Pest description and crop damage Adult woolly apple aphids are reddish to purple and are completely covered with a thick, woolly white wax. The insects feed on roots, trunks, limbs and shoots, producing galls at the site of the infestation. Heavy infestations on roots or above-ground portions of the tree can stunt growth and even kill young trees.
Biology and life history These aphids overwinter as adults on roots and aerial parts of apple trees. In severe winters the aboveground colonies may be killed. In spring and early summer, nymphs move up and down the tree to find a new spot to settle and produce new colonies. Preferred feeding sites are leaf axils on new shoots.
Scouting and thresholds Inspect trees during the growing season for the characteristic white, waxy colonies. Aerial colonies are mainly found in rough areas of bark and in wounds caused by pruning.
Lacewings, ladybeetles and syrphid fly larvae are predators, as well as the parasitic wasp Aphelinus mali. The predators will consume all but the waxy secretion left by the aphids.
This aphid is considered a minor pest in the PNW. If colonies are found on trees, they can be physically removed. Many Geneva and Malling-Merton rootstocks are resistant.
Management-chemical control: HOME USE
Spring and summer
- carbaryl-Highly toxic to bees.
- imidacloprid-Soil drenches may have residual activity in woody plants lasting for 12 or more months. If short-term management is the goal, consider other approaches. Highly toxic to bees.
- insecticidal soap-Some formulations are OMRI-listed.
- malathion-Highly toxic to bees.
- pyrethrins-Highly toxic to bees. Some formulations are OMRI-listed for organic use.
- zeta-cypermethrin-Highly toxic to bees.
Management-chemical control: COMMERCIAL USE
Spring and summer
- diazinon (Diazinon 50W) at 4 lb of product/a in up to 100 gal water per application. Do not apply more than one application as an in-season spray. REI 4 days. PHI 21 days. [Group 1B]
- flonicamid (Beleaf 50 SG) at 2.0 to 2.8 oz of product/a in up to 100 gal water per application. Do not apply more than 3 applications per season. REI 12 hr. PHI 21 days. [Group 9C]
- thiamethoxam (Actara WDG) at 4.5 to 5.5 oz/a in up to 100 gal water per application. Do not exceed 16.5 oz/a per season. REI 12 hr. PHI 35 days. [Group 4A]