Effect of Stage of Growth on Metribuzin Tolerance

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Abstract
Six species of Solanaceae including tomato (Lycopersicon esculentumMill ‘Campbell 28′) were sprayed in the greenhouse at weekly intervals for 4 weeks starting when tomato plants had one true leaf. All species gained tolerance to metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] with age but tomato and black nightshade (Solarium nigrumL.) were the most tolerant and gained tolerance fastest with age. Jimsonweed (Datura stramoniumL.) and eggplant (Solanum melongenaL. ‘Black Beauty’) were the most susceptible species and the ones that gained least tolerance with age. Potato (Solanum tuberosumL.) from true seeds and pepper (Capsicum annuumL. ‘Yolo wonder’) were intermediate in tolerance. In the field, tomato and nine weed species planted in separate plots and kept free from competition were sprayed at weekly intervals starting when tomato plants had one true leaf. Tomato, large crabgrass (Digitaria sanguinales(L.) Scop.), ivyleaf morningglory (Ipomoea hederaceae(L.) Jacq.) and yellow foxtail (Setaria glauca(L.) Beauv.) were the most resistant species to metribuzin and the ones that gained tolerance fastest with age. The most susceptible weeds were velvetleaf (Abutilon theophrastiMedic), common purslane (Portulaca oleraceaL.), pale smartweed (Polygonum lapathifoliumL.), redroot pigweed (Amaranthus retroflexusL.), common lambsquarters (Chenopodium albumL.), and jimsonweed. Low amounts of sunlight during the 3 days before spraying greatly reduced the resistance of tomato to metribuzin.