SELECTIVITY OF SMY-1500 -6-TERT-BUTYL-3-ETHYLTHIO-1,2,4,TRIAZIN-5(4H)-ONE) IN TRITICUM-DURUM

Susceptibility to SMY 1500 -tert-butyl-3-ethylthio-1,2,4-tri-azin-5-(4 H)-one) was studied in durum wheat (Triticum durum Desf.) cultivars in growth-chamber assays. Weight reduction, photosynthesis inhibition an d herbicide levels were determined at various times after a 24-h herbi cide treatment in two cultivars of durum wheat, one cultivar of spring wheat (Triticum aestivum L.), and in the weed Bromus diandrus (Roth). Measurements of weight reduction distinguished between plants toleran t and plants susceptible to SMY 1500. Tolerant cultivars showed a lowe r herbicide content and photosynthesis inhibition than susceptible pla nts after the 24-h treatment. Thereafter, herbicide levels and photosy stem II inhibition decreased faster in tolerant plants. Comparison wit h previous work showed that plants tolerated doses of SMY 1500 about f our times higher than of its analogue, metribuzin. Herbicide content i n leaves just after treatment, and rate of detoxification may explain the selectivity of SMY 1500 in these cereals.