Sensitivity of Grass Crops to Low Rates of Quizalofop
2018
Lancaster, Zachary D. | Norsworthy, Jason K. | Scott, Robert C.
With the widespread occurrence of herbicide-resistant weeds in midsouthern U.S. rice, new technologies are needed to achieve adequate weed control. A new non—genetically modified rice trait has been commercialized that is resistant to quizalofop, an acetyl coenzyme A carboxylase (ACCase)-inhibiting herbicide. The addition of quizalofop-resistant rice to production systems will increase the use of quizalofop, possibly increasing the risk for injury to other grass crops. Experiments were conducted in 2014 and 2015 to determine the sensitivity of corn, grain sorghum, and conventional rice to low rates of quizalofop (1/10× to 1/200× of 160 g ai ha⁻¹). Conventional rice was not affected by quizalofop rate or application timing. Corn displayed the greatest response to the 1/10× quizalofop rate at the two- to three-leaf stage, with 50% to 65% injury and 35% to 37% relative yield compared to the nontreated check. Grain sorghum was injured 31% to 34% by the 1/10× quizalofop rate applied at the twoto three-leaf stage, and there was 20% to 26% injury at the panicle exertion growth stage. The highest rate of quizalofop at the panicle exertion stage reduced yields 28% to 46%. Overall, risk for injury to any of the three evaluated crops from quizalofop appears low, with greatest injury observed at the highest quizalofop drift rate, with minimal injury at lower rates. Nomenclature: Quizalofop; corn, Zea mays L.; grain sorghum, Sorghum bicolor (L.) Moench.; rice, Oryza sativa L.
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