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Chapter 5 – Weed Control, No. 1, December-January 1985

Promising Grassy Weed Herbicides for No-till Winter Wheat

Roger Veseth

One of the tougher groups of weeds to control in no-till winter wheat has been grassy weeds, particularly the winter annual downy brome (cheatgrass). In the higher precipitation areas of eastern Washington and northern Idaho, windgrass and smooth brome are also problem weeds in some fields. A new experimental herbicide and new application practices for presently available herbicides offer some exciting grassy weed control possibilities in the future.

STEEP researchers Dorm Thin, University of Idaho weed scientist, and Don Morishita, weed scientific aide, have recently summarized the results of a grassy weed research study in no-till winter wheat near Potlatch, ID. The experimental Mobay and Dupont herbicide, ethyl metribuzin, applied at the 1- to 3-leaf stage of the crop gave good control of downy brome (86 percent), windgrass (89 percent) and smooth brome (95 percent). It also gave excellent control of several common broadleaf weeds. A tank mix of ethyl metribuzin and metribuzin increased downy brome control to 92 percent.

diclofop, marketed as Hoelon by American Hoechst, is present~y registered for downy brome control applied preplant incorporated in the fall. Under no-till, however, thorough soil incorporation is not possible. The researchers have been studying the effectiveness of diclofop applied postplant-pre-emergence in the fall without incorporation. Rainfall after surface application of diclofop is then necessary to move the herbicide into the soil for effective weed control. Results from this first year of research look promising. Diclofop controlled 91 percent of the downy brome, 96 percent of the windgrass and 98 percent of the smooth brome. American Hoechst has expressed interest in a registration label change for preemergence nonincorporated application of diclofop on no-till winter wheat. This particular use of Hoelon is not presently registered. More work needs to be done.

These herbicide developments offer some bright future prospects for grassy weed control in no-till. This, along with other important crop management options such as longer crop rotations with spring crops, should help to enhance the adoption of no-till in the Pacific Northwest.

Use of Trade Names

Research results are given for information only and are not to be construed as a recommendation for an unregistered use of a pesticide. Always read and follow label instructions carefully. To simplify the information, trade names have been used. Neither endorsement of named products is intended nor criticism implied of similar products not mentioned.


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