Herbicide combinations for weed management in direct-seeded rice

Abstract

Ten treatments were evaluated during Kharif 2013, 2014 and 2015 at Palampur (Himachal Pradesh) to study their impacts on weeds, crop and economics. Echinochloa colona was the most competitive weed followed by Aeschynomene indica and Panicum dichotomiflorum. Oxadiargyl fb bispyribac, pyrazosulfuron fb bispyribac, pendimethalin fb bispyribac fb manual weeding and bispyribac + chlorimuron + metsulfuron-methyl gave significantly lower count of E. colona and Panicum dichotomiflorum. The economic threshold levels (no/m2) with the weed management practices studied varied between 2.5–17.8/m2. With every 1 weed/m2 increase in density, the grain yield of dry-seeded rice was reduce by 62.4 kg/ha. Manual weeding engaged more labour and had higher cost tending to increase the economic threshold over herbicidal treatments. Cost of weed control under herbicidal/integrated treatments was 14–49% of weed free and 19.9–69.3% of that under mechanical weeding. Oxadiargyl fb bispyribac resulted in highest net return due to weed control. Crop resistance index and efficiency index were highest and weed index was minimum under pendimethalin fb bispyribac fb manual weeding. Weed management index, agronomic management index and integrated weed management index were highest under pendimethalin fb manual weeding followed by bispyribac, pendimethalin fb bispyribac and mechanical weeding. The overall performance index (OPi) was highest under pendimethalin fb bispyribac fb manual weeding (1.34) followed by oxadiargyl fb bispyribac (1.31), pyrazosulfuron fb bispyribac (1.18), bispyriac + chlorimuron + metsulfuron (1.14) and bisppyribac (1.12). Weeds reduced the grain yield of rice by 67.1%.