Herbicide application timing in preharvest desiccation of soybean cultivars with different growth habits

In order to evaluate the ideal time of herbicide applications to desiccate soybean cultivars with determinate and indeterminate growth habits in preharvest, an experiment was carried out at the University of Ponta Grossa (PR), during 2002--2003. The experimental design used was a randomized blocks arranged in a factorial scheme 4 x 5 (herbicides and time of application), with three replications, using four soybean cultivars: Spring, V-Max, BR-16, and BRS-133. The herbicides glufosinate, diquat, and paraquat were used at the rate of 400 g ha(-1), when soybean was at stage of R6.0, R6.5, R7.0, R7.5, and R8.0. The assessments included yield, as well as yield components, considering each cultivar separately. The results show that desiccation should be done on cultivars with determinate growth habit at stages between R7.0 and R7.5, independent of herbicide used. For indeterminate growth habit cultivars, desiccation should be done later, because those pods formed after R6.5 stage are important to define yield; although herbicides have different mode of action, yield results were similar. In cultivars, desiccation should start when all pods in the middle of plants become yellow and grains are not held by fibers.