Ash Decline

Need to know

• Ash trees due to more than one condition.
• Symptoms include short internodes and tufting of foliage at branch ends. Leaves become pale green to chlorotic (yellowed) and might develop fall colors prematurely.
• Ash yellows disease is caused by a phytoplasma, and are spread by phloem-feeding insects.
• There are no cures for any of these maladies of ash, but keep in mind that deep planting, girdling roots, mulch mounds around the trunk, soil compaction, root injury, and other common landscape problems can contribute to ash decline.

Overview of ash decline

Ash decline is a term that is often used loosely to refer to more than one factor affecting the tree. Ash decline may involve ash yellows disease or even verticillium wilt, as well as other environmental or abiotic stressors.  

Symptoms of ash decline

Symptoms include short internodes and tufting of foliage at branch ends. Leaves become pale green to chlorotic (yellowed) and might develop fall colors prematurely. The tree may or may not defoliate, but the canopy generally appears sparse. Cankers may form on both branches and the trunk, causing twigs and branches to die back. Witches-broom sprouts of growth might appear on some branches but are more common on the trunk near the ground. Cracks in the trunk may appear in this area as well. 

Ash decline usually includes branch tip death, defoliation of enough leaves to give the tree a sparse look, and a slow decline of the tree over a number of years.  Scorching is common. Trees with ash decline may appear to be recovering each year in the spring and then decline in July and August.

Signs of ash decline

No signs are visible, specialized nucleic acid testing is required to confirm this fastidious bacteria-like organism causing the symptoms. The bacterial-like organisms cannot be cultured in a lab, but instead, PCR testing is necessary.

Disease cycle of ash decline

Ash yellows disease is caused by phytoplasma. Phytoplasmas are spread by phloem-feeding insects. They are limited to the phloem tissue of the tree. Yellows disease is characterized by a loss of vigor over 2 to 10 years before the tree dies.

Type of Sample Needed for Diagnosis and Confirmation

The Iowa State University Plant & Insect Diagnostic Clinic can help you to investigate and confirm if your plant has this disease. Please see our website for current forms, fees, and instructions on collecting and packing samples. Contact information for each state's diagnostic laboratory for U.S. residents.  If your sample is from outside of Iowa please do not submit it to the Plant & Insect Diagnostic Clinic without contacting us.

Want to submit a sample? Follow the instructions at Submitting Trees and Shrubs, branches with living yellowing leaves are tequired. Select the "DNA additional testing" box on the submission form.

Management of ash decline

Prevention is key. Keep in mind that deep planting, girdling roots, mulch mounds around the trunk, soil compaction, root injury, and other common landscape problems can contribute to ash decline, and can be prevented with proper tree planting, see Tree and Shrub Care page.

There are no cures for declining trees. Suggested management to slow disease progression includes removing trees with severe dieback, watering the trees in periods of extended drought lasting at least 2 weeks, and fertilizing in the fall with a balanced tree fertilizer. Removal of dead limbs may help as well. Ash trees are very resilient and may respond well to this pampering. In addition, pull mulch away from the trunk and keep weed trimmers away as well.  to learn more see the free to download Common Problems of Ash Trees publication.

See this bulletin about ash decline.