Management of Herbicide Resistant Italian Ryegrass in Oklahoma.

The use of preemergence (PRE) herbicides in Oklahoma winter wheat may improve the control of acetolactate synthase resistant Italian ryegrass [Lolium perenne L. spp. multiflorum (Lam.) Husnot]. Two studies were conducted at the Cimarron Valley Research Station near Perkins, OK in 2016 to evaluate weed management systems that included pyroxasulfone and pyroxasulfone + carfentrazone applied PRE or very early post (VEPOST). Visual weed control and crop response were evaluated 4, 6, 9, and 13 weeks after planting (WAP). Six WAP, the highest levels of wheat injury (7 to 14%) occurred following VEPOST applications of metribuzin or flufenacet + metribuzin. Italian ryegrass control was at least 95% for all treatments that included pyroxasulfone PRE or VEPOST or pinoxaden VEPOST. Similar control was achieved with pyroxasulfone + carfentrazone except when applied alone PRE at the reduced rate of 35 g ai ha^-1. Overall, several successful systems were identified using pyroxasulfone and pyroxasulfone + carfentrazone. Wheat response to these products is influenced by planting depth, application timing, herbicide rate, soil type, and rainfall following application. To reduce crop injury, plant seed to a depth of at least 2.5 cm and closely follow herbicide labels with regard to application rate and timing.