The basis for differences in response of eastern black nightshade (Solanum ptycanthum Dun.), a tolerant species, and velvetleaf (Abutilon theophrasti Medic. ♯3 ABUTH), a susceptible species, to foliar-applied chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide} was investigated by evaluating differences in spray retention and herbicide absorption, translocation, and metabolism. Based upon a foliar-applied rate causing a 50% reduction in dry weight, velvetleaf was greater than 20000 times more susceptible to chlorsulfuron than was eastern black nightshade. The differences detected in spray retention, absorption, and translocation were inadequate to account for the large response differences between the two species. The primary difference found was in the rate of chlorsulfuron degradation. In eastern black nightshade, 69.9% of the absorbed chlorsulfuron was metabolized within 24 h of application and 81.1% within 72 h of application. Only 7.1% of absorbed chlorsulfuron was metabolized in velvetleaf in a 72-h period.
