Pests

Trees in poor health or lacking proper nutrition are more liable to succumb to attack, so make sure that you address these needs as well as dealing with any immediate problems.

Most pests of walnuts are not too serious and cause mostly cosmetic damage or result in a reduced crop rather than threatening the life of the tree. Grafted walnut trees suffer from even fewer pests and diseases, there are a few you should watch out for.

Here are the main culprits in the UK climate…

Leaf Gall Mite

The Walnut Leaf Gall Mite (Aceria erinoea, previously known as Eriophyes erineus) causes unsightly damage to the leaves, causng a raised hollow bump about half an inch long and with the appearance of a caterpillar’s body. The mites are tiny – less than 0.1mm – and lurk overwinter in unopened buds, doing their damage before the leaf is properly developed. Unless the infestation is huge it will not cause the tree much strain, and is in any case very difficult to get rid of entirely

Woodpeckers

These birds are not primary pests of Walnuts, but where either poor growing conditions or burrowing insects have created cavities inside the tree, they will sound them out and dig around looking for grubs.

The resulting holes can do serious and even fatal damage to young trees. The only reliable way to keep the birds away is to make sure that the trees are as healthy as possible in the first place.

Codling Moth

Officially ‘Laspeyresia pomonella’, this moth can destroy the nut kernels early in the fruiting season and also stain both shell and kernel later.

Pheremone traps to catch male moths are effective from early-mid Spring, otherwise there is no defence apart from sprays.

Minor Pests

You are unlikely to meet the following pests, but it is as well to be able to recognise them even if only to eliminate their presence

Husk Flies

In Canada and the USA there is danger from the ‘Rhagoletis’ species of ‘Walnut Husk Flies’, which feed in the husk and stain the fruits, as well as spoiling the flavour of the kernel. Sprays are the only widely used control.

Others

In most places from time to time there may be outbreaks of these very minor pests:

  • Panonychius ulmi Red Spider Mite
  • Lecanium coni European Fruit Lecanium
  • Chromaphis juglandicola Walnut Aphid
  • Pratylenchus vulnus Root Lesion Nematode

Generally confined to North America there are also:

  • Datuna integerrima Walnut Caterpillar
  • Amyelous transitella Navel Orangeworm
  • Conotrachelus juglandis Walnut Weevil

Scroll to Top