Efficacy and selectivity of 2,4-D applied at different rates, growth stages and formulations in paddy rice

Abstract

An experiment was carried out at Epagri, in Itajaí, Santa Catarina State (26°56'35"S and 48°45'37"W), during 1996/ 97 and 1997/98 growing seasons, to evaluate the efficacy and selectivity of 2,4-D herbicide at four rates, two times of application and two formulations, in infested rice. Herbicides were applied postemergence, with rice plants at the 3-4 leaf stage, and late postemergence, 38-39 days after planting. Herbicide formulations and rates evaluated were: 2,4-D amine at 200,400,800 and 1200 g/ha a.e. (acid equivalent) and ester at 56, 112,224 and 336 g/ha a.e. Overall results showed that higher 2,4-D rates of both formulations at both application timings, injured rice. However, crop injury did not increase spikelet sterility because the rice cultivar was a late season variety and lhe second application was carried out at least 30 days before panicle differentiation. Herbicide 2,4-D, ester or amine, applied postemergence, at low rates (100 g/ha a.e. of ester formulation or 200 g/ha a.e. of amine formulation), controlled Fimbristylis miliacea, Ludwigia longifolia, and L. octovalvis. Heteranthera reniformis was less sensitive to 2,4-D, and higher rates were required for good control. These results suggest that 2,4-D application in rice should be carried out before tillering because, in such conditions, even low rates ofthe herbicide would provi de good broadleaf and sedge control, besides minimizing crop injury.