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.

Herbicides are necessary for successful vegetable production in the Southeastern United States. Along with bare-ground production, low density polyethylene (LDPE) mulches are often utilized to produce multiple crops (2–4) by rotation over the course of a 12-to-24-month period. These include fresh market tomato, pepper, cucurbits, eggplant, and cabbage. For LDPE mulch vegetable production, between each crop growers must apply contact and residual herbicides to mitigate weeds. However, these herbicides can remain on the mulch and injury transplants. Herbicides are often soil applied for bare soil production as well as under the LDPE mulch. Herbicide carryover in soil using these vegetable production methods can also result in management issues. Proper quantification analyzing the dissipation is critical in the decision-making process for growers to prevent unnecessary crop losses. A series of experiments have been conducted to quantify the dissipation of the herbicides flumioxazin, fomesafen, ammonium-glufosinate, glyphosate, halosulfuron-methyl, paraquat, S-metolachlor, and sulfentrazone over time using UPLC/MS and bioassay methods. These methods are presented.

Flumioxazin is a preemergence, N-phenylpththalimide herbicide that can be applied to control a broad spectrum of weeds in a variety of cropping systems. Limited information exists concerning the environmental fate of flumioxazin, therefore the present studies investigated the kinetic behavior of flumioxazin in soil and aqueous solution using field and analytical techniques to establish its degradation properties. Flumioxazin half-life in a Greenville sandy clay loam and Faceville loamy sand was 26.6 d. Flumioxazin was determined to have a groundwater ubiquity score of 1.79, indicating a low leachability potential. There was an inverse correlation between flumioxazin concentration in soil, rainfall, and solar radiation. There was no direct correlation between flumioxazin concentration and soil temperature. Flumioxazin activation energy was 58.4 (+/- 1.2) kJ mol- 1 with a Q10 value of 2.2. Even at the lowest amount of solar radiation and soil temperature, the energy from these environmental measures exceeded the activation energy needed for flumioxazin degradation. Flumioxazin stability in solution and field dissipation indicate that, with the input of thermal energy, degradation can be rapid.

Abstract Glyphosate and paraquat are effective preplant burndown herbicide options for multicrop vegetable production that uses plastic mulch, but problematic weeds such as wild radish, cutleaf evening primrose, annual morningglory, or horseweed may not be adequately controlled with these herbicides alone. The herbicides 2,4-D and dicamba could help control these troublesome weeds prior to planting if they can be removed from plastic mulch and thus avoid crop damage. Treatments included 2,4-D (1,065 and 2,130 g ae ha–1) and dicamba (560 and 1,120 g ae ha–1) applied broadcast over plastic mulch a day before transplanting. Just before transplanting, treatments received either 0.76 cm of water via overhead irrigation or no irrigation. Plastic mulch samples were collected at application and planting to determine herbicide presence using analytical techniques, and cantaloupe and zucchini squash were subsequently transplanted on the plastic beds. Analytical ultra-high performance liquid chromatography revealed that 88% to 99% of the initial herbicide concentration was present at crop planting when irrigation was not implemented. At most, a 1/50 rate of dicamba and a 1/500 rate of 2,4-D was present at planting when overhead irrigation was applied prior to transplanting. Maximum cantaloupe and squash injury from 2,4-D with irrigation was 10% and did not influence plant growth, biomass, or yield. For dicamba with overhead irrigation, cantaloupe injury was 35%, vine lengths were reduced by 24%, and maturity was delayed, whereas squash injury ranged from 9% to 12%, with no influence on growth or yield. Without irrigation to wash herbicides from the mulch prior to planting, 60% to 100% injury of both crops occurred with both herbicides. Zucchini squash was more tolerant to dicamba than cantaloupe. Results demonstrated that 2,4-D can be adequately removed from the surface of plastic mulch with irrigation, whereas a single irrigation event was not sufficient to remove dicamba. Nomenclature: 2,4-D; dicamba; annual morningglory; Ipomea spp.; cutleaf evening primrose; Oenothera laciniata Hill; horseweed; Conyza canadensis (L.) Cronq.; wild radish; Raphanus raphanistrum L.; cantaloupe; Cucumis melo var. cantalupo (Ser.); zucchini squash; Cucurbita pepo (L.)

The loss of methyl bromide led vegetable growers to rely more heavily on herbicides to control weeds. Although herbicides can be effective, limited options in vegetable production challenge growers. Identifying new, effective tools to be applied over plastic mulch before planting, for improved weed control with minimal crop injury, would be beneficial. The objective of these experiments was to evaluate the persistence of preplant applications of glyphosate (1,125 or 2,250 g ae ha(-1)) plus 2,4-D (1,065 or 2,130 g ae ha(-1)) or dicamba (560 g ae ha(-1)) over plastic mulch, using analytical techniques and subsequent yellow squash and watermelon response. Glyphosate and 2,4-D were not analytically detected at damaging concentrations on plastic mulch when at least 3.5 cm of rainfall was received after application and before planting. In addition, bioassay results showing less than 10% visual injury for either squash and watermelon, with no growth or yield suppression observed, supported analytical results. In contrast, dicamba concentrations on plastic mulch, regardless of rainfall amount or time between application and planting, remained at damaging levels. Squash yields were reduced by dicamba applied 1 to 30 d before planting, whereas watermelon was more resilient. 2,4-D plus glyphosate applied preplant over plastic mulch can provide an additional herbicide option for vegetable growers. More research is needed to understand the impact of residual activity of 2,4-D when transplants land directly in holes in plastic mulch at the time of application. The relationship of dicamba with plastic mulch is complex, because the herbicide cannot be easily removed by rainfall. Thus, dicamba should not be included in a weed management system in plasticulture vegetable production.

Planting cole crops and leafy greens in plastic mulch free of summer and winter annual broadleaf weeds is challenging. Because these crops are often grown as a second or third crop on mulch, weeds emerge in previously punched plant holes, tears in plastic, and row middles. Without the ability to use tillage and with limited herbicide options available for weed control, achieving a weed-free planting window is not often feasible. Additional herbicide options are needed, but their interaction with plastic mulch must be understood. Therefore, research has determined the persistence of preplant applications of 2,4-D tank-mixed with glyphosate applied over plastic mulch. Analytical laboratory analyses of plastic samples from field experiments, in conjunction with bioassays using broccoli ( Brassica oleracea var. botrytis L.) and collard ( Brassica oleracea var. viridis L.), evaluated herbicide dissipation. Analytical studies determined that 0.5 cm of irrigation after herbicide application and 1 day before planting removed 99% of 2,4-D, and 100% of glyphosate from the plastic mulch. Waiting an additional 14 days after application and irrigation further reduced the amount of 2,4-D on the plastic mulch 88% to 95%. For the field bioassay, preplant applications of 2,4-D tank-mixed with glyphosate resulted in 7% or less visual broccoli or collard injury without influencing crop growth, biomass, early season yield, or total yield as long as the mulch was washed with 0.5 cm of irrigation before planting. These studies also demonstrated there were no differences between the 1× and 2× use rates with respect to all response variables measured. Results suggest that 2,4-D and glyphosate can be effectively removed from the surface of plastic mulch with irrigation or rainfall before planting broccoli and collard.

ABSTRACT Weed control is an integral part of peanut (Arachis hypogaea L.) production systems. Paraquat is a staple postemergence (POST) herbicide used in peanut production in the Southeast US. Inorganic liquid nutrient (ILN) concentrates are liquid fertilizers that are recommended for use by producers in tank-mixtures with paraquat by some distributors. Irrigated and non-irrigated field trials were conducted to quantify the safening effect of ILN in various herbicide tank-mixtures on peanut and determine the suitability as tank-mix replacements for bentazon. Field studies indicated similar POST herbicide responses for peanut injury. Greenhouse experiments evaluated POST paraquat tank-mixtures with ILN for weed control and biomass reduction. Paraquat plus S-metolachlor caused significant leaf burn and stunting. Greatest peanut foliar injury occurred 3 d after treatment (DAT) but was transient. For the irrigated field trial, paraquat plus S-metolachlor plus ILN had similar injury levels as compared to paraquat plus S-metolachlor plus acifluorfen plus bentazon at 22 to 25%. For the non-irrigated field study, the application of paraquat plus ILN had 10% injury compared to paraquat at 22%. While injury was the greatest directly following application, peanut was able to recover with no yield or grade loss for both the irrigated and non-irrigated studies. In the greenhouse study, the effect of ILN varied by weed species and reduced leaf injury on several broadleaf weeds. While the addition of ILN to the various paraquat tank-mixtures initially reduced injury, it did not correspond to increases in yield or grade. The variability in weed control, transient injury mitigation, and no yield increase indicates that Georgia peanut growers will receive no benefit for including ILN in their paraquat tank-mixtures but if needed to improve crop nutrition, ILN will not reduce weed control.

Plantago lanceolata L. (buckhorn plantain) is an encroaching winter weed described as one of the most successful noncultivated colonizing species around the world. Control of P. lanceolata in southeastern USA Carya illinoinensis (Wangenh.) K. Koch production has not been studied, nor has the role of temperature on germination using a thermal gradient table. Seed of P. lanceolata collected from a Georgia C. illinoinensis grove were tested for the effects of temperature over time to establish differences in effects on germination using a thermal gradient table. Temperatures ranged from 13.5 to 30.5 °C for 288 h. Cumulative P. lanceolata seed germination was 66% occurring at 17.8 °C at 242 h. Over the 288 h experiment, maximum P. lanceolata germination was 27% occurring at 17.0 °C, 187 h after initiation. Control of P. lanceolata with residual herbicides, or in combination with 2,4-dichlorophenoxyacetic acid (2,4-D) was evaluated in the interrow of C. illinoinensis groves containing Trifolium repens L., and in greenhouse experiments. Pre- and post-emergent herbicides included indaziflam, halosulfuron-methyl, and simazine applied alone, or in combination with 2,4-D in late autumn after P. lanceolata emergence in a C. illinoinensis grove. Indaziflam in combination with 2,4-D controlled P. lanceolata greater than 90% when applied in C. illinoinensis groves and greenhouse experiments. Halosulfuron-methyl and simazine applied alone, or in combination with 2,4-D, provided 67% or less P. lanceolata control in the grove experiments, and 83% or less in greenhouse experiments. Results suggested that herbicide applications should be made during the time when diurnal temperatures are between 15 and 30 °C, while abiding pre-harvest interval restrictions. Post- and pre-emergent herbicides may aid in controlling emerged weeds and reducing further weed emergence during the autumn of that year.

ABSTRACT Paraquat postemergence (POST) applied is often used to control broadleaf and grass weed species in peanut in the Southeast US. The objective of this study was to determine the effects of POST herbicide tank-mixtures including paraquat on vegetation, yield, and grade for runner-type peanut cultivars under irrigated and non-irrigated conditions. Two separate experiments (irrigated and non-irrigated) were conducted in 2016 and 2017 in Ty Ty and Plains Georgia. Georgia-06G, Georgia-14N, TUFRunner™ ‘511’, and FloRun™ ‘157’ cultivars were evaluated. Herbicide tank-mixtures included paraquat, paraquat plus acifluorfen plus bentazon, paraquat plus acifluorfen plus bentazon plus S-metolachlor, and paraquat plus acifluorfen plus bentazon plus acetochlor. Leaf burn, stunting injury, yield, and grade were evaluated. There were no interactions between herbicide and cultivar for all variables. Paraquat alone resulted in significantly greater foliar injury (3 DAT) than the other herbicide treatments for the irrigated (34 to 16%) and non-irrigated (28 to 15%) studies. Stunting for paraquat alone was noted at 15 and 35% for irrigated and non-irrigated, respectively. Similarly, in both studies, Georgia-06G and TUFRunner™ ‘511’ yielded 10 to 12% greater than Georgia-14N and FloRun™ ‘157’. Overall, the herbicide tank-mixtures did not have a negative effect on yield. With no interactions observed, these herbicide treatments can be used in conjunction with the given runner-type peanut cultivars in either irrigated or non-irrigated conditions without concern for excessive injury or decline in yield or grade.