Aphids (Rosy Apple and Green Apple)
Aphids are small, soft-bodied insects that often occur in clustered colonies. They suck sap from the phloem vessels in leaves and reduce tree vigor. Watch for curled and sticky leaves due to honeydew excreted by the aphids. Black sooty mold is a fungus that may grow on the honeydew staining the leaves and fruit.
Both rosy apple (Dysaphis plantaginea) and green apple (Aphis pomi) aphid species overwinter as eggs on smooth twigs and water sprouts. Migrate to alternate hosts during summer. They hatch when the buds start to open and begin reproducing immediately. Aphids will feed on leaves from budbreak through early October. Some will form wings and migrate to alternate hosts (weeds or grasses) for the rest of the summer. In September and October, they migrate back to the fruit trees to lay eggs.
- Curled leaves and shoots
- Yellowed leaves
- Sticky honeydew
- Blackish gray mold
- Deformed fruit
Aphids prefer feeding on succulent shoots and their populations are more likely to build up to high levels when there is a lot of succulent tissue present in the orchard. Pruning and fertilization practices that minimize growth of water-sprouts and lush shoot growth should be used to help manage aphids. Apple varieties that are vigorous growers and produce a lot of lush growth may be more prone to large populations of aphids. In most years, succulent shoots are beginning to harden off at the time when aphid populations are beginning to increase. This will slow down the rate at which the aphid populations increase and may be sufficient to prevent damaging population levels from developing.
Insecticides can be very effective against aphids, however, repeated use of the same products has resulted in aphid resistance. Good coverage is important. Aphid feeding causes leaves to curl and within these curled leaves the aphids are partially protected from insecticides. The available materials which are effective are limited and some are very toxic to natural enemies. Having a limited variety of materials increases the possibility that the aphids will develop resistance to them. For these reasons insecticide use should be limited.