University of Arkansas, Fayetteville Division of Agriculture
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Abstract

Field experiments were conducted in 2005 to evaluate potential weed control interactions when MON 3539 (glyphosate) was applied with several insecticides and a plant growth regulator to RoundupReady Flex® cotton. Applications were made at the 1-3 leaf stage, the 6-8 node stage, and at the 12-14 node stage. Different combinations of tank mixes were used in each of the three applications. In the first application, all plots received the same treatment: MON 3539 at a rate of 0.75 lb ae/a. A second application was made to evaluate crop injury. Only the MON 3539 + Dimate (dimethoate) mixture significantly increased crop injury 7 days after treatment two (DAT2) when compared with MON 3539 alone (20 vs. 13% injury). Bidrin (dicrotophos), Trimax (imidacloprid), Mustang Max (zeta-cypermethrin), Karate Z (lambda-cyhalothrin), Baythroid (cyfluthrin), Intrepid (methoxyfenozide), Steward (indoxacarb), Denim (emamectin benzoate), insecticides or Mepichlor (mepiquat chloride) plant growth regulator in combination with MON 3539 showed less than 8% crop injury at 7 DAT2, which was significantly less than MON 3539 applied alone (13% injury). Crop injury ratings were taken following a third application and only the MON 3539 + Mepichlor mixture significantly increased crop injury at 7 days after treatment three (DAT3) when compared with MON 3539 alone (13 vs. 5% injury). None of the remaining treatments in the third application significantly differed from that of MON 3539 alone. Weed control rating indicated that MON 3539 + Centric (thiamethoxam) significantly reduced weed control at 15 DAT2 when compared with MON 3539 alone (72 vs. 84% control). MON 3539 tank mixed with each of the following significantly differed from the 95% rating of MON 3539 alone at 14 DAT3: Bidrin at 75%, Centric at 72%, and Denim at 79%.

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