Residual herbicide impact on cover crops utilized within cropping systems for weed suppression
Annual ryegrass (Lolium multiflorum Lam.), and red clover (Trifolium pratense L.) interseeded into V4 corn, and oilseed radish (Raphanus sativus var. oleiformis L.) planted after winter wheat harvest were evaluated for weed suppression. A concern with these practices is how the herbicide applied to the main crop will affect the establishment and growth of the cover crop, and whether the interseeded cover crop competes with the main crop. Experiments were conducted at two locations per study year (2016, 2017) at the University of Guelph Ridgetown Campus. S-metolachlor/mesotrione/atrazine, S-metolachlor/mesotrione/bicyclopyrone and S-metolachlor/mesotrione/bicyclopyrone/atrazine applied preemergence (PRE) caused 91-99% red clover, and 74-94% annual ryegrass injury. S-metolachlor, atrazine and S-metolachlor/atrazine, applied PRE caused 73 to 86%, <1% and 83 to 89% annual ryegrass injury, respectively. As intercrops, annual ryegrass and red clover did not reduce grain corn yields. Bromoxynil/bicyclopyrone and bromoxynil/pyrasulfotole applied postemergence (POST) in winter wheat neither injured nor reduced oilseed radish biomass.