Field experiments were conducted near Blackville, SC, and Tifton, GA, in 2004 and 2005, to evaluate the effect of wild radish and rye cover crops on weed control and sweet corn yield when used in conjunction with lower-than-recommended herbicide rates. Cover crop treatments included wild radish, rye, and no cover crop, alone and in conjunction with half and full rates of atrazine (0.84 and 1.68 kg ai ha−1) plus S-metolachlor (0.44 and 0.87 kg ai ha−1) applied before sweet corn emergence. Florida pusley, large crabgrass, spreading dayflower, ivyleaf morningglory, and wild radish infested the test sites. Wild radish and rye cover crops without herbicides reduced total weed density by 35 and 50%, respectively, at 4 wk after planting (WAP). Wild radish in conjunction with the full rate of atrazine plus S-metolachlor controlled Florida pusley, large crabgrass, and ivyleaf morningglory better than rye or no cover crop treated with a full herbicide rate in 2004 at Blackville. In 2005, at Blackville, weed control in sweet corn following wild radish cover crop plots alone was not different from that following rye. Wild radish or rye in conjunction with a half or full rate of atrazine and S-metolachlor controlled > 95% Florida pusley, wild radish, and large crabgrass in sweet corn at Tifton during both years. Ten glucosinolates, potential allelopathic compounds, were identified in wild radish, including glucoiberin, progoitrin, glucoraphanin, glucoraphenin, glucosinalbin, gluconapin, glucotropaeolin, glucoerucin, glucobrassicin, and gluconasturtin. Sweet corn yields at Blackville and Tifton following wild radish or rye cover crops were similar between the half and full rates of atrazine plus S-metolachlor. Sweet corn in wild radish or rye cover crop plots without herbicides produced less-marketable ears than herbicide-treated plots, indicating that a combination of cover crops and herbicides are required to optimize yields and to obtain desirable weed control.

A 2-yr field study was conducted in Blackville, SC, to assess the potential for using small-grain cover crops and glyphosate as a means of reducing or eliminating the need for atrazine in irrigated Southeastern corn production. Oats, rye, and wheat were no-till, drill seeded each fall and subsequently desiccated in early spring before corn planting. A bareground conventional tilled treatment also was included. Within each cover crop system, the herbicides evaluated included (1) no herbicide; (2) 1.68 kg ai/ha atrazine plus 1.08 kg ai/ha S-metolachlor at corn planting followed by 0.84 kg ae/ha glyphosate; or (3) two applications of 0.84 kg/ha glyphosate alone, applied sequentially. All systems were compared with conventional tillage without a cover crop with 1.68 kg/ha atrazine plus 1.08 kg/ha S-metolachlor at planting followed by 1.12 kg/ha atrazine. Biomass of rye, oats, and wheat at dessication was 497, 369, and 340 g/m2, respectively. All cover crops delayed early-season corn growth. Detrimental effects on early-season corn growth from the oats cover crop were still apparent 7 wk after emergence (WAE), with corn height and biomass reduced 8 and 19%, respectively. Weed biomass in nontreated plots was reduced 84, 68, and 21% by oats, rye, and wheat, respectively, 3 WAE. Oats were more inhibitory of corn and weed growth than rye, although rye produced greater surface residue, indicating possible allelopathy affects. In the presence and absence of each cover crop, atrazine plus S-metolachlor followed by glyphosate or sequential glyphosate applications alone were effective in providing season-long control of pitted morningglory, entireleaf morningglory, Palmer amaranth, Florida pusley, large crabgrass, and common bermudagrass. Corn yields and gross profit margins in sequential glyphosate–treated plots were equivalent or superior to the standard atrazine-based program, which indicates that effective and economical alternatives to atrazine are available.