If you have ash trees on your Warren, Michigan property, you need to read this. The emerald ash borer is the most destructive forest insect ever introduced to North America, and it has fundamentally changed the tree landscape of southeast Michigan over the past two decades. Understanding this pest — how it spreads, how to identify an infestation, and what your options are — is essential for every homeowner in Macomb County.

What Is the Emerald Ash Borer?

The emerald ash borer (Agrilus planipennis) is a small, metallic green beetle native to northeastern Asia. It was first detected in North America in the Detroit area in 2002, almost certainly arriving in wooden packing material from Asia. Since its discovery, it has spread to dozens of states and Canadian provinces, killing hundreds of millions of ash trees.

The adult beetle is about half an inch long and brilliant metallic green — beautiful, in a way, for something so destructive. But it’s the larval stage that does the damage. Female beetles lay eggs in the bark of ash trees, and when the eggs hatch, the larvae bore into the tree and feed on the phloem — the layer of tissue just beneath the bark that transports sugars from the leaves to the roots. As the larvae feed, they create winding, S-shaped galleries that disrupt the tree’s vascular system. A heavily infested tree essentially starves to death as its ability to move nutrients is progressively destroyed.

Why Ash Trees Are Particularly Vulnerable

The emerald ash borer attacks all species of true ash (Fraxinus spp.), including green ash, white ash, black ash, and blue ash. It does not attack mountain ash (Sorbus spp.), which is not a true ash despite its name. In North America, ash trees have no natural resistance to the beetle — unlike in Asia, where native ash species have co-evolved with the beetle and developed some degree of resistance.

This lack of resistance means that virtually every untreated ash tree in an infested area will eventually be killed. In Warren and throughout Macomb County, the infestation is now so widespread that any ash tree that has not been treated with a systemic insecticide should be considered at risk.

How to Identify an Infested Ash Tree

The signs of emerald ash borer infestation are distinctive once you know what to look for:

Canopy dieback is typically the first visible sign. The upper canopy begins to thin and die back, starting at the tips of the branches and progressing inward. This dieback is caused by the disruption of the tree’s vascular system.

Epicormic sprouting — the growth of small shoots directly from the trunk and major branches — is a stress response that infested trees often exhibit. The tree is essentially trying to grow new foliage below the point where the vascular system has been damaged.

Bark splitting occurs as the larvae feeding beneath the bark cause the bark to crack and separate from the wood. Woodpeckers, which feed on the larvae, often excavate the bark in search of food, creating distinctive “blonding” — areas where the outer bark has been removed, revealing the lighter-colored inner bark.

D-shaped exit holes are left by adult beetles as they emerge from the tree in late spring and early summer. These holes are about 1/8 inch in diameter and distinctively D-shaped rather than round.

S-shaped galleries are visible if you peel back a section of bark from a suspected infested tree. The winding, serpentine tunnels packed with frass (a mixture of sawdust and insect excrement) are unmistakable.

Your Options: Treatment or Removal

If you have ash trees on your Warren property, you have two basic options: treat them with a systemic insecticide to protect them from the beetle, or remove them before they die and become hazardous.

Treatment is a viable option for ash trees that are still in good health — with less than 30 to 50 percent canopy dieback. The most effective treatments are systemic insecticides applied as soil injections or trunk injections. These products are taken up by the tree’s vascular system and distributed throughout the tree, killing larvae that feed on the treated tissue. Treatment must be repeated every one to three years, depending on the product used.

Removal is the appropriate choice for ash trees that are already significantly infested, that have more than 50 percent canopy dieback, or that are in locations where a dead tree would pose a hazard. Dead ash trees deteriorate rapidly — the wood becomes extremely brittle within two to three years of death, making removal progressively more dangerous and expensive the longer it’s delayed.

The Cost of Waiting

Many Warren homeowners have watched their ash trees decline over the past decade without taking action, hoping the trees would somehow recover on their own. They won’t. And the longer a dead or dying ash tree is left standing, the more dangerous and expensive it becomes to remove.

A dead ash tree that’s been standing for three or four years may have wood so brittle that it can’t be safely climbed. Removal requires aerial equipment and specialized rigging, which significantly increases the cost. In some cases, severely deteriorated ash trees must be taken down in very small sections to prevent uncontrolled falls — a time-consuming and expensive process.

If you have ash trees on your property that you haven’t had assessed recently, now is the time to act.

Ready for expert tree care in Warren? Contact the team at County Tree LLC today for a free estimate.