Why Are My Plum Tree Leaves Sticky and Distorted?

Sticky, puckered or curled leaves on a plum tree are almost always caused by one of two aphid species that specialise on plums and related stone fruit. The stickiness comes from honeydew — a sugary excretion the aphids produce as they feed — and the distortion results from the aphids injecting saliva into leaf tissue as they feed. Once you can identify which species you have, management becomes straightforward.

Leaf curl plum aphid — tight spring distortion

The leaf curl plum aphid (Brachycaudus helichrysi) is a small, yellow-green insect that hatches from overwintering eggs on plum bark in early spring. Colonies build rapidly on expanding shoots, causing leaves to curl so tightly that the aphids inside are protected from contact sprays. The damage is most severe in April and May. By early summer the aphids migrate to other host plants and the tree produces new undistorted leaves. For established trees, the impact is mainly cosmetic — unless young trees are being grown on, where shoot tip distortion can affect form.

Mealy plum aphid — late-season stickiness

The mealy plum aphid (Hyalopterus pruni) is a larger, waxy grey-green insect that appears on leaf undersides from June onward. Unlike the leaf curl aphid it does not cause severe distortion but produces copious honeydew, which coats leaves, fruits and garden furniture beneath the tree, and on which sooty mould grows. Heavy late infestations on trees in fruit can affect fruit flavour and appearance if the honeydew drips directly onto developing plums. By late summer this species also migrates to reeds and rushes.

Sooty mould on sticky surfaces

The black, sooty coating that develops on honeydew-covered surfaces is a secondary fungal growth (Capnodium species). It is not directly harmful to the tree but looks unsightly and can reduce photosynthesis in very heavy infestations. Once the aphids are gone and the honeydew stops being produced, the sooty mould weathers off naturally over a few weeks of rain.

Controlling aphids — intervention threshold

On established trees, a moderate aphid infestation in late spring rarely needs treatment — natural predators (ladybirds, lacewing larvae, hoverfly larvae and blue tits) usually arrive and collapse the population within two to three weeks. On young trees where shoot growth is being seriously distorted, or when populations are building rapidly without predator activity, insecticidal soap spray applied to leaf undersides provides a targeted, low-impact knockback. Avoid spraying when trees are in flower as this can harm pollinators.