University of Arkansas, Fayetteville Division of Agriculture


Weed control, cotton


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%.