Tolerance of interseeded annual ryegrass and red clover cover crops to residual herbicides in Mid-Atlantic corn cropping systems

Authors: WALLACE, JOHN - Pennsylvania State University; CURRAN, WILLIAM - Pennsylvania State University; Mirsky, Steven; RYAN, MATT - Cornell University

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2017
Publication Date: 9/1/2017
Citation: Wallace, J.M., Curran, W.S., Mirsky, S.B., Ryan, M.R. 2017. Tolerance of interseeded annual ryegrass and red clover cover crops to residual herbicides in Mid-Atlantic corn cropping systems. Weed Technology. 31:641-650.

Interpretive Summary: Cover crops are crops that are typically not planted for harvest, but rather to provide economic and environmental benefits in cropping systems. For example, legume cover crops fix nitrogen, which can decrease the amount of fertilizer that needs to be applied to a following cash crop and thus fertilizer costs; grass cover crops protect the soil from erosion. In spite of the well-documented benefits of cover crop use, relatively few farmers grow cover crops. One major reason for low cover crop adoption is the difficulty in establishing a cover crop after corn harvest, before the onset of winter weather. Researchers are experimenting with interseeding cover crops when corn is less than two feet tall using specialized interseeder equipment. The cover crops germinate and emerge and then go dormant once the corn begins to shade them. As soon as corn is harvested, the increased light levels prompt the cover crops to grow and become well-established prior to freezing weather. A common interseeded cover crop mixture consists of annual ryegrass (a grass) plus red clover (a legume). However, herbicides applied to the cash crop in which the cover crop is interseeded may damage cover crops due to residual soil activity, interfering with the viability of interseeding as a way to incorporate cover crops into corn-based rotations. The purpose of this research was to test the impact on annual ryegrass and red clover of herbicides used to control either grasses or broadleaf weeds. Among the grass herbicides tested, s-metolachlor, pyroxasulfone, pendimethalin and dimethenamid-P damaged annual ryegrass when compared to the control; acetochlor did not cause damage. As would be expected, none of the grass herbicides tested damaged red clover. Among the broadleaf herbicides, mesotrione caused notably significant damage to red clover, while saflufenacil, rimsulfuron, and atrazine did not. As would be expected, none of the broadleaf herbicides damaged annual ryegrass. The impact of herbicides varies by herbicide, location, and weather and soil conditions. This research promotes the use of cover crops by adding to the basis for herbicide and cover crop recommendations to farmers who wish to establish cover crops via interseeding. This information will be useful to scientists developing strategies to integrate cover crops into cropping systems.

Technical Abstract: In the Mid-Atlantic region, there is increasing interest in the use of relay-cropping strategies to establish cover crops in corn cropping systems. Recent studies have demonstrated the potential to establish annual ryegrass and red clover cover crops at the V5 corn growth stage using a high-clearance no-till grain drill. However, this strategy may be limited by injury to cover crops from residual herbicide programs. We conducted field experiments from 2013 to 2015 at Pennsylvania, Maryland and New York locations (8 site-years total), to evaluate the effect of common residual corn herbicides on interseeded red clover and annual ryegrass. We tested 22 herbicide treatments in at least two-site years and collected cover crop biomass in late-fall to evaluate herbicide injury. Cover crop establishment and response to herbicide treatments was variable across study locations. In 2014, red clover and annual ryegrass biomass were greatly reduced (> 45%) across herbicide treatments at the MD location, whereas negligible to moderate (< 20%) biomass reductions were observed at other locations. Among herbicides commonly used for annual grass control, s-metolachlor, pyroxasulfone, pendimethalin and dimethenamid-P resulted in reduced annual ryegrass biomass relative to the untreated check, whereas annual ryegrass biomass in acetochlor treatments was no different than the untreated check. The rank order of observed annual ryegrass biomass reduction among chloroacetamide herbicides was s-metolachlor > pyroxasulfone > dimethenamid-P > acetochlor. Red clover biomass was not reduced by any of the grass herbicides. Among herbicides used for broadleaf weed control, mesotrione resulted in significant (80%) red clover biomass reduction compared to the untreated check. No differences in red clover biomass were observed between saflufenacil, rimsulfuron and atrazine treatments from the untreated check. Annual ryegrass was not reduced by any of the broadleaf herbicides. This research shows that annual ryegrass and red clover can be interseeded following use of several shorter-lived residual corn herbicides, but that longer-lived residual herbicides likely preclude interseeding practices in corn cropping systems in the Mid-Atlantic region. We also demonstrate that the potential for herbicide injury to interseeded cover crops can vary significantly across different soil and environmental conditions.