Frost moth: Recognize, combat and prevent

You can find out what you can do as a preventive measure to keep the winter moth away from trees and how to recognize and combat it when it is infested.

The Frost Moth (Operophtera brumata) is polyphagous, which means it likes to attack all kinds of different trees and shrubs. Deciduous trees, fruit trees, berry bushes and roses are just as much on his menu as many ornamental shrubs. Fortunately, the insatiable caterpillars are easy to spot and fighting them is relatively easy - if you know how.

The Little Frost Moth (Operophtera brumata) is a worldwide common butterfly that can cause great damage to deciduous trees. The adult moths hatch between mid-October and early November, presumably depending on soil temperature. The flightless females climb the trunk of the host tree and are mated by the winged males on their way to the crown. The eggs are preferably laid in the immediate vicinity of buds and around the onset of the first night frosts. A female can lay up to 300 eggs. When the winter is over, the moth caterpillars hatch from the eggs at exactly the same time as the young buds burst, until the beginning of May. In the course of their caterpillar life, the moths eat buds, leaves, flowers and even young fruits. Once they have developed sufficiently, the caterpillars lower themselves to the ground using a caterpillar silk thread pupate in the ground - to then hatch as adult winter moths in October and the next generation procreate.

To ensure that your plants do not fall victim to the voracious moth caterpillars, you will find everything you need to know about recognizing, preventing and combating the winter moth below.

Note on the Great Frost Moth: The Great Frostmoon (Erannis defoliaria) occurs far less frequently in the home garden. Its biology is similar to that of the lesser winter moth, although they are not the same genus. The control measures are also the same as for the small winter moth.

Recognize Frostbite

If you check the buds of your trees, you can already find the red eggs of the winter moth, which are about half a millimeter in size, in autumn. The caterpillars that hatch are initially only about a millimeter long and dark gray. As they develop, they grow to two and a half centimeters and turn light green. The special way the caterpillars move is easy to recognize: Because tensioner caterpillars only one only pair of rear abdominal legs, they take a very high one with every step "Humpback". In order to be able to eat undisturbed, the caterpillars like to spin themselves between the leaves of the host plant, which is where their German name comes from. If the infestation is very severe, the leaves can even skeletonize, so that only the leaf skeleton remains. However, the damage usually looks worse than it actually is. Frost moth caterpillars like to eat half of the young fruit of sweet cherries – also known as “spoon feeding”. The caterpillars can be found between April and June. The finished moths show a clear sexual dimorphism - males and females are very different from each other. While the males are colored gray-yellow to beige-brown and brown-yellow fringed wings of maximum two and a half Centimeters wide, the females are brownish-grey and have only vestigial stumpy wings in the same Colour. Both have short, hairy antennae and a useless proboscis - the moths do not eat and die after a few days.

Prevent frostbite

Anyone who has been able to observe damage caused by the winter moth in recent years should ask themselves one thing above all: Is the damage relevant? Especially for hobby gardeners, for whom high yields are not a must, a regular, weak infestation can often be tolerated and is hardly worth the effort to combat.

promote beneficials

A lot of preventative plant protection is already being done – unconsciously – in gardens that are close to nature in particular: the promotion of beneficials and avoiding pesticides that are harmful to insects often creates a large number of natural opponents that prevent severe yield losses. Setting up nesting boxes is particularly worthwhile: great tits can consume several hundred caterpillars daily during the breeding season.

glue rings

Glue rings are a tried and tested means of preventively combating the winter moth. They are attached to the trunk or trunks of the endangered trees by mid-October at the latest. Any support posts and neighboring trees that are very close should also be ringed. The females crawling upwards then stick to the sticky glue. Make sure the ring fits snugly so the caterpillars can't crawl underneath. You should check the rings after stormy weather: sometimes leaves or twigs that are blown in build “bridges” over the glue rings. In the spring, however, the rings should definitely be removed so that any beneficial insects are not prevented from climbing the trunk as well.

Combat frostbite

If your preventive measures were not sufficient and you notice a clear infestation in the spring, you can also fight the moth directly. Well suited are preparations with the active ingredient Bacillus thuringiensis. They are very specific only against caterpillars and only if they are ingested. The application should be carried out in warm weather (at least 15 °C) - then the caterpillars have a big appetite and they will ingest the product safely. In the best case, the spray is applied early so that the damage caused by feeding is limited. For example, ours is an officially approved Bt preparation against the winter moth Plantura Zünslerfrei XenTari®.

Tip: In the home garden, one can speak of a stronger infestation if 10 out of 100 leaf clusters checked have caterpillars.