Research has been done in the United States and Canada to determine the tolerance of cover crops to various soil-applied corn herbicides. This article provides an overview of the results of that work, and provides some consensus across the different locations.
Two important factors influence the potential for carryover injury to rotational crops:
- The sensitivity of the cover crop to herbicide residues.
- How long the herbicide persists in the soil. Herbicides with shorter half-lives (the time it takes for 50 per cent of the active ingredient to dissipate) offer less risk of injury to rotational crops or, in this case, an inter-seed cover crop.
Several factors will influence the rate of dissipation, such as rainfall, soil texture and soil pH. In general, products with a four month or less rotation restriction for the cover crops of interest should pose little risk to establishment. These products typically have half-lives of less than 30 days.
The table at the top of this page provides an estimation of the range of injury levels, as well as consensus on the potential for carryover of some commonly pre-emergence corn herbicides to injure inter-seeded annual ryegrass and clover (crimson and red).
Dr. Darren Robinson is a Horticultural Crop Weed Management Associate Professor at the University of Guelph, and Mike Cowbrough is a weed specialist with OMAFRA