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Southeastern Apple ProductionENTOMOLOGY |
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Woolly Apple Aphid
Eriosoma lanigerum (Hausmann)
Description
Young woolly apple aphid (WAA) nymphs have a dark purple body covered with powdery grayish wax. Larger nymphs and adults vary from dark purple to a rosy color and are nearly covered by a woolly mass of long wax filaments. They generally live in colonies, creating white cottony patches that are easy to detect. Adults and nymphs both have needle-like mouthparts. Eggs are almost as large as adults.
 Adult |
 WAA colony |
Life History
WAA overwinter on elms (if present) either as eggs or as immature nymphs in cracks and crevices of bark. The eggs hatch in the spring as wingless stem mothers that then give birth to daughters. Two generations are produced on elm, with the aphids feeding on buds and young leaves (infested leaves will curl into a rosette).
 Colony on elm |
The third generation has wings and migrates to apple and other hosts (including pear, hawthorn, and mountain ash). Repeat generations are then produced on apple. When populations are high, some nymphs may migrate downward, attacking basal roots where the soil has been loosened by the swaying of the tree. Organic matter, root suckers, stones, and soil cracks are other avenues of entrance to the root system. Reproduction may be continuous in the underground colonies.
In the fall, winged females are produced in both the aerial and underground colonies. These females migrate back to elm trees where they give birth to both wingless males and wingless females. A short time after mating, the female inserts a single egg in a rough area of the elm bark.
WAA can spread during the nymph stage, being dispersed by wind, birds, and other insects. Young nymphs are most abundant in spring and fall, but aerial colonies are not a good indicator of root infestations. A tree may have aerial infestations and never develop root infestations.
Damage
Aboveground on apple, WAA feeds on new growth around pruning cuts and other injuries and on leaf axils on sprouts. Feeding around wounds prevents the bark from healing properly. Feeding on new growth can produce gall-like swellings on the small branches. Aboveground infestations produce relatively little damage, especially on older trees.
The most serious problems occur from colonies that feed on the roots and underground parts of the
trunk. Underground feeding often produces large knots, and heavily infested
trees often develop a short fibrous root system and have yellowish foliage.
Young trees that are heavily infested can be easily uprooted.
 WAA on twig |
 WAA on roots |
Monitoring and Control
WAA can be difficult to control because of alternate hosts outside the orchard. Careful selection of insecticides is important, as some of the carbamate and pyrethroid insecticides may increase problems by killing naturally occurring parasites. When aerial colonies are detected, an application of a good aphicide will provide control. There is no control for underground colonies, but some of the Malling-Merton series of rootstocks are resistant to WAA. Since nursery stock may have infestations, trees should be inspected prior to planting and infested trees refused.
Insect and Mite Management Overview
Insect and Mite Index
Southeastern Apple Production Mountain Horticultural Crops Research & Extension Center 455 Research Drive Mills River, NC 28759 Phone: 828.684.3562 ~ Fax: 828.684.8715 Email: jim_walgenbach@ncsu.edu |
Web Crafters: Anne S. Napier and
Steve Schoof |
Updated March 13, 2007