Herbicide Resistant Weeds

Common cocklebur (Xanthium strumarium) resistance to selected ALS-inhibiting herbicides.

Sprague, C. L., E. W. Stoller, and L. M. Wax. 1997. Common cocklebur (Xanthium strumarium) resistance to selected ALS-inhibiting herbicides. Weed Technology. 11: 241-247.

Five biotypes of common cocklebur that were not controlled with acetolactate synthase (ALS)-inhibiting herbicides were tested in greenhouse and laboratory studies to determine the magnitude of resistance and cross-resistance to four ALS-inhibiting herbicides. In vivo inhibition of ALS was also evaluated. Based on phytotoxicity, all five ALS-resistant biotypes of common cocklebur were >390 times more resistant than the susceptible biotype to imazethapyr. However, only four of these biotypes were also resistant to another imidazolinone, imazaquin. Two biotypes were cross-resistant to the sulfonylurea, chlorimuron, and the triazolopyrimidine sulfonanilide, NAF-75 (N-(2-carboxymethyl-6-chlorophenyl)-5-ethoxy-7-fluoro(1,2,4)triazolo-(1,5c)-pyrimidine-2-sulfonamide). One biotype demonstrated intermediate susceptibility to imazaquin, chlorimuron and NAF-75. In all cases, the resistance exhibited at the whole plant level was associated with an insensitive ALS.