Control of Selected Broadleaf Weeds with Glufosinate as Influenced by Insecticide Coapplication1

Coapplication of herbicides and insecticides affords growers an opportunity to control multiple pests with one application, given that efficacy is not compromised. Glufosinate was applied at 470 g ai/ha both alone and in combination with the insecticides acephate, acetamiprid, bifenthrin, cyfluthrin, dicrotophos, emamectin benzoate, imidacloprid, indoxacarb, lambda-cyhalothrin, methoxyfenozide, spinosad, or thiamethoxam to determine coapplication effects on control of some of the more common and/or troublesome broadleaf weeds infesting cotton. Hemp sesbania, pitted morningglory, prickly sida, redroot pigweed, and sicklepod were treated at the three- to four- or the seven- to eight-leaf growth stage. When applied at the earlier application timing, glufosinate applied alone provided complete control at 14 d after treatment, and control was unaffected by coapplication with insecticides. When glufosinate application was delayed to the later application timing, visual weed control was unaffected by insecticide coapplication. Fresh-weight reduction from the herbicide applied to larger weeds was negatively impacted by addition of the insecticides dicrotophos and imidacloprid with respect to redroot pigweed and prickly sida, but only in one of two experiments. In most cases, delaying application of glufosinate to larger weeds resulted in reduced control compared to that from a three- to four-leaf application, with the extent of reduction varying by species. Results indicate that when applied according to the herbicide label (three- to four-leaf stage), glufosinate/ insecticide coapplications offer producers the ability to integrate pest management strategies and to limit application costs without sacrificing control of the broadleaf weeds evaluated. Nomenclature: Acephate, O,S-dimethyl acetylphosphoramidothioate; acetamiprid, (E)-N1-[(6-chloro-3-pyridyl)methyl]-N2-cyano-N1-methylacetamidine; bifenthrin, 2-methylbiphenyl-3-ylmethyl (Z)-(1RS,3RS)-3-(2-chloro-3,3,3-trifluoroprop-1-enyl)-2,2-dimethylcyclopropanecarboxylate; cyfluthrin, (RS)-α-cyano-4-fluoro-3-phenoxybenzyl (1RS,3RS,1RS,3SR)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylate; dicrotophos, 3-dimethoxyphosphinoyloxy-N,N-dimethylisocrotonamide; emamectin benzoate, mixture of (10E,14E,16E,22Z)-(1R,4S,5′S,6S,6′R,8R,12S,13S,20R,21R,24S)-6′-[(S)-sec-butyl]-21,24-dihydroxy-5′,11,13,22-tetramethyl-2-oxo-(3,7,19-trioxatetracyclo[15.6.1.14,8.020,24]pentacosa-10,14,16,22-tetraene)-6-spiro-2′-(5′,6′-dihydro-2′H-pyran)-12-yl 2,6-dideoxy-3-O-methyl-4-O-(2,4,6-trideoxy-3-O-methyl-4-methylamino-α-l-lyxo-hexapyranosyl)-α-l-arabino-hexapyranoside and (10E,14E,16E,22Z)-(1R,4S,5′S,6S,6′R,8R,12S,13S,20R,21R,24S)-21,24-dihydroxy-6′-isopropyl-5′,11,13,22-tetramethyl-2-oxo-(3,7,19-trioxatetracyclo[15.6.1.14,8.020,24]pentacosa-10,14,16,22-tetraene)-6-spiro-2′-(5′,6′-dihydro-2′H-pyran)-12-yl 2,6-dideoxy-3-O-methyl-4-O-(2,4,6-trideoxy-3-O-methyl-4-methylamino-α-l-lyxo-hexapyranosyl)-α-l-arabino-hexapyranoside; imidacloprid, (EZ)-1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine; indoxacarb, methyl (S)-N-[7-chloro-2,3,4a,5-tetrahydro-4a-(methoxycarbonyl)indeno[1,2-e][1,3,4]oxadiazin-2-ylcarbonyl]-4′-(trifluoromethoxy)carbanilate; 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; methoxyfenozide, N-tert-butyl-N′-(3-methoxy-o-toluoyl)-3,5-xylohydrazide, spinosad, mixture of 50 to 95% of (2R,3aS,5aR,5bS,9S,13S,14R,16aS,16bR)-2-(6-deoxy-2,3,4-tri-O-methyl-α-l-mannopyranosyloxy)-13-(4-dimethylamino-2,3,4,6-tetradeoxy-β-d-erythropyranosyloxy)-9-ethyl-2,3,3a,5a,5b,6,7,9,10,11,12,13,14,15,16a,16b-hexadecahydro-14-methyl-1H-8-oxacyclododeca[b]as-indacene-7,15-dione and 5 to 50% (2S,3aR,5aS,5bS,9S,13S,14R,16aS,16bR)-2-(6-deoxy-2,3,4-tri-O-methyl-α-l-mannopyranosyloxy)-13-(4-dimethylamino-2,3,4,6-tetradeoxy-β-d-erythropyranosyloxy)-9-ethyl-2,3,3a,5a,5b,6,7,9,10,11,12,13,14,15,16a,16b-hexadecahydro-4,14-dimethyl-1H-8-oxacyclododeca[b]as-indacene-7,15-dione; thiamethoxam, (EZ)-3-(2-chloro-1,3-thiazol-5-ylmethyl)-5-methyl-1,3,5-oxadiazinan-4-ylidene(nitro)amine; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A. W. Hill #3 SEBEX; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; redroot pigweed, Amaranthus retroflexus L. # AMARE; sicklepod, Senna obtusifolia (L.) Irwin and barneby # CASOB. Additional index words: Herbicide-insecticide combinations, pesticide compatibility. Abbreviation: DAT, days after treatment.