August Is Tree Check Month!

Posted: August 22, 2013

Penn's Woods are under threat from myriad invasive pests and diseases. Learn about two more - the Asian longhorned beetle and the Thousand Cankers Disease complex - and how you can help keep watch.

With invasive pests and diseases threatening the diversity of Pennsylvania’s woods, it’s incumbent on landowners and the general public alike to keep watch over the trees that contribute to our state’s beauty. The US Department of Agriculture, Animal and Plant Health Inspection Service (USDA APHIS) has declared August “Tree Check Month.” It’s the right time to get out into the woods and watch for signs of diseased and dying trees.

In Pennsylvania, we already see the impacts of Emerald Ash Borer (EAB) and the dead and dying ash trees throughout the state (EAB has been confirmed in 39 counties, but the entire state remains under quarantine and the insect is expected to spread throughout); Hemlock Woolly Adelgid (HWA) and the dead and dying hemlocks on mountainsides and along streams, soon to impact water quality and temperature; and the native forest tent caterpillar and non-native gypsy moth, which have been and continue to be part of Pennsylvania’s forest ecosystem. And while there are practices, chemical, and biological control methods that can help mitigate the spread of these insects, the task is daunting. It’s a sad time for our forests. 

Now with two more threatening insects, one with an associated fungus, on our borders or in isolated areas of the state, it is imperative that we all become more vigilant about dead and dying trees. 

The Asian Longhorned Beetle (ALB), Anoplophora glabipennis, is a non-native insect first discovered in Brooklyn, New York in 1996 and detected in Chicago in 1998. In the 2000s, it was found in New Jersey, Massachusetts, and most recently discovered in southeastern Ohio. While not yet found in Pennsylvania, ALB is one of the more aggressive invasive insects that could easily make its way here. ALB kills trees as the larvae feed in the branches and stems. ALB grows, reproduces in, and kills up to thirteen genera of trees, including maple, birch, horse chestnut and buckeye, poplar, willow, elm, ash, and alder.

Asian Longhorned Beetles are large, shiny, black insects with random white spots. They measure 1 to 1 ½ inches long, with black and white banded antennae as long as (females) or twice as long as (males) their bodies. Adults are active from mid-May until early August. The females scrape a small notch in the bark to lay eggs. The larvae bore in to the branches and trunk to feed in the wood and cambial layer of the tree. Mature larvae pupate within the galleries they have made, and adults chew their way out leaving round, dime-sized exit holes. August is a peak emergence time for the adult beetles and a time when landowners and members of the public can help to check trees for the beetles.

In 2011 Thousand Cankers Disease, a disease complex that attacks black walnut (Juglans nigra) made up of a native (western species) walnut twig beetle (Pityophthorus juglandis) and a native fungus (Geosmithia morbida), was found in Bucks County, Pennsylvania. Until recently this disease primarily affected eastern black walnut planted outside its native range in Western States. In the summer of 2010, it was first noticed in Knoxville, Tennessee, well within the native range of black walnut and it has begun to spread. In 2012 the walnut twig beetle and the fungus were identified in southeastern Ohio. 

To kill the tree, as the beetle feeds on black walnut branches, it creates numerous galleries beneath the bark. The adult beetles carry the fungal spores and introduce them into the phloem when they construct the galleries. Small cankers develop around the galleries, which then enlarge and coalesce to completely girdle the branches. Trees die as a result of the canker infestations at the thousands of beetle attack sites. Usually the first sign of infestation is thinning crowns in the black walnuts, yellowing or wilted leaves on limbs, and then branch death.

The most important thing you can do to protect your trees is to check them regularly and encourage others to do so too. You don’t have to wait for August to roll around each year to do these checks. Learn about other symptoms and signs of infestation and disease. Early detection is crucial to maintaining Penn’s Woods. For more information on these and other insects, visit the DCNR Bureau of Forestry’s Forest Pest Insects and Disease website, at:

To report possible infested trees in Pennsylvania, contact the Pennsylvania Department of Agriculture at 1-866-253-7189, the DCNR Bureau of Forestry, Division of Pest Management at: 717-948-3941 or email:

The Pennsylvania Forest Stewardship Program provides publications on a variety of topics related to woodland management. For a list of free publications, call 800 234 9473 (toll free), send an email to, or write to Forest Stewardship Program, Natural Resources Extension, The Pennsylvania State University, 416 Forest Resources Building, University Park, PA 16802. The Pennsylvania Bureau of Forestry and USDA Forest Service, in Partnership with Penn State’s Department of Ecosystem Science and Management sponsor the Forest Stewardship Program in Pennsylvania.