Wesley J. Everman

Many forage grasses increase seed dispersal by having their seeds ingested by grazing animals and later deposited elsewhere, reducing parent‐plant offspring competition and improving germination conditions. This study discusses the dissemination of seeds by livestock to spread desired plant species across grassland and pastures. The effects of rumen and intestinal digestion on seed germination of dormancy‐prone native warm‐season grasses were investigated to assess their potential for transporting valuable forage and biomass crops in the southeastern United States. Two experiments were performed using switchgrass (SG) ( Panicum virgatum L.) and big bluestem (BBS) ( Andropogon gerardii L.) to determine viability and germination post‐exposure to two subsequent stages of the ruminant digestive system. Stage I, rumen digestion, was performed in situ in a cannulated steer for 48 h, followed by Stage II: Small intestine digestion, simulated in vitro via abomasal digestion for 24 h. The results from this study revealed that the combination of both stages, rumen and small intestine digestion, resulted in the highest percentage of seed mortality in each species; however, for the seeds that did survive, they had a delayed germination by 7 days compared to the control. Average germination percentage was reduced by 87% in SG and 81% in BBS after exposure to both digestion stages. Results of this study have shown low grass seed germination rates following digestive‐tract exposure, suggesting that using grazing livestock as a management strategy to propagate BBS and SG is impractical and would significantly reduce viability and germination.

North Carolina farmers face mounting challenges in controlling Italian ryegrass, as herbicide-resistant populations continue to be found in more fields across the state. Increased selection pressure has led to cases of multiple and cross resistance to herbicides, leaving growers with fewer options for effective weed control. The objective of this study was to understand the Italian ryegrass frequency and distribution of resistance to commonly used postemergence herbicides with various sites of action. Italian ryegrass seedheads were collected from throughout North Carolina in June 2022. A statewide grid sample resulted in 115 samples being collected from wheat fields with observed Italian ryegrass escapes. Seeds were germinated in greenhouses, and herbicides were applied to 4-leaf plants. Treatments included a nontreated check, and applications of glufosinate, glyphosate, mesosulfuron, paraquat, and pinoxaden, all at 1× rates according to each product label. Populations controlled ≤50% by a specific herbicide were considered to have putative resistant. Forty-four populations were found to exhibit putative resistance to glufosinate, 17 to pinoxaden, 10 to mesosulfuron, 2 to glyphosate, and 1 to paraquat. One population with four-way resistance and two with three-way resistance were found. The results from this collection were compared with populations from a similar statewide collection conducted in 2012. These populations were screened for response to diclofop, mesosulfuron, pinoxaden, and pyroxsulam. We also screened these populations for response to glufosinate, glyphosate, and paraquat. Out of 102 populations, none were found to be resistant to glyphosate and paraquat, while 91 were determined to exhibit resistance to glufosinate. These results are helpful for growers and Extension personnel as they develop effective weed management programs.

North Carolina farmers have extensively relied on atrazine for effective weed control in corn, particularly for Palmer amaranth. In 2016, a grower from Washington County, NC, reported a control failure of Palmer amaranth in a corn field treated with atrazine. Greenhouse studies were conducted with the objectives to confirm if the Washington County Palmer amaranth population was resistant to atrazine and to determine other effective postemergence herbicides. Two atrazine-susceptible Palmer amaranth populations collected from Edgecombe and Johnston County were used for comparison. Greenhouse response assays confirmed the Washington County population is resistant, with a lethal dose causing 50% mortality (LD ₅₀ ) of 1,253 g ai ha ^-1 . This population was 7- and 9-fold less susceptible to atrazine compared with the Edgecombe (LD ₅₀ : 208 g ai ha ^-1 ) and Johnston County (LD ₅₀ : 155 g ai ha ^-1 ) populations, respectively. Additionally, the LD ₈₀ (lethal dose causing 80% mortality) of the Washington County population (12,107 ga ai ha ^-1 ) was more than five times greater than the maximum labeled rate for atrazine. A subsequent herbicide screen that utilized field labeled rates suggested that 2,4-D, dicamba, fomesafen, glufosinate, and mesotrione provide at least 79% or greater control of the Washington County population. The Washington County population was not effectively controlled by thifensulfuron or glyphosate, both of which have widespread resistance documented throughout North Carolina. The results of these experiments provide evidence that the Washington County population is resistant to atrazine, glyphosate, and thifensulfuron, and effective herbicides to manage this population were confirmed.

Trifludimoxazin + saflufenacil is a premix protoporphyrinogen oxidase (PPO)-inhibiting herbicide with preemergence and postemergence activity pending USEPA registration for burndown application ahead of planting corn ( Zea mays L.), soybean [ Glycine max (L.) Merr.], grain sorghum [ Sorghum bicolor (L.) Moench], and wheat ( Triticum aestivum L.). With early-season soybean growth often occurring simultaneously with preplant burndown of fields in later-planted soybean and grain sorghum, odds of negative impacts associated with off-target herbicide movement to the crop increase. Field studies were conducted in 2024 to evaluate effect of reduced rates of trifludimoxazin + saflufenacil (12.5% to 0.4% of the lowest proposed labeled application rate of 38.3 g ai ha ⁻¹ ) applied to 1- to 2-leaf soybean. Reduced rates of 1/8×, 1/16×, 1/32×, and 1/64× resulted in 53%, 43%, 32%, and 21% visual phytotoxicity at 1 wk after treatment (WAT), while at 4 WAT response was 31%, 23%, 17%, and 12%. Trifludimoxazin + saflufenacil at these rates reduced soybean height 30% to 7% and 18% to 4% at 1 and 4 WAT, respectively. Soybean yield was negatively impacted 8%, 5%, 2%, and 0% at these respective rates. Off-target movement of trifludimoxazin + saflufenacil to soybean in early vegetative growth will result in severe visual injury and height reduction, especially with exposure at the three highest rates evaluated. Soybean should not be expected to fully recover and significant negative impact on yield (5% or greater) will be observed at the two highest rates evaluated in this research.

Hydrilla [ Hydrilla verticillata (L.F.) Royle] is a known, persistent aquatic weed in many lakes and reservoirs across the United States. Recently, focus has been placed on the management of invasions of H. verticillata into flowing systems due to increased difficulty in achieving effective control. In flowing environments, increased flow and water exchange rates commonly result in shorter herbicide exposure times using traditional application techniques. This research evaluated the concept of intermittent herbicide exposure as a potential management strategy to overcome operational challenges in high water exchange environments. Monoecious H. verticillata response to intermittent exposure to florpyrauxifen-benzyl, endothall, and fluridone at multiple concentrations and nontreatment intervals was evaluated in greenhouse-scale mesocosm experiments. Decreased efficacy was not observed when nontreatment intervals between exposures were introduced in florpyrauxifen-benzyl treatments. Monoecious H. verticillata treated with 30 µg ai L ⁻¹ florpyrauxifen-benzyl and a 6-d nontreatment interval resulted in 89% reduction in aboveground biomass. Nontreatment intervals did not influence endothall efficacy and biomass reduction increased with herbicide concentration (66% to 93%). Fluridone treatments at 5 µg L ⁻¹ resulted in 82% biomass reduction, while treatments at 10 and 15 µg L ⁻¹ resulted in 89% biomass reduction. Biomass reduction was slightly lower in fluridone applications with a 12-d nontreatment interval (83%) compared with other nontreatment intervals (85% to 91%). The high biomass reduction and similar response between treatments observed suggests the need for additional refinement and operational verification of intermittent herbicide exposures for monoecious H. verticillata control to increase cost-effectiveness and efficiency in public H. verticillata control programs.

The accurate estimation of soybean ( Glycine max ) stand establishment is essential for evaluating crop emergence and informing early‐season management practices. Recent advances in unmanned aerial vehicle (UAV) imagery and computer vision offer opportunities to automate plant population assessments; however, limited information exists on their accuracy in soybeans. This study evaluated two commercial UAV‐based plant counting platforms, a point‐based (convolutional neural network–derived) and a line‐based (Hough transform–derived) approach across two growing seasons, three flight altitudes (15.2, 45.7, and 91.4 m), and seven plant removal treatments, including a control (no removal). UAV imagery was collected at 7‐ to 10‐day intervals from 10 to 36 days after planting (DAP), and predictions were compared to manual on‐ground counts. The point‐based method provided the highest accuracy (within ±12% of ground‐truth; R ² = 0.81) when imagery was collected between 14 and 20 DAP at 15.2‐m altitude. Accuracy declined beyond 27 DAP as canopy overlap increased. The line‐based method remained more stable across altitudes and later growth stages but consistently overestimated plant counts, particularly in dense and narrow row canopies. Incorporating on‐ground calibration areas improved accuracy by an average of 28% and up to 48% for the line‐based approach in narrow rows. Row spacing and plant removal patterns had minimal effects on prediction error, although short repeating gaps were poorly detected by the line‐based method. Overall, UAV‐based plant counts in soybean are feasible and dependable when flights are timed during early vegetative growth and supported by calibration, providing a practical tool for in‐season management and field‐based crop monitoring.

Sorgoleone, an allelochemical exuded from root hairs of grain sorghum [ Sorghum bicolor (L.) Moench], has proven herbicidal activity on several weeds and crops. Due to its hydrophobic nature and affinity for organic matter, sorgoleone can persist in the soil for a long period. Although sorghum residues are beneficial for weed suppression, growers in the southeastern United States have raised concerns that these residues may negatively affect wheat ( Triticum aestivum L.) emergence in double-crop systems. Two independent laboratory studies were conducted to evaluate sorgoleone activity: (1) weed species/wheat variety study, which included four weed species, Italian ryegrass [ Lolium perenne L. ssp. multiflorum (Lam.) Husnot], large crabgrass [ Digitaria sanguinalis (L.) Scop.], sicklepod [ Senna obtusifolia (L.) Irwin & Barneby], and velvetleaf [ Abutilon theophrasti Medik.], and two wheat varieties, ‘USG3251’ and ‘Shirley’; and (2) wheat variety and group study, which included a total of 20 varieties distributed in four wheat groups. In both studies, sorgoleone was applied at 0.025, 0.05, 0.10, 0.15, 0.20, and 0.30 g L ⁻¹ to seeds grown in petri dishes under laboratory conditions. In Study 1, sorgoleone activity had a stronger effect on grass weeds than on broadleaf weeds. Lolium perenne ssp. multiflorum was the most susceptible weed, showing 77% growth reduction at 0.3 g L ⁻¹ of sorgoleone. At the same concentration, D. sanguinalis showed the second-highest response, with a 32% growth reduction, followed by A. theophrasti and S. obtusifolia , with reductions of 23% and 20%, respectively. No effect of sorgoleone was observed on wheat varieties. In Study 2, growth reduction was only observed for six wheat varieties at the highest sorgoleone concentrations. Furthermore, in between group comparisons, Hard Red wheat presented higher response to sorgoleone. These findings demonstrate strong herbicidal activity of sorgoleone on grass weeds, particularly L. perenne ssp. multiflorum , while having minimal effects on most wheat varieties.

Italian ryegrass is a troublesome weed species commonly found across the United States. In North Carolina, biotypes resistant to herbicides from Groups 1, 2, and 9 have been confirmed. In fall 2020, multiple growers reported unsatisfactory control of Italian ryegrass after sequential burndown applications of paraquat in the Southern Piedmont region of the state. The objectives of this study were to confirm the presence of a paraquat-resistant Italian ryegrass biotype in the state through a whole-plant dose–response bioassay and to characterize the response of Italian ryegrass accessions from the same region to commonly used burndown herbicides. Greenhouse studies were conducted at the North Carolina State University weed science laboratories to evaluate the response of three putative paraquat-resistant Italian ryegrass biotypes (B, H, SB) and four putative susceptible biotypes (S1, S2, S3, and S4) to paraquat rates ranging from 52.5 to 26,880 g ai ha⁻¹ and the response of 38 accessions to clethodim (271 g ai ha⁻¹), glyphosate (1,260 g ae ha⁻¹), glufosinate (880 g ai ha⁻¹), nicosulfuron (34 g ai ha⁻¹), and paraquat (840 g ai ha⁻¹). The effective paraquat dose required to reduce biomass by 50% (GR₅₀) for the putative paraquat-resistant biotypes ranged from 570 to 1,729 g ai ha⁻¹, equivalent to 19- to 58-fold more resistant to paraquat compared to the average GR₅₀ of susceptible biotypes. This study confirms the presence of paraquat-resistant Italian ryegrass in North Carolina. Results from the accessions study reveal that 29% of biotypes tested were resistant to paraquat, all of which also exhibited resistance to glyphosate and nicosulfuron. Additionally, a wide distribution of multiple herbicide–resistant biotypes was observed in the Southern Piedmont region, with 97% and 74% of accessions tested resistant to ≥1 and ≥2 sites of action, respectively.

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.