Establishment and Productivity of Alfalfa Following Application of Residual Corn Herbicides

Abstract

Alfalfa establishment failure has been reported in fields where corn was grown the previous season. Mixtures containing clopyralid, mesotrione, acetochlor, and/or flumetsulam have been implicated as a potential factor. To address this, experiments were conducted to assess the impact of these residual herbicides on alfalfa establishment and biomass production following corn. Clopyralid, mesotrione, acetochlor, and flumetsulam were applied into corn (V4) alone or mixed with other active ingredients found in two commercial herbicide premixes (clopyralid + acetochlor + mesotrione and clopyralid + acetochlor + flumetsulam) at two locations and compared to a nontreated control. Soil was collected in November just prior to soil freezing and a greenhouse bioassay evaluated establishment and productivity of three alfalfa cultivars. Alfalfa was then planted the following spring into fields and evaluated for establishment and resulting productivity. Greenhouse results found that locations and cultivars behaved differently to the herbicide treatments. Alfalfa aboveground biomass was reduced 24-38% with mesotrione and flumetsulam and the premix of clopyralid + acetochlor + flumetsulam. Belowground biomass increased when flumetsulam alone was present and in the premix containing mesotrione. Field bioassay did not find any differences in stand establishment or aboveground biomass. While reductions in alfalfa establishment and resulting productivity the year following application were not confirmed, the differences in the fall suggest that the potential exists if adequate breakdown does not occur over the winter/spring.