Response of Quizalofop-Resistant Rice to Sequential Quizalofop Applications Under Differential Environmental Conditions


 Quizalofop-resistant rice allows for over-the-top applications of quizalofop, an acetyl-coenzyme A carboxylase-inhibiting herbicide. However, previous reports have indicated that quizalofop applied postemergence has been shown to cause significant injury to quizalofop-resistant rice. Therefore, field experiments were conducted to evaluate the response of quizalofop-resistant rice cultivars to quizalofop applications across different planting dates. Under controlled conditions, the effects of soil moisture content, air temperature, and light intensity on quizalofop-resistant rice sensitivity to quizalofop were investigated. In the planting date experiment, 11 percentage points higher injury was observed on early-planted rice compared to late-planted rice at the 5-leaf stage, with higher injury observed under saturated soil conditions. However, quizalofop applications at labeled rate caused ≤16% reduction in yield regardless of planting environment. Quizalofop-resistant cultivars had at least 25-percentage points more injury when soil was maintained at 90% or 100% of field capacity as PVL01, PVL02, and RTv7231 MA had ≥42%, 30%, and ≥54% injury, respectively, compared to ≤10%, ≤5%, and ≤22% injury, respectively, at 40% or 50% of field capacity, pooled over rating timing. Greater injury ranging from 18% to 31% observed on quizalofop-resistant rice grown under low light intensity (600µmol m-2s-1) compared to 5% to 14% injury under high light intensity (1150µmol m-2s-1). The injury persisted from 7 to 28 days after 5-leaf stage application (DAFT), averaged over quizalofop-resistant cultivars and air temperatures (20/15 C and 30/25 C day/night, respectively). At 7 DAFT, greater injury (5- to 21-percentage points) was observed on quizalofop-resistant cultivars; PVL01, PVL02, and RTv7231 MA had 33%, 9%, and 58% injury, respectively, under 20/15 C compared to 13%, 4%, and 37% injury, respectively, under 30/25 C day/night conditions averaged over light intensities. Overall, quizalofop applications are likely to cause a greater risk for injury to quizalofop-resistant rice if applied under cool, cloudy, and moist soil conditions.