Integrated Management of Cheat (Bromus secalinus L.) and Downy Brome (Bromus tectorum L.) in Oklahoma Grain Only Winter Wheat

In Oklahoma, downy brome and cheat are difficult-to-control winter annual grasses. In the past, cheat infested most of the winter wheat hectares harvested in Oklahoma. Biotypes cross-resistant to acetolactate-synthase-inhibiting herbicides have left growers with minimal management options in conventional and herbicide-tolerant systems. Field trials at Lahoma, Oklahoma in 2019-20 and 2020-21 evaluated integrated management of cheat and downy brome using three strategies: planting date (optimal, mid-, and late), cultivar selection (high- and low-competitiveness), and herbicide choice (no herbicide, sulfosulfuron at 35.2 g ai ha-1 and pyroxsulam at 18.4 g ai ha-1). Visual control, weed species (spp.) present, wheat biomass at heading, and grain yield data were collected. In 2019-20, eight to nine weeks after treatment, visual control increased 15% with mid-planting compared to optimal planting date and 14% with late planting compared to mid-planting. In 2020-21, similar control (∼99%) was recorded for mid- and late plantings with 23% greater control than the optimal timing. Due to a lack of weed coverage, weed biomass in 2019-20 had no response to planting date, cultivar, or herbicide treatment. Downy brome biomass during 2020-21 was ∼90% lower with mid to late planting than optimal. In the same year, downy brome and cheat biomass were low (≤ 0.4 and 0.2 g m-2) and 98% less after an herbicide application than nontreated. Wheat grain yield at the optimal planting date was greatest compared to mid- and late planting date for 2019-20. A delay in planting from the optimal date to mid- or late timings decreased wheat yield 14 and 21%, respectively. In 2020-21, late planting reduced wheat yield 57% compared to optimal planting. Delaying planting date and the use of a common herbicide can suppress cheat and downy brome., but a decline in wheat yield may occur.