation vials containing the [14C]-samples were analyzed using the liquid scintillation counter. The remaining three almonds went towards a post-harvest mimicking process. The almond hulls were discarded, and the shells were opened by hand cracking through a plastic barrier then discarded. The plastic was swiped using a filter paper and the swipe was added to a glass scintillation vial with 10 mL Ultima Gold™. The swipes were analyzed using the scintillation counter. The kernels were collected, homogenized and combusted, and the combustion product was mixed with scintillant and analyzed using the scintillation counter as described above. The four almond kernels that were tumbled directly in the [14C]- herbicide treated soil were rinsed with 20 mL of water.

To accurately compare emissions of a BE truck with that of a diesel truck, it is important to consider the upstream emissions associated with the fuel cycle in addition to the tailpipe emissions, to capture the emissions associated with generation of the electricity used to charge the BE vehicles. The on-road emissions rates calculated via MOVES and shown in Table 5 were combined with upstream “well-to-pump” fuel cycle emissions from GREET Model. Fuel cycle emissions rates for diesel and electricity production are shown in Table 8. Figure 12 and Figure 13 show the total emissions for both the diesel and BEV options. As expected, the BEV option yields fewer emissions over the vehicle’s lifetime than the ICE option.The economic, business case for BEVs versus diesel trucks in this use-case example is very similar, with the BEV being about half a cent cheaper per mile. However, the break even point is not until the very end of the vehicle’s useful lifetime. If the fleet plans to operate the vehicles for their entire 20-year lifetime on this use-case, then in the long run the BEVs are the better choice. However, there are lots of external factors to consider. Finding locations suitable for installation of private EV chargers will add additional costs for this example, and current operations will need to evolve to accommodate the technology switch. Minor changes of other parameters, such as fuel prices and fuel economy, VMT, interest and discount rate and other financial terms, incentives, pollution taxes, and maintenance costs may be enough to swing the economic comparison in favor of one technology over another. Being able to analyze a wide variety of parameter adjustments, vertical grow racks tailored to a specific scenario, quickly and easily is of high value to fleet managers.

TCOST, the tool discussed in the following section, was designed to enable fleet managers to model their scenario as well as alternative scenarios with adjusted parameters more quickly and easily by removing knowledge barriers while simultaneously leveraging the power of preexisting models utilized in this use-case example.This section will familiarize the reader with the concepts, functions, and data used in TCOST before presenting a sensitivity analysis exploring the effects of parameter adjustments in the context of the use-case example from the previous section to demonstrate how the tool can be used by fleet owners to explore the effectiveness of ICE and BE technology for their business and generate insightful comparative data to make informative decisions about the future purchases of their fleet. TCOST is a parametric spreadsheet-based tool intended to assist fleet managers seeking to quantitatively evaluate the increased costs or savings of opting to acquire BE MHDV units compared to diesel MHDVs projected into the future for the duration of the vehicle’s useful life, assumed to be 20 years. The model uses a series of 21 input variables defined by the user to produce total cost of ownership for a diesel truck versus a BE truck in the same use case. The input page of the spreadsheet model is shown in Figure 14. TCOST is intended to serve a simplified model distilling the functions of several preexisting models into an easy-to-use tool that can help perform electrification analysis and allow users to vary input values to evaluate how each parameter can affect electrification potential in each scenario.

The main outputs of TCOST are comparative total cost of ownership figures broken down by cost category , both as a gross number and on a per-mile basis, as well as a series of visualizations comparing cost breakdowns, break even points, and the expected tailpipe and fuel cycle emissions for both technologies.Maintenance costs for diesel and BE vehicles were taken from AFLEET and California HVIP. Maintenance costs are set to grow by 1% compounded annually by default to reflect the aging and deterioration of vehicle components. Default fuel economy figures for each technology type and vehicle regulatory class are taken from CARB. TCOST uses EIA national average fuel price projections for diesel fuel and commercial electricity. If desired, users can enter their local fuel prices and the tool will project the EIA national trends onto the input starting prices provided by the user and use those in the calculations instead. Table 9 shows the default vehicle parameters in the tool. The model includes parameters for modeling the economic implications of the acquisition of levels 1, 2, and 3 chargers. The purchase prices for each level of charger were based on chargers for sale and listed in CALSTART’s EVSE catalogue . As a caveat, charger installation often comes with additional expenses for utility service upgrades and other necessary investments upstream on the electrical power system. That is, not all fleets can immediately install chargers if the grid conditions are not ready for such installations. These expenses can vary depending on current infrastructure status at the specific location and must be considered independently as part of the decision-making procedure.TCOST calculates WTP and PTW emissions of both technology types to compare the environmental impacts of each option. WTP emissions for diesel fuel were sourced from the “conventional diesel from crude oil for U.S. refineries” fuel pathway within the GREET model.

This fuel pathway includes emissions from the extraction, transportation, refinement, and delivery of the finished diesel fuel product. For electricity, WTP emissions were taken from the “distributed – U.S. mix” pathway in GREET. This includes the generation and transmission of electrical power, including transmission losses, for a national average generation resource portfolio. Future versions of the model will include state-specific or FERC region-specific WTP electricity emissions. PTW energy use and emissions were calculated using per-mile emissions rates by regulatory class calculated using MOVES for diesel vehicles. PTW emissions for BEVs were assumed to be null. The on-road estimates of energy use were multiplied by GREET energy use and emissions rates to estimate upstream emissions and energy use associated with fuel and electricity production. Emissions are reported by TCOST for CO2, VOCs, CO, NOx, CH4, PM10, and PM2.5. Emissions rates are depicted in a table in Appendix A of this report. Upstream vehicle cycle emissions associated with vehicle manufacturing and retirement were excluded in this version of TCOST due to insufficient data coverage for every regulatory class in GREET. In future versions, these will be calculated through a simulated reconstruction of vehicle components in a vehicle-cycle simulation model like Autonomie® to expand the available inventory of vehicle cycle data. Inputs are set by the user and TCOST calculates the corresponding economic comparison of both technology types, reporting lifetime savings and generating four comparative visualizations: cost schedules for the diesel and BE truck , a cost of ownership comparison line graph , and a clustered column chart showing the emissions difference between each technology. Critically, TCOST allows users to override all default parameters with custom values which makes the tool useful for modeling a huge variety of operational and economic scenarios. Users of the tool need only type directly into the input cells to tailor the tool to their fleet conditions and drastically improve model precision for their scenario. Using their conditions as a baseline, they can evaluate the effects of minor parameter changes on cost comparisons between the two technologies.TCOST inputs were set to reflect the conditions described by the use-case example. The example inputs are shown in Appendix B of the report. Where input values were not known, default values were assumed to be reasonable estimates of conditions and were left unchanged. The fuel economy values were taken directly from the results of the MOVES-Matrix simulation and are reflective of the on-road conditions for the use-case. The total cost of ownership reported by TCOST was $630,715.29 for the diesel option and $626,982.88 for the BE option, 4×4 plastic tray resulting in a lifetime savings of $3,732.41 for the BE option with a break even point in the 20th and final year of operational life.

While the BE option costs over twice as much for the initial acquisition of the vehicle, the operation and maintenance costs combined are less than half that of the diesel option over the vehicle lifespan. These cost savings come with the caveat of charger citing and utility upgrade costs, as well as any potential alterations to the drayage operation that might incur additional costs or lost revenue . The visualizations produced by TCOST are shown in Figure 15 through Figure 18. These visuals show the large influence of purchase capital cost and taxes during the first six years of vehicle ownership, and the large difference in on-road operating costs and maintenance costs that show up in the cumulative cost curves across the diesel and BEV alternatives. By comparing these charts, fleet owners and operators can quickly gain insight into the economics and environmental impacts of each potential fleet procurement decision.The use case example presented above for Appalachian Regional Port Drayage results in very small savings that take almost the entire life of the vehicle to realize, compared to some use case examples in the literature that appear to take less than five years to reach payback. Fortunately, TCOST can be customized to specific use cases, allowing fleet owners to easily adjust parameters to identify sub-fleets that make more sense to electrify and to perform sensitivity analysis, helping to assess specific deployment scenario risk and make informed investment decisions. A selection of parameters was adjusted, one at a time, to isolate their effects on the TCO difference between the two technologies. The results of the sensitivity analysis are shown in Figure 19 and are discussed in more detail below. The parameters with the highest sensitivities are BEV purchase price and ICE fuel economy , followed by miles per day, diesel price, and ICE maintenance cost . The sensitivity analysis indicates that a high amount of risk involved in the investment decision, as altering these parameters even slightly can affect total cost savings by over 100%. However, this percentage difference in savings is some when misleading, because the savings were so small to begin with. That is, the high percentage changes observed here do not equate to high absolute values. But, the model sensitivity analysis does indicate that assumed future conditions does have a large impact on the simulation.Because diesel fuel economy won’t change very much over time, due to the consistent on-road conditions of the vocation, the most critical parameter in play is the purchase prices of the BEVs. If there are any incentives available to the fleet for investing in BE trucks, a simple reduction of purchase price by only 1% would almost double expected savings under these conditions. Much recent regulatory focus has been on monetary incentives for BE technology because purchase price represents the largest expense occurred by an electrifying fleet. Fuel prices are notoriously hard to project. If diesel becomes more expensive in the long-term, it would improve the savings of BE investments. Even if diesel fuel prices in the operational area are notably higher than the national average used in TCOST, it would have a large impact on savings. If the fleet is expected to travel more daily miles in the future, additional miles travelled would also have significant impact on the fleet’s savings . Finally, under a diesel option, if future retrofits are required to keep the vehicle and fleet compliant with evolving emissions standards, diesel maintenance costs might increase, positively impacting fleet savings under the BE option. TCOST enables fleet managers to quickly and accurately adjust parameters to model a variety of possible scenarios to produce sensitivity analyses like this. TCOST customizability and parametric design allow the tool to quickly model case-specific conditions or a variety of alternative futures. Its spreadsheet-based nature is accessible, reducing modeling knowledge and information barriers, and allowing fleets of all shapes and sizes to gather data to make informed decisions about the futures of their fleets.Fruit trees should be planted where they will receive full sun for 6 or more hours per day during the growing season. For maximum production, fruit trees need soil that is deep and well drained. Such soils do not occur everywhere in California, especially in residential areas where the topsoil may have been partially removed by land grading and the remaining soil has been compacted by the weight of construction machinery.

Perennial weeds are usually most susceptible to glyphosate in the bud stage of growth immediately prior to flowering and in the fall when weed foliage is still green. Both stages represent times when weeds are translocating most of their photosynthates from leaves to roots. Since glyphosate primarily moves in the same direction as sugar in phloem tissues, glyphosate translocation to perennial roots is maximized when applied at these timings. It is also important to consider the stage of growth and age of the crop prior to using glyphosate. In woody perennial crops, most glyphosate formulations can be safely applied as a directed spray to the base of dormant plants. Use extreme care on smooth-barked crops, however, as certain formulations or surfactants may allow glyphosate to be absorbed through the bark, resulting in injury or death of treated crop plants. Shielded nozzles and low sprayer pressure may aid in preventing accidental glyphosate application or drift to crop plants, whether dormant or not.Glyphosate is a broad-spectrum foliar herbicide that, when applied at the proper rate, is able to control emerged annual, biennial, and perennial broadleaf and grass weeds. It is available in a wide variety of formulations and from multiple manufacturers, so most growers have ready access to glyphosate to use in their farming operations. To get the most consistent weed control with this herbicide, adjuvants should be added to the spray mixture as necessary. Target weeds should be inspected to determine whether they are actively growing or are species best controlled at a different stage of growth. Physically damaged weeds or weeds that are stressed by drought or excess water may not be fully controlled. Foliage should be clean and dry at the time of application, pot growing systems and environmental conditions should be favorable for herbicide application and optimal uptake into the plant.

Mixtures or sequential application of glyphosate with other herbicides may enhance control of difficult weed species and potentially delay onset of herbicide resistance in the weed population. If these factors are considered and any necessary corrective actions taken prior to application, glyphosate can remain a very effective herbicide for years to come.Allelopathy, the production of chemicals by a plant species that might influence nearby plants or soil microbes, is an important functional characteristic that can change neighbor plant performance and eventually plant structure and function. The allelopathy phenomenon was identified for the first time in the late 1930s by Hans Molisch as the influence of one plant on another through the release of chemicals into the environment . It was further characterized as any direct or indirect harmful or helpful influence of one plant on another through the synthesis of chemical substances that are released into the environment . Allelopathy significantly influences the spread of invasive plants, acting as a key factor for species like Hirschfeldia incana to dominate new territories. These invasive plants release chemicals that inhibit the growth of surrounding native flora, thereby gaining an upper hand in these environments. This chemical interaction not only affects individual species but also extends its impact to whole ecosystems. Invasive species can change the composition of native plant communities, disrupting local food chains and nutrient cycles. Moreover, allelopathic activities can lead to drastic changes in soil microbial populations, affecting soil quality and nutrient dynamics.

These alterations can create a self-reinforcing cycle, further solidifying the presence of invasive species and complicating restoration efforts. A thorough understanding of allelopathic relationships in plant invasions is crucial for effective ecological conservation and for anticipating the long-term effects of invasive species on biodiversity and ecosystem functions.The application of allelopathy in agriculture is emerging as a sustainable alternative to traditional weed control methods. Utilizing allelopathic plants or their by-products can naturally curb weed growth, diminishing the dependence on chemical herbicides. This method aligns with ecofriendly farming practices and aids in maintaining ecological balance and soil integrity. For example, incorporating allelopathic cover crops into crop rotations can manage weeds effectively while improving soil fertility. Identifying specific allelochemicals and understanding how they work could lead to new, environmentally safe herbicides. However, leveraging allelopathy in agricultural settings requires careful evaluation of its effects on non-target species and the overall environmental impact. Research in this domain is poised to offer key insights into the best combinations and sequences of crops for efficient weed control, contributing to more sustainable and ecologically conscious farming methods. Invasive species adopt a wide array of strategies to establish in new habitats. Among these qualities is the capacity to create allelopathic compounds that can directly restrict neighboring native plants or indirectly depress native plants via disruption of beneficial below ground microbial mutualisms or changed soil resources. Allelopathy is most likely to be associated with non-native plant invasion, which means that most invasive species spread faster because of their allelopathy. Allelopathy has become well-known in the field of invasion biology as one of the possible weapon traits in the novel weapon hypothesis because of these potential negative impacts on neighbor plant fitness .

The physiology and rate of population development of native species are known to be altered by non-native invaders, as are the abundance of species within a community and even the stable states of entire ecosystems . Although there are obvious negative effects on specific plant species and their communities, it is unclear how important allelopathy is as a characteristic of many invaders as opposed to a few well-studied examples. In other words, the degree to which allelopathy is a key characteristic in the toolkit that boosts the success of exotic invasions is still unknown. Brassica plants, including species like cabbages, broccoli, cauliflower, kale, and Brussels sprouts, contain allelochemical compounds like glucosinolates. These compounds, under exceptional conditions, can be released into the environment and have been observed to affect seed germination and plant growth . Hirschfeldia incana, commonly known as short pod mustard, is closely related to the Brassica genus and belongs to the Brassicaceae family, often referred to as the mustard family. This family includes a wide range of well-known vegetables and oilseed plants. The relationship between Hirschfeldia incana and Brassica species is characterized by their genetic, morphological, and ecological similarities. These similarities include the production of glucosinolates , four-petaled flowers arranged in a cross shape, and seed pods known as siliques. The taxonomy of the Brassicaceae family is complex and subject to revisions as new genetic information becomes available. The close relationship between Hirschfeldia incana and Brassica species is not only evident in their physical appearance but also supported by molecular studies that examine DNA sequences to understand their evolutionary relationships.Furthermore, Hirschfeldia incana’s ability to thrive in disturbed soils and its widespread distribution as a weed can provide valuable insights into adaptability and ecological strategies shared with some Brassica species. These Brassica species are known for their capacity to grow in various environmental conditions. Understanding these relationships has significant implications for agriculture and horticulture, planting racks as it can aid in the development of more resilient crop varieties. This research has many benefits, one of them is being able to Identify another plant species that has the potential to suppress the growth of an invasive species.. Also over the course of time researchers might discover a native plant that might inhibit the growth of the invasive species. It can also open some for scientists ideas like how to control allelopathy. Also it would show us if there is a significant characteristic that both plants share. In this research, we delve into the sample collection and preparation methods employed for shortpod mustard, a species with potential allelopathic properties, and provide insights into how similar procedures can be adapted for studying sunflowers . These distinct plant species offer valuable insights into the world of plant ecology, allelopathy, and ecological interactions, shedding light on the intricate relationships that exist within ecosystems. The main goal of the study was to see how the liquid from shortpod mustard leaves affects the growth of sunflower seeds. We did this by comparing how many seeds sprouted in two different petri dishes. One dish had plain water , and the other had the mustard leaf liquid. By looking at the differences in how many seeds grew in each dish, we could understand the effect of the mustard leaves on the sunflower seeds.Shortpod mustard and sunflower are two plant species that have captured the attention of ecologists and botanists alike due to their distinct characteristics and significant ecological roles. Each of these plants possesses unique traits and ecological significance, making them compelling subjects of study in the realm of plant science.

Hirschfeldia incana, commonly known as shortpod mustard, is a remarkably resilient plant species with allelopathic properties that have piqued the interest of researchers. This member of the Brassicaceae family thrives in a variety of environments, including disturbed ecosystems like roadside verges, agricultural fields, and other areas with disrupted natural habitats. What sets shortpod mustard apart is its ability to release biochemical compounds into its surroundings, thus potentially influencing the growth and development of neighboring plants. Understanding the allelopathic interactions of shortpod mustard, as well as the chemical constituents responsible for these effects, holds profound ecological importance. This knowledge can shed light on its ecological impact and uncover potential applications in areas such as weed management and sustainable agriculture. On the other hand, Helianthus annuus, known as the common sunflower, boasts its own distinctive characteristics and ecological significance. Belonging to the Asteraceae family, sunflowers are easily recognizable by their vibrant yellow flowers and towering stalks, making them iconic in the botanical world. Beyond their aesthetic appeal, sunflowers serve multiple practical purposes, including the production of edible seeds and oil. However, their ecological role extends beyond human consumption. Sunflowers are renowned for their competitive growth and allelopathic potential, which can influence neighboring plant species and ecosystem dynamics. Thus, delving into the study of sunflowers offers valuable insights into their ecological interactions, growth patterns, and potential impacts on surrounding vegetation. In essence, shortpod mustard and sunflower, with their contrasting yet complementary attributes, form a captivating duo for ecological research. By unraveling the mysteries of their allelopathic interactions and biochemical constituents, we gain a deeper understanding of their roles in the natural world and unlock potential applications that can benefit both science and society.Mature shortpod mustard leaves, known for their potential allelopathic properties, were collected during the early morning hours from the vicinity of Crest Plaza Riverside. Following the collection, to preserve the leaves, we used a freeze-drying method right after collection. This method, called freeze-drying or lyophilization, involved freezing the leaves at very low temperatures and reducing the pressure around them. Once the freeze-drying was done, we roughly split the dried leaves into 8 Eppendorf tubes and weighed the samples. The total weight of dried leaf tissue was 0.69 grams.To initiate the extraction process, a combination of disruption beads and bead silica mobile was added to each sample. Then the samples were homogenized at a consistent speed of 1800 rpm for a precise duration of one minute. This was followed by the addition of a calculated 5.5 ml of water, distributed evenly across the 8 tubes . These samples were mixed vigorously. Once done, these samples were incubated on a calibrated heating block at 25°C for a 24-hour cycle, promoting maximum extraction. Following the incubation, a brief centrifugation process at high speed was applied for 10 seconds. The centrifuge was used to separate the heavier parts from the liquid. After this process, the clear liquid was carefully moved into a single 15 ml tube, and more water was added to bring the total volume up to 6.9 mL . The leachate, now at a 1:10 dilution , was ultimately stored in the larger tube and refrigerated for stability, ready for the next phase of the experimental procedure involving seed germination tests.From each of these populations, a subset of 14 seeds was chosen. Prior to any treatment, it was of paramount importance to ensure the seeds were free from contaminants and in prime condition for the experiment. To this end, they were subjected to a sterilization regimen which began with a brief 10-second immersion in 70% ethanol. Following this, the seeds were washed twice in sterile water to rid them of any residual ethanol.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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