Although small numbers of these aphids may be present on trees early in the season, populations generally start to increase in mid- to late June. Large numbers of both species build up on growing terminals on apple trees during summer, particularly when there is an abundance of succulent new foliage. Our bountiful rains over the past month have resulted in considerable new growth, which in turn has favored high aphid populations in a number of blocks. Nymphs and adults of both species suck sap from growing terminals and water sprouts. High populations cause leaves to curl and may stunt shoot growth on young trees.
Aphids excrete large amounts of honeydew, which collects on fruit and foliage.
Sooty mold fungi that develop on honeydew cause the fruit to turn black, reducing its quality. Aphids should be sampled several times throughout the season starting in mid-June. Inspect 10 rapidly growing terminals from each of 5 trees throughout the orchard, and record the percentage of infested terminals. The larvae of syrphid and cecidomyiid flies prey on aphids throughout the summer. These predators complete about three generations during the summer.