A mixed stand of big sagebrush and bitterbush growing in the ponderosa pine zone of eastern Oregon was treated with 2 lb/A of 2,4-D at five dates in 1960, 1961, and 1962. Brush mortality was evaluated by individual plant count and bitterbrush crown reduction in each year after treatment. Sprays applied in May, when Sandberg bluegrass heads were in late boot, caused sagebrush mortality of about 95 percent, bitterbrush mortality near 10 percent, and bitterbrush crown reduction of about 25 percent. After the onset or twig elongation on big sagebrush and flower eruption on bitterbrush, significant increase in crown damage and mortality of bitterbrush was realized from applied sprays. All bitterbrush leaves were killed at each spray date. Therefore, bitterbrush recovery was directly related to the earliness of spraying and to the length of growing season remaining after spraying. The results of this study on a typical big sagebrush-bitterbrush site substantiate the results of an earlier study on a marginally-dry site and extend the information to a greater area.
Document Type: Journal Article
Research Agronomist, Crops Research Division, Agricultural Research Service, U. S. Dept. Agric., Fort Collins, Colo., formerly of Burns, Ore.
Publication date: October 1, 1966
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