Several labeled herbicide treatments reduced winter wheat height and grain yield when applied at different growth stages in 1984 and 1985. Yield reductions were related to reduced spike production. Wheat height and yield generally were greatest when herbicides were applied at Zadoks' Stage 29 and lowest at Stage 13. Herbicide treatments did not affect wheat kernels per spike, kernel weight, volume weight, or germination either year. However, most herbicide treatments either increased or decreased seed protein content, depending on the year.
Since the inception of 2,4‐D [(2,4‐dichlorophenoxy) acetic acid], many herbicides have been developed for broadleaf weed control in wheat (Triticum aestivum L.). However, many of these herbicides have not been thoroughly evaluated with respect to application timing and effects on wheat yield and quality. Field studies were conducted at Torrington, WY on a Bayard fine sandy loam (coarse loamy, mixed, mesic Torriothentic Haplustoll) in 1984 and 1985 to evaluate the response of ‘Oslo’ spring wheat to 10 broadleaf herbicide treatments applied at three growth stages. Dicamba (3,6‐dichloro‐2‐methoxybenzoic acid), dicamba plus 2,4‐D and dicamba plus MCPA [(4‐chloro‐2‐methylphenoxy)acetic acid] reduced wheat yield 28, 21 and 24%, reduced kernels per spike 27, 33 and 21%, and increased seed protein 8, 10 and 13%, respectively, when applied at Zadoks Stage 44 (mid‐boot). Several other auxin herbicides increased seed protein content, particularly when applied at Zadoks Stage 44. Proline and lysine content were not influenced by herbicide treatment at any stage of application. Spring wheat tolerance to bromoxynil (3,5‐dibromo‐4‐hydroxybenzonitrile), chlorsulfuron (2‐chloro‐Ar‐[[4‐methoxy‐6‐methyl‐l,3,5‐triazin‐2‐yl)amino]carbonyl] benzenesulfonamide} and MCPA was excellent regardless of growth stage at application.
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.
The response of irrigated spring barley (Hordeum vulgare L. ‘Steptoe’) to broadleaf herbicides applied at three growth stages was studied at Torrington, WY, in 1984 and 1985. Dicamba (3,6-dichloro-2-methoxybenzoic acid), dicamba plus 2,4-D [(2,4-dichlorophenoxy)acetic acid], and dicamba plus MCPA [(4-chloro-2-methylphenoxy)acetic acid] visibly injured barley when applied at all growth stages. These same treatments reduced barley height when applied at the 2- to 4-leaf and fully tillered stages. Yield differences among treatments were not significant. However, kernels/spike and kernel weight were reduced by dicamba or dicamba plus MCPA when applied at the fully tillered or boot stages, and test weight was reduced when dicamba was applied at all growth stages. Seed protein content did not differ in 1984. However, several herbicide treatments increased seed protein in 1985, especially when applied at the boot stage. Proline or lysine content did not differ among treatments.
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