Evaluation of new generation herbicides in transplanted rice (Oryza sativa.L)

Abstract

An investigation entitled “Evaluation of new generation herbicides in transplanted rice (Oryza sativa L.)” was undertaken during December 2011 to April 2012. The main objectives were to evaluate the weed control efficiency of two new generation herbicides; ie;bensulfuron methyl + pretilachlor and azimsulfuron, in transplanted rice, to assess their selectivity and influence on growth and yield of rice, and to work out the economics. The design was Randomised Block Design and the treatments were , bensulfuron methyl + pretilachlor @ 45+450 g ai ha-1, 60+600 g ai ha-1 and 75+750 g ai ha-1, azimsulfuron @ 25 g ai ha-1, 30 g ai ha-1 and 35 g ai ha-1, hand weeding at 20 and 40 days after transplanting (DAT) and weedy check. The results indicated that both bensulfuron methyl + pretilachlor and azimsulfuron were broad spectrum herbicides. Bensulfuron methyl + pretilachlor, applied as pre emergence herbicide was found effective for controlling weed growth especially during the early crop growth stages and among the three doses tried, bensulfuron methyl + pretilachlor @ 75+750 g ai ha-1 was found performing better than the lower doses. The efficiency of azimsulfuron for managing weeds as a broad spectrum post emergence herbicide was evident from observations on 40 DAT, 60 DAT and at harvest stage. On 40 DAT azimsulfuron @ 35 g ai ha-1 recorded 100 per cent weed control efficiency and at later stages also it was superior to other treatments. Grain yield recorded was significantly higher under azimsulfuron @ 35 g ai ha-1. The next best treatment was hand weeding andit was followed by bensulfuron methyl + pretilachlor @ 75+750 g ai ha-1 and azimsulfuron @ 30 g ai ha-1. Straw yield also was highestin azimsulfuron @ 35 g ai ha-1 but it was on par with bensulfuron methyl + pretilachlor @ 75+750 g ai ha-1, hand weeding and azimsulfuron @ 30 g ai ha-1.The lowest grain and straw yield were recorded underweedy check. The net income under the herbicide treated plots was found to be substantially higher than that of hand weeding and weedy check. Among the various herbicide treatments, the best result was under azimsulfuron @ 35 g ai ha-1.The B: C ratio also confirmed the superiority of the new generation herbicides for weed management in transplanted rice. None of the treatments showed any phytotoxic symptoms on rice plants. The results on soil microbial population showed that the soil samples from the herbicide treated plots had a higher microbial population than that of the untreated plots. Overall inference from the study is that both azimsulfuron and bensulfuron methyl + pretilachlor are promising broad spectrum herbicides for transplanted rice.