Damage to Ash trees

It is becoming increasingly obvious that ash trees are under attack by the emerald ash borer in our county. Many ash trees now display the characteristic signs of infestation, exhibiting bark that has been stripped off or is sloughing off the tree. In many instances, this loss of bark is due to woodpeckers removing it to get to the emerald ash borer larvae inside the tree.

Emerald Ash Borer damage to an Ash tree
Credit: frederick.forestryboard.org - Mike Kay

Other tell-tale signs that ash trees are under attack include small D-shaped holes in the tree, dieback in tree crowns, and small epicormic branches that develop along the main trunk of the tree. The emerald ash borer (Agrilus planipennis) is an insect that has gained a lot of notoriety because of the devastating impact on most of our native ash trees. This insect is native to Eastern Russia, Northern China, Korea, and Japan. In its native habitat, emerald ash borer is held in check by parasitic wasps and birds, so that populations rarely build to the point that the insects do extensive damage. However, in our country where no natural controls exist, populations of this insect have exploded in ways such that most species of ash trees have come under attack.

The emerald ash borer is a metallic green beetle that emerges from ash trees from May until July, where they have two to three months to disperse, mate, and lay their eggs on ash trees before dying. The eggs hatch in about two weeks. Then, the grub-like larvae burrow into the tree and feed on the inner bark and sapwood of the host ash tree. The feeding activity cuts off the transport of water and nutrients inside the tree, effectively girdling the tree. Infested trees generally die within one to three growing seasons.

Emerald ash borer was first identified near Detroit during the summer of 2002. This insect was detected in Maryland in 2003 when an inspector with Maryland Department of Agriculture located tainted ash nursery stock in a nursery in Southern Price George’s County. Once identified, a quarantine area was delineated in a two-mile radius around the nursery; efforts were made to eradicate the pest before it could spread further.

These efforts delayed, but did not prevent, further spread; and the quarantine was enlarged to include southern Prince George’s and Charles counties. The 2013 survey indicated that this serious insect pest had also spread into Frederick County. While Maryland was waging a battle with this insect within its borders, the emerald ash borer was spreading east and westward from Michigan, and today it is found in 24 states.

The most recent Maryland survey indicates that emerald ash borer has been found in most counties except for a few on the Eastern Shore and the northeast section of the state. Most of Frederick County has been invaded by this destructive insect.

Losing our native ash trees will impact the biodiversity of the forests, and affect landowners, the forest products industry, and local and state governments. These financial impacts will significantly affect urban areas that have to deal with treatment or removal of ash trees.

It should be noted that treatment options are available, and many ash trees found in residential and urban landscapes are being treated to prevent infestation. Local tree expert companies may be able to evaluate ash trees to determine if treatment is an option or if the tree is too far gone and should be removed.

Some experts speculate that it will take up to 10 years for emerald ash borer to run its course and to witness a population collapse. Forest inventories reveal that a significant amount of the ash found in Maryland is located in our backyard in the mountainous areas between Frederick and Washington counties.

Article by FCFCDB member

Nature Note for 3/5/2017