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Excerpt from Results of the Entomological Aspects of the 1963 Western Hemlock Looper Control Project in Southwest Washington
In July 1963, acres of a -acre western hemlock looper infestation in southwest Washington were treated with aerial applications of either Sevin or ddt. Sevin was applied to acres and ddt to acres by helicopter, This control project was administered by the State of Washington Department of Natural Resources. The U. S. Forest Service furnished technical assistance and guidance.
The technical staff consisted of U. 8. Forest Service and Washington State Department - of Natural Resources personnel and was headed by'a Forest Service Entomologist. The main duties of the technical crew were to determine: spray initiation dates; spray coverage and deposit; and spray-caused 100per mortality.
On June 25, results of continuous studies on larval develop ment by the Project Entomologist indicated that most looper larvae would be in the second instar by July 5, so spraying could begin on that date, weather permitting.
Treatment began on July 5, as scheduled, and continued through July 24. Spray coverage was very good in ddt - treated areas and variable in Sevin-treated areas. Spray distribution from the tops of trees to the ground was excellent.
Weather was poor during much of the treatment period with frequent rain and high winds. Precipitation measurements were taken at several stations from July 13 through August 1 and averaged inches.
Looper larval mortality was sampled at 19 plots-l8 in the Sevin area and 1 in the ddt area. Mortality was poor and variable for Sevin and excellent for ddt. Larval kill on the 18 Sevin plots averaged 20 percent and ranged from O to 86 percent. Looper mor tality on the one ddt plot was 98 percent. Sevin-caused mortality was insufficient to prevent tree mortality in areas with heavy looper populations. The reason for variability in Sevin-caused mortality is unknown, but kill was not directly related to Spray deposit.
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