A Test with Large Scale Aerial Photographs to Sample Balsam Woolly Aphid Damage in the Northeast

The balsam woolly aphid (Chermes piceae Ratz.) has caused an undetermined amount of mortality, tree deformation, and stand deterioration of balsam fir, (Abis balsamea (L.) Mill) in the northeastern United States and the Maritime Provinces of Canada. A sampling technique to detect and estimate this damage by photo interpretation of large scale color transparencies is described. Several scales (1:796 to 1:3960) and camera angles were tried before establishing 1:HSS vertical scale as best. Tree killing resulting from heavy aphid stem attacks was estimated with accuracies of 95 percent or better. Gouting damage on the tops of the tree crowns could not be detected better than 75 percent of the time, but this level of accuracy was consistent from one year to the next. A sampling scheme is proposed for possible use in estimating present damage in Maine annd Vermont. It consists of periodic rephotography, every three to four years, of the same sites, as a basis for establishing trends of mortality. Based on comparable costs to undertake a ground survey of an equal number of randomly located fir sites within the infested zone, a combined aerial photo interpretation-ground survey would be about 2.5 times cheaper.