Pyrithiobac and Insecticide Coapplication Effects on Cotton Tolerance and Broadleaf Weed and Thrips (Frankliniella spp.) Control1

Field studies investigated possible interactions associated with early-season coapplication of the herbicide pyrithiobac and various insecticides. Pyrithiobac at 70 g ai/ha, in combination with the insecticides acephate or dicrotophos at 370 g ai/ha, fipronil at 56 g ai/ha, imidacloprid at 52 g ai/ha, lambda-cyhalothrin at 37 g ai/ha, or oxamyl, carbofuran, or dimethoate at 280 g ai/ha did not reduce cotton leaf area, height, main stem node number, main stem nodes to first square, days to first square or flower, main stem nodes above white flower, or seed cotton yield compared with pyrithiobac alone. Pyrithiobac alone reduced dry weight of pitted morningglory, hemp sesbania, prickly sida, velvetleaf, and entireleaf–ivyleaf morningglory 28 d after treatment (DAT) 86, 98, 51, 94, and 91%, respectively, and weed control was not affected by the coapplication of insecticides. Control of thrips (adult plus larvae) 5 DAT with insecticides was unaffected by pyrithiobac addition at the P = 0.05 level of significance. At the P = 0.1 level, however, addition of pyrithiobac to dimethoate resulted in a reduction in insecticide efficacy in one of three experiments. Efficacy of other insecticides was unaffected. Nomenclature: Acephate, O,S-dimethyl acetylphosphoramidothioate; carbofuran, 2,3-dihydro-2,2-dimethylbenzofuran-7-yl methylcarbamate; dicrotophos, 3-dimethoxyphosphinoyloxy-N,N-dimethylisocrotonamide; dimethoate, O,O-dimethyl-S-methylcarbamoylmethyl phosphorodithioate; fipronil, 5-amino-1-(2,6-dichloror-α,α,α-triflouro-p-tolyl)-4-trifluoromethylsulfinylpyrazole-3-carbonitrile; imidacloprid, (EZ)-1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine; lambda-cyhalothrin, reaction product comprising equal quantities of (S)-α-cyano-3-phenoxybenzyl (Z)-(1R,3R)-3-(2-chloro-3,3,3-trifluoropropenyl)-2,2-dimethylcyclopropanecarboxylate and (R)-α-cyano-3-phenoxybenzyl (Z)-(1S,3S)-3-(2-chloro-3,3,3-trifluoropropenyl)-2,2-dimethylcyclopropanecarboxylate or of (S)-α-cyano-3-phenoxybenzyl (Z)-(1R)-cis-3-(2-chloro-3,3,3-trifluoropropenyl)-2,2-dimethylcyclopropanecarboxylate and (R)-α-cyano-3-phenoxybenzyl (Z)-(1S)-cis-3-(2-chloro-3,3,3-trifluoropropenyl)-2,2-dimethylcyclopropanecarboxylate; oxamyl, (EZ)-N,N-dimethyl-2-methylcarbamoyloxyimino-2-(methylthio)acetamide; pyrithiobac; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray #3 IPOHE; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A. W. Hill # SEBEX; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; velvetleaf, Abutilon theophrasti Medic. # ABUTH; cotton, Gossypium hirsutum L. Additional index word: Herbicide–insecticide interaction. Abbreviations: DAT, days after treatment; NAWF, node above white flower; POST, postemergence; PPI, preplant incorporated; PRE, preemergence.