Winter moth
Operophtera brumata
Looper caterpillars that hatch inside the swelling buds in spring and eat the leaves and blossom before they open. The moths fly on mild nights in December.
How to know it
A pale green looper 20–25 mm long with a white stripe along each side, arching its back as it walks. It hatches inside the bud, so the first evidence is a bud that opens already shredded. The male moth is a drab buff insect that flies at night in late autumn and winter; the female is wingless and crawls up the trunk to lay.
What you'll see
- Buds that open already holed and shredded, in spring.
- Leaves emerging ragged and full of holes, with fine silk webbing among them.
- Blossom eaten out before it opens, so the tree flowers thinly or not at all.
- Green loopers dropping on silk threads from the canopy in late spring.
- Small drab moths flying against a lit window on a mild evening in November or December.
Where it comes from
One generation a year, on an unusual calendar. Moths emerge in late autumn and fly on mild nights through the winter; the flightless female climbs the trunk and lays in bark crevices. Eggs hatch at bud swell in spring, exactly matched to the bud break of the host, and the caterpillars feed for six weeks before dropping to the soil to pupate.
Established in the northeast, the Pacific northwest and maritime Canada, as well as its native Europe. Warm autumns extend the flight, and a spring in which bud break and egg hatch coincide closely produces the worst damage.
Dealing with it
- Fit grease bands or sticky bands around the trunks in October and keep them sticky until spring — the female cannot fly, so this stops her getting up.
- Band the stake as well as the tree, or she will simply climb that.
- Spray Bt at bud break, while the caterpillars are small and before the leaves close over them.
- Encourage blue tits and other insectivorous birds, which time their broods to this caterpillar and take enormous numbers.
- Accept the damage on a mature tree; it refoliates and the following year is usually better.
Keeping it out
- Band every fruit tree in early autumn, every year, in an area where it is established.
- Put nest boxes up for tits and chickadees near the fruit trees.
- Keep young trees watered and mulched so a defoliated year does not stunt them.
- Check the bands after storms and top up the grease.
- Watch for the released parasitic fly Cyzenis albicans where a biocontrol program is running; it has worked well in New England.
What it goes for
Apple, pear, plum, cherry, blueberry, oak, maple, hazel and many broad-leaved trees.
Who hunts it for you
- BatsChiroptera A single bat takes hundreds of moths and mosquitoes in a night, and the moths are the parents of your cutworms, corn earworms and hornworms. Put up a bat box on a warm south wall, leave a night-scented corner unlit, and never spray after dark. Grow to recruit it: Evening Primrose,Honeysuckle,Nicotiana,Summer Jasmine
- Garden birdsPasseriformes Both things are true: birds strip your currants and a brood of blue tits takes several thousand caterpillars out of one fruit tree in a fortnight. Net what you must and welcome them everywhere else — a nest box near the apples is worth more than a spray. Grow to recruit it: Echinacea,Elderberry,English holly,Goldenrod,Rudbeckia,Sunflower
See also
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com