Extension Educator, Horticulture
Lately ash trees have been in the news. An exotic pest called the emerald ash borer has wreaked havoc on ash trees in Michigan. We don't want that kind of excitement here in Illinois, so we have asked homeowners to keep a look out. Check with your local U of I Extension office for information on emerald ash borer or www.na.fs.fed.us/spfo/eab. To complicate matters ash trees already suffer from other problems here in Illinois.
First, make sure it is an ash tree. Ashes have compound leaves. That means their leaves are composed of 5-9 (usually 7) leaflets along a main rib. The leaves are attached opposite each other on the stem. We have mainly green and white ash, but we also find European, black and blue ash. Mountain Ash is a completely different beast, so it doesn't enter into this discussion.
Nancy Pataky, U of I Plant Clinic director, in a recent Home, Yard and Garden Pest Newsletter described other causes of ash problems.
One possible cause of decline is ash yellows. This disease mainly infects white and green ash. It is difficult to know just how widespread it is in Illinois since it difficult to confirm. Ash yellows disease is caused by a phytoplasma. These pathogens are somewhat like virus and cannot be cultured in a lab making confirmation dependant on symptoms.
Ash yellows is characterized by a loss of vigor over 2 to 10 years before the tree dies. We would expect ash to put on at least 6-8 inches of new growth each year. Trees infected with ash yellows may put on only one inch a year. Symptoms include short lengths between leaf attachments on the stem and tufts of leaves at branch tips. Leaves become pale green to yellow and may develop fall color early. The tree may lose many leaves and appear sparse. Cankers form on branches and the trunk, causing twigs and branches to die back. Witches-broom sprouts of growth may appear on branches but are more common on the trunk near the ground. Cracks in the trunk may appear in this area as well.
It is rare for an ash tree to recover from ash yellows. A great percent of ash trees in our landscapes are green ash, which do not show symptoms as clearly as white ash. It is likely that this disease is more common than we realize because the typical witches-brooms and yellowing are not always seen with green ash. Instead, we see only the cankers and stem dieback.
Sometimes you will see borer holes in these already stressed ash trees. These are more than likely lilac/ash borers. The round holes are about 4-5mm in diameter and do not have the characteristic "D" shaped hole of emerald ash borer.
Ash decline is often used loosely to refer to more than one condition. It may involve the ash yellows disease or Verticillium wilt (a fungal wilt disease) but is often used for any decline of ash for which a single pathogenic cause has not been identified. Ash decline usually includes branch tip death, leaf loss/sparse leaves and a slow decline over years. Affected trees may appear to recover each spring, then decline in July and August.
There are no cures for ash yellows or Verticillium wilt. Your best bet is to slow disease progression by removing trees with severe dieback, watering the trees during drought periods lasting two weeks or more, and fertilizing in the fall with a balanced tree fertilizer. Removing dead limbs may help. Pataky reports some very good testimonials involving the value of fertilization and watering to ash tree recovery. Vow now to take care of your ash.