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Effect of Thiamethoxam on Injurious Herbicides in Rice

Martin SM, Norsworthy JK, Scott RC, Hardke J, Lorenz GM and Gbur E

Increases in the number of herbicide-resistant weeds in rice has led to the need for new herbicides and modes of action to control these troublesome weeds. Previous research has indicated that insecticide seed treatments can safen rice from herbicide drift. In 2014 and 2015, two field experiments were conducted at the Rice Research and Extension Center (RREC) near Stuttgart, Arkansas, and at the University of Arkansas Pine Bluff (UAPB) farm near Lonoke, Arkansas, to determine if insecticide seed treatments could prevent unacceptable levels of herbicide injury from preemergence (PRE)- and postemergence (POST)-applied herbicides that are typically injurious to rice. Both studies were planted with the imidazolinone-resistant, inbred variety CL151. ‘Treated’ plots contained the insecticide seed treatment thiamethoxam while ‘nontreated’ plots contained no insecticide seed treatment. Seven herbicides were evaluated in the PRE experiment: clomazone, pethoxamid, fluridone, S-metolachlor, thiobencarb, clethodim, and quizalofop to determine crop injury, stand counts, groundcover, and rough rice yield with and without an insecticide seed treatment compared to plots with no herbicide treatments. Overall, an insecticide seed treatment provided increased rice stands and less herbicide injury than the ‘nontreated’ seed while increasing yield by 500 kg ha^-1. Of the herbicides tested, clomazone-, thiobencarb-, clethodim-, and quizalofop-treated plots had equivalent yields to the no-herbicide plots. The POST experiment evaluated propanil, saflufenacil, carfentrazone, and acifluorfen in various tank-mixtures and application timings. Similar to the PRE experiment, plants from treated seed had less herbicide injury 1 and 5 weeks after treatment (WAT) along with an increased canopy height and groundcover percentage. Plants having treated seed also had increased yields when used with some herbicide programs. Overall, the use of an insecticide seed treatment can give the added benefit of less injury from injurious herbicides as well as increased groundcover.