Q What is woolly aphid?
A This aphid (Eriosoma lanigerum) arrived in Britain in the 18th century and is now very common. Woolly aphids feed on apples and ornamentals that are closely related, such as crab apples, chaenomeles, cotoneaster and pyracantha.
Caption: Woolly aphids are covered in fluff which helps to protect them
Q How do I recognise woolly aphid?
A You will not see the small, brown or greyish-purple aphids, but rather their woolly protective coating which is white and waxy. This coating looks rather like a fungus, especially when the woolly aphids cluster together in large numbers.
Woolly aphids feed on sap and are attracted to younger, woody shoots and damaged areas such as pruning wounds. Unsightly galls form where aphid colonies have attacked. These can split, letting in diseases such as apple canker.
Woolly aphids don’t attack the roots, but they can infest the base of the trunk.
Q When should I expect to see woolly aphid?
A They overwinter as young aphids. These are not covered by waxy strands, so they are hard to spot. In March and April they become active, and soon breeding colonies covered in a white, woolly coating will be noticeable.
They spread by producing crawling young which find new areas to colonise then produce young. In July winged forms fly off to infest other plants. Breeding stops in autumn when immature aphids seek sites to overwinter.
Q How much of a problem are woolly aphids?
A On a healthy tree, woolly aphid is unlikely to do much damage, though it can harm young trees or those weakened by disease or poor growing conditions However, sticky masses can be a nuisance when harvesting fruit.
Infestations are often kept in check by predators. Both native predators, such as ladybirds, hoverflies and lacewings, and an introduced parasite attack woolly aphids.
The introduced parasite, a tiny wasp Aphelinus mali, now lives wild in southern England and is especially effective during hot, dry years. You can tell that this parasitic wasp is at work in your garden if the wool has been reduced, leaving a shiny, blue-black, naked aphid with a circular hole in its back through which the parasite has made its exit.
Although this parasite is very susceptible to insecticides, it will thrive in an organic garden.
Q How can I control woolly aphid?
A Watch for signs of woolly aphid in the spring. Scrub them off using water with a drop of detergent in it. If you can get rid of the bark colonies before the aphids begin to move on to young shoots in July, it will make spraying unnecessary.
If early control is unsuccessful, spray with Growing Success Fruit and Veg Bug Killer or Provado Ultimate Bug Killer Ready to Use.