INTERROW CULTIVATION TO REDUCE HERBICIDE USE IN CORN FOLLOWING ALFALFA WITHOUT TILLAGE

Information on integrated weed management systems for conservation tillage systems is needed so that producers can minimize the environmental impacts of crop production without sacrificing profitability. Our objective was to evaluate reduced levels of reemergence herbicides in combination with interrow cultivation for weed control in corn (Zea mays L.) planted into an untilled, deteriorated alfalfa stand treated with glyphosate [N-(phosphonomethyl)glycine] the previous fall. Fall application of glyphosate controlled 97% of the perennial vegetation without additional treatment the following spring. Atrazine 16-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine] at 1.1 kg a.i. ha-1 or cyanazine (2-[[4-chloro-6-(ethylamino)1, 3,5-triazin-2-yl]amino]-2-methylpropanenitrile) at 2.2 kg a.i. ha-1 applied within 1 d after corn planting greatly reduced weed densities compared with no herbicide use, but did not control annual weeds as well as a standard treatment (atrazine at 2.2 kg ha-1 plus 2.8 kg a.i. ha-1 metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide]). In most cases, one or two interrow cultivations following atrazine or cyanazine increased control of annual weeds to > 90%, which was similar to the standard treatment. Corn grain yields were affected by varying environmental conditions during the three years of research, but in the two years without drought, integrating cultivation and reduced levels of herbicide resulted in corn yields equal to the standard herbicide treatment. This research indicates that integrating interrow cultivation with reduced levels of herbicide is a sound weed management option for corn planted into untilled, fall-controlled alfalfa stands infested with perennial weeds.