Abstract

With the intent to control glyphosate–resistant and hard to control weeds, a formulation of 2,4-D choline (24.4%) and glyphosate (22.1%) (Enlist Duo™ herbicide) (Note 1) has been developed recently to be used post-emergence in corn and soybean tolerant to Enlist Duo™ in the United States. Dose response studies were conducted under greenhouse conditions for the evaluation of effective rates of Enlist Duo™ to control glyphosate-resistant common waterhemp (Amaranths rudis Sauer), giant ragweed (Ambrosia trifida L.), and kochia [Kochia scoparia (L.) Schrad] and to determine the effect of growth stage of these weeds on the efficacy of Enlist Duo™. Three parameter log-logistic models were used to develop dose response curves. Glyphosate-resistant giant ragweed was the most sensitive of the three weed species, followed by common waterhemp, and kochia. Based on the visual control or injury estimates, the Enlist Duo™ rates required for 90% control (ED₉₀) of common waterhemp, giant ragweed, and kochia were 1179, 825, and 4,382 g ae ha^-1, respectively, for 10-cm tall plants compared to 2,480, 1,101, and 5,305 g ae ha^-1, respectively, for 20-cm tall plants at 21 days after treatment (DAT). The ED₉₀ values calculated on the basis of percent shoot biomass reduction and visual control or injury estimates were usually similar at 21 DAT. The greenhouse studies indicate that Enlist Duo™ can effectively control less than or equal to 20-cm tall glyphosate-resistant giant ragweed and less than or equal to 10-cm tall glyphosate-resistant common waterhemp at the recommended rate (1,640 g ae ha^-1).

This work is licensed under a Creative Commons Attribution 4.0 License.