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 o n winter wheat injury in absence of noncompetitive weeds and weed cont rol during a winter wheat-fallow and a winter wheat-sorghum-fallow rot ation were investigated. Winter wheat was planted at different dates t o obtain different growth stages for spraying in the spring. Winter wh eat produced greater grain yields when planted Sept. 15 or Sept. 25, 1 987, 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, 1 988, 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 no t 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 dica mba at 0.3 plus 0.1 kg ae ha(-1), metsulfuron at 0.007 kg ai ha(-1) pl us 0.25% nonionic surfactant (NIS), and metsulfuron plus 2,4-D ester a t 0.007 plus 0.3 kg ha(-1) plus NIS decreased grain yields compared to one handweeding. At North Platte in 1988-89, when UAN was applied wit h 2,4-D ester, 2,4-D amine plus dicamba, or metsulfuron plus 2,4-D plu s MS grain yields were reduced compared to the handweeded check on whe at planted Sept. 15. Occasionally, metsulfuron plus 2,4-D ester plus M S treated wheat yielded less grain than metsulfuron plus NIS treated w heat. One or more herbicide treatments reduced wheat grain yields 4 of 15 application dates. Crop injury was related to growth stage and hea lth of winter wheat when treatments were applied. Wheat under stress w as more susceptible to herbicide damage than healthy wheat. Metsulfuro n and metsulfuron plus 2,4-D controlled kochia, tumble thistle, and re droot pigweed better after wheat harvest than 2,4-D or 2,4-D plus dica mba at North Platte, but allowed summer annual grass weeds to grow. Yi elds 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.