Effect of Herbicide Residues on Spring- and Fall-seeded Cover Crops
Field studies were conducted from 2012 to 2014 to determine the effects of residues of commonly used herbicides on growth and function of four spring-seeded and four fall-seeded cover covers. Imazethapyr was applied PRE to processing pea (Pisum sativum L.) at rates of 100 and 200 g ha-1, s-metolachlor/atrazine plus mesotrione at rates of 2880+140 and 5760+280 g ha-1, and saflufenacil/dimethenamid-p at rates of 735 and 1470 g ha-1 were applied PRE to sweet corn (Zea mays L.). Spring-seeded cover crops (buckwheat (Fagopyrum esculentum Moench), annual ryegrass (Lolium multiflorum Lam.), sorghum sudangrass (Sorghum bicolor (L.) Moench × Sorghum sudanense (P.) Stapf) and spring wheat (Triticum aestivum L.) were seeded one year after herbicide application, and fall-seeded cover crops (oat (Avena sativa L.), hairy vetch (Vicia villosa Roth), oilseed radish (Raphanus sativus L.) and fall rye (Secale cereale L.) were seeded three months after herbicide application. There was a significant difference in the effect of herbicide residues on cover crop growth and development between study years which may be explained by differences in soil and weather conditions. In the spring-seeded cover crops, buckwheat and sorghum sudangrass were sensitive to imazethapyr residues. Annual ryegrass showed sensitivity to s-metolachlor/atrazine plus mesotrione residues. There were no negative effects from the herbicides tested on spring wheat. In the fall-seeded cover crops, there was no negative effect from residues of the herbicides tested except for oilseed radish was very sensitive to imazethapyr soil residues. Therefore, it is recommended that buckwheat, sorghum sudangrass and oilseed radish not be grown following a PRE application of imazethapyr, and annual ryegrass should not be grown after a PRE application of s-metolachlor/atrazine plus mesotrione.