Environmental and application effects on MON 37500 efficacy and phytotoxicity

Abstract

Experiments were conducted in an environmentally controlled growth chamber to determine the effects of temperature (10/5 or 21/7 C, day/night), soil moisture (7, 14, or 20%), timing (preemergence [PRE] or postemergence [POST]), and rate (9 or 18 g ai ha−1) of application on MON 37500 efficacy onBromus secalinusL. and toxicity toTriticum aestivumL. MON 37500 reducedB. secalinusplant density an average of 40% but did not reduceT. aestivumdensity. PRE treatments reducedB. secalinusdensity 40% compared to 12% with POST applications when plants were grown at 10/5 C. Soil moisture level also influenced plant density, with 7.9 plants per pot when soil moisture was maintained at 7%, compared to 8.5 plants per pot with 14 or 20% soil moisture. MON 37500 reducedB. secalinusdry weight more at 18 g ha−1than at the 9-g ha−1rate when grown at 21/7 C, but no rate response occurred at 10/5 C. PRE applications of MON 37500 at 10/5 C decreasedB. secalinusdry weight 22% more than PRE applications at 21/7 C or POST applications under either temperature regime. However, PRE applications of MON 37500 at 21/7 C decreasedT. aestivumbiomass an average of 16%, compared to 3% or less with other treatments. At 21/7 C,B. secalinusdry weight decreased 46% as soil moisture increased from 7 to 20%.Bromus secalinuswas 10 to 12% less susceptible to MON 37500 when grown at 7% soil moisture at 10/5 C than when grown at the same temperature at 14 or 20% soil moisture.Triticum aestivuminjury was greater at 20% soil moisture under each temperature regime.