Hyperspectral imaging provides rich spectral information for plant phenotyping, yet analyzing these high-dimensional data remains challenging due to limited labeled datasets and the reliance on manually extracted features, such as vegetation indices. Here, we present LeafVAE, a variational autoencoder framework that learns spectral signatures directly from hyperspectral leaf images without manual annotation. Our model encodes leaf spectra into a compact, two-dimensional latent space where pixels cluster by spectral similarity, creating quantitative leaf descriptors from signature composition that facilitate downstream phenotyping tasks. We show that the learned representations generalize robustly across genotypes, years, and imaging equipment on four different corn leaf datasets. We further demonstrate that LeafVAE outperforms traditional vegetation indices across multiple applications, including detecting nitrogen deficiency in corn, classifying herbicide stress in soybean, and identifying beech leaf disease using an affordable six-band multispectral camera. Pixel-level explainability, achieved by combining spectral signature composition with interpretable machine learning methods, identifies regions with abnormal spectral characteristics and highlights areas of the leaf that contribute to model predictions. By learning spectral features in an unsupervised manner while still allowing labels for interpretable diagnosis, LeafVAE provides a scalable foundation for automated plant phenotyping across diverse applications.

Saflufenacil, a herbicide that inhibits protoporphyrinogen oxidase, has been reformulated as a microencapsulation for preemergence and postemergence applications to corn, with the primary purpose of the encapsulation to reduce the risk of corn injury from foliar applications. Field experiments on corn were conducted in 2023, 2024, and 2025 to evaluate the efficacy of encapsulated saflufenacil alone and in the formulated premixture with pyroxasulfone for residual broadleaf weed control and crop injury. Applications of encapsulated saflufenacil across a dose range resulted in incomplete control (less than 60%) of giant ragweed. Combinations of the encapsulated saflufenacil + pyroxasulfone premixture with atrazine were efficacious in controlling giant ragweed up to 28 d after planting (DAP), but efficacy declined sharply by 42 DAP. The reduced efficacy on giant ragweed was attributed to a lack of an activating rain for the encapsulated saflufenacil. Conversely, encapsulated saflufenacil applications, with or without pyroxasulfone, were highly efficacious (83% to 99% control) on waterhemp and common lambsquarters, two small-seeded broadleaf species. Furthermore, the most extensive weed control with encapsulated saflufenacil resulted from sequential applications (preemergence and postemergence) of a residual herbicide. Overall, encapsulated saflufenacil was effective in controlling small-seeded broadleaf weeds until a postemergence herbicide was applied. However, additional herbicides in a mixture may be needed to manage large-seeded broadleaf species such as giant ragweed. Regardless of the target species, management of problematic, herbicide-resistant weeds with encapsulated saflufenacil should focus on combinations with other effective herbicides in both preemergence and postemergence applications, in addition to other weed control tactics.

Abstract Encapsulated saflufenacil uses a solid phase encapsulation, which is different than traditional herbicide encapsulations. Saflufenacil is released following dry conditions that allow the microcapsule to fracture. Thus, encapsulated saflufenacil is not available for foliar uptake using standard application methods. A trace amount of non-encapsulated saflufenacil remains in the formulation from an incomplete purification process and may cause foliar phytotoxicity from postemergence applications. Experiments were conducted using relative photosystem II (PS II) efficiency of corn leaf tissue to determine encapsulated saflufenacil bioavailability and to characterize saflufenacil microcapsule release under extended solution storage time. To evaluate injury potential, non-encapsulated, free saflufenacil was separated from the encapsulated formulation using microfiltration. An open-capsule treatment was created by allowing the encapsulated formulation to dry and then resolubilizing the herbicide. Relative PS II efficiency of the free, open-capsule, and encapsulated saflufenacil formulations were compared over 48 hours after treatment (HAT). By 48 HAT, dry and non-encapsulated saflufenacil reduced relative PS II efficiency greater than the encapsulated saflufenacil, indicating that saflufenacil was not released from the encapsulation unless it underwent a period of drying. Furthermore, the reduced relative PS II efficiency was similar for the encapsulated and free saflufenacil, corroborating that the level of phytotoxicity from foliar encapsulated saflufenacil applications originates from the trace levels of free saflufenacil in the product. Saflufenacil microcapsule stability was evaluated following mixing with water and storage for 0, 1, 3, 5, or 7 days. Phytotoxicity did not increase with extended storage times, as the reduction in relative PS II efficiency from 0 to 48 HAT remained mostly constant across solution storage times. Overall, this research substantiates that saflufenacil encapsulation works to reduce foliar injury and documents the encapsulation durability under extended storage in water solution.

The widespread use of atrazine in corn since the 1960s has raised environmental concerns such as ground and surface water contamination. The U.S. Environmental Protection Agency has proposed label restrictions on atrazine to address these concerns and requires applicators to achieve herbicide mitigation points before applying herbicides. One way to achieve mitigation points is to reduce the proportion of the field that is treated. Therefore, research was conducted in 2023 in Arkansas, Indiana, Mississippi, North Carolina, Tennessee, and Virginia, and in 2024 in Arkansas, Indiana, and Tennessee to determine whether targeted applications can mitigate atrazine use in corn while maintaining weed control levels comparable to those achieved with broadcast applications. All plots, except the nontreated controls, received paraquat and S-metolachlor immediately after planting in 2023, with amicarbazone and metribuzin added in 2024. Combinations of atrazine, glyphosate, and mesotrione were applied postemergence either broadcast, target-applied to emerged weeds, or a combination of broadcast and target-applied. Targeted applications of herbicides did not differ in control of Palmer amaranth and morningglory species, compared to broadcast applications of the same active ingredients. No injury or differences in corn grain yield were observed. Targeted applications in 2023 covered 86% of the area, on average, while 52% of the area was sprayed on average in 2024. Differences in the area sprayed during the targeted application between years can be attributed to the reduced area of weed emergence from a more robust residual herbicide combination in 2024. Based on this research, targeted spray technology can reduce atrazine use in corn while providing weed control comparable to that achieved with broadcast applications.

Producers who grow strawberries in plasticulture and who intend to maintain the strawberry plants into a second harvest season find that stolons (runners) are undesirable because they produce daughter plants that divert resources from the mother plant and complicate field maintenance. Removing runners by hand is labor-intensive and becomes more challenging once daughter plants have rooted in the row middles. Napropamide and pendimethalin were evaluated in greenhouse studies to assess their potential to suppress daughter plant rooting and facilitate runner removal. Greenhouse studies used a three-pot experimental unit consisting of one strawberry mother plant with two runners, each bearing one unrooted daughter plant, and two side pots simulating row middles. Three treatments were evaluated, including broadcast (foliar + side pot spray), in-row (foliar spray only), and row-middle (side pot spray only) herbicide applications, and were compared against a nontreated control. On mother plants, napropamide caused transient foliar injury but did not affect runner production or biomass. On daughter plants, napropamide caused transient injury and suppressed new growth at 4 wk after treatment (WAT), reducing daughter plant biomass by 59% to 68%. Napropamide also eliminated the pull force required for removal relative to the nontreated control and reduced aboveground and belowground biomass by up to 49% and by >95%, respectively, demonstrating effective suppression of runner establishment by reducing daughter plant rooting. However, suppression was transient; by 8 WAT, only the broadcast treatment consistently maintained rooting inhibition, likely due to herbicide degradation over time. Pendimethalin caused no effects on mother plants or daughter plants under any application method and failed to inhibit daughter plant rooting entirely. These results suggest that napropamide applied to the row middles, the only label-compliant method evaluated, can effectively suppress daughter plant rooting for at least 1 mo, providing growers with a supplementary benefit of eased runner removal during summer weed management.

Foliar-applied postemergence applications of glufosinate are often applied to glufosinate-resistant crops to provide nonselective weed control without significant crop injury. Rainfall, air temperature, solar radiation, and relative humidity near the time of application have been reported to affect glufosinate efficacy. However, previous research may have not captured the full range of weather variability to which glufosinate may be exposed before or following application. Additionally, climate models suggest more extreme weather will become the norm, further expanding the weather range to which glufosinate can be exposed. The objective of this research was to quantify the probability of successful weed control (efficacy >= 85%) with glufosinate applied to some key weed species across a broad range of weather conditions. A database of >10,000 North American herbicide evaluation trials was used in this study. The database was filtered to include treatments with a single postemergence application of glufosinate applied to waterhemp [Amaranthus tuberculatus (Moq.) Sauer], morningglory species (Ipomoea spp.), and/or giant foxtail (Setaria faberi Herrm.) <15 cm in height. These species were chosen because they are well represented in the database and listed as common and troublesome weed species in both corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] (Van Wychen 2020, 2022). Individual random forest models were created. Low rainfall (<= 20 mm) over the 5 d before glufosinate application was detrimental to the probability of successful control of A. tuberculatus and S. faberi. Lower relative humidity (<= 70%) and solar radiation (<= 23 MJ m(-1) d(-1)) on the day of application reduced the probability of successful weed control in most cases. Additionally, the probability of successful control decreased for all species when average air temperature over the first 5 d after application was <= 25 C. As climate continues to change and become more variable, the risk of unacceptable control of several common species with glufosinate is likely to increase.

Cover crops and soil-residual herbicides are considered essential tools within integrated weed management practices. However, interception of soil-applied herbicides by cover crop residue can reduce weed control and crop yield. Field trials were conducted in 2022 and 2023 in Indiana to investigate the effect of cereal rye (Secale cereale L.) termination strategies on the concentration of sulfentrazone, S-metolachlor, and cloransulam-methyl in soil, weed control, and soybean [Glycine max (L.) Merr.] yield. Soybeans were planted at cereal rye anthesis. Termination strategies included roller-crimped cereal rye, standing cereal rye, and a fallow control. The average cereal rye biomass in 2022 and 2023 was 4.06 and 14.2 Mg ha-1, respectively. Soybean stands were unaffected in 2022 but were reduced by 24% and 69% in the presence of roller-crimped and standing cereal rye, respectively, in 2023. On average, 75% and 84% of the soil-residual herbicides applied were intercepted by the roller-crimped cereal rye residue in 2022 and 2023, respectively. The use of cereal rye did not improve overall weed control relative to fallow at 18 after soybean planting in 2022 and 2023. In 2022, roller-crimped cereal rye reduced soybean yields by up to 13% in comparison with the fallow. In 2023, regardless of management strategy, the use of cereal rye as a cover crop reduced soybean yields by an average 44% in comparison to the fallow. Results from this research suggest that the adoption of the planting green system can significantly reduce soybean yield primarily due to stand losses if proper planting equipment is not used. Furthermore, the high levels of cereal rye biomass achieved in both years of the study did not provide additional season-long weed suppression relative to the non-cover crop control.

Commercial targeted sprayer systems allow producers to reduce herbicide inputs but risks the possibility of not treating emerging weeds. Currently, targeted applications with the John Deere system have five spray sensitivity settings, and no published literature discusses the effects of these settings on detecting and spraying weeds of varying species, sizes, and positions in crops. Research was conducted in Arkansas, Illinois, Indiana, Mississippi, and North Carolina on plantings of corn, cotton, and soybean to determine how various factors might influence the ability of targeted applications to treat weeds. These data included 21 weed species aggregated to six classes with height, width, and densities ranging from 25 to 0.25 cm, 25 to 0.25 cm, and 14.3 to 0.04 plants m−2, respectively. Crop and weed density did not influence the likelihood of treating the weeds. As expected, the sensitivity setting alters the ability to treat weeds. Targeted applications (across sensitivity settings, median weed height and width, and density of 2.4 plants m−2) resulted in a treatment success of 99.6% to 84.4% for Convolvulaceae, 99.1% to 68.8% for decumbent broadleaf weeds, 98.9% to 62.9% for Malvaceae, 99.1% to 70.3% for Poaceae, 98.0% to 48.3% for Amaranthaceae, and 98.5% to 55.8% for yellow nutsedge. Reducing the sensitivity setting reduced the ability to treat weeds. The size of weeds aided targeted application success, with larger weeds being more readily treated through easier detection. Based on these findings, various conditions can affect the outcome of targeted multinozzle applications. Additionally, the analyses highlight some of the parameters to consider when using these technologies.

The combination of soil residual herbicides and cover crops is an integral part of best management practices for herbicide-resistant weeds. However, the interception of soil residual herbicides by cover crop biomass interferes with herbicides reaching the soil, which can lead to lower weed control efficacy and increased selection pressure for herbicide resistance. Once intercepted, these herbicides can only move to the soil with water from rainfall or irrigation. Field trials were conducted in 2022 and 2023 to investigate the effect of cover crop termination strategies (fallow, standing, and roller crimped) and simulated rainfall volumes (0, 4.2, and 8.3 mm simulated over 20 min; equivalent to 0, 12.5, and 25 mm h-1) on atrazine wash off from cereal rye (Secale cereale L.) biomass onto the soil. The use of roller crimper resulted in an average of 10% greater ground cover relative to the standing cereal rye. Atrazine interception that was bound to rye biomass reached 29 and 94% in 2022 and 2023, respectively. In 2022, the concentration of atrazine in the soil under roller crimped cereal rye was 9% greater than that understanding cereal rye, after 4.2 mm of rainfall. In 2023, when cereal rye biomass more than doubled, only 6% of the applied atrazine was found under roller crimped cereal rye, after 8.3 mm of rainfall. Cereal rye biomass accumulation negatively impacted the amount of atrazine reaching the soil at the time of application. Although the roller crimped cereal rye reduced the amount of herbicide reaching the soil relative to the standing cereal rye, it also reduced atrazine leaching below the 0–5 cm of soil. In cover cropping systems with high levels of cereal rye biomass (e.g., > 7,000 kg ha-1), more than 8.3 mm of rain are required to wash most of the atrazine off of the biomass.

Residual herbicides are primarily degraded in the soil through microbial breakdown. Any practices that result in increased soil biological activity, such as cover cropping (between cash crop seasons), could lead to a reduced persistence of herbicides in the soil. Furthermore, cover crops can also interfere with herbicide fate by interception. Field trials were conducted between 2020 and 2023 in a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation to investigate the influence of cover crop (cereal rye [Secale cereale L.] and crimson clover [Trifolium incarnatum L.]) use on soil enzyme activities (beta-glucosidase [BG] and dehydrogenase [DHA]), its effect on the concentration of residual herbicides (sulfentrazone, S-metolachlor, cloransulam-methyl, atrazine, and mesotrione) in the soil, and the interception of herbicides by cover crop residue. The use of cover crops occasionally resulted in increased BG and DHA activities relative to the fallow treatment. However, even when there was an increase in the activity of these two enzymes, increased degradation of the residual herbicides was not observed. The initial concentrations of all residual herbicides in the soil were significantly reduced due to interception by cereal rye biomass. Nevertheless, significant reductions in early-season weed biomass were observed when residual herbicides were included in the tank mixture applied at cover crop termination relative to the application of glyphosate plus glufosinate. Results from this research suggest that the use of cereal rye or crimson clover as cover crops (between cash crop seasons) do not impact the persistence of residual herbicides in the soil or reduce their efficacy in controlling weeds early in the growing season.

Trifludimoxazin is a protoporphyrinogen oxidase (PPO)-inhibiting herbicide currently under development for preplant burndown and soil-residual weed control in soybean [Glycine max (L.) Merr.] and other crops. Greenhouse dose-response experiments with foliar applications of trifludimoxazin, fomesafen, and saflufenacil were conducted on susceptible and PPO inhibitor-resistant (PPO-R) waterhemp [Amaranthus tuberculatus (Moq.) Sauer] and Palmer amaranth (Amaranthus palmeri S. Watson) biotypes. These PPO-R biotypes contained the PPO2 target-site (TS) mutations Delta G210 (A. tuberculatus and A. palmeri), R128G (A. tuberculatus), and V361A (A. palmeri). The resistant/susceptible (R/S) ratios for fomesafen and saflufenacil ranged from 2.0 to 9.2 across all PPO-R biotypes. In contrast, the response of known PPO inhibitor-susceptible and PPO-R biotypes to trifludimoxazin did not differ within each Amaranthus species. In 2017 and 2018, experiments at the Meigs and Davis Purdue Agriculture Centers were conducted in fields with native A. tuberculatus populations composed of 3% and 30% PPO-R plants (Delta G210 mutation), respectively. At Meigs in 2018, A. tuberculatus control following foliar applications of fomesafen, lactofen, saflufenacil, and trifludimoxazin was greater than 95%. When averaged across the other 3 site-years, applications of 25 g ai ha-1 trifludimoxazin resulted in 95% control of A. tuberculatus at 28 DAA, while applications of fomesafen (343 g ai ha-1), lactofen (219 g ai ha-1), or saflufenacil (25.0 or 50 g ai ha-1), resulted in 80% to 88% control. Thus, at these relative application rates, the foliar efficacy of trifludimoxazin was comparable or greater on A. tuberculatus when compared with other commercial PPO inhibitors, even in populations where low frequencies of PPO-R plants exist. The lack of cross-resistance for common PPO2 TS mutations to trifludimoxazin and the level of foliar field efficacy observed on populations containing PPO-R individuals suggest that trifludimoxazin may be a valuable herbicide in an integrated approach for managing herbicide-resistant Amaranthus weeds.

Trifludimoxazin is a novel protoporphyrinogen oxidase (PPO)-inhibiting herbicide currently under development for foliar and residual control of several problematic weeds in preplant applications for soybean production. Field experiments were conducted in 2017 and 2018 to evaluate the foliar efficacy of trifludimoxazin applied alone and in combination with other herbicides on waterhemp, giant ragweed, and horseweed. Foliar applications of trifludimoxazin alone at 12.5 or 25.0 g ai ha-1 were highly efficacious on glyphosate-resistant waterhemp (94% to 99% control) and moderately effective on giant ragweed (78% to 79% control) and resulted in minor efficacy on horseweed (<= 20% control). Combinations of trifludimoxazin with glufosinate, glyphosate, paraquat, or saflufenacil remained highly effective (>= 91% control) on waterhemp and giant ragweed. All herbicide mixtures with trifludimoxazin applied to horseweed were classified as additive interactions. Greenhouse experiments and Isobole analysis indicated that trifludimoxazin mixtures with glyphosate and glufosinate on waterhemp and giant ragweed were additive. Mixtures of trifludimoxazin + paraquat were slightly antagonistic under greenhouse conditions when applied to either waterhemp or giant ragweed, whereas trifludimoxazin + saflufenacil was synergistic when applied to giant ragweed. Overall, trifludimoxazin applied alone at 12.5 or 25.0 g ha-1 is effective for managing waterhemp and, to an extent, giant ragweed, but not horseweed, in preplant burndown applications. Furthermore, the addition of glufosinate, glyphosate, paraquat, or saflufenacil to applications of trifludimoxazin does not appreciably reduce weed control for these mixtures. As such, applications of trifludimoxazin alone and in combination with these herbicides may be utilized for effective preplant management of several problematic weeds in soybean.

Foliar-applied postemergence herbicides are a critical component of corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] weed management programs in North America. Rainfall and air temperature around the time of application may affect the efficacy of herbicides applied postemergence in corn or soybean production fields. However, previous research utilized a limited number of site-years and may not capture the range of rainfall and air temperatures that these herbicides are exposed to throughout North America. The objective of this research was to model the probability of achieving successful weed control (>= 85%) with commonly applied postemergence herbicides across a broad range of environments. A large database of more than 10,000 individual herbicide evaluation field trials conducted throughout North America was used in this study. The database was filtered to include only trials with a single postemergence application of fomesafen, glyphosate, mesotrione, or fomesafen + glyphosate. Waterhemp [Amaranthus tuberculatus (Moq.) Sauer], morningglory species (Ipomoea spp.), and giant foxtail (Setaria faberi Herrm.) were the weeds of focus. Separate random forest models were created for each weed species by herbicide combination. The probability of successful weed control deteriorated when the average air temperature within the first 10 d after application was <19 or >25 C for most of the herbicide by weed species models. Additionally, drier conditions before postemergence herbicide application reduced the probability of successful control for several of the herbicide by weed species models. As air temperatures increase and rainfall becomes more variable, weed control with many of the commonly used postemergence herbicides is likely to become less reliable.

Preemergence applications of mesotrione, an herbicide that inhibits 4-hydroxyphenolpyruvate dioxygenase (HPPD), have recently gained regulatory approval in soybean varieties with appropriate traits. Giant ragweed is an extremely competitive broadleaf weed, and biotypes resistant to acetolactate synthase inhibitors (ALS-R) can be particularly difficult to manage with soil-residual herbicides in soybean production. This study investigated control of giant ragweed from preemergence applications of cloransulam (32 g ai ha(-1)), metribuzin (315 g ai ha(-1)), and S-metolachlor (1,600 g ai ha(-1)) in a factorial design with and without mesotrione (177 g ai ha(-1)) at two different sites over 2 yr. Treatments with mesotrione were also compared with two commercial premix products: sulfentrazone (283 g ai ha(-1)) and cloransulam (37 g ai ha(-1)), and chlorimuron (19 g ai ha(-1)), flumioxazin (69 g ai ha(-1)), and pyroxasulfone (87 g ai ha(-1)). At 42 d after planting, control and biomass reduction of giant ragweed were greater in treatments with mesotrione than any treatment without mesotrione. Giant ragweed biomass was reduced by 84% in treatments with mesotrione, whereas treatments without mesotrione did not reduce biomass relative to the nontreated. Following these preemergence applications, sequential herbicide treatments utilizing postemergence applications of glufosinate (655 g ai ha(-1)) plus fomesafen (266 g ai ha(-1)) and S-metolachlor (1,217 g ai ha(-1)) resulted in at least 97% control of giant ragweed at 42 d after planting, which was greater than sequential applications of glufosinate alone in 3 of 4 site-years. Preemergence applications of mesotrione can be an impactful addition to soybean herbicide programs designed to manage giant ragweed, with the potential to improve weed control and delay the onset of herbicide resistance by providing an additional effective herbicide site of action.

The use of soil residual herbicides, along with other practices that diversify weed management strategies, have been recommended to improve weed management and deter the progression of herbicide resistance. Although soil characteristics influence recommended application rates for these herbicides, the common practice is to apply a uniform dose of soil residual herbicides across fields with variable soil characteristics. Mapping fields for soil characteristics that dictate the optimal dose of soil residual herbicides could improve the efficiency and effectiveness of these herbicides, as well as improve environmental stewardship. The objectives of this research were to develop and quantify the accuracy of management zone classifications for variable-rate residual herbicide applications using multiple soil data sources and soil sampling intensities. The maps were created from soil data that included (i) Soil Survey Geographic database (SSURGO), (ii) soil samples (SS), (iii) soil samples regressed onto soil electrical conductivity (EC) measurements (SSEC), (iv) soil samples with organic matter (OM) data from SmartFirmer® (SF) sensors (SSSF), and (v) soil samples regressed onto EC measurements plus OM data from SmartFirmer® sensor (SSECSF). A modified Monte Carlo cross validation method was used on ten commercial Indiana fields to generate 36,000 maps across all sources of spatial soil data, sampling density, and three representative herbicides (pyroxasulfone, s-metolachlor, and metribuzin). Maps developed from SSEC data were most frequently ranked with the highest management zone classification accuracy compared to maps developed from SS data. However, SS and SSEC maps concurrently had the highest management zone classification accuracy of 34% among maps developed across all fields, herbicides, and sampling intensities. One soil sample per hectare was the most reliable sampling intensity to generate herbicide application management zones compared to one soil sample for every 2 or 4 hectares. In conclusion, soil sampling with EC a data should be used for defining the management zones for variable-rate (VR) residual herbicide applications.

Cereal rye (Secale cereale L.) cover crop and preemergence herbicides are important components of an integrated weed management program for waterhemp [Amaranthus tuberculatus (Moq.) Sauer] and Palmer amaranth (Amaranthus palmeri S. Watson) management in soybean [Glycine max (L.) Merr.]. Accumulating adequate cereal rye biomass for effective suppression of Amaranthus spp. can be challenging in the upper Midwest due to the short window for cereal rye growth in a corn-soybean rotation. Farmers are adopting the planting green system to optimize cereal rye biomass production and weed suppression. This study aimed to evaluate the feasibility of planting soybean green when integrated with preemergence herbicides for the control of Amaranthus spp. under two soybean planting time frames. The study was conducted across 19 site-years in the United States over the 2021 and 2022 growing seasons. Factors included cover crop management practices ("no-till," "cereal rye early-term," and "cereal rye plant-green"), soybean planting times ("early" and "late"), and use of preemergence herbicides ("NO PRE" and "YES PRE"). Planting soybean green increased cereal rye biomass production by 33% compared with early termination. Greater cereal rye biomass production when planting green provided a 44% reduction in Amaranthus spp. density compared with no-till. The use of preemergence herbicides also resulted in a 68% reduction in Amaranthus spp. density compared with NO PRE. Greater cereal rye biomass produced when planting green reduced soybean stand, which directly reduced soybean yield in some site-years. Planting soybean green is a feasible management practice to optimize cereal rye biomass production, which, combined with preemergence herbicides, provided effective Amaranthus spp. management. Soybean stand was a key factor in maintaining soybean yields compared with no-till when planting green. Farmers should follow best management recommendations for proper planter and equipment setup to ensure effective soybean establishment under high levels of cereal rye biomass when planting green.

AbstractProtoporphyrinogen oxidase (PPO)-inhibiting herbicides remain an important and useful chemistry 60 yr after their first introduction. In this review, based on topics introduced at the Weed Science Society of America 2021 symposium titled “A History, Overview, and Plan of Action on PPO Inhibiting Herbicides,” we discuss the current state of PPO-inhibiting herbicides. Renewed interest in the PPO-inhibiting herbicides in recent years, due to increased use and increased cases of resistance, has led to refinements in knowledge regarding the mechanism of action of PPO inhibitors. Herein we discuss the importance of the two isoforms of PPO in plants, compile a current knowledge of target-site resistance mechanisms, examine non–target site resistance cases, and review crop selectivity mechanisms. Consistent and reproducible greenhouse screening and target-site mutation assays are necessary to effectively study and compare PPO-inhibitor resistance cases. To this end, we cover best practices in screening to accurately identify resistance ratios and properly interpret common screens for point mutations. The future of effective and sustainable PPO-inhibitor use relies on development of new chemistries that maintain activity on resistant biotypes and the promotion of responsible stewardship of PPO inhibitors both new and old. We present the biorational design of the new PPO inhibitor trifludimoxazin to highlight the future of PPO-inhibitor development and discuss the elements of sustainable weed control programs using PPO inhibitors, as well as how responsible stewardship can be incentivized. The sustained use of PPO inhibitors in future agriculture relies on the effective and timely communication from mode of action and resistance research to agronomists, Extension workers, and farmers.

The rapid adoption of glyphosate-resistant crops at the end of the 20th century caused a simplification of weed management that relied heavily on glyphosate for weed control. However, the effectiveness of glyphosate has diminished. A greater understanding of trends related to glyphosate use will shed new light on weed adaptation to a product that transformed global agriculture. Objectives were to (1) quantify the change in weed control efficacy from postemergence (POST) glyphosate use on troublesome weeds in corn and soybean and (2) determine the extent to which glyphosate preceded by a preemergence (PRE) improved the efficacy and consistency of weed control compared to glyphosate alone. Herbicide evaluation trials from 24 institutions across the United States of America and Canada from 1996 to 2021 were compiled into a single database. Two subsets were created; one with glyphosate applied POST, and the other with a PRE herbicide followed by glyphosate applied POST. Within each subset, mean and variance of control ratings for seven problem weed species were regressed over time for nine US states and one Canadian province. Mean control with POST glyphosate alone decreased over time while variability in control increased. Glyphosate preceded by a labeled PRE herbicide showed little change in mean control or variability in control over time. These results illustrate the rapid adaptation of agronomically important weed species to the paradigm-shifting product glyphosate. Including more diversity in weed management systems is essential to slowing weed adaptation and prolonging the usefulness of existing and future technologies.

Weeds resistant to PPO-inhibiting herbicides threaten the profitability of crop producers relying on this chemistry. In Amaranthus palmeri, mutations at G210 (∆G210) and R128 (R128G/M) of the PPX2 gene were reported to confer PPO-inhibitor resistance. Here, A. palmeri samples from nine states in America, having survived a field application of a PPO-inhibitor, were genotyped to determine the prevalence of these mutations. Less than 5% of the 1828 A. palmeri plants screened contained the ∆G210 mutation. Of the plants lacking ∆G210, a R128 substitution was only found in a single plant. An A. palmeri population from Alabama without mutations at G210 or R128 had a resistance ratio of 3.1 to 3.5 for fomesafen. Of the candidate PPX2 mutations identified in this population, only V361A conferred resistance to lactofen and fomesafen in a transformed bacterial strain. This is the first report of the V361A substitution of PPX2 conferred PPO-inhibiting herbicide resistance in any plant species. Future molecular screens of PPO-inhibitor resistance in A. palmeri and other species should encompass the V361A mutation of PPX2 to avoid false-negative results.

Field experiments were conducted in 2017-2018 and 2018-2019 at three locations in Indiana to assess weed suppression by cereal rye and residual herbicide premixes in no-till corn.Cereal rye biomass ranged from 540 to 3700 kg ha -1 when terminated in late April and early May.When cereal rye termination was delayed until corn planting in mid-May to mid-June, cereal rye biomass ranged from 1710 to 6200 kg ha -1 .Early-season weed biomass was suppressed 27 to 84% by cereal rye residue in three of five site-years.Early-season weed biomass reduction by a residual herbicide premix was similar whether applied to cereal rye or non-cover crop treatments in four of five site-years.In one site-year, weed biomass reduction by a residual herbicide premix was 16% greater when applied to cereal rye compared to non-cover crop ground.Weed biomass decreased by approximately 12% for every 1000 kg ha -1 of additional cereal rye or wheat biomass, and peak weed biomass suppression was estimated to occur at 8000 kg ha -1 of cover crop biomass.Corn yield was similar in all treatments in all but one site-year, when a 57% yield reduction from cereal rye was observed in 2018 due to corn stand reduction from cereal rye competition.Overall, cereal rye did not reduce residual herbicide efficacy regardless of herbicide application timing.