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Suppression of cranberry girdler damage in beds of Douglas-fir seedlings, Coeur d'Alene Nursery, Idaho Panhandle National Forest, 1984 Public Deposited
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The cranberry girdler, Chrysoteuchia toparia Zeller, has caused increasing damage to tree seedlings in the Coeur d'Alene Nursery since 1980. Heaviest feeding has occurred on the tap roots of 2+0 Douglas-fir stock. By 1983, 8.2 percent of the seedlings examined in seedbeds were injured by this moth. A spray program was adopted in 1984 to reduce the amount of damage. Three applications of Diazinon at 1 lb. active ingredient per acre were used to kill adult moths, and three applications of Dursban at the same rate were used to reduce larval populations in the soil of Douglas-fir beds. Results of the insecticidal treatments were determined in November 1984 during lifting operations. In sprayed beds, only 0.01 percent of the 2+0 Douglas-fir seedlings examined were injured, and 0.9 percent of the 3+0 Douglas-firs examined were injured. There were no beds of unsprayed Douglas-fir seedlings to use as a check. Because damage was 8.2 percent in beds during 1983, and moth populations were high in 1984, damage in unsprayed beds could have been 8 percent or greater in 1984. Nurseries consider damage tolerable when it is below 1.0 percent.
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