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1 July 2009 Halosulfuron Resistance in Smooth Pigweed (Amaranthus hybridus) Populations
Brian W. Trader, Henry P. Wilson, E. Scott Hagood, Thomas E. Hines
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Greenhouse experiments were conducted to evaluate the response to halosulfuron of several smooth pigweed populations that had been shown to be resistant to acetolactate synthase (ALS, EC herbicides. Five ALS-resistant smooth pigweed populations (R1, R2, R3, R4, and R5) and one susceptible (S) population were treated with halosulfuron POST at 0.27, 2.7, 27, 270, and 2,700 g ai/ha. Percentage injury and dry weight were used to determine resistance of smooth pigweed populations to halosulfuron. Populations of smooth pigweed with previous reports of resistance to ALS-inhibiting herbicides showed varying degrees of resistance to halosulfuron compared with the susceptible population. Concentrations of halosulfuron required to reduce ALS-resistant smooth pigweed dry weights 50% were 2 to 12-fold higher than that of the susceptible population. One population, designated R2, had increased resistance to halosulfuron applications, requiring 97 g/ha halosulfuron to reduce shoot dry weight 50% compared with only 8 g/ha for S. Our results show that populations of smooth pigweed with a history of ALS-inhibiting resistance can have differing degrees of resistance to halosulfuron.

Nomenclature: Halosulfuron; smooth pigweed, Amaranthus hybridus (L.).

Brian W. Trader, Henry P. Wilson, E. Scott Hagood, and Thomas E. Hines "Halosulfuron Resistance in Smooth Pigweed (Amaranthus hybridus) Populations," Weed Technology 23(3), 460-464, (1 July 2009).
Received: 11 August 2008; Accepted: 1 March 2009; Published: 1 July 2009
Acetolactate synthase-inhibiting herbicides
ALS inhibitors
weed resistance
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