Winter moth caterpillars

Winter moth caterpillars are responsible for eating holes in the leaves of many deciduous trees and shrubs during spring.

Winter moth caterpillar

Quick facts

Common name Winter moth, Mottled umber moth and March moth
Scientific name Operophtera brumata, Erannis defoliaria,  Alsophila aescularia
Plants affected Fruit trees, oak, sycamore, hornbeam, Sorbus spp., roses and many other deciduous trees and shrubs
Main symptoms Holes eaten in leaves, blossom and apple fruitlets
Most active Bud burst to early June

What are winter moth caterpillars?

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 yields and quality.

Winter moth is a general name that can be used for a number of species that have adult moths that emerge and lay eggs between November and April.  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 attacked as well, including oak, sycamore, hornbeam, beech, dogwoods, hawthorns, Sorbus, roses, hazels and elms.

Symptoms

You may see the following symptoms:

  • Attacks by winter moth caterpillars are usually first noticed in spring when emerging leaves are eaten
  • The damage is particularly noticeable in mid-summer when the leaves are fully expanded and the small holes made during the spring have enlarged due to leaf growth, at which point the pest has left the tree
  • Blossom and developing fruitlets can also be damaged
  • Early damage on apple fruitlets causes a deep cleft in the side of the fruits to develop by the time they have reached full size in late summer

Control

Non-chemical control

Egg laying can be reduced by placing a sticky grease band or barrier glue around the trunk and tree stake in October to intercept the 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.

Chemical control

Shortly after bud burst - but not during flowering due to the danger to pollinators - apples, pears and small ornamental trees can be sprayed with deltamethrin (e.g. Bayer Sprayday Greenfly Killer) or lambda cyhalothrin (e.g. Westland Resolva Bug Killer), provided the label instructions relating to the food plant are followed.

An organic alternative is pyrethrum (e.g. Py Spray Garden Insect Killer, Bug Clear Gun for Fruit & Veg) to control the young caterpillars. Caterpillar damage on tall trees has to be tolerated.

Download

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

Biology

Wingless female winter moths emerge from pupae in the soil during November to February 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.

Advertise here

We love free entry to our local RHS garden

Lucy, mum, part-time lectureer & RHS member

Become a member

Discuss this

for the site or to share your experiences on this topic and seek advice from our community of gardeners.