Mon 37532 Phytotoxicity is Affected by Surfactant and Ammonium Nitrate

Abstract

Herbicides often are applied with surfactants and with the addition of 2 to 4% (v/v) 28% nitrogen liquid fertilizer (ammonium nitrate + urea). Greenhouse experiments were conducted to determine the influence of surfactant hydrophilic:lipophilic balance (HLB) on efficacy of MON 37532, a new herbicide by Monsanto, applied with surfactant alone and with ammonium nitrate. Linear alcohol ethoxylate (LAE) surfactants with C8–10 or C12–14 alcohol were or tended to be more effective with 12 than 8 or 16 HLB. HLB did not influence C16–18 LAE surfactant enhancement of MON 37532 phytotoxicity to oats. However, all LAE were similar in enhancing phytotoxicity to green foxtail, except C12–14 with 8 HLB was less effective. The presence of ammonium nitrate increased or decreased LAE efficacy depending on the specific LAE and varied with species. Ethoxylated alkylphenols, Triton® X, and secondary alcohol ethoxylate, Tergitol® 15-S surfactants generally increased in efficacy as HLB increased. Ammonium nitrate did not enhance efficacy of Tergitol® 15-S or Igepal CO, but with Triton® X often enhanced MON 37532 phytotoxicity to green foxtail. MON 37532 phytotoxicity enhancement from ammonium nitrate was inpart from increase spray retention, and did not appear to relate to droplet deposit.