Plum aphids

What are plum aphids?

Symptoms

• Plum leaf-curling aphid causes severe leaf distortion on the foliage of all types of plum during April to late May
• Leaves that develop later are not affected, although the earlier damage remains visible throughout the summer
• Mealy plum aphid is active in mid- to late summer, when dense colonies of pale greenish white aphids cluster on the underside of leaves and shoot tips
• This aphid does not cause leaf distortion but it excretes a sugary honeydew that makes the foliage and fruit sticky and allows the growth of sooty mould

Control

Non chemical

Aphids are eaten by a wide range of predators and parasites but they are not usually present in sufficient numbers to prevent aphid infestations developing.

Chemical

Overwintering eggs on the branches can be reduced by applying a plant oil winter wash (Growing Success Winter Tree Wash, Vitax Winter Tree Wash) on a mild dry day in winter. To control plum-leaf curling aphid, spray with thiacloprid (Bayer Provado Ultimate Bug Killer) shortly after bud burst. If mealy plum aphid begins to develop in mid-summer, spray with thiacloprid (Bayer Provado Ultimate Bug Killer), lambda-cyhalothrin (Westland Plant Rescue Fruit & Vegetable Bug Killer), deltamethrin (Bayer Sprayday Greenfly Killer) or pyrethrum (Py Spray Garden Insect Killer).

Do not spray during the blossom period. The minimum interval that needs to be left between treatment and picking the fruit is 14 days for thiacloprid, seven days for deltamethrin and lambda-cyhalothrin and one day for pyrethrum.

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Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

Biology

Both aphids overwinter as eggs that are laid in autumn in bark crevices and around the buds. Eggs of leaf-curling plum aphid hatch at bud burst but those of mealy plum aphid hatch later in April.

Aphids feed by sucking sap from the foliage. Leaf-curling plum aphid secretes chemicals into the foliage that cause the young leaves to develop in a crumpled and distorted fashion. In this species, winged forms of the aphid develop during May and the winged adults then fly away to various herbaceous plant where they spend the summer.

The infestation on plums dies out in late May-early June and after that time the tree is able to produce normal foliage again.

However, if mealy plum aphid is also present on the tree, its population begins to build up and heavy infestation may develop during mid- to late summer. Winged mealy plum aphids develop during the summer and these migrate away to various grasses and reeds.

Both species produce another winged generation in autumn that flies back to plums and other suitable host plants to lay the overwintering eggs.