Sensitivity of Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) and ponderosa pine (Pinus ponderosa Laws.) seedlings to operational-type brush control treatments was tested with simulated aerial sprays on potted 2-0 seedlings. Treatments of one to four pounds per acre of several herbicides applied at two-week intervals indicated that Douglas-fir might be expected to recover from applications used to kill brush in a four-month period during spring and summer. Ponderosa pine was more severely damaged than Douglas-fir, but demonstrated its greatest resistance in late summer, and its greatest sensitivity in spring and early summer. Douglas-fir, while it suffered the greatest apparent damage during the period of most rapid growth, recovered most readily from the early-season treatments. The effects of late-season treatments were especially noticeable with Amitrol; all trees treated with 2,4,5-T made complete recovery by the end of the second growing season; 2,4,5-T amine and 4-(2,4,5-TB) ester caused no measurable damage at any time, indicating that selectivity for Douglas-fir may be brought about by manipulation of solvent and formulation as well as molecular configuration.
Document Type: Journal Article
Instructor, School of Forestry, Oregon State University, Corvallis
Publication date: September 1, 1963
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