Q What are aphids?
A Small insects, including greenfly and blackfly, which are found in clusters on the leaves and shoots of many plants.
Caption: Distorted shoots and clusters of small insects are characteristic of aphid attack
Q How do I recognise them?
A The insects are green, brown or black. They are egg-shaped, about 2mm long, usually without wings and are often grouped in large numbers. Even at a distance you’ll notice shiny honeydew deposits, distorted or rolled-up leaves, or distorted shoots.
Q What damage do aphids cause?
A Aphids feed by sucking sap from the plant, distorting its growth. This may mean that new shoots are stunted, leaves cannot photosynthesise very effectively, or fruit is disfigured and fails to mature properly.
Aphids also excrete shiny, sticky honeydew as a waste product which can cover leaves, encouraging the growth of black sooty mould. This is unsightly and may further damage a plant’s health by blocking out the light it needs. Aphids are also responsible for spreading viruses.
Q How can I control aphids?
A In the majority of cases, it’s best to do nothing. Trees tolerate some damage, and the aphids’ natural predators will help get rid of them.
If the infestation is heavy, you can squash them with your finger and thumb or spray with Bayer Natria Bug Control or Westland Resolva which are approved for use on fruit.
Q What about natural predators?
A Insectivorous birds such as tits can consume huge numbers of aphids and aphid eggs. Feed birds in winter and put up nest boxes to encourage them. Ladybirds and lacewings are also big aphid-eaters. Entice them into your garden by allowing some aphids to survive and avoid using insecticides that can harm them.
Q Which aphids attack cherry trees?
A The main pest is cherry blackfly (Myzus cerasi).
Q How do I recognise this pest?
A Colonies of small, black insects infest young leaves and shoots and can smother an entire tree, causing distorted leaves and the death of shoot tips.
Sooty mould growing on the honeydew adds to the disfigurement. Large trees can tolerate such attacks, but the shape and future cropping of small trees can be affected.
Q When does cherry blackfly appear?
A The blackfly hatch in April and feed on the undersides of leaves. By the time you see the distorted leaves, much of the damage has been done, so check from early April and take action if needed. Stop any spraying in July, when the aphids migrate to bedstraws and other wild plants for the summer, and allow natural predators to finish off those remaining on the trees. In the autumn, mature aphids return to the fruit trees and lay their eggs on the bark.
Q Which aphids attack plum trees?
A Three species of aphid affect plums and damsons:
Damson-hop aphids (Phorodon humuli) are yellow-green and shiny, and occur on young shoots. They cause only slight distortion of the leaves. They hatch in April, migrating to hops from early summer, where they become a troublesome pest. In autumn they return to the trees to lay eggs.
Plum leaf-curling aphids (Brachycaudus helichrysi) occur in large colonies on young shoots, causing severe leaf-curling. They hatch in December and January, attacking the leaves in bud. Yellow-green in colour, they spend summer on border perennials.
Mealy plum aphids (Hyalopterus pruni) are bluish-green with a waxy coating and live in tightly packed masses on the undersides of leaves. They hatch in April and can build up to damaging levels by June. They do not distort the leaves, so this aphid is usually first detected when the foliage and fruit become sticky with honeydew and black sooty mould develops.
These aphids spend the summer on reeds and waterside grasses, though they may stay on the fruit trees as late as August. They return to the fruit trees in autumn to lay eggs.
Q How do I control these pests?
A Check shoots in early spring (no later than March) and take action if large colonies of early-hatching aphids are visible. If sooty mould occurs later in the season, you may need to spray the undersides of leaves against mealy plum aphids.