Fighting Willow Borers: Damage and Means

Small willow caterpillars compete against a large tree and still win the duel. Time is their secret ally and of course their diligence. It may take years, but at some point every tree gives up. Too many holes run through the trunk and weaken its vitality. Hurry to block the caterpillars' way into the deepest interior of the fruit trees.

Characteristics

• Willow borer is a species of butterfly (moth)
• comes from the wood drill family
• Cossus cossus is its scientific name
• only attacks deciduous trees
• Willows are preferred host plants, but also apple and pear trees
• the moth is hairy, the wings spotted gray-brown
• Wingspan: up to 8 cm in males, 10 cm in females
• crepuscular and nocturnal
• Larvae reach up to 10 cm in length
• strong red coloring, black nape of the neck

Toxicity

The caterpillar is not poisonous per se. But she has powerful cutting tools and knows how to defend herself. That hurts. Direct contact with it can also cause skin irritation.

Damage image

The moth is well camouflaged in color on the tree bark, the caterpillars stick deep in the tree trunk. How can an infestation be identified clearly and, above all, in good time? The traces left behind are what give clear indications of the presence of the willow borer.

• The bark has large, round oval holes
• there is reddish drill dust in the openings
• the caterpillar droppings are carried out of the borehole
• it can therefore also be discovered at the hole opening
• large areas of the brittle bark can be peeled off
• the tree gives off a strong vinegar smell

The typical vinegar smell is an invitation to other butterflies. They lay their eggs in addition, which gives a powerful boost to the progression of the infestation. The damage done can now be clearly seen on the tree at the latest.

• withered branches
• withering leaves

In the final stage of the infestation, the tree eventually dies.

Tip: A heavily perforated tree increasingly loses its stability and can "unexpectedly" bend. The falling parts of the tree pose a danger. Preventive felling is advisable if the infestation is known and can no longer be contained.

Natural enemies

The willow borer has some natural enemies in this country:

• birds of prey
• Woodpeckers
• Parasitic wasps

However, these enemies are also powerless against the caterpillars hidden deep in the trunk.

prevention

Keeping the moth away from your own fruit trees is impossible. So far there is no suitable means available to make the tree less attractive to this pest. All that remains is to check the tree regularly in order to at least discover the infestation at an early stage.

• check twice a year
• especially in areas where the willow borer is common
• look for eggs laid in June and July
• Search the trunk for openings from July to September
• especially the part close to the ground

Combat

Fighting the willow borer is not easy. The caterpillars that cause the damage hide inside the tree, which is difficult to reach. Only in their early stages are they close to the surface and therefore more easily accessible. Unfortunately, only a few resources are available for combating it. It is not always certain that the tree will actually be saved. Reaching over to nearby trees is possible at any time, which increases the pressure to succeed. Emergency felling is often the only way to limit the impact of the red caterpillars.

Quassia broth

Quassia wood is a very special kind of bitter wood. The active ingredient quassin it contains is deadly for numerous types of vermin, including the eggs and the newly hatched larvae of the willow borer. To extract quassin from the bitterwood, it is necessary to prepare a broth. You can easily produce this natural plant protection product yourself.

1. You need 150 grams of bitter wood. Pour 2 liters of water over it and let it stand for a day.

2. Boil the solution vigorously for an hour.

3. Sieve out the wood chips and let them dry. They can be used up to three times.

4. Before using, dilute the broth with 10 liters of water.

5. Spray the tree trunk with the quassia broth at regular intervals. Rinse off the base with clear water after 2-3 days. Start treatment in early spring and stick with it through autumn. The broth can be kept for the entire period.

Tip: Be cautious about using quassia broth. Only spray them locally in a limited way. It is not only poisonous for the willow borer, but also for many beneficial insects.

insecticide

The contact poison pyrethrum is also effective against eggs and newly hatched larvae of the willow borer. Different types of chrysathmas are the basis for the production of insecticides with this active ingredient. Several preparations, each with different names, are available on the market. The poison damages the nerve cells of the willow borer but also other insects. It does not matter whether it is a pest or a beneficial insect. This is why this insecticide should also be used sparingly.

Parasitic wasps

Parasitic wasps are tiny insects that should not be confused with the large, feared wasps. They have been used successfully against food and clothing moths for years. The ichneumon wasps are not only specialized in these two species. That makes them interesting for combating other butterflies.

• are very small, around 0.4 mm
• don't fly, they crawl
• feed on eggs and caterpillars
• are completely harmless to humans
• also for other animals and plants
• once they have eaten their food, they disappear from the scene
• die and turn to dust
• Cards with parasitic wasps can be obtained on the Internet

Kill caterpillars

Caterpillars that have already penetrated deep into the tree can hardly be reached by the aforementioned measures. That is precisely why it is extremely important not to let it get that far. If the infestation is discovered late, however, there is no choice but to leave the tree to the caterpillars or to try an extremely brutal method. The holes visible from the outside are pierced with a sturdy wire. The large caterpillars are pierced by the wire and killed. This is not for the sensitive. Unfortunately, not all caterpillars are caught this way, but their number is certainly significantly reduced.

Cut away the infected parts

If the whole tree is badly damaged, it must be felled and the rootstock dug up. If, on the other hand, only some of the branches are infested with the willow borer, generously cutting away the affected areas can be a viable escape route.

• cut into the healthy wood
• the month of May is the ideal time
• Seal cuts with appropriate protective agents

Tip: Regardless of whether the whole tree or only parts are felled, the proper disposal of the wood waste must always be ensured. Otherwise, the caterpillars survive in the dead wood and soon attack other trees. The most effective type of extermination is incineration.
Conclusion
Willow borers are a deadly threat to our apple and pear trees. Especially when the caterpillars remain undetected and hollow out the trunks undisturbed for years. An attentive fruit tree owner who knows the signs and takes up the fight early on, on the other hand, has a good chance of driving away the caterpillars and harvesting them from his fruit trees for a long time.