Woolly apple aphids infest roots, trunks, limbs, shoots, and occasionally fruit of apple trees. The bodies of these bark-feeding aphids are completely covered by masses of white, wool-like, waxy materials. This aphid is found in colonies on the aerial portions of the tree and on roots during winter. The nymphs migrate up or down the trunk of infested trees during summer and fall.
The main injury to young and mature trees is stunting due to the formation of root galls. If populations are high, honeydew and sooty mold will also be problems, and aphids may enter the calyx end of fruit.
Woolly apple aphid is found throughout California’s apple-growing regions, and it is a major pest in coastal counties. It occasionally infests pyracantha, hawthorn, and pear.