Winter wheat and cheat seed response to foliar nitrogen applications

Growing winter wheat (Triticum aestivum L.) cultivars in a weed-free enviro nment is necessary for optimum grain yield. Cheat (Bromus secalinus L.) is an important grass weed in winter wheat and can cause grain yield loss in e xcess of 40% in heavily infested fields. Two field experiments were conduct ed during the 1994-95 and 1995-9Ci crop years to evaluate the effect of fol iar nitrogen (N) fertilizer on wheat grain yield and quality, and cheat see d reduction in winter wheat. Foliar fertilizer solutions were urea ammonium nitrate (UAN), ammonium hydroxide (NH,OH), and ammonium sulfate [(NH4)(2)S O4]. Wheat varieties were 'Tonkawa', 'Longhorn', and 'Jagger'. Foliar N was applied after winter wheat had completed flowering, but one to two wk prio r to cheat flowering in an attempt to desiccate immature cheat heads. Wheat grain yield, grain protein, and cheat seed yield were determined after har vest. Wheat grain yield was not affected by foliar applied N following whea t flowering, while wheat grain protein increased 1 to 4%. Foliar N applicat ions significantly reduced cheat seed production. Linear-plateau models ind icated that cheat seed reduction (percent germination * cheat yield versus check) ranged from 41.7 to 70.3% when foliar N was applied at rates between 0.4 and 19.4 lb N acre(-1) prior to cheat flowering. Average cheat seed re duction over years, N source, and variety was 54.9% when N was foliar appli ed at an average rate of 6.7 Ib N acre(-1). This reduction in the cheat pop ulation could prove to be beneficial to subsequent winter wheat crops. Simi lar differences in flowering between weed and crop in other production syst ems may reveal additional windows of opportunity for applying foliar N fert ilizers aimed specifically at weed control.