Notes: Simultaneous Infestation by Dwarf Mistletoe and Western Spruce Budworm Decreases Growth of Douglas-fir in the Blue Mountains of Oregon
Abstract:One-hundred paired branches, half with dwarf mistletoe plants and half without, were sampled from 100 Douglas-fir in five stands defoliated by the western spruce budworm. The budworm completely defoliated new shoots and buds of all branches sampled including those infected by dwarf mistletoe. Radial growth of host trees (Douglas-fir) was significantly less during the budworm outbreak compared with a similar period before the outbreak. Nonhost trees (ponderosa pine) showed significantly more radial growth during the outbreak than before it. Regression analyses showed that decreases in radial growth were associated primarily with increases in dwarf mistletoe severity (R² = 16.2-18.1). Trees within all dwarf mistletoe infection classes were defoliated by the budworm, and the additional growth reduction caused by defoliation was not significantly different among dwarf mistletoe severity classes. For. Sci. 33(3):767-773.
Document Type: Miscellaneous
Affiliations: Plant Pathologist, Pacific Northwest Research Station, USDA Forest Service, La Grande, OR 97850
Publication date: September 1, 1987
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