By John Wallace, Ph.D. and Dwight Lingenfelter
Weed regrowth and new seedlings in small grain stubble or fields harvested for corn silage should be controlled prior to cover crop seeding to start clean and give cover crops a competitive advantage. Early September seeding windows allow for the use of diverse cover crop mixtures as well as winter-killed species. Whether you plan to use grass cover crops or diverse mixtures, make sure to consider the following issues related to herbicide program approaches.
Burndown programs prior to cover crop establishment?
It is important to understand the potential for burndown products to impact cover crop establishment due to soil residual activity. The simplest and most risk-free approach is to use only glyphosate or paraquat to start clean prior to cover crop seedings. These broad-spectrum products have no soil residual activity. However, additional products are often needed to control glyphosate-resistant species (horseweed, Palmer amaranth, waterhemp) as well as some other no-till weeds.
Sharpen (1 fl oz) or a glufosinate product (32-43 fl oz; Liberty 280) are options for control of glyphosate-resistant species prior to cover crop seedings. Our field trials suggest that there is limited risk of injury to establishing cover crops when seeding at least 7 days after application of these products. The Liberty label has a 7-day plant-back interval for cover crops and suggests waiting for a half-inch of rainfall prior to seeding cover crops. The use of either Sharpen or glufosinate products prevents legal use of cover crops for forage due to rotation interval restrictions.
Source : psu.edu