Woolly aphid

This pest isn’t easy to spot and, unfortunately, it can do a lot of damage to apple trees,

The woolly aphid is a sap-sucking insect that spends most of the year underground, feeding on the plant’s root system. During the warmer months, it can also be found above ground, feeding on new growth as well as woody parts of the tree where the bark is thin or damaged. You might also see them on fruit stalks and the dry leaf-like calyx at the end of the fruit.

Woolly aphids are blue-grey in colour, and produce white waxy threads (above) that give them the characteristic woolly appearance. They reproduce quickly and feed in colonies, creating large woolly clusters that produce copious amounts of sticky honeydew, which falls on the shoots and fruit and then turns black with mould. A badly infested apple tree may be thin and sparse, with curled leaves, fruit that drops prematurely and woody galls where feeding has taken place.

Some seasons are worse than others. Healthy trees growing in fertile soil will tolerate small infestations, and natural predators provide some control, including the large spotted ladybird (Harmonia conformis) and a specific parasitoid wasp (Aphelinus mali). If the population of woolly aphids explodes during the growing season, use soap and oil-based sprays to keep numbers down, but bear in mind that organic sprays can affect beneficial insects, too.

Some apple varieties such as Anna are more susceptible to attack. There are chemicals available that can help manage the issue, but you will probably need to keep using them into the future, which will cause more problems than good. When you have a tree that is constantly under attack, your best option is to bite the bullet and replace it.

Many apple trees that are sold these days are grafted onto woolly-aphid-resistant rootstock. Ask at your nursery when purchasing a tree. Keep in mind, while the roots are less susceptible, the growth on top may still be attacked, so ask for a variety that’s a proven performer in your area.