Advice
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Winter moth caterpillars (Operophtera brumata)
Plants affected
Fruit trees and many other deciduous trees.
Symptoms
In the spring, leaves are loosely bound together with silk threads and eaten by pale green looper-type caterpillars. The damage is particularly noticeable in midsummer when the leaves are fully expanded and the small holes made during the spring have enlarged due to leaf growth. Blossom and developing fruitlets can also be damaged.
Biology
Wingless female winter moths emerge from pupae in the soil during November to January and crawl up trunks to lay eggs on the branches. Eggs hatch at bud burst and the caterpillars complete their feeding by early June. They then go down into the soil where they pupate.
Control
Egg laying can be reduced by placing a sticky band around the trunk and tree stake in late October to intercept the females. Garden centres stock ready-prepared strips for tying round the trunk or grease for direct application to the bark.
Shortly after bud burst - but not during flowering - apples, pears and small ornamental trees can be sprayed with bifenthrin (Bayer Sprayday Greenfly Killer Plus, Scotts Bug Clear Gun or Doff All in One Garden Pest Killer). Organic alternatives are rotenone* (Bio Liquid Derris*) or pyrethrum (Py Spray Garden Insect Killer, Scotts Bug Clear Gun for Fruit & Veg) to control the young caterpillars.
* Rotenone/derris-based insecticides are being withdrawn from sale. Gardeners who have this pesticide may continue using it until 10 October 2009. Any unused products after that date should be disposed of safely by handing them to the staff at a local authority manned waste disposal facility.
Disposing of old chemicals