Graduate Thesis Or Dissertation
 

Factors influencing metribuzin use in strip-planted wheat

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/9p290c835

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  • Equipment for strip-till planting is under development in wheat-fallow rotations in the Columbia Basin of Oregon. This involves the absence of tillage during the fallow season. At planting time, the strip-till planter creates a narrow band into which the wheat seed is placed. The area between the rows is undisturbed except for the deposition of a 2-cm thick layer of soil displaced from the tilled area. Chemical weed control is required between the rows. Preliminary work has shown that metribuzin [4-amino-6-tert-butyl-3- (methylthio)-as-triazin-5(4H)-one] is a promising herbicide for this purpose. Factors influencing the application, effectiveness, and selectivity of metribuzin used in conjunction with strip-till planting were investigated in the laboratory and greenhouse. Application of metribuzin in combination with liquid fertilizer would be convenient and economical. Laboratory experiments were conducted to determine the physical compatibility of four liquid fertilizers: Solution 32 at 56 kg N/ha, 10-34-0 at 45 kg P₂0₅/ha, 0-0-15 at 22 kg K/ha, and 11-0-0-26 at 22 kg S/ha, with three metribuzin formulations each of Sencor and Lexone at 112 g a.i./ha. Wettable powder, flowable, and dispersible granule formulations of both Sencor and Lexone were tested. Only the wettable powder formulations were sufficiently compatible with the liquid fertilizers tested to be recommended for practical commercial use. Large differences were seen between the other formulations. Their use with liquid fertilizers might require the addition of compatibility agents or mixing them with water first, before adding them to the fertilizers. When compatibility is obtained after mixing them with water first, continuous agitation might be required to maintain the suspension. No major differences were observed between comparable formula tions of Sencor and Lexone. Greenhouse experiments were conducted to determine the biological compatibility of Solution 32 and metribuzin on downy brome (Bromus teetorum LJ, the effect of Solution 32 on downy brome and wheat emergence, the effect of soil layer on metribuzin effectiveness for downy brome control, and the effect of banding width over the wheat row and wheat seeding depth on metribuzin phytotoxicity to wheat. More effective downy brome control was obtained when metribuzin was mixed with Solution 32 than when it was used alone. Solution 32 was used at 0, 36, 54, and 79 kg N/ha, and metribuzin at 0, 14, 28, 56, and 112 g a.i./ha. Solution 32 itself had some phytotoxic effects on downy brome at the high rates. Wheat was not affected as severely as downy brome. Application of metribuzin to the surface of the newly deposited soil layer was more effective in controlling downy brome than when the herbicide was applied and then covered with the soil layer. Results suggested that better downy brome control could be obtained with metribuzin applied after the strip-tiller had deposited the soil layer between the rows, especially if adequate rainfall is expected. Under such rainfall conditions, metribuzin covered with a soil layer may leach deeper out of the root zone and less effectiveness could result. Both seeding depth of wheat and width of the unsprayed area were factors influencing metribuzin phytotoxicity to wheat. Greater wheat injury was observed when the herbicide was applied on top of, or too close to, the seed row, particularly when wheat was planted shallow. The results suggested that wheat should be planted 3 cm deep or deeper when the unsprayed band is 15 cm wide, and at least 5 cm deep when the unsprayed band is 10 cm wide.
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