Growth Stage Affects Dose Response of Selected Glyphosate-Resistant Weeds to Premix of 2,4-D Choline and Glyphosate (Enlist Duo™ Herbicide*)

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 (ED 90 ) 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 ED 90 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 ).

An integrated approach to control glyphosate‐resistant Ambrosia trifida with tillage and herbicides in glyphosate‐resistant maize

“…In glasshouse studies, Chahal et al . () and Ganie et al . () reported that A. trifida control declined and higher herbicide rates were needed for effective control at 20 cm height compared with 10 cm height following application of 2,4‐D choline plus glyphosate and fluthiacet‐methyl plus mesotrione respectively.…”

EPSPS Gene Copy Number and Whole-Plant Glyphosate Resistance Level in Kochia scoparia

“…scoparia was first identified in Kansas [7] and has now been identified in multiple Great Plains States including Colorado, South Dakota, North Dakota [8], Montana [9], Nebraska [10], and in the Canadian provinces of Alberta [11], Saskatchewan and Manitoba [12]. Most of the reported GR K .…”

Glyphosate-Resistant Weed Control and Soybean Injury in Response to Different PPO-Inhibiting Herbicides

“…Wats.] have been confirmed resistant to glyphosate (Chahal et al, 2015a;. The occurrence of GR weeds is a serious concern, particularly for midwestern soybean growers, because of limited effective POST herbicide options.…”