Bioefficacy of herbicides against weeds in greengram (Vigna radiata) and their residual effect on succeeding Indian mustard (Brassica juncea)

Abstract

An experiment was carried out during the rainy season of 2012 and 2013 at Hisar, Haryana, to study the efficacy of different herbicides against weeds in greengram [Vigna radiata (L.) R. Wilezek] and their carry over effect on succeeding Indian mustard [Brassica juncea (L.) Czernj & Cosson]. Post emergence (PoE) application of imazethapyr at 50 and 70 g/ha and imazethapyr + imazamox (RM) at 60, 70 and 80 g/ha significantly reduced the density and dry weight of weeds compared to weedy check, although, PoE application of both these herbicides caused phytotoxicity to greengram. At 30 days after sowing (DAS), dry weight of weeds was minimum (2.1 and 7.8 g/m2 ) in pre-emergence (PRE) application of imazethapyr +pendimethalin (RM) at 1,000 g/ha in 2012 and 2013 respectively, but at 60 DAS, PoE use of imazethapyr and its ready-mix combinations with imazamox caused significant reduction in weed dry matter. Higher doses of imazethapyr (60 and 70 g/ha) and its ready-mix combination with imazamox applied at 3–4 leaf-stage caused 11.3–23.3% toxicity to greengram which mitigated within 15 days after application during both the years. Presence of weeds throughout the season caused 85.6 and 70.9% reduction in grain yield of greengram during 2012 and 2013 years respectively. Grain yield was the maximum in weed free treatment during both the years, which was at par with post emergence application of imazethapyr at 50 and 70 g/ha and imazethapyr + imazamox (RM) at 60 g/ha in 2012; but during 2013, imazethapyr + imazamox (RM) at 80 g/ha applied at 3–4-leaf stage recorded the maximum seed yield (995 kg/ha). No residual effect of different herbicides applied to greengram at various rates was observed on Indian mustard due to enhanced microbial degradation of these herbicides, as heavy rainfall occurred between time of herbicide application and planting of Indian mustard.