Research was conducted at the Mississippi State University Delta Research and Extension Center from 2016 to 2018 to determine the effects of sub-lethal concentrations of paraquat, glyphosate, saflufenacil, and sodium chlorate exposure to rice at late-season growth stages, determine the effects of exposure to sub-lethal concentrations of glyphosate or paraquat on multiple rice cultivars, and characterize the effects of paraquat exposure and Oebalus pugnax feeding on rice grain quality. In the current research, rough rice grain yields were reduced by exposure to sub-lethal concentrations of soybean desiccants 0 to 28 DAH. Rice injury was determined to not be an accurate predictor of rough rice grain yield loss as injury did not exceed 20% with any desiccant, and no injury was observed from glyphosate applications. Rough rice grain yield reductions were reflected in yield component reductions following desiccant exposure. Applications of sub-lethal concentrations of glyphosate or paraquat to rice at 50% heading caused rough rice grain yield decreases ranging from 0 to 20 and 9 to 21 % respectively. Hybrid cultivars were unaffected following glyphosate exposure at 50% heading. In the current research, observations of paraquat exposure or O. pugnax infestation of rice at the soft dough growth stage suggest rice may exhibit severe sensitivity to both events in the form of reduced kernel weight and reductions in rice milling quality. Rough rice grain yield reductions coupled with milling quality reductions and driven by the proximity of rice to corn, cotton, soybean, and sorghum in Mississippi creates the need to exercise caution when applying desiccants.

Distinguishing 2,4-D and dicamba herbicide formulations in cotton and soybean tissue is challenging in regulation of crop injury from these herbicides. Additionally, stewardship of 2,4-D and dicamba technologies is important to maximize their longevity and efficacy. Research was conducted to (1) characterize cotton and soybean response to various formulations of 2,4-D or dicamba with or without glyphosate, (2) develop a method for classifying these formulations in crop tissue, and (3) optimize use of chloroacetamide herbicides in dicamba systems for mitigation of selection pressure on dicamba. Formulations evaluated include dicamba diglycolamine (DGA), dimethylamine (DMA), N,N-Bis-(3-aminopropyl) methylamine (BAPMA), and DGA plus potassium acetate (KAc); and 2,4-D DMA, acid, isooctyl ester (ESTER), and choline. Weed management by the chloroacetamides s-metolachlor and acetochlor was evaluated with applications preemergence (PRE), early postemergence (EP), late postemergence (LP), PRE followed by (fb) EP, PRE fb LP, and EP fb LP. Cotton and soybean response differed by 2,4-D and dicamba formulation, and glyphosate presence. Cotton yield was reduced by 200 to 500 kg ha-1 following exposure to 2,4-D choline or DMA relative to acid or ESTER. Glyphosate presence led to a reduction in cotton and soybean yield of 377 and 572 kg ha-1, respectively. Exposure to dicamba DMA resulted in a 263 kg ha-1 reduction in soybean yield relative to dicamba DGA, and glyphosate presence reduced yield by 439 and 246 kg ha-1 in cotton and soybeans, respectively. Chemometric analyses generated models capable of up to 85% accuracy in identifying dicamba formulation in cotton and soybean tissue, and up to 80% accuracy in identifying 2,4-D formulation. Split chloroacetamide applications improved cotton yield up to 60%, reduced weed densities up to 90%, and improved control up to 56% relative to single applications. Cotton height was reduced up to 23% if a single chloroacetamide application was made. Soybean yield was maximized following any chloroacetamide application timing except PRE alone, and weed control was reduced up to 31% following single chloroacetamide application relative to split applications. These results will aid regulatory bodies in managing use of new weed control technologies and will assist producers in stewarding these new technologies.

Off-target herbicide movement onto rice is an annual problem in rice-producing areas within Mississippi. In Mississippi, rice is routinely drill‐seeded in April to early May. Because these dates often coincide with preplant and/or preemergence (PRE) herbicide applications to corn (Zea mays L.), cotton (Gossypium hirsutum L.), and soybean [Glycine max (L.) Merr.], drift onto neighboring rice crops is likely to occur. Although the effects of off-target movement of paraquat on rice may not be visibly apparent, the potential effect on rough rice yield could be detrimental. Field research was conducted at the Delta Research and Extension Center in Stoneville, MS, in 2019, 2020, and 2021 to characterize rice response to exposure to a range of sub-lethal concentrations of paraquat during the vegetative and reproductive growth phases. Other field experiments characterized rice response to exposure to a sub-lethal concentration of paraquat at different stages of reproductive growth. A final field experiment evaluated rice response and barnyardgrass control with labeled herbicides after exposure to a sub-lethal concentration of paraquat.

This study was conducted to determine whether soybean productivity is affected by multiple, sublethal herbicide exposures. The effects of dicamba and 2,4-D on soybean (Glycine max) productivity was investigated at 17 site-years. Relative to a single exposure of dicamba at R1, an additional exposure at either V3 or R3 reduced yield up to 23%. Three or more applications did not further decrease yields relative to an R1&R3 exposure. For 2,4-D, a single application to V3, R1, R3, or R5 soybean did not affect grain yield. However, two exposures of 2,4-D occurring from V3 through R3 reduced yield 5 to 7%. Three or more applications of 2,4-D had no effect on yield relative to exposing soybean to 2,4-D twice between V3 and R3. Exposing soybean to multiple, sublethal rates of auxin herbicides can reduce yield relative to a single exposure and may be most deleterious from flowering to initial pod set.