Bartlett Tree Experts: Emerald Ash Borer

Agrilus planipennis

Ash tree affected by emerald ash borer.

Since emerald ash borer arrived in the United States in 2002, hundreds of millions of ash trees have been destroyed. The pest, which originated in China and accidentally arrived in the U.S. in wooden packing materials, has cut a devastating swath through forests and gardens. Emerald ash borer (EAB) attacks all varieties of ash trees; the trees have no natural defenses against this insect and can die within three years of infestation.

The 1" adult insects have intense green, elongated bodies. The adult insects themselves cause little damage; it is the hungry larvae, which gnaw channels into the sapwood beneath the bark, which ultimately disrupt the tree's ability to distribute water and nutrients.

There is a window of opportunity for treating trees to prevent or control infestation but it is narrow. Property owners with ash trees must be diligent if they live in an area where the pest is present.

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Affected Areas

States in green have confirmed EAB infestations (as of early 2024).

From its arrival in southeast Michigan, EAB has extended its range to wherever ash trees are common.

Visit the EAB Information Network web site for more information on the spread of emerald ash borer.

Lifecycle

In early spring, adult borers emerge from infested trees, leaving inconspicuous D-shaped exit holes behind them. They mate after the ash leaves have established in spring (early May to mid-June). The females feed on the leaf margins for several weeks, but typically cause little damage to the foliage. Each female deposits 40 to 70 individual eggs into cracks or crevices in the bark of the ash tree. Larvae hatch in approximately two weeks and bore through the bark into the sapwood.

Symptoms

When the larvae hatch and start to feed, emerald ash borers form galleries beneath the bark.

Non-uniform discoloration of Douglas fir needles

Tiny (1/8") D-shaped exit holes are a sign of emerald ash borer infestation.

Since EAB prefer to lay their eggs in the upper trunk of the ash tree, their presence is often not apparent until the tree shows signs of damage. The disruption of water and nutrients caused by the feeding larvae can cause individual branches to die, and frequently leads to the loss of the entire tree. In addition to the yellowing and loss of canopy, an increase in woodpecker activity can signal the presence of EAB larvae. The appearance of the D-shaped exit holes confirms that boring insects have been colonizing beneath the bark.

Control

When EAB is present or has been discovered within a 10-mile radius, preventative measures should be taken. There are multiple application methods and options available depending on the level of pressure due to beetle population density. When the tree has lost 50% of its canopy, removal of the tree is the safest option.

It is important to properly dispose of all wood from infested trees. EAB larvae can survive in firewood; to avoid the spread of EAB, wood should never be transported to another area.

Emerald Ash Borer