Residual herbicides in corn and their effect on fall-planted cover crop species

The use of residual herbicides as a part of preemergence (PRE) and in-season layered treatments has proven to be an effective strategy for controlling late-emerging broadleaf weed species in annual crops. However, the use of residual PRE herbicides has the potential to negatively affect other crops within an annual two-crop rotation, such as fall-planted cover crops. The intent of this study was to determine if PRE herbicides commonly used in the upper Midwest United States would affect stand density, height, and biomass production of fall-planted cover crops. Field studies were conducted at three locations that differed in soil type and climate. Four PRE herbicides were applied in silage corn (Zea mays L.) in the spring: dimethenamid-P (single application), dimethenamid-P + saflufenacil, acetochlor + clopyralid + mesotrione, and a layered treatment of dimethenamid-P at planting and 30 days after first application. Three cover crops were planted in the fall following silage corn harvest with a no-till drill: winter cereal rye (Secale cereale L.), winter camelina (Camelina sativa L.), and red clover (Trifolium pratense L.). Although some of the PRE HBs tested affected cover crop spring plant density and height in sandy soils, there was no difference in cover crop biomass production at termination between herbicide treatments, regardless of soil type. These results indicate that the application of these residual PRE herbicides for control of late-emerging weed species did not interfere with cover crop biomass production as long as soil moisture was not limiting. Cover crop plant density and height was reduced by some herbicides in sandy soils.Cover crop biomass at termination was not affected by herbicides regardless of location.Preemegence herbicides and fall-planted covers are compatible provided adequate soil moisture occurs during the growing season.