Columns, In the Garden

Check Trees for Signs of ALB

photo by Joe Boggs, Ohio State University
The adult Asian longhorned beetle is .75 to 1.5 inches long with a shiny black body with white spots and antennae one to two times its body length.

by Ginger Nickerson, Extension Forest Pest Education Coordinator, University of Vermont

BURLINGTON – When working in their sugarbush this winter, maple producers are encouraged to be on the lookout for signs of the Asian longhorned beetle (ALB). This wood-boring insect, native to southeast Asia, will kill many hardwood trees. However, its preferred host is the beloved maple.

This highly destructive pest has not yet been confirmed in Vermont. However, there is an active infestation in Worcester County, Mass.

The beetle threatens all species of maples, not just sugar maples. It is typically spread through nursery stock, infested wood products or by moving infested firewood.

While the summer and early fall are the best times to spot the adult beetles, winter is an excellent time to examine trees for signs of ALB damage. Take photos of any signs and report suspicious trees to

photo by Joe Boggs, Ohio State University
A pencil can be used to determine if a round, dime-sized hole in a hardwood tree is at least one inch deep, indicating an exit hole made by an adult Asian longhorned beetle that emerged in summer.

Signs include multiple round, shallow indentations with rough edges in the bark. These are dime-sized spots that the beetles chew to lay their eggs. The spots may ooze sap in the summer and fall when they are fresh.

Perfectly round, pencil- to dime-sized holes are another indication. These are left when the adults emerge in the summer. The exit hole will be straight and at least one inch deep.

Stick a pencil in the hole to determine if it is deeper than a tap hole. There may be bits of sawdust-like material around these holes, in branch crooks or at the base of the tree.

Adult beetles are .75 to 1.5 inches long with antennae that are one to two times their body length. These beetles are shiny black with white spots and antennae with bluish-black and white stripes. They resemble our native whitespotted sawyer beetle. However, the latter has a white spot between its wing covers.

In addition to attacking all maple species, ALB also will harm healthy ash, poplar, birch, willow and elm. When ALB is found, all hardwood trees within a certain radius must be removed and destroyed by chipping or burning to stop the pest from spreading. The infested area is quarantined to prevent people from moving wood.

photo by Joe Boggs, Ohio State University
The Asian longhorned beetles chew round, dime-sized holes in maple and other hardwood trees to lay their eggs.

The infestation in Massachusetts had probably been in the area for about 10 years before it was found. Over 36,265 trees in 1 110-square-mile area in Worcester County have been removed to try to get rid of the beetle. In contrast, Chicago eradicated an ALB infestation and destroyed only 1,500 trees because the infestation was discovered early.

Checking hardwoods, especially maples, for signs of ALB is key to early detection. So, woodland owners, hikers and anyone who spends time in the woods should also be on the lookout for signs of this invasive pest. Let’s keep Vermont’s maples ALB free!

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