Efficacy of Postemergence Herbicides in Soybean Applied at 1 Day before Irrigation.

Abstract

Three experiments were conducted during December 1995-May 1996 in Mae Rim and Mae Taeng district, Chiang Mai province to study the efficacy of postemergence herbicides in soybean when applied at different stages of weed at 1 day before irrigation. Herbicide; quizalofop-p-tefuryl [(±)-tetrahydrofurfuryl(R)-2-[4-(6-chloroquinoxalin-2-yloxy)phenoxy]propanoate] 60 g(ai)/ha, fluazifop-butyl [(±)-2-4 (4-((5 (trichloromethyl)-2-pyrdinyl)oxy)phenoxy)-propanoic acid)] 50 g(ai)/ha, haloxyfop-R-methyl ester [(R-methyl-2-(4-(3-chloro-5(trifluoro-methyl)-2-yridyloxy)phenoxy) propionate)] 54 g(ai)/ha and clethodim ((E, E)-( ±) 2- (1-(((3-chloro-2-propenyl)oxy)aminopropyl)-5- (2-(ethylthio)propy10-3-hydroxy-2-cyclohexen-1-one) 150 g(ai)/ha were applied at the early and late stage of weed growth. The field was irrigated at 1 day after herbicides application by flooding. The herbicides were applied with knapsack sprayer in the spray volume of 375 l/ha. It was found that the posternergence herbicides provided very good control of annual grass weeds; Digitaria sp., Echinochloa cros-galli, Eleusine indica and Setaria sp. The efficacy of postemergence herbicides applied at early stage of weed growth (T1) was better than that the application at later stage (T2) since the weeds at T2 stage were older than at T1 stage. However, the use of postemergence herbicides at T1 or T2 stage could efficiently reduce weed competition in soybean. In cornparison, application of clethodim gave more efficacy on annual grass weed than all other herbicides. The use of postemergence herbicides at the early or late stage of weed growth was able to significantly increase yield of soybean when compared with untreated plot.