Residual Herbicides and Fall Cover Crop Establishment
Recently there has been increased interest in utilizing cover crops in corn and soybean production systems because of government-sponsored cost share programs and soil health benefits, write Purdue Extension Weed Science specialists Bill Johnnson and Travis Legleiter. Concurrently, there has also been increased utilization of soil residual herbicides in corn and soybean production systems to help manage herbicide-resistant weeds such as marestail, pigweeds, and ragweeds. Soil residual herbicides can remain active in the soil for anywhere from weeks to months after application. The length of time a residual herbicide remains biologically active in the soil is influenced by soil type, soil pH, organic matter, rainfall, and temperature. Since these factors will vary from field to field, definitive time intervals of residual herbicide activity can be difficult to predict.
A significant challenge has arisen because use of residual herbicides in corn and soybean production systems may interfere with establishment of fall seeded cover crops. An unfortunate coincidence is that many of the crops being used for cover crops were not evaluated for herbicide carryover when field research was being conducted for support of the EPA label of the respective herbicide. As a result, data are lacking regarding rotational intervals for establishment of many cover crop species.
Over the last couple of growing seasons Purdue has established experiments designed to evaluate the impact of commonly used residual herbicides on the establishment of many cover crop species.