How To Save A Dying Walnut Tree?

How To Save A Dying Walnut Tree?

If a walnut tree is dying, it is likely due to an environmental factor affecting the overall health of the tree.

The most common causes of a dying walnut tree are diseases, pests and overwatering.

The first step in saving your dying tree is to correctly identify the cause of the problem. Once you have diagnosed the condition, you can quickly proceed with the appropriate treatment.

In this article, we will discuss the different causes of a dying walnut tree, and how to save it.

Why is my walnut tree dying?

Diseases

Armillaria root rot

This is also known as oak root fungus, and it causes the leaves of the walnut tree to become discolored and drop off prematurely. You will also notice honey-colored mushrooms growing on the base of your tree. Eventually branches will start to die, until the entire tree succumbs to the disease.

The fungus that causes the disease lives in the soil and waits for the opportunity of the tree’s roots becoming rotten, which it can then feed and survive on. 

Unfortunately, Armillaria root rot cannot be controlled, especially if it has already seriously affected the tree. You are better off uprooting the tree and disposing of it properly. If you do plan on replacing the walnut tree, choose a resistant rootstock to prevent the disease in the future.

Anthracnose

This is a fungus that causes brown or black lesions to appear on the foliage. The lesions tend to fade toward the center, with a yellowish halo. As more lesions form, they will grow into one another and coalesce to form patches near the margins of the leaves.

You can control anthracnose by using a fungicidal spray, removing the tree debris from around the tree, avoiding overwatering, not planting the trees too closely together, and feeding the tree properly and regularly.

Powdery mildew

This disease is also caused by a fungus. In this case, white, powdery spots will start to appear on the foliage and on the fruit. The young leaves will also crinkle as they grow older if the tree has powdery mildew.

This disease, like most fungal diseases, emerges in conditions of moderate temperatures, insufficient sunlight and poor air circulation.

Blackline disease

This viral disease makes the walnut tree lose its vigor, which is noticeable when the leaves turn yellow and start drooping. The leaves will then start to drop off and the terminal shoots will die back.

This disease most likely infects the tree through infected pollen or infected graft wood.

Prevent the virus from infecting your trees by making sure your graft is virus-free. If your tree does become infected, remove it as soon as possible so that it does not spread to your other trees.

Crown gall

This bacterial disease causes galls of all sizes to grow on the walnut tree’s root and root crown, and will then make its way to the trunk. At first, the galls are smaller and lighter in color, but they will eventually become bigger and darker. Over time, the galling will become so serious that the tree’s constricted vascular tissue will cause its growth to become stunted, and the tree might die.

The pathogen infects the tree through wounds on the surface and disrupts the plant’s cells, making them proliferate and become undifferentiated, which leads to the formation of the gall.

Avoid the disease by using well-draining soil and disease-free stock, and try as best you can not to wound the tree.

Walnut blight

This disease presents itself as spots on the tree’s fruit that tend to enlarge and darken. It is important to know the time of infection, because if the bacteria are present before the walnut shells harden, the kernel inside will be affected.

The bacteria will weather the winter inside the dormant buds of the walnut, and when the bud breaks the following year, they will once again infect the fruit and leaves.

Remove the blight by using bactericides that contain copper once a week, especially during wet weather, in order to protect new growth.

Phytophthora rot

When your walnut tree has phytophthora rot, its growth is affected and the leaves will turn yellow and begin to wilt. The branches will die back. If the rot is in the root crown, the tree will likely die within the season. This is because the roots have become rotten. In severe cases, cankers will develop on the root crown and even extend above the soil line. The cankers have discolored bark and will have a zonate appearance underneath the bark.

The infection is encouraged by waterlogged soil and contaminated water, soil and plants.

Pests

Walnut gall mites

This species of mite cannot be seen by the naked eye. These tiny insects feed on the leaf’s tissue, especially during the summer. This results in blisters forming on the top of the leaf and orange masses on the underside of the leaf.

Get rid of the mites by spraying the tree’s leaves with water to dislodge. Wet leaves also discourage the mites from attacking them. If certain branches have been seriously affected, it is best to prune them away.

Codling moth

This insect will find cracks in the bark or space under the leaves, and will burrow into the soil during the winter. They will lay eggs near or on the fruits of the walnut so that their larvae can penetrate the fruit and feed on the kernel for nutrition.

Aphids

These insects travel easily from one tree to another. They form colonies on the underside of the leaves and feed on the juices of the plant. The tree can become stressed to the point where it becomes less resistant to other opportunistic pathogens.

Overwatering

Many of the abovementioned diseases or infestations owe their success to the ill effects of overwatering.

Walnut trees appreciate the occasional watering, as long as the soil they are planted in is well-draining. This means that any excess water that passes the tree’s roots will simply flow out through the soil. If the soil is not well-draining, the roots will be left to stand in stagnant water and the roots may drown and die. When the roots die, they are compromised, and pathogens and pests will have an easier time attacking the tree.

How do I save a dying walnut tree?

If you have narrowed down the possible cause of your dying walnut tree, treatment will become much easier.

First, check the tree’s soil to make sure that it is rich and well-draining. Make sure the tree gets full sunlight or at least only partial shade. Six to eight hours of sunlight is what the tree needs to thrive.

Water your tree once a week when it is still young during the warmer months. Give it up to five gallons of water each time for the first four months.

Walnut trees love plenty of nitrogen in the soil, so make sure the fertilizer you are using has plenty of nitrogen and add phosphorus and potassium as well.

If you grow multiple walnut trees and notice that one of them is infected with a disease, it is best to consider the well-being of the majority of the trees and to sacrifice the infected tree by burning and burying it.

Generally, if you are still not sure whether or not your walnut tree is truly dying, you can wait it out one more season to be really sure if anything is wrong with it.

Prune the tree during the winter when it is dormant, right before the leaves drop. Prioritize the removal of diseased, damaged and dead branches.

Conclusion

Your walnut tree is dying because there is an environmental factor that is causing it stress. Identify the cause of the problem to make treatment easier and faster.

The most common reasons your walnut tree may be dying are diseases, pests and overwatering.

Walnut trees are one of the easiest kinds of tree to grow in your backyard, so as long as you keep your eyes peeled for any possible problems and catch them in their early stages, you should have no problem growing this tree.

Image: istockphoto.com / Fotofreak75