PEST MANAGEMENT: WEEDS Response of Conventional and Imidazolinone-Resistant Rice and -Susceptible Red Rice to Acetolactate Synthase-Inhibiting Herbicides in Mixture with Malathion

Malathion in mixture with acetolactate synthase (ALS)-inhibiting herbicides synergizes the control of weed species that have evolved metabolism-based resistance to ALS-inhibiting herbicides. However, the effect of malathion-based herbicide programs on conventional and imidazolinone-resistant (Clearfield) rice systems still need to be evaluated. Studies were conducted to determine the tolerance of conventional (Roy J) and Clearfield (CL152) rice to ALS-inhibiting herbicides in mixture with malathion and to evaluate control of red rice with ALS-inhibiting herbicides in mixture with malathion. Clearfield rice injury at 28 days after treatment (DAT) with bispyribac-sodium (Regiment), imazamox (Beyond), imazethapyr (Newpath), and penoxsulam (Grasp) alone or in mixture with malathion was <5%. In contrast, injury to conventional rice at 28 DAT from bispyribac-sodium, imazamox, and imazethapyr applied in mixture with malathion (10% to 46%, 89% to 93%, and 88% to 89%, respectively) was greater than these herbicides applied alone (2% to 13%, 59% to 74%, and 55% to 71%, respectively). A similar trend was observed for the yield of Clearfield and conventional rice following treatment with ALS-inhibiting herbicides alone and in mixture with malathion. Red rice control (ALS-susceptible) with imazethapyr or imazamox was not improved by the addition of malathion to either of these herbicides due to the high level of control with each herbicide alone.