Abstract :
Velvetleaf is one of the most troublesome weeds in soybean and cotton in Mazandaran. Field study was conducted in Sari, Mazandaran (Iran) to evaluate the effect of reduced rates of bentazon at various growth stages of velvetleaf. The experiment was initiated as a factorial design in a randomized complete block with four replications in 2007. Bentazon at 0.84 (recommended rate), 0.67, 0.59, 0.50, 0.42 and 0.25 kg ai ha-1 were applied on a 6, 18, 33, and 54 cm velvetleaf. There was a possibility of 70% reduction in bentazon rate when applied on 6-cm velvetleaf. This rate (0.252 kg ai ha-1) provided 94% control of velvetleaf. Bentazon application at 0.42 kg ai ha-1 gave 96% control of 18-cm velvetleaf. As velvetleaf height reached to 33 cm, the only reduce rate which provided 86% control, was bentazon application at 0.672 kg ai ha-1. When bentazon applied at 54 cm velvetleaf, none of theses rates gave acceptable control and the recommended rate provided only 46% control at 2 weeks after of bentazon. These results indicated that there is a possibility of reduction in bentazon rates (even 70%) if herbicide is applied at the right growth stages of weed.
