Ash Tree Decline

Ash tree damage can result from borers, fungus, weather or even birds!

©2013 Sandy Feather


Q. We have a large ash tree in our backyard that may have been here before our house was built in the late 1960s. I have heard about an insect that is killing ash trees, but ours has seemed fine for the past few years. This year, however, we see a lot more dead branches, some brown leaves, and some of the green leaves are dropping already. Now I am wondering if this insect is attacking our tree.

A. The emerald ash borer is the introduced insect that has been killing ash trees since it was first discovered in southeast Michigan and Ontario, Canada, in 2002. Entomologists believe that the infestation was present for 15-20 years before it was identified. Since then emerald ash borer has been identified in 15 states, including Pennsylvania, where it was discovered in June 2007 in Cranberry, Butler County. Shortly thereafter, this pest was identified in Marshall. Emerald ash borer has been found in 23 Pennsylvania counties, with the heaviest infestation in Western Pennsylvania.


It is possible -- even likely, given your location in northern Allegheny County -- that your tree is infested with it, but not all of the symptoms you describe are consistent with damage from this pest. There are native ash borers that typically attack stressed trees as well as a number of diseases that impact ash. The warm spell we had in March forced trees into growth earlier than normal, followed by frosts and freezes that damaged or killed the tender new growth. That was followed by cool, wet weather that created perfect conditions for ash anthracnose, a fungal disease that kills areas of the leaves. Frost damage and anthracnose could explain the brown leaves and leaves dropping while they are still green.


Dead branches in the crown of the tree are typical symptoms of emerald ash borer infestation. Other symptoms include woodpecker activity, vertical splits in the bark (more evident on smaller trees), winding galleries under those splits where the larvae feed, and "D"-shaped holes where the adults emerge after pupation (all of our native ash borers leave round exit holes).


"D"-shaped exit holes in the bark of an Ash tree
Photo: Sandy Feather

Severely infested trees begin to produce sprouts low on the tree in a last-ditch effort to survive, known as epicormic shoots. Unfortunately, infested trees often show no symptoms at all until they are almost dead. By then, their vascular systems are too damaged for any treatment to be effective.


Adult female emerald ash borers lay their eggs on the bark of ash trees. The larvae tunnel into the bark as soon as they hatch and begin feeding in the cambium. The cambium is the actively growing tissue just under the bark that gives rise to the tree's vascular system. It transports water and nutrients from the roots to the leaves, and it takes the products of photosynthesis down to the roots for storage. Once the cambium is destroyed around the circumference of the tree, the tree dies.


Ash tree infested with EAB has started to send out new shoots low on the trunk called epicormic sprouts

Emerald ash borers pupate under the bark, and adults hatch from late May into July, with peak emergence occurring from late June to mid-July. Adults feed on foliage, mate and lay eggs, and the whole cycle starts over again. Adults have a long period of egg-laying, perhaps right through August. Research has shown that emerald ash borers can take from one to three years to complete their life cycle.


The best advice is to contact a certified arborist to evaluate the tree. The most effective insecticides to control emerald ash borer are systemic products that move in the tree's vascular system. If too much of the vascular system has been destroyed, the insecticides cannot get to where they are needed to protect the tree. Given the expense of treating large ash trees, it makes sense to make sure the tree is worth treating before spending the money.

The International Society of Arboriculture (ISA) is the organization that certifies arborists. You can find certified arborists who work in your area by visiting the ISA website.


Treating Emerald Ash Borer

Tree FAQ

Sandy’s Tree Tips