Liz Bosak, Outreach Specialist, Department of Agronomy, University of Wisconsin-Madison
Tough, cold Wisconsin winters translate into fewer cover crop species requiring spring termination before planting. For a quick chart of cover crop species that tend to winterkill, download the “Cover Crop Termination” fact sheet at https://host.cals.wisc.ed/wcws/wp-content/uploads/sites/54/sites/4/2013/03/WCWS_204_cover_crop_termination_WEB.pdf . Here is a short list of the cover crops that will need to be terminated in the spring: winter (cereal) rye, winter barley, winter wheat, winter triticale, red clover, sweet clover, and hairy vetch. There are a few cover crops that may or may not winterkill depending on the severity of winter and degree of snow cover; these include canola, winter pea, and annual ryegrass. If cereal rye will be harvested for forage, then consult the herbicide rotational restrictions fact sheet, http://wcws.cals.wisc.edu/wp-content/uploads/sites/54/sites/4/2013/03/WCWS_201_Herbicide_Rotation_Restrictions_WEB.pdf . For overwintering cover crops sown after winter wheat, some may prefer to terminate in the fall to simplify their spring planting schedule.
At Arlington Agricultural Research Station, cereal rye, planted during the first week of September, is ready to be terminated prior to planting soybean (Fig. 1). A general rule of thumb for termination of cereal rye with herbicides is to target the application before it reaches 18 inches in height. In another field trial, cereal rye planted in October can definitely be given some time to grow before termination (Fig. 2). There are a few termination methods for cereal rye outlined in the fact sheet including rolling-crimping, mowing, and applying herbicides. For the no-till soybean research fields planted with a cereal rye cover crop, typically we use glyphosate and 2,4-D ester (0.5 lb ai/A) seven days before planting to terminate the rye. Otherwise, glyphosate (4.5 lb ae per gal, 22 fl oz/A) will terminate the winter grasses: rye, barley, triticale, and wheat. Recommendations for red clover, sweet clover, and hairy vetch are in the fact sheet.
Annual ryegrass or Italian ryegrass can be a concern for spring termination because it can be challenging to predict winterkill and to terminate, if necessary. In the 2014 field season, annual ryegrass overwintered in all of the field research plots at Arlington. However, this year annual ryegrass experienced partial winterkill (Fig. 3). To ensure termination success, plan on applying glyphosate at the full labeled rate before the ryegrass reaches 6 inches in height with the understanding that two applications may be necessary, see page two of the factsheet, https://host.cals.wisc.edu/wcws/wp-content/uploads/sites/54/sites/4/2013/03/WCWS_204_cover_crop_termination_WEB.pdf. Also, be aware that annual ryegrass has shown resistance to five different herbicide sites-of-action and is one of the eleven weeds that weed scientists have identified as a serious resistance threat, http://takeactiononweeds.com/wp-content/uploads/sites/54/2014/01/Weed_Chart_Poster.pdf . The United Soybean Board and its TakeAction campaign worked with university weed scientists to develop a fact sheet specific to managing ryegrass, available here http://takeactiononweeds.com/wp-content/uploads/sites/54/FactSheet_ItalianRyegrass.pdf . For more information on terminating annual ryegrass, Purdue University has a great fact sheet, https://www.extension.purdue.edu/extmedia/ws/ws-50-w.pdf . More cover crop resources, on an array of topics, are available at Cooperative Extension’s cover crop website, http://fyi.uwex.edu/covercrop .