Tolerance of Tomato (Lycopersicon esculentum) Cultivars to Metribuzin

Twenty-six cultivars of tomatoes from several countries were divided into four metribuzin [4-amino-6- tert -butyl-3-(methylthio)-1,2,4-triazin-5(4 H )-one] tolerance groups: tolerant, semi-tolerant, semi-susceptible, and susceptible. Early maturity and tolerance to metribuzin were correlated (r = −0.78) in the field experiment and (r = −0.72) in a sinking leaf-disc bioassay. New super early cultivars were especially sensitive to metribuzin. Chlorophyll a and b content were not highly correlated with tolerance to metribuzin. Metribuzin rates used for weed control are close to toxic concentrations for very early cultivars of tomatoes. Plants in the 9-leaf stage were less sensitive than plants in the 5- or 7-leaf stage. Metribuzin tolerance came at later stages in early maturing cultivars than in later maturing cultivars.