Bedding plants

Walnut tree: identify and combat diseases and pests

There is hardly a plant that can be permanently protected against diseases and pests, not even the walnut tree. Although it is quite robust, various pathogens can affect it severely.

Many trees and plants have natural protection against pests. So also the walnut tree. While human noses find the smell of the tree pleasant, it repels pests relatively reliably. But even the best natural protection does not mean that your walnut cannot get sick.

In this article we explain how you can recognize diseases or pests and what you can do about them.

Common pests in the walnut tree

Some pests cannot be put off by the smell of the walnut tree. Gall mites, mealybugs and aphids, but also caterpillars can sometimes be found in the tree. Another troublemaker is the walnut fruit fly, which rightly bears its name.


Aphids, which are among the sucking pests, are increasingly found on the underside of the leaf. As a rule, you do not have to act immediately when you discover the lice. Only if there is heavy infestation and many leaves curl up, you should take the following measures:

  • Remove the affected shoots
  • In the case of less infestation: spray the lice directly with an alkali. Alternatively, you can use natural pesticides made from potash soap, pyretrum and rapeseed oil.
  • If the infestation is severe, chemical agents are recommended - but be careful: the walnuts are no longer suitable for consumption.

A good way to not only curb lice infestation, but to prevent it, is to use natural predators from aphids. Establish parasitic wasps, ladybugs or lacewings in your garden. The insects need a suitable environment for their species, but subsequently protect not only your walnut tree, but many other plants in the garden.

Foliage on the walnut:

Butterfly caterpillars, blue sieve and wicker drill caterpillars can be found on walnut trees. Again, first try to control the caterpillars organically. If the tree has not yet grown large, you can certainly pick up the caterpillars with your hands.


Bluebirds are pests that can cause massive damage to the walnut tree. The insects eat through the bark and leave passages in trunks and in the branches. You can recognize the caterpillars by their yellowish-white body, which is covered by point warts. The caterpillar can be up to six centimeters long. To combat them, the following way is recommended:

  • Remove all infested shoots
  • If the caterpillar has already settled in the trunk, the tree should be felled.

Walnut fruit fly:

Another pest that affects the tree is the walnut fruit fly. You recognize the pest primarily by the damage it leaves behind: black dots on the still green skin of the fruit. The maggot of the fruit fly penetrates into the pericarp and eats it slowly, making it soft and moist. Combat tips: Collect all infested fruits and destroy them.

Prevention is of course more sensible. Yellow boards, e.g. these, just hang them up in different places in the tree and keep the walnut fly away accordingly. An alternative, but more cumbersome, is to tie the tree down with a fly net.

Diseases of the walnut tree

It is not always easy to tell which disease is hidden behind a symptom. Therefore, we recommend that you consult a specialist in advance and take specific action in case of doubt.

Cherry leaf roll virus

The cherry leaf roll virus is one of the diseases of a walnut tree that cannot be controlled. The virus causes spots that appear on both the fruit and the leaves and develop a line pattern.


Powdery mildew forms light areas on the leaf beams that have a mealy touch. Carefully remove the shoots and control them with pesticides. Pay attention to agents based on night sulfur or organic substances. Apply the product once a year before flowering, if possible.

Fungal infections:

Brown and gray-brown leaves indicate mushrooms. If you lift the leaves, you can partially recognize fruiting bodies on the underside. The diseases often occur, especially in wet summers. As part of the control, remove the affected plant parts again. There are no special pesticides in this case.


If growths form on shoots, it is often a bacterial attack. To prevent the bacteria from penetrating, you should regularly check the walnut tree for damage and keep fresh damaged areas clean. Even after the tree has been cut, bacterial infection can occur at the interfaces. Therefore dry the cut edge carefully.