Ash Decline

Encyclopedia Article

Ash decline on Ash Trees
Ash decline on Ash Trees

Overview of ash decline

Ash decline is a term that is often used loosely by many diagnosticians to refer to more than one condition. Ash decline may involve Ash Yellows Disease or even Verticillium wilt, but it is often used to indicate any decline of ash for which a single pathogenic cause has not been identified.

Signs and 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 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.

Disease cycle of ash decline

Ash yellows disease is caused by a phytoplasma. These pathogens are somewhat like virus particles, cannot be cultured in a lab, and 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 you plant has this disease. Please see our website for current forms, fees, and instructions on collecting and packing samples. Contact information for each states 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

Management of ash decline

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.

There are no cures for any of these maladies of ash. 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.

See this bulletin about ash decline.