What are the Ash Tree Diseases and How to Treat them?

If you have ash trees planted around your yard or garden and happen to see decay or damage to them, it’s time to learn more about the diseases of ash trees and their treatment methods. Thanks to pest control and gardening experts at Eden, we have listed the most common ash tree diseases and how to treat them.

Ash Tree Diseases and their Treatment

1. Ash anthracnose disease

Effect

Ash anthracnose disease is most common in green ash. This is a tree-specific disease and affects only one particular kind of tree, while being almost harmless to other types of trees. However, the treatment and management methods for anthracnose of different trees are the same. 

Signs

This disease causes ash tree leaves to develop large tan or black patches and also deforms the leaves. The middle of the leaves can also develop small brown-to-purple spots and even result in complete defoliation of the affected tree. 

Causes

This disease is caused by a fungus (Gnomoniella fraxini) breeds in the upper parts of the tree. This fungus begins affecting the tree as the leaves are budding out. You can find the signs of infection on the inner and lower canopy leaves at this stage. Fungus spores are spread by wind and can infect buds, twigs and new leaves. 

This infection usually occurs in the spring, mostly in wet, cool weather. 

Treatment

You should prune the affected branches. Once the leaves fall in autumn, make sure to dispose them to prevent the spores from re-infecting in the spring. It is not recommended to use fungicide to get rid of this disease as it rarely causes severe problems in ash trees. 

2. Emerald Ash Borer

Effect

The damage caused by the emerald ash borer insect usually becomes noticeable after 2 to 5 years since the initial bug infests the tree. The first sign of damage by the emerald ash borer are cracks in the highest branches. This is usually followed by canopy wilting. 

Signs

As the larvae dig the tunnel, it begins to girdle and kill branches, even the trunk. This often causes new shoots, called epicormic branching to develop on the tree trunk. 

Causes

The emerald ash borer is an invasive wood-boring beetle that is native to Asia. This pest was first found in 2002 in Detroit and has since spread to several states and destroyed millions of ash trees. These bugs become active usually between mid-June and early July.

Treatment

Infested trees will need to be removed and destroyed as soon as possible. If emerald ash borer has infested trees in your area, landscaping experts at Eden advise to spray a systemic insecticide as a drench to the base of the tree, usually in May or early June, right before the bugs become active. 

3. Ash Yellows

Effect

Ash yellows mostly affect white ash trees. This disease can affect ash trees of any age but the symptoms are usually seen within 3 years of infection. 

Signs

The infected tree tends to grow at a noticeably slower rate than normal ash trees and may only reach about half its maximum height. The leaves may also appear thinner, smaller and lighter green in color. Besides this, the tree may end up growing branches in tufts.

Causes

Ash yellow is caused by the phytoplasma Candidatus Phystoplasma fraxini, which is a bacterial-like organism. The phytoplasma lives on the food-conducting tissue of the infected tree. Though there are no definitive causes of ash yellows, it is suspected that leafhoppers may be the primacy carriers of the phytoplasma from tree to tree. 

Treatment

Unfortunately, there is no known cure for treating ash yellow disease. You can remedy the situation by removing visibly infected trees immediately and prevent the spread of phytoplasma to the surrounding healthy trees. However, you can use the wood from the infected tree as firewood or chip it for mulch. 

4. Verticillium Wilt

Effect

Verticillium wilt is a fungal disease and can affect ash tree and 300 other types of trees. This disease is most noticeable as it usually causes only one side of the infected tree to wilt. 

Signs

When this disease infects ash trees, it turns the leaves yellow before drying them to a deep brown color. You may even notice one branch suddenly wilting. The wood underneath drooping branches often develops discolored streaks. Most of the time, this sign is noticeable only after pruning an infected ash tree.

Causes

Malnourished and weak trees, such as those stressed by salt, lack of nutrient or by drought are more vulnerable to this disease. It is caused by a soil-based fungus – Verticillium albo-atrum. Infection usually begins at the roots where the fungus produces structures that can survive in the soil for years. The fungi that grow from these structures can penetrate roots and affects the water movement within the tree.

These signs are usually seen in midsummer. 

Treatment

As the fungus can survive in the soil for significant periods of time, it is recommended to plant resistant trees in the contaminated soil. You can delay the progression of this disease by pruning affected limbs and providing the tree with sufficient fertilizer and water. 

5. Banded Ash Borer

Effect

Apart from ash trees, banded borer bugs also infect elm, hickory, mesquite and white oak trees too. The damage caused by banded ash borer is similar to the emerald ash borer, but with erratic, zigzagging tunnels built deep into the tree. 

Signs

The larvae of the banded ash borer can weaken the tree’s limbs and make the more likely to break in strong winds. The banded borer bug makes random deep tunnels that bore into the trunk. You can identify a banded borer bug infestation by the circular small holes they create for tunnel exits. 

Causes

The banded ash borer tends to attack stress, diseased, dying or dead trees, instead of healthy trees. During spring, adult banded ash borers deposit their eggs in the cracks and crevices in the bark of the host ash tree. The larvae feed under the bark before finally boring into the sapwood where they feed until the end of simmer. During fall, the larvae transform to pupae and emerge as adults the next spring. 

Treatment

Pest control and gardening experts Eden recommend using systemic insecticides as a soil drench. These insecticides can help to get rid of adult females that chew on the bark to lay their eggs. These bugs can also infest firewood and come out to infest your home when you bring in the kindles inside. To prevent this, you can simply leave the firewood outside till you need to burn it, instead of spraying the infested firewood with insecticide. 

Conclusion

Ash anthracnose disease, emerald and banded ash borers, ash yellow and verticillium wilt are the most common types of ash tree diseases. Besides this, the ash trees in your yard are also susceptible to other ailments, such as ash flower gall, ash rust, powdery mildew, cotton rot root and mycosphaerella leaf spot. It is highly recommended to consult with gardening and pest control experts, such as at Eden to decide the best-suited treatment for ash tree diseases.