Residual Activity of ACCase-Inhibiting Herbicides on Monocot Crops and Weeds

Field experiments were conducted in 2014 and 2015 in Fayetteville, Arkansas, to evaluate the residual activity of acetyl-CoA carboxylase (ACCase)-inhibiting herbicides for monocot crop injury and weed control. Conventional rice, quizalofop-resistant rice, grain sorghum, and corn crops were evaluated for tolerance to soil applications of six herbicides (quizalofop at 80 and 160 g ai ha⁻¹, clethodim at 68 and 136 g ai ha⁻¹, fenoxaprop at 122 g ai ha⁻¹, cyhalofop at 313 g ai ha⁻¹, fluazifop at 210 and 420 g ai ha⁻¹, and sethoxydim at 140 and 280 g ai ha⁻¹). Overhead sprinkler irrigation of 1.3 cm was applied immediately after treatment to half of the plots, and the crops planted into the treated plots at 0, 7, and 14 d after herbicide treatment. In 2014, injury from herbicide treatments increased with activation for all crops evaluated, except for quizalofop-resistant rice. At 14 d after treatment (DAT) in 2014, corn and grain sorghum were injured 19% and 20%, respectively, from the higher rate of sethoxydim with irrigation activation averaged over plant-back dates. Conventional rice was injured 13% by the higher rate of fluazifop in 2014. Quizalofop-resistant rice was injured no more than 4% by any of the graminicides evaluated in either year. In 2015, a rainfall event occurred within 24 h of initiating the experiment; thus, there were no differences between activation via irrigation or by rainfall. However, as in 2014, grain sorghum and corn were injured 16% and 13%, respectively, by the higher rate of sethoxydim, averaged over plant-back dates. All herbicides provided little residual control of grass weeds, mainly broadleaf signalgrass and barnyardgrass. These findings indicate the need to continue allowing a plant-back interval to rice following a graminicide application, unless quizalofop-resistant rice is to be planted. The plant-back interval will vary by graminicide and the amount of moisture received following the application. Nomenclature: Clethodim; cyhalofop; fenoxaprop; fluazifop; quizalofop; sethoxydim; barnyardgrass, Echinochloa crus-galli (L.) Beauv.; broadleaf signalgrass, Urochloa platyphylla (Munro ex C. Wright) R.D. Webster; corn, Zea mays L.; grain sorghum, Sorghum bicolor (L.) Moench.; rice, Oryza sativa L.