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Abstract
Cotton, rye, and vegetables are planted on over 567, 23, and 46 thousand ha of land in Georgia, respectively, and collectively account for a farm gate value of over $1.9 billion. These crops are not only critical for the success of local agriculture but for the nation. To maximize yields and preserve crop quality, weeds must be controlled in each of these crops. Cotton engineered to resist dicamba provides an effective option to control Georgia’s most problematic pest, glyphosate-resistant Palmer amaranth. However, overuse of dicamba postemergence in cotton is a concern and sustainable weed management programs must be implemented to delay resistance development. A study, conducted at 4 locations, demonstrated that adding 1) a rye cover crop, 2) preemergence herbicides, or 3) both the cover crop and preemergence herbicides reduced Palmer amaranth exposure to dicamba in a standard program by 65, 98, and 99%, respectively. These results are critical helping farmers implement sound diversified weed management systems.
In multi-cropped plasticulture vegetable production, plastic mulch is often used over 18 months thereby facilitating dense weed infestations. With formulation improvements and effective broadleaf weed control, 2,4-D and dicamba may serve as new tools to manage weeds between crops but only if they can be removed from the mulch. A study, conducted 8 times, used HPLC analysis and bioassay plantings of squash, watermelon, cantaloupe, broccoli, and collard to determine if 0.6 cm of overhead irrigation could remove these herbicides from the mulch. Irrigation effectively removed 2,4-D from the mulch to levels that were non-lethal for all crops. In contrast, irrigation did not successfully remove dicamba from the mulch.
Herbicide options in cereal rye are lacking, particularly for Italian ryegrass control. Cereal rye tolerance to 8 wheat herbicides was evaluated at 5 locations to potentially pursue registrations for cereal rye. Thifensulfuron-methyl + tribenuron-methyl, pyroxsulam, and halauxifen-methyl + florasulam resulted in minimal injury (≤15%) and growth reductions at the 2X rate and are candidates for potential labeling. In contrast, unacceptable injury was noted with pyroxasulfone, pyroxasulfone + flumioxazin, mesosulfuron-methyl, pinoxaden, and pinoxaden + fenoxaprop-p-ethyl.