SECOND MEMORANDUM ON THE DOUGLAS FIR TUSSOCK MOTH OUTBREAK NEAR TROY, OREGON
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Buckhorn, Walter J. 1947. Second memorandum on the Douglas fir tussock moth outbreak near Troy, Oregon. 
Abstract: This report is a detailed supplement to a memorandum dated September 23, 1946, in which a Douglas-fir tussock moth outbreak near Troy, Oregon was briefly described. The outbreak was first found on August 20, 1946, when a pine beetle survey crew was cruising a check plot near Troy. On September 18 and 19 of that fall, the author made a general examination of the general area and estimated that the infestation involved some 10,000 to 12,000 acres. Almost complete mortality of Douglas-fir and white fir had occurred on 500 to 600 acres in patches ranging up to 50 acres. Due to extremely rough terrain and the general lack of roads, the area could not be adequately examined from the ground in the time remaining that fall. Reports from local residents indicated that 1946 was the second year of the outbreak. Heavy deposits of eggs throughout the examined area indicated that the tussock moth population was still increasing and that considerable timber would probably be killed in 1947. The presence of this outbreak was of particular interest because of a concurrent, though much larger, outbreak in Idaho. The proximity of the two outbreaks offered an opportunity to coordinate control efforts if it was decided that direct control measures were warranted for the Troy outbreak. Since the ground examination in September had been incomplete, it was decided to conduct an aerial examination in late March of 1947. Aerial observations of the outbreak area were made on March 24th and 25th. A major complication associated with the March timeframe was that western larch was still dormant, which made it difficult to discern whether brownish trees were defoliated fir or Douglas-fir, or undamaged western larch. Since western larch often comprised a significant proportion of the mixed-conifer stands in the outbreak area, this complication posed a major problem in deriving an accurate damage estimate. Results of the aerial survey showed heavy defoliation on approximately 1265 acres, moderate defoliation on 23,890 acres, and light defoliation on 30,910 acres. In all, about 56,065 acres supporting 140 million board feet of timber were infested to some extent. Most of the infested acreage occurred on the divide between the Wenaha and Grande Ronde rivers in townships 5 and 6 north, ranges 40, 41, and 42 east. The author believed that the outbreak would eventually subside due to parasites, disease, and other natural factors, but preliminary indications were that it had not yet peaked at the time this report was written and that extensive timber mortality was possible during 1947. Although the author did not yet have enough information to definitively recommend whether aerial control should be initiated, it is clear that he felt that it was feasible and should be considered in conjunction with the Idaho project. The Idaho project was proposing to spray DDT at the rate of one pound in one gallon of oil and at an estimated cost of $1.70 per acre. The author recognized that salvage logging of insect-caused mortality was also an option, although the lack of roads and milling capacity in the area made salvage an unattractive alternative. In 1946, a small lumber mill had just been constructed in Troy and the area opened to logging for the first time. This report includes a colored map showing light, medium, and heavy infestation areas in the area. It is unknown if the map could be digitized; if it could, it certainly should be.

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