The cause of a dying ash tree is usually either pests or infection by pathogens.
The most common of these are the emerald ash borer, banded ash clearwing, ash flower gall, ash plant bug, ash aphids, scale insects, Verticillium wilt, ash anthracnose, ash yellows and ash rust.
Correctly identifying the cause of the tree’s declining health is the first step in saving it.
In this article, we will discuss the different causes of dying ash trees, and how to save them.
Why is my ash tree dying?
Emerald ash borer
This insect is a beetle with a jewel-green color, hence the name, that is native to the Asian continent but found its way to North America.
The larval stage is when this insect is at its most destructive. They feed on the inner bark of the tree, which affects the transfer of nutrients and water within it.
When the larvae eventually turn into adults, they will leave through the holes they created in the bark. This makes the tree susceptible to bacterial and fungal diseases. Aside from the holes left behind by the borers, woodpeckers will also do damage when they feed on the larvae. If the bark is split and removed from the tree, you can see the tracks left by burrowing borer larvae. The tree will start to die back from the crown, and eventually die completely, albeit slowly.
The tree’s chances of survival if you try to save it will depend on whether it is still healthy. If the tree has lost several branches, its chances of survival are thin. If you are able to catch the infestation in its early stages, however, treatment may be more effective. If the tree is not valuable to you, you are better off cutting it down to keep the insects from spreading.
If you choose to proceed with treatment, you will need the skills of a professional to apply insecticide injections into the trunk.
Banded ash clearwing
The banded ash clearwing is a wasp-like moth. These insects tend to attack the greener ash trees, and damage their tissue enough to disrupt the flow of the tree’s food and water. The tree’s bark will eventually become rough and damaged. The branches will weaken, and eventually the entire tree will die.
You can get rid of these insects by applying pesticides at the end of summer, since this is when they appear.
Ash flower gall
Ash flower gall is a disease caused by the Eriophyid mite. The insects form the galls that are characteristic of the disease. A gall is an abnormal growth in the plant that looks like brown or green clusters on the branches.
When the mites attack, the male flowers will turn into small, green structures, which become galls. If you see galls forming, it usually means it is too late to cure the disease. They may not be fatal, but they can ruin the aesthetic of the tree.
You can treat ash flower gall by applying insecticide even before the first blossom to avoid the growth of galls. Exposing the tree to more sunlight than shade can also help keep these insects at bay.
Ash plant bug
Adult plant bugs and nymphs both feed on the ash tree’s leaflets that appear in the spring. You will know that your ash tree has plant bugs if parts of the leaves are turning brown and wilting. When the infestation is severe, the tree will suffer from leaf drop.
When treating your ash tree for plant bugs, make sure you maintain the tree’s health by watering and mulching it. Insecticides are effective against plant bugs, but you need to know exactly when they are going to attack. Check the tree for plant bugs in the early spring, just as the leaf buds are starting to open.
Ash aphids
These small, green insects are covered in a waxy substance that looks like thread. The ash leaves will curl and deform when the aphids feed on the sap on the underside of the leaves.
You can get rid of these aphids by blasting the tree with water from your garden hose and by using insecticidal soap. Insecticides may not be very effective in this situation.
Scale insects
These insects appear from late May to early June, and feed on the bark of the ash tree. They can cause the bark to crack, and if the infestation is severe, the branches may weaken to the point that they fall off.
You need to cut off any affected branches and apply insecticidal soap to the remaining branches and the rest of the tree, every seven days until the infestation has been handled.
Verticillium wilt
This disease is caused by a fungus that releases a toxin that blocks the vessels that carry water throughout the plant. As a result, the leaves wilt and there will be branch dieback. The leaves will turn yellow and have a burned appearance around the edges.
There is no known cure for Verticillium wilt once it infects an ash tree. It is so resilient that even if you cut down and remove the entire tree, the disease still remains in the soil. The best you can do is prevent infection from other opportunistic fungi by pruning off damaged and dead branches.
Ash anthracnose
This disease, caused by a fungus, can result in major leaf loss. The fungus thrives during the rainy season and its symptoms include brown and purple blotches on the older leaves that appear during the start of spring. The leaves will start to look wrinkled and twisted, and leaves will fall prematurely from the lower branches of the tree.
You can prevent this disease by keeping the garden sterile in the summer. If there are parts of the tree that are decaying, prune them off. Apply mulch on the soil, about six inches away from the base of the tree.
Ash yellows
This disease is caused by Phytoplasma and affects mostly green and white ash trees. It spreads through the soil and results in the yellowing of the leaves and quick death of the tree. Early detection is key if you want to save your tree, as vulnerable trees can die as soon as one to three years after initial infection.
Control the disease in its early stages by pruning any affected foliage. Use a fungicide on the affected areas. Fertilize the soil bed around the tree to boost the tree’s health and prevent outbreaks of the disease.
Ash rust
This disease is caused by the Puccinia sparganioides fungus. It affects mostly green and white ash trees. Symptoms include yellow or orange spots on the leaves’ surface, and the leaves will eventually wilt and die. Repeated ash rust infections can greatly weaken the tree.
Spray the tree with fungicide three times every two weeks when the buds break open, and prune the tree in early spring when it is in its growth phase.
Conclusion
If an ash tree is dying, it is most likely due to pests or disease.
The most common causes of dying ash trees are emerald ash borer, banded ash clearwing, ash flower gall, ash plant bug, ash aphids, scale insects, Verticillium wilt, ash anthracnose, ash yellows and ash rust.
Knowing the proper cultural techniques for growing ash trees can help avoid most of these problems, so remember to do your research before growing them.
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