Ash trees are popular landscape trees due to their beautiful fall foliage and fast growth. However, they are susceptible to several diseases that can greatly reduce their lifespan or even kill them. Being aware of the most common ash tree diseases and issues can help you properly care for your ash trees and catch problems early before they become fatal. Here are 8 of the most notable ash tree diseases and issues to look out for:
Emerald Ash Borer
The emerald ash borer is an invasive beetle that has killed millions of ash trees across North America since it was first detected in 2002. Adult beetles lay eggs on ash tree bark. When the eggs hatch, the larvae burrow into the tree and feed on the inner bark and phloem, disrupting the tree’s ability to transport water and nutrients.
Signs of an emerald ash borer infestation include:
- D-shaped exit holes in the bark where adult beetles have emerged
- Cracked and peeling bark
- New sprouts growing from the trunk and branches
- A thinning canopy
- Serpentine tunnels under the bark packed with sawdust-like material
Once a tree is infested, it usually can’t be saved. Prevention involves not transporting firewood, which spreads emerald ash borer. Systemic insecticides can be applied preventatively. Trees generally die within 2-4 years of becoming infested. Prompt removal of infected trees helps slow the spread.
Ash Yellows
Ash yellows is a phytoplasma disease that causes a slow decline and eventual death of ash trees. The disease is spread from tree to tree by insect vectors like leafhoppers. Ash yellows is common in white, green, and black ash trees.
Symptoms include:
- Premature yellowing and loss of leaves in summer
- Thinning canopy with tufts of leaves at branch ends
- Dead tops of trees and dieback in branches
- Wittches’ brooms or clusters of twigs sprouting from branches
- Slow overall decline
There is no cure for infected trees. Providing optimal care through watering and fertilization may prolong the life of diseased trees. Removing infected trees as soon as symptoms appear helps prevent spread.
Anthracnose
Anthracnose is a fungal disease caused by several species that results in leaf loss, twig dieback, and cankers on ash trees. It is most severe during wet, cool springs.
Look for the following signs:
- Irregular dead areas on leaves that look water-soaked
- Premature leaf drop
- Sunken cankers on twigs and branches
- Dieback of shoots and twigs
Raking up and disposing of fallen diseased leaves helps reduce infection. Fungicide sprays applied starting at bud break through petal fall can prevent infections. Prune out affected twigs and branches.
Ash Rust
Ash rust is a fungal disease caused by the pathogen Puccina sparganioides. It causes brightly colored growths on ash tree leaves and may lead to reduced growth and early leaf drop if severe.
Symptoms of ash rust include:
- Yellow, orange or brown swellings on leaves
- Clustered raised growths on the undersides of leaves
- Leaves that are stunted, twisted or drop early
- Dead areas on leaves surrounded by a yellow halo
Raking up and disposing of fallen leaves, pruning infected branches, and applying fungicides when infection first appears can help control ash rust. Make sure to disinfect pruning tools between cuts.
Verticillium Wilt
Verticillium wilt is a soil-borne fungal disease that infects the vascular system of ash trees, impeding the flow of water and nutrients. It eventually causes wilting, dieback, and tree death over a period of years. The disease is difficult to control once established.
Early signs of verticillium wilt include:
- Leaves wilting and browning in summer, especially on one side of the tree
- Dieback progressing through branches
- Discolored streaks under the bark
Avoiding unnecessary injury to the bark and roots helps prevent infection. Boosting tree health with deep watering and mulching may delay symptoms. Injecting fungicides into the trunk may help protect high value ash trees.
Ash Decline
Ash decline refers to a general decline in health and eventual death due to some combination of factors like drought, old age, verticillium wilt, and anthracnose. Affected trees lack vigor and slowly deteriorate.
Signs of ash decline include:
- Thinning canopy with tufts of foliage at branch tips
- Dying branches throughout the crown
- Evidence of past trunk injuries that serve as entry points for decay fungi
- Smaller than normal leaves that are pale green or yellowed
Careful watering and fertilization may prolong the life of declining ash trees. However, removal is recommended once the decline becomes advanced since it is usually irreversible at that point.
EAB Look-alikes
Some problems can mimic the symptoms of emerald ash borer infestation. It’s important to properly identify whether EAB is the cause before taking serious measures like removing trees. Carpenter ants or bark beetles can cause similar tunneling in the trunk. Leaf miners and leaf rollers cause brown leaves that could be mistaken for EAB damage. Getting an expert arborist to inspect is recommended if you suspect EAB.
Ash Tree Borer
The ash tree borer (Podosesia syringae) is a native North American beetle that infests and damages ash trees, particularly under stress. The larvae bore into the sapwood and cause dieback. Adults emerge through D-shaped exit holes. Keeping trees healthy with irrigation and avoiding mechanical injury is the best prevention. Insecticides may be applied to deter egg-laying adults.
Frequently Asked Questions About Ash Tree Diseases and Issues
What is the most common disease affecting ash trees?
Currently, emerald ash borer is the most destructive and widespread disease impacting ash trees across North America. It has killed hundreds of millions of ash trees since its accidental introduction.
How can I tell if my ash tree has emerald ash borer?
Look for symptoms like canopy dieback, sprouts growing from the trunk, split bark with S-shaped tunnels underneath, and D-shaped exit holes on the branches and trunk. Trapping adults is also used for early detection.
What should I do if my tree has EAB?
If EAB is confirmed, removal and replacement with a non-ash species is usually the recommendation. Treatment with systemic insecticides can sometimes prolong the life of high value ash trees.
Are white, green, and black ash trees all susceptible?
Yes, all North American ash species are at risk for EAB infestation and death. Blue ash is slightly less preferred by the beetles.
How can I prevent anthracnose on my ash trees?
Prompt leaf cleanup in fall, pruning out affected branches, and applying fungicide sprays at bud break and petal fall can help prevent serious anthracnose infections.
What causes ash yellows disease?
Ash yellows is caused by a phytoplasma organism transmitted by insects like leafhoppers. Diseased sap from one tree infects healthy trees when the insects feed. Managing the insects can help control spread.
Should I fertilize my ash tree that has verticillium wilt?
Fertilization is not recommended for trees impacted by verticillium wilt, since it can stimulate more top growth than the root system can support. Focus on watering during dry periods.
How long do ash trees typically live?
Without major diseases, ash trees can live 80-150 years or longer when grown in preferred conditions. Their lifespans are now often cut short by emerald ash borer 10-20 years after planting.
What conditions do ash trees prefer?
Ash grow best in moist, well-drained soils in full sun to partial shade. They are tolerant of pollution and urban sites but decline without sufficient water and become prone to diseases.
Conclusion
Ash trees are clearly facing serious threats from invasive pests and endemic diseases that are shortening their lifespans. Being aware of the most common problems like EAB and ash yellows can help you identify issues early and decide on proper management. Provide your ash trees with regular care and be vigilant for symptoms of disease to protect your landscape investment. Consider replacing dead or dying ash trees with other species that are not susceptible to the same diseases impacting ashes. With proactive management, you can maintain beautiful ashes for many years or decades before they eventually succumb to inevitable threats.