Selectivity of SMY 1500 (4-amino-6-tert-butyl-3-ethylthio-l,2,4,triazin-5(4H)-one) in Triticum durum

Susceptibility to SMY 1500 (4-amino-6-tert-butyl-3-ethylthio-1.2.4-triazin-5(4H)-one) was studied in durum wheat (Triticum durum Desf.) cultivars in growth-chamber assays. Weight reduction, photosynthesis inhibition and herbicide levels were determined at various times after a 24-h herbicide 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 tolerant and plants susceptible to SMY 1500. Tolerant cultivars showed a lower herbicide content and photosynthesis inhibition than susceptible plants after the 24-h treatment. Thereafter, herbicide levels and photosystem II inhibition decreased faster in tolerant plants. Comparison with previous work showed that plants tolerated doses of SMY 1500 about four times higher than of its analogue, metribuzin. Herbicide content in leaves just after treatment, and rate of detoxification may explain the selectivity of SMY 1500 in these cereals.