What is mealy aphid?
Mealy aphid, Hyalopterus pruni, is a type of aphid specific to plums, greengages and damson. It may also colonize apricot, peach or almond. It is pale green, with dusky red forms as well. Eggs laid on the trunk and branches overwinter on the tree and hatch in April. Colonies of mealy aphid form on the underside of leaves but usually don’t cause much leaf curling. Some aphids remain on the plum tree all year, and infestation may become heavy in mid and late summer.
The winged form of the aphid migrates to the secondary hosts, reeds and other grasses. Some winged aphids then return to the plum from September, and lay their eggs. The mealy aphids on plums don’t seem to be farmed by ants, but occasionally ants and wasps arrive to feed on the honeydew that the aphids excrete.
The damage caused by mealy aphid comprises a reduction in nutrients, some physical damage to the leaves, and the development of sooty mould that grows on the sticky exudate, which reduces the leaves’ ability to photosynthesise.
How to treat mealy aphid
You can encourage the presence of predators – principally ladybirds and earwigs – by means of insect hotels. These can be purchased and hung in trees.
Watch a video about insect hotels for fruit trees.
You can also improvise an insect hotel by putting some hay into a flower pot and putting the pot somewhere in the tree. An organic winter wash applied from November to early February can get rid of the overwintering eggs. Apply winter wash on a dry day, without any risk of frost. Organic sprays based on fatty acids or plant oils can be used to reduce the numbers of aphid. You can also spray with a dilute soap solution, a few drops of washing-up liquid in a litre of water, once every 2 or 3 days for a couple of weeks.