Behaviour of soybean (Glycine max (L.( Merrill) cultivars in response to different application times of metribuzin

In order to evaluate the behaviour of seven soybean cultivars in response to application times of the herbicide metribuzin, an experiment was conducted at the Agronomic Experimental Station of the Federal University of Rio Grande do Sul, located in Guaíba, RS, Brazil, during the 1978/1979 growing season. The cultivars were tested under three application times pre-sowing soil incorporated (PSI), pre-emergence (PRÉ) and postemergence (POS), using 490 g/ha of metribuzin. For visual evaluation of plant toxic ity it was observed that the treatment in PSI caused the greate st phyto toxic effect, while the treatments in PRE and PÓS showed the lowest level of damage. For plant population, the cultivars Planalto, Paraná, and IAS5 showed differentiation in relation to the herbicide application times tested. The grain number produced was the main factor responsible for the differences observed in grain yield. There were significant differences among application times for grain yield the average grain yield observed fo r the appl ications in PRE and PSI were 10 and 21%, lower, respective ly, than the applications in PÓS which produced 2.300 kg/ha.

metribuzin; soybean; cultivars; application times