Response of four fall-seeded cover crops to residues of selected herbicides

Currently, there are no published data available to describe the influence of herbicide residues on establishment and function of fall-seeded cover crops. Field experiments were conducted in 2012/2013 and 2013/2014 in Ontario, Canada, to characterize the effects of soil residues of selected herbicides on establishment and function of oat (Avena sativa L.), hairy vetch (Vicia villosa L.), oilseed radish (Raphanus sativus L.) and cereal rye (Secale cereale L.). These cover crops were planted three months after application of imazethapyr at 100 and 200 g ha−1, s-metolachlor/atrazine plus mesotrione at 2880 + 140 and 5760 + 280 g ha−1, and saflufenacil/dimethenamid-p at 735 and 1470 g ha−1. Imazethapyr residues caused up to 65 and 30% visible injury to oilseed radish at 1 and 4 WAE, respectively. Plant light attenuation, shoot dry weight and shoot nitrate-nitrogen uptake from imazethapyr residues three months after application were reduced up to 77, 34 and 43%, respectively in oilseed radish compared to non-treated control. Oat, hairy vetch and cereal rye were not negatively impacted by any of the herbicide residues tested. Preliminary evidence suggests that oat, hairy vetch and cereal rye may be safely seeded three months after saflufenacil/dimethenamid-p, s-metolachlor/atrazine plus mesotrione, and imazethapyr applied PRE at the currently registered rates. It is recommended however, that oilseed radish not be seeded three months after imazethapyr application.