Context: Warm-season legume cover crops in subtropical environments provide many agroecosystem services but have not been widely adopted because their use usually entails replacing cash crops. Planting short-term legume cover crops following maize (Zea mays L.) to replenish soil nitrogen (N) pools for cool-season cash crops, such as wheat (Triticum aestivum L.), is an innovative approach for integrating legumes into subtropical cereal cropping systems that has not been widely investigated. Objectives: A maize-legume cover crop-wheat cropping sequence under conservation tillage management was investigated with the following objectives: 1. Evaluate the performance of short-term cowpea [Vigna unguiculata (L.) Walp)] and sunn hemp (Crotalaria juncea L.) cover crops in terms of N accumulation, 2. Track soil N availability and wheat N recovery following cover crops, and 3. Assess wheat productivity in response to cover crops terminated and left on the soil surface. Methods: A five site-year study was conducted in Citra and Jay, Florida, USA beginning in 2016. The experiment was arranged as a split-plot in which cover crop (cowpea, sunn hemp, and weed-free fallow) was the main plot factor, while N rate (0, 34, 67, and 101 kg N ha-1) to wheat was the split plot factor. Corn was planted under strip-tillage, while cover crops and wheat were planted into residues using a no-till grain drill. Results: Cover crops accumulated 58-126 kg N ha-1 in eight to 11 weeks, with cowpea and sunn hemp deriving up to 67 and 90% of N from biological N fixation, respectively. Plant Root Simulator probes and Normalized Difference Vegetation Index data provided evidence for higher N uptake by wheat following cover crops compared to weed-free fallow during early stages of wheat growth. However, N availability following cover crops was either short-lived or insufficient as wheat stover production, grain yields, and grain N recovery were not affected by cover crops in most cases. On the few occasions when positive cover crop effects were detected, results were both marginal and inconsistent. Conclusions: Maintaining cowpea and sunn hemp residues on the soil surface may be beneficial from a soil conservation perspective, but this strategy does not result in consistent improvements in the productivity of cool-season cereals. Additional research that elucidates the environmental pathways by which legume cover crop-derived N is lost from soil is warranted to facilitate the development of management practices that increase the likelihood and size of N benefits from short-term legumes.

Field studies were conducted in North Carolina to determine the critical period of weed control (CPWC) for Italian ryegrass in winter wheat. Soft red winter wheat was planted in late fall in 2017 and 2018 in no-till fields near Salisbury, NC. Treatments consisted of allowing weeds to grow from crop emergence for different intervals until removal (“weedy”), maintaining “weed-free” conditions from crop emergence for the same intervals, and then letting the weeds emerge and compete with the crop for the duration of the season. In 2017, weed removal occurred in two-week intervals from crop emergence up to 18 weeks after crop emergence (WAE) and three-week intervals up to 18 WAE in 2018. Additional biological measurements, including Italian ryegrass density and height, were collected at 6, 12, and 18 WAE to characterize the effect of crop-weed interactions on the CPWC and weed populations. Non-linear regression analysis was conducted to relate the timing of weed removal and yield loss. The analysis was done using growing degree days (GDD) accumulated at corresponding WAE. Italian ryegrass density ranged from 292 to 824 plants m-2, which created intense competitive conditions with wheat. In the absence of weed control, yield loss surpassed 60%. Using 5% yield loss as an accepted threshold, the CPWC for Italian ryegrass in no-till planted wheat was estimated to be from 1100 to 1900 GDD. This relatively short period makes it possible to reduce weed control intensity if control actions are properly timed.

A survey was conducted among teak and melina growers across Costa Rica to assess their perceptions of problematic weed species and to document current weed management practices in forest plantations. A total of 180 farmers were selected from six provinces, yielding an 87% response rate. Results revealed that 47% of respondents had established plantations on formerly forested land, while 43% did so on previously used pastureland. Most farmers employed an integrated approach toward weed management that included manual, mechanical, and chemical methods. The most problematic species cited most frequently included coyol palm, jaraguagrass, orchid vine, raspa guacal, and arrocillo. Herbicide use was widespread, with glyphosate, metsulfuron-methyl, and paraquat being the most common active ingredients, typically applied singly, in mixtures, or sequentially. The findings reveal a heavy reliance on only three herbicides and highlight the need for targeted control of species in the Poaceae family and climbing vines. This work contributes valuable insights into weed dynamics in tropical forest plantations and emphasizes the need for region-specific and sustainable management strategies to mitigate potential productivity constraints and reduce reliance on herbicides.

Este documento es una herramienta de apoyo para una audiencia no profesional, que incluye propietarios de viviendas en Florida y a público entusiasta de las plantas, con el objetivo de gestionar de manera efectiva la invasión de malezas en áreas de césped. Sin embargo, este documento también puede ser utilizado por profesionales del césped, incluyendo, entre otros, productores de tepes, superintendentes de campos de golf, gerentes de campos deportivos y de atletismo, gerentes de paisajismo y especialistas de Extensión. Este documento es ENH884-Span, una publicación del Department of Agronomy, UF/IFAS Extension. Publicación original de febrero 2025.

Cereal rye (Secale cereale L.) is grown as a cover crop due to its ability to enhance soil health and suppress weeds through allelopathy, but germination responses of different weed species to allelochemicals have not been studied for seeds varying in age and consequently vigor. This study investigated the allelopathic effects of cereal rye on the germination of Palmer amaranth (Amaranthus palmeri S. Watson), large crabgrass [Digitaria sanguinalis (L.) Scop.], giant foxtail (Setaria faberi Herrm.), and lettuce (Lactuca sativa L.). Seeds were germinated in vitro in media with allelochemicals secreted by roots of cereal rye lines varying in allelopathic activity. Seeds were subjected to an accelerated aging treatment to modify their vigor. Results showed that aged seeds exhibited 31% lower germination than non-aged seeds. The magnitude of the germination reduction due to the presence of allelochemicals was species dependent. In the absence of allelochemicals, L. sativa exhibited a 20% reduction in germination due to aging, while the reduction was greater than 60% when allelopathy and aging were combined. Non-aged S. faberi seeds increased germination under low allelopathy conditions, with 20% greater germination compared with the non-treated control. Digitaria sanguinalis did not respond to seed aging, and the high allelopathy treatment reduced germination less than 10%. Amaranthus palmeri exhibited the highest germination and was the only species that was not affected by the seed aging and allelopathy treatments. Germination rate was reduced by seed aging and to a lesser extent by allelochemicals. Results suggest that incorporating allelopathic S. cereale varieties in cover crop rotations can reduce weed populations. However, the age structure of the seedbank might determine the importance of allelochemicals for emergence at the species level, likely causing weed community shifts.

Typically, weed density is used to predict weed-induced yield loss, as it is easy and quick to quantify, even though it does not account for weed size and time of emergence relative to the crop. Weed-crop leaf area relations, while more difficult to measure, inherently account for differences in plant size, representing weed-crop interference more accurately than weed density alone. Unmanned aerial systems (UASs) may allow for efficient quantification of weed and crop leaf cover over a large scale. It was hypothesized that UAS imagery could be used to predict maize (Zea mays L.) yield loss based on weed-crop leaf cover ratios. A yield loss model for maize was evaluated for accuracy using 15- and 30-m-altitude aerial red-green-blue and four-band multispectral imagery collected at four North Carolina locations. The model consistently over- and underpredicted yield loss when observed yield loss was less than and greater than 3,000 kg ha-1, respectively. Altitude and sensor type did not influence the accuracy of the prediction. A correction for the differences between predicted and observed yield loss was incorporated into the linear model to improve overall precision. The correction resulted in r2 increasing from 0.17 to 0.97 and a reduction in root mean-square error from 705 kg ha-1 to 219 kg ha-1. The results indicated that UAS images can be used to develop predictive models for weed-induced yield loss before canopy closure, making it possible for growers to plan production and financial decisions before the end of the growing season.

The success of weed management decisions must be assessed not only in the short-term within season but also in the long-term over several seasons. This study investigated the effects of crop rotation and herbicide program structure on the population growth rates of Palmer amaranth (Amaranthus palmeri S. Watson) and common ragweed (Ambrosia artemisiifolia L.). A field experiment was conducted over a 3-year period in North Carolina to compare cotton (Gossypium hirsutum L.)-sweetpotato [Ipomoea batatas (L.) Lam.]-soybean [Glycine max (L.) Merr.], cotton-peanut (Arachis hypogaea L.)-soybean, cotton-tobacco (Nicotiana tabacum L.)-soybean, and cotton-soybean-soybean rotations and preemergence and postemergence herbicide application timings. Results showed that preemergence herbicide application in the soybean phase of the rotation reduced Palmer amaranth populations 79%. However, the preemergence herbicides were only effective at reducing weed populations for the current season, not beyond. Common ragweed population growth rate was highest after the first 2 years (lambda = 1.63) of the cotton-tobacco-soybean rotation. Preemergence herbicides were effective in reducing common ragweed populations, particularly in rotations with cotton-sweetpotato and cotton-peanut. Soybean yields were similar across rotations ranging from 62 bu/ac to 68 bu/ac. Annual use of preemergence herbicides was essential to reduce Palmer amaranth populations. For common ragweed, the effectiveness of preemergence herbicides to mitigate population growth was reduced when poorly competitive crops were part of the rotation.

AbstractFarmers need accurate estimates of winter cover crop biomass to make informed decisions on termination timing or to estimate potential release of nitrogen from cover crop residues to subsequent cash crops. Utilizing data from an extensive experiment across 11 states from 2016 to 2020, this study explores the most reliable predictors for determining cereal rye cover crop biomass at the time of termination. Our findings demonstrate a strong relationship between early‐season and late‐season cover crop biomass. Employing a random forest model, we predicted late‐season cereal rye biomass with a margin of error of approximately 1,000 kg ha−1 based on early‐season biomass, growing degree days, cereal rye planting and termination dates, photosynthetically active radiation, precipitation, and site coordinates as predictors. Our results suggest that similar modeling approaches could be combined with remotely sensed early‐season biomass estimations to improve the accuracy of predicting winter cover crop biomass at termination for decision support tools.Core Ideas Cereal rye winter cover crop biomass modeled on data from 35 site‐years. We found a strong relationship between early and late‐season biomass. Random forest model with early‐season biomass and weather data performed well. Similar approach could improve decision support tools for cover crop management.

ABSTRACT This study examined the growth parameters of both glyphosate‐susceptible and glyphosate‐resistant biotypes of Amaranthus palmeri, designated as GA2005 and GA2017, respectively. A two‐year microplot field study was conducted to assess their growth characteristics. Scheduled destructive harvests on named harvest days (HD) were conducted to collect measurements for further calculation of net assimilation rate (NAR; g m−2 day−1), specific leaf area (SLA), leaf weight ratio (LWR), stem‐to‐leaf ratio (SLR), leaf area index (LAI), leaf area ratio (LAR; cm2 g−1), leaf area duration (LAD; days), relative growth rate (RGR; g.g−1 day−1) and plant volume (m3). In addition, stem diameter, number of leaves, and Chlorophyll content (μmol m2) were determined. The main objective was to identify growth parameters that differentiate biotypes along the plant life cycle. While certain growth parameters showed no variation among biotypes, differences in leaf area index (LAI) over HD and chlorophyll content and leaf area duration (LAD) were observed as the main effects. Glyphosate‐resistant biotypes exhibited higher LAD and chlorophyll content, potentially conferring a competitive advantage, especially in heavily used glyphosate environments. The study highlights the complexity of intraspecific genetic differentiation, adaptation, and environmental factors affecting A. palmeri. It may offer insights into biotype distinction and resistance spread while advancing our comprehension of species adaptation and growth strategies for enhanced control.

Weed control has relied on the use of organic and inorganic molecules that interfere with druggable targets, especially enzymes, for almost a century. This approach, although effective, has resulted in multiple cases of herbicide resistance. Furthermore, the rate of discovery of new druggable targets that are selective and with favorable environmental profiles has slowed down, highlighting the need for innovative control tools. The arrival of the biotechnology and genomics era gave hope to many that all sorts of new control tools would be developed. However, the reality is that most efforts have been limited to the development of transgenic crops with resistance to a few existing herbicides, which in fact is just another form of selectivity. Proteolysis-targeting chimera (PROTAC) is a new technology developed to treat human diseases but that has potential for multiple applications in agriculture. This technology uses a small bait molecule linked to an E3 ligand. The 3-dimensional structure of the bait favors physical interaction with a binding site in the target protein in a manner that allows E3 recruitment, ubiquitination and then proteasome-mediated degradation. This system makes it possible to circumvent the need to find druggable targets because it can degrade structural proteins, transporters, transcription factors, and enzymes without the need to interact with the active site. PROTAC can help control herbicide-resistant weeds as well as expand the number of biochemical targets that can be used for weed control. In the present article, we provide an overview of how PROTAC works and describe the possible applications for weed control as well as the challenges that this technology might face during development and implementation for field uses.

Rapid increase in the hectarage and agricultural systems that use cover cropping for soil conservation and improvement, soil moisture retention, and weed management has highlighted the need to develop formal breeding programs for cover crop species. Cereal rye ( Secale cereale L.) is preferred by many growers due to high biomass production and weed-suppression potential, which is believed to be partially due to allelopathy. Rye germplasm exhibits large variability in allelopathic activity, which could be used to breed rye with enhanced weed suppression. Here, we provide an overview of rye history and breeding and describe a strategy to develop rye lines with increased allelopathic activity. The discussion focuses on ways to deal with important challenges to achieving this goal, including obligate cross-pollination and its consequent high segregation levels and the need to quantify allelopathic activity under field conditions. This review seeks to encourage weed scientists to collaborate with plant breeders and promote the development of cover crop cultivars better suited to reduce weed populations.

Field experiments were conducted at Clayton and Rocky Mount, NC, during summer 2020 to determine the growth and fecundity of Palmer amaranth plants that survived glufosinate with and without grass competition in cotton. Glufosinate (590 g ai ha(-1)) was applied to Palmer amaranth early postemergence (5 cm tall), mid-postemergence (7 to 10 cm tall), and late postemergence (>10 cm tall) and at orthogonal combinations of those timings. Nontreated Palmer amaranth was grown in weedy, weed-free in-crop (WFIC) and weed-free fallow (WFNC) conditions for comparisons. Palmer amaranth control decreased as larger plants were treated; no plants survived the sequential glufosinate applications in both experiments. The apical and circumferential growth of Palmer amaranth surviving glufosinate treatments was reduced by more than 44% compared to the WFIC and WFNC Palmer amaranth in both experiments. The biomass of Palmer amaranth plants surviving glufosinate was reduced by more than 62% when compared with the WFIC and WFNC in all experiments. The fecundity of Palmer amaranth surviving glufosinate treatments was reduced by more than 73% compared to WFNC Palmer amaranth in all experiments. Remarkably, the plants that survived glufosinate were fecund as WFIC plants only in the Grass Competition experiment. The results prove that despite decreased vegetative growth of Palmer amaranth surviving glufosinate treatment, plants remain fecund and can be fecund as nontreated plants in cotton. These results suggest that a glufosinate-treated grass weed may not have a significant interspecific competition effect on Palmer amaranth that survives glufosinate. Glufosinate should be applied to 5 to 7 cm Palmer amaranth to cease vegetative and reproductive capacities.

Peanut (Arachis hypogaea L.) and maize (Zea mays L.) are essential crops for Ghana's economy and food security, but weed infestation poses a significant threat to their cultivation. Crop rotations influence weed communities, but little is known about these processes in peanut-cropping systems in West Africa. This study investigated the impact of different crop rotations and input levels on weed communities in Ghana over 3 yr. Results showed that low inputs (absence of herbicide and fertilization) favored species richness, while higher input levels (weed control with herbicides and fertilizer use) reduced it. Diversity and evenness were also affected by inputs, with varying patterns across locations and seasons. Weed population growth rates (lambda) varied significantly by location and treatment; all management programs resulted in increasing weed populations. Principal component analysis revealed distinct associations between weed species and crop management. The majority of weed species exhibited a generalist behavior and did not associate with a particular management. However, billygoat weed (Ageratum conyzoides L.) and Benghal dayflower (Commelina benghalensis L.) were positively associated with high-input systems, while purple nutsedge (Cyperus rotundus L.) exhibited strong associations with low and medium inputs. The weed-crop rotation dynamics described here demonstrate how management drives the selection of weed species that are more pervasive and interfere with important food crops in Ghanaian agriculture.

Background: Various herbicide-resistant redroot pigweed (Amaranthus retroflexus) have been confirmed recently in North Carolina, USA. Objective: Determine which postemergence herbicides would effectively control ALS- and PPO-inhibiting herbicide-resistant redroot pigweed populations. Methods: Two ALS- and PPO-inhibiting herbicide-resistant (Camden and Pasquotank County) and two putative herbicide-susceptible (Yadkin and Wake County) populations were treated with a discriminating rate of 2,4-D, atrazine, dicamba, glyphosate, glufosinate and mesotrione. Populations that survived the discriminating rate were further subjected to dose-response assays. Results: All populations except for Pasquotank County survived to 2,4-D and/ or dicamba 21 days after treatment. Twelve and 37% of the Pasquotank County plants survived after treatment with atrazine and mesotrione, respectively. Only 12% of the Yadkin County population survived after treatment with glyphosate. No plants survived glufosinate. The Pasquotank County population did have reduced susceptibility to atrazine compared to other populations. The Pasquotank County population (LD50: 918 g ai ha-1) was less susceptible to mesotrione compared to other populations (LD50: 10 to 28 gai ha-1). The Yadkin County population (LD50: 151 g ae ha-1) had reduced susceptibility to glyphosate compared to other populations (LD50: 52 to 72 g ae ha-1). Conclusion: These studies provide evidence that there are effective postemergence herbicides to control the multiple herbicide-resistant redroot pigweed populations. The studies also provided evidence of resistance to mesotrione in a previously identified herbicide-resistant population and low-level glyphosate resistance in a previously deemed susceptible redroot pigweed population.

Palmer amaranth (Amaranthus palmeri S. Watson) is the most problematic weed of cotton (Gossypium hirsutum L.)-cropping systems in the U.S. Southeast. Heavy reliance on herbicides has selected for resistance to multiple herbicide mechanisms of action. Effective management of this weed may require the integration of cultural practices that limit germination, establishment, and growth. Cover crops have been promoted as a cultural practice that targets these processes. We conducted a 2-yr study in Georgia, USA, to measure the effects of two annual cover crops (cereal rye [Secale cereale L.] and crimson clover [Trifolium incarnatum L.]), a perennial living mulch ('Durana (R)' white clover [Trifolium repens L.]), and a bare ground control on A. palmeri population dynamics. The study was conducted in the absence of herbicides. Growth stages were integrated into a basic demographic model to evaluate differences in population trajectories. Cereal rye and living mulch treatments suppressed weed seedling recruitment (seedlings seed(-1)) 19.2 and 13 times and 12 and 25 times more than the bare ground control, respectively. Low recruitment was correlated positively with low light transmission (photosynthetic active radiation: above canopy photosynthetically active radiation [PAR]/below cover crop PAR) at the soil surface. Low recruitment rates were also negatively correlated with high survival rates. Greater survival rates and reduced adult plant densities resulted in greater biomass (g plant-1) and fecundity (seeds plant(-1)) in cereal rye and living mulch treatments in both years. The annual rate of population change (seeds seed-1) was equivalent across all treatments in the first year but was greater in the living mulch treatment in the second year. Our results highlight the potential of annual cover crops and living mulches for suppressing A. palmeri seedling recruitment and would be valuable tools as part of an integrated weed management strategy.

Germination variability enables weedy species to colonise disturbed habitats and is expected to evolve in response to changing selection pressures. The paucity of information about germination variability in weeds prompted a detailed study of this topic with two agricultural and two non-agricultural populations of Capsella bursa-pastoris (Shepherd's purse). Variance in germination time was partitioned amongst and within populations, and amongst racemes and silicles within individual plant, and broad-sense heritability (H-2) was estimated. Agricultural populations exhibited a shorter and more uniform germination timing than non-agricultural populations. However, differences amongst populations explained 7%-12% of the total variance, while differences amongst individuals and racemes accounted for approximately 40-54% and 10% of the total variance for germination time. For germination time, H-2 = 0.4 when averaged across all time points, peaking at H-2 = 0.7 at a time coinciding with the exponential phase of the germination curve. Maintaining predominantly intrapopulation variability in germination timing appears to be important for long-term fitness in this species.

New tools are critically needed to diversify weed control in many crops and to combat herbicide resistant weeds. PROteolysis-TArgeting Chimera (PROTAC) is a new molecular technique that consists of using an organic molecule designed to interact with a target protein and to recruit an E3 ligase. By bringing these two molecules together, PROTAC can trigger the action of the proteasome, a natural cellular mechanism, to degrade the protein of interest. PROTAC can potentially degrade enzymes, including those that are herbicide resistant, and structural proteins. Because of its potential to increase the number mechanisms and selectivity to interfere with plant metabolism, PROTAC should be explored as an innovative form of weed control for agricultural and non-agricultural systems.

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Abstract In areas surrounding large poultry industries, poultry litter is often an alternative nitrogen fertilizer for crop production. However, farmers who have not used poultry litter in the past have concerns regarding potential weed seed contamination. A survey was conducted to determine the occurrence of germinable weed seed in poultry litters (n = 61) submitted by growers and industry representatives across North Carolina. In a 9:1 potting media:poultry litter mix, a single grass seed germinated from the 61 surveyed poultry litters, equating to 0.3 viable seeds 100 g−1 poultry litter. Viable seed content averaged 1.1 seeds 100 g−1 litter using the extractable seedbank method on 25% of the litters from the survey, much higher than the grow out method, and the majority of seeds found were Amaranthaceae. A growth chamber experiment was then conducted and demonstrated that there was a negative relation between poultry litter application and weed seedling emergence. There was a 65%, 75%, and 85% reduction in Senna obtusifolia (L.) H.S. Irwin & Barneby, Setaria pumila (Poir.) Roem. & Schult., and Amaranthus palmeri S. Watson germination, respectively, from the control to highest application rate of poultry litter (26.9 Mg ha−1). A laboratory study showed that poultry litter leachates can decrease seed radicle length and integrity and is likely due to osmotic or salinity stress. The weed seed content in litter as well as the negative impact of poultry litter and its leachates on weed seedling emergence make it unlikely that poultry litter applications will significantly increase seedbanks above levels commonly observed in agricultural fields.

Winter cover crop performance metrics (i.e., vegetative biomass quantity and quality) affect ecosystem services provisions, but they vary widely due to differences in agronomic practices, soil properties, and climate. Cereal rye (Secale cereale) is the most common winter cover crop in the United States due to its winter hardiness, low seed cost, and high biomass production. We compiled data on cereal rye winter cover crop performance metrics, agronomic practices, and soil properties across the eastern half of the United States. The dataset includes a total of 5,695 cereal rye biomass observations across 208 site-years between 2001–2022 and encompasses a wide range of agronomic, soils, and climate conditions. Cereal rye biomass values had a mean of 3,428 kg ha−1, a median of 2,458 kg ha−1, and a standard deviation of 3,163 kg ha−1. The data can be used for empirical analyses, to calibrate, validate, and evaluate process-based models, and to develop decision support tools for management and policy decisions.