Use of Herbicides to Control Weeds for Increasing Soybean Yield after Rice Cultivation

Abstract

The objective of this study was to investigate the use of herbicides to control weeds to increase soybean yield after rice cultivation in the dry season, from October 2015 to September 2018, at Chiang Mai Field Crops Research Center. Design of the experiment was RCB with 4 replications, and the 7 treatments were alachlor, 240 g.a.i/rai spray mulching after planting, imazethapyr 20 g.a.i/rai at 7-10 days after planting (DAP), fluazifop-P-butyl + fomesafen 24 + 40 g.a.i/rai, quizalofop-P-tefuryl + fomesafen 12 + 40 g.a.i/rai, haloxsifop-R-methyl+fomesafen 20+40 g.a.i/rai, fenoxaprop-P-ethyl+fomesafen 12+40 g.a.i/rai at 15-20 DAP and control (no weeding). Results revealed that all treatments showed low to moderate level phytotoxicity to soybean. The treatment of fluazifop-P-butyl + fomesafen 24+40 g.a.i./rai gave good controls of grass and broadleaf weeds and was better than other treatments. Yields of the treated plots were significantly higher; all treatments increased soybean yield by 57-65 percent when compared with no weeding. Applications of haloxsifop-R-methyl + fomesafen, fluazifop-P-butyl+fomesafen and quizalofop-P-tefuryl+fomesafen gave maximum yield (307, 307 and 294 Kg./rai respectively) and benefit cost ratio (BCR) more than 1 (worth investing).The application of  fluazifop-P-butyl + fomesafen at 24 + 40g.a.i/rai had the highest value of investment. However,haloxsifop-R-methyl or quizalofop-P-tefuryl could be substituted for fluazifop-P-butyl because they were similarly cost-effective.