SULFONYLUREA HERBICIDE RESISTANCE IN COMMON CHICKWEED, PERENNIAL RYEGRASS, AND RUSSIAN THISTLE

Sulfonylurea herbicide resistance was demonstrated in two broadleaf species, common chickweed (Stellaria media [L]. Vill.) and Russian thistle (Salsola iberica Sennen & Pau), and in one grass species, perennial ryegrass (Lolium perenne L.), in greenhouse tests by determining the sulfonylurea and imidazolinone herbicide rates required to reduce the dry weight accumulation of resistant and susceptible weed biotypes. The herbicide resistance in each of the three weed biotypes was due to an acetolactate synthase (ALS) enzyme that was less sensitive to inhibition by ALS-inhibiting herbicides, including five sulfonylurea, one imidazolinone, and one dichlorosulfonanilide herbicides. The Km (pyruvate) and specific activity values associated with ALS isolated susceptible biotypes. Both susceptible and resistant biotypes of each weed species metabolized radiolabeled sulfonylurea herbicides at similar rates, indicating that herbicide metabolism was not contributing to the differential plant response of the biotypes to ALS-inhibiting herbicides. © 1992.