Faculty Mentor

Dr. Sharon Clay


Spring preemergence herbicide applications are often used for burndown of existing weeds and residual control, eliminating weed presence during early season crop growth. There has been an increase in the interest in planting cover crops soon after cash crop removal, due to the potential soil and production benefits. However, soil herbicide residuals may result in poor cover crop growth. This study examined the growth of radish (Raphanus sativa) and rye (Secale cereal), species often used as cover crops, in soils that had been treated with residual herbicides about 100 d prior to cover crop planting. The herbicides were applied at recommended rates to silage corn in mid-May to early June at two sites, at a southern site near Beresford, SD (Egan-Trent Silty Clay Loam soil), and a northern site near Groton, SD (Beotia Silt Loam soil). Soil samples were collected in mid-September, and greenhouse studies were conducted to examine if herbicide activity was great enough to injure the cover crops. Plant height, and fresh weights of shoots and roots were compared to these parameters in plants grown in herbicide-free soil after six weeks of growth using a one-way paired t-test. Radish growth was unaffected by any herbicide. Several herbicides applied to the Groton soil reduced rye shoot weight, whereas in the Beresford soil, several herbicides reduced rye shoot height and root weight. Rye shoot weight was reduced by 59% in Warrant treated soil at Beresford, however, at Groton, three herbicides reduced shoot weight by about 25% (Python, Warrant, and Spirit). Rye shoot height was reduced by about 23% by two herbicides (Parallel, Warrant) in Groton soil and by about 16% by three herbicides (Glory, Python, Acuron) in the Beresford soil. Rye root weight was reduced by 35% or more by five herbicides (Parallel, Glory, Python, Warrant, and Acuron) in the Beresford soil, but only by Warrant (44%) in the Groton soil. These data indicate that herbicide residuals can be present in high enough concentrations after a short season crop to injure fall planted cover crops and that injury is herbicide, crop species, and soil specific. Further studies are needed to understand the influence of specific soil, herbicide, climatic conditions, and cover crop species where herbicide injury is possible. The results can be used by growers to select herbicide/cover crop species combinations that will be most successful for their farm.



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