Cover crops can provide many benefits to peanut and cotton crops planted in rotation including suppressing weeds, conserving soil moisture after termination, increasing soil organic matter, and reducing soil erosion. However, herbicide carryover can affect cover crop establishment. The objective of this study was to investigate the responses of 6 cover crops (daikon radish, cereal rye, oat, crimson clover, winter wheat, and common vetch) to 12 soil residual herbicides. A multiyear (2016–2018), multilocation study was conducted in Macon and Henry counties, Alabama. Herbicide treatments included S-metolachlor, acetochlor, pyroxasulfone, diclosulam, imazapic, chlorimuron-ethyl, bentazon plus acifluorfen, pyrithiobac-sodium, trifloxysulfuron-sodium, diuron, prometryn, and flumioxazin, each applied at 10% of the full-labeled rate. At 42 to 52 and 145 to 149 d after planting (DAP), cover crop plant heights and stand counts were evaluated, as was biomass at 145 to 149 DAP. Treatments varied from year to year but not locations. In 2016, significant stand reductions (P ≤ 0.10) of 36% to 43% in rye and 44% to 75% in wheat were observed at 48 to 52 DAP for S-metolachlor, acetochlor, pyroxasulfone, imazapic, and bentazon plus acifluorfen compared with nontreated plants. Vetch had stand reductions ranging from 14% to 80% for all treatments 50 DAP except for plants treated with prometryn. S-metolachlor, pyroxasulfone, and acetochlor reduced stands of rye, wheat, and vetch more than any other herbicides. In 2017, at 147 to 149 DAP, clover stands were reduced by 29% with diclosulam and by 38% with trifloxysulfuron-sodium. Similarly, radish stands were reduced by 64% with diclosulam treatment. No significant biomass reductions were observed for any cover crop species either year. Oat showed the most tolerance with no treatments reducing any growth parameters either year. Although initial injury and stunting may occur, biomass at termination of cover crops were not affected by herbicide residues evaluated in this study.

Experiments were conducted in 2008, 2009, and 2010 to determine the influence of water source as carrier and other agrochemicals on glyphosate efficacy and physicochemical compatibility. Glyphosate efficacy was not affected by most water sources, when compared with deionized water, although response was not consistent across all weed species, including cereal rye, common lambsquarters, common ragweed, goosegrass, Italian ryegrass, large crabgrass, Palmer amaranth, tall morningglory, and wheat. Control by glyphosate was not negatively affected when coapplied with cloransulam-methyl, dicamba, flumioxazin, pyrithiobac-sodium, thifensulfuron-methyl plus tribenuron-methyl, trifloxysulfuron-sodium, and 2,4-D but was affected by acifluorfen and glufosinate. Calcium, manganese, and zinc solutions consistently reduced weed control by glyphosate, whereas boron seldom affected efficacy. Compared with deionized water, Italian ryegrass control was affected by water sources when applied at seedling and jointing stages more so than at tillering and heading growth stages. Calcium, manganese, and zinc reduced control regardless of growth stage. Precipitates were not produced when glyphosate was applied with the water sources or fertilizer solutions. However, transient precipitates developed when glyphosate was coapplied with cloransulam-methyl, flumioxazin, thifensulfuron-methyl plus tribenuron-methyl, and trifloxysulfuron-sodium but not when coapplied with acifluorfen, dicamba, glufosinate, pyrithiobac-sodium, and 2,4-D. Solution pH ranged from 4.11 to 5.60 after glyphosate was added, regardless of solution pH before glyphosate addition.