Spring‐applied corn herbicides impact fall‐planted cover crops in South Dakota

Abstract

AbstractEarly spring herbicide applications can have residuals that impede fall‐planted cover crop growth. A greenhouse study examined radish (Raphanus sativus L.) or rye (Secale cereale L.) growth in silty clay loam (southeastern South Dakota) and silt loam (north‐central South Dakota) where corn herbicides had been applied about 120 d prior to collection. S‐metolachlor, acetochlor, flumetsulam, metribuzin, bicyclopyrone + mesotrione + S‐metolachlor + atrazine, and primisulfuron‐methyl + prosulfuron (northern site only) were applied at the suggested timing and highest recommended rate and planted to corn (Zea mays L.). Two 11‐cm diam. soil cores to a 10‐cm depth were collected per plot after silage harvest, with nontreated soils also collected. Soil was mixed within each core and two subsamples were placed into conetainers and planted with four seeds of the crop species. Plant height, and fresh shoot and root weights were quantified after 6 wk and compared to growth in nontreated soil. Radish was unaffected by any herbicide in either soil. Rye growth was influenced by soil and herbicide. In the silt loam, rye shoot biomass was reduced 15–25% by flumetsulam, acetochlor, and primisulfuron + prosulfuron; and acetochlor reduced root biomass by 44%. In the silty clay loam, acetochor reduced shoot biomass by 59%; and all treatments reduced root biomass by 35% or more. These data suggest that spring herbicide applications and cover crop species should be carefully matched to help in cover crop success.