Journal of Crop Production and Processing

Field study was conducted in order to evaluate the efficacy of new herbicide quinclorac to control barnyardgrass and bulrush, the most important weeds of paddy rice. Treatments consisted of rice cultivars (Hashemi and Khazar) and quinclorac rates (50, 100, 200 and 400% the recommended dose), recommended dose of butachlor and quinclorac, each alone and plus bensulfuronmethyl (BSM), weedy and hand weeded control. Results showed that bulrush control was variable, depending on rice cultivar and herbicide treatments. Neither butachlor nor quinclorac controlled bulrush effectively. Bulrush produced 47% more biomass in Khazar cultivar compared with Hashemi averaged over treatments. The most consistent bulrush and barnyardgrass control occurred with BSM + butachlor but quinclorac + BSM. Control of barnyardgrass with quinclorac varied from 48 to 100% depending on dose and time of evaluation with high efficacy early season and gradually decreased residual effect toward the end of the season. Butachlor and quinclorac responded similarly in barnyardgrass control in recommended dose. Visual evaluation showed no symptom of phytotoxicity on both rice cultivars in vegetative stage, but quinclorac caused irregular panicles with abnormal growth emerged from aboveground nodes in Hashemi cultivar. Treatments efficacy in weed control was reflected well in grain yield ranged from 21 to 97% compared with hand weeded control, the greatest in butachlor + BSM and the least in weedy check. Biological yield response to treatments was similar to grain yield. Harvest index was not affected by herbicide treatments in Hashemi, but decreased in Khazar except for quinclorac in 4 times the recommended dose, and butachlor + BSM. Overall quinclorac efficacy in barnyardgrass control was eligible, both inadequate in bulrush control and Khazar cultivar provided better ecological niche for bulrush invasion.