The Effect of Planting Strategies, Imazethapyr Rates, and Application Timings on CLEARFIELD® Hybrid Rice Injury
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CLEARFIELD® rice, which is a non-genetically modified crop that is tolerant to herbicides in the imidazolinone family has helped producers combat red rice problems in rice since itʼs introduction in 2002. Recently, breeders introduced hybrid CLEARFIELD® lines hoping to maintain the desired herbicide-resistant traits while having the added benefits of a hybrid. Soon after the hybrid line was released, farmers noticed herbicide injury to these new varieties while following the label recommendations. Research was performed to test the hybrids on the effect of planting date, planting density, and imazethapyr application rate on visual plant injury at Beaumont and Eagle Lake, TX in 2008 and 2009. A secondary experiment was designed to test the effect of imazethapyr application timing and rate on plant height, fresh weight, and dry weight in Eagle Lake and Beaumont, TX in 2010 with a greenhouse experiment in College Station, TX in 2009. The 2008 and 2009 field trials were planted at three different densities, (28, 39, and 50 kg ha-1) with two different planting dates representing the months of March and April. Herbicide treatments consisted of four 1- to 2-leaf rates of imazethapyr that included 0.035, 0.07, 0.105, and 0.14 kg ha-1, followed by two 4- to 6-leaf rates of imazethapyr of 0.07 and 0.105 kg ha-1. Rice showed injury symptoms two weeks after the second application of imazethapyr but was able to recover soon after nitrogen fertilizer application and flood establishment. Grain yield was not significantly different in plots that received a full labeled rate of imazethapyr or more for either location in either year. The 2009 greenhouse study and 2010 field studies included treatments that had one early post at 1- to 2-leaf and one of two different late post applications that included either a 3- to 4-leaf or a 5- to 6-leaf treatment. The three rates included in the early 1- to 2-leaf application were 0, 0.035 and 0.07 kg ai ha-1. The four rates included in the late application were 0, 0.07, 0.105, and 0.14 kg ai ha-1. Plants treated with the labeled rate, 0.07 to 0.105 kg ai ha-1 at each 1- to 2-leaf and 3- to 6-leaf stage, showed no significant differences in yield, or quality; however, significant differences were recorded in height. According to this data, hybrid rice seems to be tolerant to imazethapyr applications and timings.
Turner, Aaron Lyles (2011). The Effect of Planting Strategies, Imazethapyr Rates, and Application Timings on CLEARFIELD® Hybrid Rice Injury. Master's thesis, Texas A&M University. Available electronically from