Suppression of cranberry girdler damage in beds of Douglas-fir seedlings, Coeur d'Alene Nursery, Idaho Panhandle National Forest, 1984

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