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Carrier water quality is an important consideration for herbicide efficacy. Field and greenhouse studies were conducted from 2021 to 2023 to evaluate the effect of carrier water pH and hardness on imazapic efficacy for sicklepod control in peanut crops. In separate field experiments imazapic was applied postemergence at 0.071 kg ai ha−1 with carrier water pH levels of 5, 6, 7, 8, or 9; and hardness levels of 0 (deionized water), 100, 200, 400, or 500 mg L−1 of CaCO3 equivalent. In greenhouse experiments, imazapic was applied to sicklepod that was either 10 cm, 15 cm, or 20 cm tall at similar carrier water pH levels and hardness levels of 0, 100, 200, 400, or 800 mg L−1 of CaCO3. In the field study, sicklepod control, density, and biomass reductions were lower with carrier water pH 5 or 9 compared with pH 7. In the greenhouse study, control was not different among carrier water pH levels when imazapic was applied to 10-cm-tall sicklepod; however, when applied to 15- or 20-cm-tall sicklepod, control was at least 25% greater with acidic (pH 5) compared to alkaline (pH 9) carrier water. Results from the field study showed that carrier water hardness ≤500 ppm did not reduce the efficacy of imazapic to control sicklepod. In the greenhouse study, regardless of sicklepod height, carrier water hardness of 800 mg L−1 reduced sicklepod control by 15% and biomass reduction by 17% compared with deionized water (pH 7). The effects of carrier water pH and hardness on imazapic efficacy did not compromise peanut yield in the field study. However, this study indicates that both acidic and alkaline carrier water pH and hardness (800 mg L−1 CaCO3 L−1) have the potential to reduce imazapic efficacy on sicklepod, and appropriate spray solution amendments maybe be needed to maintain optimum efficacy.
Herbicides are the primary tool for controlling weeds in peanut (Arachis hypogaea L.) and are crucial to sustainable peanut production in the United States. The literature on chemical weed management in peanut in the past 53 yr (1970 to 2022) in the United States was systematically reviewed to highlight the strengths and weaknesses of different herbicides and identify current research gaps in chemical weed management. Residual weed control in peanut is achieved mainly with dimethenamid-P, ethalfluralin, pendimethalin, and S-metolachlor. More recently, the use of the protoporphyrinogen oxidase inhibitor flumioxazin and acetolactate synthase inhibitors, such as diclosulam, for residual weed control in peanut has increased considerably. Postemergence broadleaf weed control in peanut is achieved mainly with acifluorfen, bentazon, diclosulam, imazapic, lactofen, paraquat, and 2,4-DB, while the graminicides clethodim and sethoxydim are the major postemergence grass weed control herbicides in peanut. Although several herbicides are available for weed control in peanut, no single herbicide can provide season-long weed control due to limited application timing, lack of extended residual activity, variability in weed control spectrum, and rotational restrictions. Therefore, effective weed management in peanut often requires herbicide mixtures and/or sequential application of preplant-incorporated, preemergence, and/or postemergence herbicides. However, the available literature showed a substantive range in herbicide efficacy due to variations in environmental conditions and flushes of weed germination across years and locations. Despite the relatively high efficacy of herbicides, the selection of herbicide-resistant weeds is another area of increasing concern. Future research should focus on developing new strategies for preventing or delaying the development of resistance and improving herbicide efficacy within the context of climate change and emerging constraints such as water shortages, rising temperatures, and increasing CO2 concentration.
Weed interference is a major factor that reduces peanut (Arachis hypogaea L.) yield in the United States. Peanut growers rely heavily on herbicides for weed control. Although effective, herbicides are not a complete solution to the complex challenge that weeds present. Therefore, the use of nonchemical weed management options is essential. The literature on weed research in peanut in the past 53 yr in the United States was reviewed to assess the achievements and identify current research gaps and prospects for nonchemical weed management for future research. More than half (79%) of the published studies were from the southeastern United States. Most studies (88%) focused on weed management, while fewer studies (12%) addressed weed distribution, ecology, and competitive mechanisms. Broadleaf weeds were the most frequently studied weed species (60%), whereas only 23% and 19% of the published studies were relevant to grasses and Cyperus spp., respectively. Seventy-two percent of the published studies focused on curative measures using herbicides. Nonchemical methods using mechanical (5%) and preventive (13%) measures that influence crop competition and reduce the buildup of the weed seedbank, seedling recruitment, and weed seed production have received less attention. In most studies, the preventive weed management measures provided weed suppression and reduced weed competition but were not effective enough to reduce the need for herbicides to protect peanut yield. Therefore, future research should focus on developing integrated weed management strategies based on multiple preventive measures rather than one preventive measure combined with one or more curative measures. We recommend that research on mechanical weed management should focus on the role of cultivation when integrated with currently available herbicides. For successful weed management with lasting outcomes, the dominant weed communities of specific target locations should be addressed within the context of climate change and emerging constraints rather than focusing on single problematic species.
Herbicide resistance has been studied extensively in agronomic crops across North America but is rarely examined in vegetables. It is widely assumed that the limited number of registered herbicides combined with the adoption of diverse weed management strategies in most vegetable crops effectively inhibits the development of resistance. It is difficult to determine whether resistance is truly less common in vegetable crops or whether the lack of reported cases is due to the lack of resources focused on detection. This review highlights incidences of resistance that are thought to have arisen within vegetable crops. It also includes situations in which herbicide-resistant weeds were likely selected for within agronomic crops but became a problem when vegetables were grown in sequence or in adjacent fields. Occurrence of herbicide resistance can have severe consequences for vegetable growers, and resistance management plans should be adopted to limit selection pressure. This review also highlights resistance management techniques that should slow the development and spread of herbicide resistance in vegetable crops.
Weeds are managed in Florida strawberry production systems with plastic mulches, fumigants, and herbicides. There are limited post-transplant options to control weeds that emerge in the planting holes in the plastic-covered beds, but flumioxazin at 107 g ai ha−1 can be applied pretransplant under the plastic mulch to control broadleaf and grass weeds. Three research trials were conducted in Balm and Dover, FL, in 2017 and 2018 to evaluate tolerance of the strawberry cultivar ‘Radiance’ to flumioxazin rates ranging from 54 to 6,854 g ha−1 and to estimate herbicide persistence under the plastic mulch. Shoot damage was observed at 428 to 857 g ha−1 (4× and 8× the label rate, respectively), but a significant increase in the number of dead plants was not observed until the treatment rate was 857 g ha−1 at one site and 3,427 g ha−1 at a second site (8× and 32× the label rate, respectively). Berry yields were unaffected by rates lower than 857 g ha−1. Flumioxazin persisted throughout the growing season (approximately 150 d) with no reduction in soil concentration. We conclude that applied at the label rate, flumioxazin is a safe pretransplant weed management option for season-long weed control in strawberry with no yield reduction at rates below 8× the label rate. Caution is recommended for growers who plant a second crop on the same bed.
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