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Weed species that escape control (hereafter called residual weeds) coupled with changing weather patterns are emerging challenges for snap bean processors and growers. Field surveys were conducted to identify associations among crop/weed management practices and environmental factors on snap bean yield and residual weed density. From 2019–2023, a total of 358 snap bean production fields throughout the major U.S. production regions (Northwest, Midwest and Northeast) were surveyed for residual weeds. Field-level information on crop/weed management, soils, and weather also were obtained. To determine associations among management and environmental variables on crop yield and residual weed density, the machine learning algorithm random forest was utilized. The models had 24 and 22 predictor variables for crop yield and residual weed density, respectively, and both were trained on 80% of the data with the remainder used as a test set to determine model accuracy. Both models had pseudo- R 2 values of over 0.50 and accuracy over 80%. The models showed that crop yield was higher in the Northwest compared to the Midwest region, while higher average temperatures during early season growth and planting midseason (June-July) predicted greater crop yield compared to other time periods. The use of row cultivation was associated with lower snap bean yield and weed density, suggesting row cultivation had less-than-ideal selectivity between the crop and weed. Moreover, multiple spring tillage operations prior to planting were linked with an increase in weed density, implying that excessive tillage may favor the emergence of residual weeds in snap bean. Over the coming decades, climate change-driven weather variability is likely to influence snap bean production, both directly through crop growth and indirectly through weeds that escape control practices that also are influenced by the weather.

In the Mid-Atlantic United States, there is increasing interest in delaying cereal rye termination until after soybean planting (i.e., planting green). Improved understanding of cereal rye seeding rate effects is needed to balance weed and agronomic management goals. We investigated the effects of cereal rye seeding rates on weed control and crop performance when planting green in complementary experiments in two Mid-Atlantic regions. The Pennsylvania experiment was replicated at three site-years and the Delaware experiment at two site-years. In both experiments, population-level weed responses were evaluated across four cereal rye seeding rates: 0, 51, 101, and 135 kg ha-1. The Delaware experiment also implemented a nitrogen treatment factor (0 and 34 kg N ha-1; spring applied). Both experiments showed that integrating cereal rye in the fall significantly improved winter- and summer-annual weed suppression compared with the fallow control, but no differences in total cereal rye biomass production or weed suppression were found among alternative cereal rye seeding rates (51 to 135 kg ha-1). Soybean yield did not differ among treatments in any of the studies. These results show there is no reason to increase cereal rye seeding rates for weed suppression services or to decrease seeding rates for agronomic reasons (i.e., soybean population and yield) when employing planting-green tactics in no-till soybean production within the Mid-Atlantic region of the United States. Nomenclature: Cereal rye, Secale cereale L.; soybean, Glycine max (L.) Merr.

Cucurbit crops comprise ∼25% of the vegetable acreage in the mid-Atlantic and Northeastern United States. However, options for postemergence weed control in these crops are limited. Overlapping herbicides is a technique that involves sequential applications of soil-applied residual herbicides to lengthen herbicidal activity before the first herbicide dissipates. Residual herbicides such as S -metolachlor will not control emerged weeds, but weed control efficacy may be extended if these herbicides are applied after crop emergence, but before weed emergence occurs. Currently S- metolachlor is not labeled for broadcast applications over cucurbit crops. Greenhouse studies were conducted to evaluate pumpkin, cucumber, and summer squash variety response to varying S- metolachlor rates. S -metolachlor was applied at 1.42 and 2.85 lb/acre at the two-leaf stage of pumpkin and 0.71, 1.42, 2.85, and 5.7 lb/acre at the two-leaf stage of cucumber and summer squash. Cucumber showed a greater response to S- metolachlor with up to 67% injury observed at 5.70 lb/acre. S- metolachlor applications to pumpkin and summer squash resulted in less than 6% injury, regardless of application rate or crop variety. S- metolachlor applied at 2.85 lb/acre reduced pumpkin and cucumber dry weight 6% and 19%, respectively, but did not reduce squash dry weight. S- metolachlor reduced cucumber dry weight 78% for all varieties. Pumpkin varieties ‘Munchkin’ and ‘Baby Bear’ exhibited a 23% difference in dry weight, but no other differences were observed among other varieties because of S -metolachlor applications. Summer squash varieties ‘Respect’ and ‘Golden Glory’ exhibited a 31% difference in dry weight, but no other differences were observed among other varieties. Results show that pumpkin and summer squash demonstrated good crop safety when S- metolachlor was applied as a broadcast treatment after crop emergence. However, caution should be urged when applying this herbicide to cucumber.

1. Glyphosate-resistant Conyza canadensis populations now infest more than 44 000 ha of arable land in eastern USA, only 5 years after the first resistant population was reported. Seed dispersal, the expansive use of glyphosate and the lack of tillage are all factors contributing to this high invasion speed. 2. Seed collected from deliberately established C. canadensis source populations were found at the furthest seed traps in our empirical studies, providing one of the most complete dispersal kernels for studying long-distance dispersal. The results indicate that seed regularly disperses at least 500 m from source populations. While a relatively small number of seeds moves long distances, 99% of the seed was found within 100 m of the source. 3. Empirical and mechanistic models were fitted to the data to predict the dispersal in the prevailing wind direction. Both models underestimated seed deposition beyond 200 m but the mechanistic model provided a better fit to the data (lower Akaike information criterion). A two-dimensional analysis examined the correlation between angular directions of wind and seed movement. All trials were anisotropic but only the cumulative wind and seed direction were significantly correlated (P < 0.05). 4. The empirical model was used to explore the effect of increasing source strength, which would be expected as an infestation of glyphosate-resistant C. canadensis expands on a producer's farm. At infestation levels consistent with a heavy infestation in a 5-ha field, seed dispersed further than 1.5 km, easily affecting 10s to 100s of surrounding farms. 5. Synthesis and applications. Emigration of C. canadensis seed, from a source farm to adjacent farms, means that population dynamics and weed management are dependent on both intra- and interfield dispersal phenomena. Wind-dispersed plants challenge the common practice of single field management as a viable management option for herbicide-resistant weeds. Farms coupled by seed dispersal require proactive management practices by every producer to prevent and minimize the development of glyphosate-resistant infestations of undesirable and alien plants.

Weeds interfere with lima bean production by reducing crop yield, hindering harvest, and contributing contaminants to harvested beans, yet there are very few trials documenting the impact of weeds on lima bean. This research was designed to evaluate weeds on lima bean yield, quality, as well as Rhizoctonia solani and pod-feeding insects in order to assist in implementing a more integrated approach to pest management. Field studies at four sites evaluated the impact of common cocklebur ( Xanthium strumarium L.), jimsonweed ( Datura stramonium L.), and ivyleaf morningglory [ Ipomoea hederacea (L.) Jacq.] at densities of 0, 7, 10, or 20 plants 10 m -1 row in the presence and absence of Rhizoctonia solani on lima bean ( Phaseolus lunatus L.). The planting dates of late June to mid-July represented a typical planting period for the mid-Atlantic region of USA, while one site represented an early planting date in this region (28 May). Differences in response to weed competition for total lima bean yield, marketable yield, yield components, and R. solani discoloration on lima bean occurred at one or more sites. Weed competition from 7 plants 10 m -1 of row or higher, reduced number lima bean pods by as much as 40%. However, weed density had little impact on percentage of flat, plump, or dry pods. Marketable yield was reduced at two sites in response to 7 plants 10 -1 row (19% yield loss) and higher weed densities resulted in 29 to 33% yield loss. The presence of lima bean resulted in 40 to 60% reduction of common cocklebur and jimsonweed biomass and burs or seeds compared to weeds grown without crop competition. Weed competition in lima bean was influenced by many factors including weed species and planting date. Weed management is important to not only preserve yield but limit weed seed return to the soil seedbank and maintain harvest efficiency.

Cover crop-based, organic rotational no-till (CCORNT) corn and soybean production is becoming a viable strategy for reducing tillage in organic annual grain systems in the mid-Atlantic, United States. This strategy relies on mechanical termination of cover crops with a roller-crimper and no-till planting corn and soybean into cover crop mulches. Here, we report on recent research that focuses on integrated approaches for crop, nutrient and pest management in CCORNT systems that consider system and regional constraints for adoption in the mid-Atlantic. Our research suggests that no-till planting soybean into roller-crimped cereal rye can produce consistent yields. However, constraints to fertility management have produced less consistent no-till corn yields. Our research shows that grass-legume mixtures can improve N-release synchrony with corn demand and also improve weed suppression. Integration of high-residue inter-row cultivation improves weed control consistency and may reduce reliance on optimizing cover crop biomass accumulation for weed suppression. System-specific strategies are needed to address volunteer cover crops in later rotational phases, which result from incomplete cover crop termination with the roller crimper. The paucity of adequate machinery for optimizing establishment of cash crops into thick residue mulch remains a major constraint on CCORNT adoption. Similarly, breeding efforts are needed to improve cover crop germplasm and develop regionally-adapted varieties.

A population of common ragweed from Delaware was not controlled in the field by herbicides that inhibit acetolactate synthase (ALS) or protoporphyrinogen oxidase (PPO). Research was conducted to ascertain if this population was resistant to these herbicidal modes of action and, if so, to determine the resistance mechanism(s). Resistance was confirmed by dose-response studies on greenhouse-grown plants with multiple ALS- and PPO-inhibiting herbicides. DNA sequence data revealed that resistance to ALS-inhibiting herbicides was due to the previously reported W574L ALS mutation. To assist in determining the mechanism of resistance to PPO-inhibiting herbicides, an F2 population was derived from a cross between the resistant biotype (Del-R) and a sensitive biotype (DV1-S). This population segregated in the ratio of three resistant ∶ one sensitive when treated with fomesafen, indicating that resistance to PPO-inhibiting herbicides was conferred by a single, (incompletely) dominant, nuclear gene. Sequences of the target-site genes, PPX1 and PPX2, for PPO-inhibiting herbicides were obtained through the screening of a common ragweed cDNA library and subsequent cDNA extension (5′-RACE). Molecular marker analysis with the F2 population revealed that the PPX2 gene cosegregated with resistance to PPO-inhibiting herbicides. A mutation substituting an arginine codon for a leucine codon at a conserved location (R98L) of the PPX2 gene was suspected of being responsible for resistance. By using a transgenic Escherichia coli system, it was demonstrated that the R98L mutation was sufficient to confer resistance to PPO-inhibiting herbicides. The level of resistance to acifluorfen conferred by the R98L mutation in the E. coli system was about 31-fold, similar to the level of resistance seen in the whole-plant dose-response study. Last, a DNA-based assay was developed to identify the presence or absence of the common ragweed PPX2 R98L mutation. The R98L PPX2 mutation is the second mechanism identified for evolved resistance to PPO-inhibiting herbicides. Nomenclature: Common ragweed, Ambrosia artemisiifolia L. AMBEL

Drone flights are often only performed during the growing season, with no data collected once harvest has been completed, although they could be used to measure winter annual weed growth. Using a drone mounted with a multispectral sensor, we flew small plot corn (Zea mays L.) fertility, cover crop, and population studies at black layer and 0–14 d after harvest (DAH). Yields had positive correlations to normalized difference vegetation index (NDVI) at black layer but often had negative correlations to corn yields 0–14 DAH. After harvest, NDVI could be associated with weed growth, and negative correlations to yield could point to reduced corn canopy allowing light to reach late‐season weeds. In fertility studies, excess nitrogen appears to increase weed biomass after harvest, which can be easily identified through drone imagery. Flights should be performed after corn harvest as weed growth may provide additional insight into management decisions. Core Ideas Corn yields can be correlated to post‐harvest weed biomass by using NDVI. Drone flights efficiently mapped weeds and made correlations to yield and management. Fall weed control can be prioritized using drone mapping.

Cereal rye as a cover crop is often used to improve soil health and as part of integrated weed management programs. Despite this, cereal rye biomass is often not managed for optimal weed suppression. This study evaluated the effects of managing cereal rye as part of an integrated weed management strategy in soybean. Factors consisted of levels of cereal rye management (no cereal rye, no nitrogen, or 20 kg/ha of nitrogen); cereal rye termination timing (20 or 10 d before soybean planting); and residual herbicide treatment applied at cereal rye termination (with or without). Winter annual weed control with cereal rye was generally greater compared to no cereal rye. Winter annual weed control was consistently better when cereal rye was terminated at 20 d before soybean planting compared to 10 d; while summer annual weed control was improved if termination was delayed. Effect of cereal rye management on summer annual weed control varied by weed species. In the absence of residual herbicides, Palmer amaranth control responded to the different levels of cereal rye management. However, morningglory spp. only responded to rye with supplemental N applications. Large crabgrass control was similar for treatments containing cereal rye, regardless of nitrogen input. Our results demonstrate the importance of cover crop management when incorporating cereal rye into an integrated weed management program for soybean.

Crop losses from weed interference have a significant effect on net returns for producers. Herein, potential corn yield loss because of weed interference across the primary corn-producing regions of the United States and Canada are documented. Yield-loss estimates were determined from comparative, quantitative observations of corn yields between nontreated and treatments providing greater than 95% weed control in studies conducted from 2007 to 2013. Researchers from each state and province provided data from replicated, small-plot studies from at least 3 and up to 10 individual comparisons per year, which were then averaged within a year, and then averaged over the seven years. The resulting percent yield-loss values were used to determine potential total corn yield loss in t ha−1 and bu acre−1 based on average corn yield for each state or province, as well as corn commodity price for each year as summarized by USDA-NASS (2014) and Statistics Canada (2015). Averaged across the seven years, weed interference in corn in the United States and Canada caused an average of 50% yield loss, which equates to a loss of 148 million tonnes of corn valued at over U.S.$26.7 billion annually. Nomenclature: Corn, Zea mays L.