Cultural Practices in Wheat (Triticum aestivum), on Weeds in Subsequent Fallow and Sorghum (Sorghum bicolor)

The effect of herbicide and urea-ammonium nitrate (UAN) combinations on winter wheat injury in absence of noncompetitive weeds and weed control during a winter wheat-fallow and a winter wheat-sorghum-fallow rotation were investigated. Winter wheat was planted at different dates to obtain different growth stages for spraying in the spring. Winter wheat produced greater grain yields when planted Sept. 15 or Sept. 25, 1987, 1988, and 1989 vs. Sept. 1 at North Platte, NE, while at Sidney, NE, grain yield was higher in wheat planted on Sept. 10 or Sept. 20, 1988, compared to Aug. 26. Spring-applied UAN increased grain yield on wheat planted Sept. 10 compared to no UAN in 1988–89 at Sidney, but not in 1987–88, while at North Platte, grain yields were not affected by UAN. At Sidney 2,4-D ester at 0.6 kg ae ha−1, 2,4-D amine plus dicamba at 0.3 plus 0.1 kg ae ha−1, metsulfuron at 0.007 kg ai ha−1plus 0.25% nonionic surfactant (NIS), and metsulfuron plus 2,4-D ester at 0.007 plus 0.3 kg ha−1plus NIS decreased grain yields compared to one handweeding. At North Platte in 1988–89, when UAN was applied with 2,4-D ester, 2,4-D amine plus dicamba, or metsulfuron plus 2,4-D plus NIS grain yields were reduced compared to the handweeded check on wheat planted Sept. 15. Occasionally, metsulfuron plus 2,4-D ester plus NIS treated wheat yielded less grain than metsulfuron plus NIS treated wheat. One or more herbicide treatments reduced wheat grain yields 4 of 15 application dates. Crop injury was related to growth stage and health of winter wheat when treatments were applied. Wheat under stress was more susceptible to herbicide damage than healthy wheat. Metsulfuron and metsulfuron plus 2,4-D controlled kochia, tumble thistle, and redroot pigweed better after wheat harvest than 2,4-D or 2,4-D plus dicamba at North Platte, but allowed summer annual grass weeds to grow. Yields of grain sorghum planted after a 10-mo fallow period were higher following winter wheat treated with three of four herbicides than the handweeded treatment.