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Winter moth caterpillars can be responsible for eating holes in the leaves of many deciduous trees and shrubs during spring.
Winter moth caterpillars eat holes in the leaves, blossom and developing fruitlets of many tree fruits, ornamental trees and shrubs. Severe attacks can weaken plants. Extensive damage to fruit trees can affect crop yield and quality.
Winter moth is a name that can be used for a number of species that have adult moths that emerge and lay eggs between November and April. These moths have wingless females that emerge from pupae in the soil and crawl up trunks to lay eggs on branches. The most important are the winter moth (Operophtera brumata), mottled umber moth (Erannis defoliaria) and March moth (Alsophila aescularia). The caterpillars of these moths hatch in the spring as buds are opening and they will attack most types of tree fruit and many deciduous trees and shrubs. The main fruit trees attacked are apples, pears, plums and cherries. Many ornamental trees are also hosts, including oak, sycamore, hornbeam, beech, dogwoods, hawthorns, Sorbus, roses, hazels and elms.
You may see the following symptoms:
Egg laying can be reduced by placing a sticky grease band or barrier glue around the trunk and tree stake (if present) in October to intercept the wingless females. This needs to be kept sticky and free of detritus until mid-April. Many birds, especially tits, feed their chicks with large numbers of winter moth caterpillars during the spring.
Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)
Wingless female winter moths emerge from pupae in the soil during November to April and crawl up trunks to lay eggs on the branches.
Eggs hatch at bud burst and the pale green looper-type caterpillars emerge and start feeding. The caterpillars are up to 25mm (about 1in) long and complete their feeding by early June. They then go down into the soil where they pupate.
In some years oaks and other deciduous trees are largely defoliated during the spring by the caterpillars of winter moth and other species. Such trees will survive and produce more leaves during the summer.
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