Invasive Tree Pests
Wood Boring Insect Pests
The most important vector for many tree pests is movement of infested wood. Please, don't move firewood!
You can help protect Pennsylvania's urban, suburban, and forested areas from nonnative invasive forest pests and diseases by doing the following:
- Buy/burn locally cut firewood.
- If you have already brought firewood from another area, BURN IT. Do not leave it. Do not take it with you.
- Encourage your friends and neighbors not to move firewood distances greater than 50 miles.
Insects and diseases moved with firewood include: Asian Longhorned Beetle, Emerald Ash Borer and Thousand Canker Disease
Asian Longhorned Beetle
Asian Longhorned Beetle (Aniplophora glabris) is large (0.75 - 1.5 inch), glossy jet black, very smooth with up to 20 irregular white spots on its back. It has antennae with distinctive black and white banding that are 1 1/2 to 2 1/2 times as long as it's body. Eggs are laid in dime-sized oval grooves chewed into the tree bark. Adult beetles are evident in mid to late summer. Infestations usually start in the crown of the trees and may not be detected until advanced. Signs of tree decline that may be caused by ALB or some other stressors include: upper crown dieback, yellow foliage or small branches coming directly out of the trunk. Signs specific to ALB include: adult beetles, large (3/8"), round (dime-sized) exit holes, oozing sap, coarse sawdust at the base of the tree or where branches meet other branches.
The Problem – ALB is a very destructive wood boring beetle that prefers maple trees, but is also known to infest alders, birches, elms, horsechestnut, poplars and willows. There is no effective control other than removing and finely chipping infested trees.
For more information:
Emerald Ash Borer
Adult Emerald Ash Borers (Agrilus planipennis) are one-half inch long and one-eighth inch wide, metallic green, and fly only from mid-May through September, primarily during May and June. The larvae spend the rest of the year under the bark of the trees feeding until they emerge as adults through an one-eighth inch "D" shaped hole. EAB attacks all species of ash in the genus Fraxinus, including green, white, and black ash but not mountain ash, which is not a true ash.
Infested trees typically die within four years, regardless of age, vigor or species.
Some of the symptoms of EAB infestation that homeowners will want to watch for are: excessive woodpecker activity in April and May in your ash tree, leaving mocha colored areas on the bark where the woodpeckers have removed the dark gray ridges in search of EAB larvae and pupae; crown thinning; branch yellowing; cracks in the bark; and shoots coming off the trunk. Ash yellows, a bacterial disease, can cause some of these symptoms, but will not be accompanied by small D shaped exit holes on the trunk or excessive woodpecker activity.
For additional information on EAB including treatment information:
Thousand Cankers Disease (TCD)
This is actually a complex, the vector is the walnut twig beetle (Pityophthorus juglandis) that carries the disease fungus Geosmithia morbida. The fungus needs the vector to penetrate the bark, and the infection develops in the galleries in the bark and the phloem. It is not systemic. Mortality is a result of many beetle-created gallery infections coalescing to girdle the tree. Research is ongoing to better understand this newly emerging disease complex.
The walnut twig beetle (WTB) is a tiny beetle (1/16th of an inch long). Two logs, 5-6 inches in diameter and 18 inches long were found to contain over 23,000 beetles. Movement of infested raw wood for firewood or lumber can easily move large numbers of this pest.
WTB is native to the southwest U.S. and Mexico where it lives, without causing major damage, on the Arizona walnut. Other walnut trees, however, are more susceptible to infection that leads to tree damage and death, usually within 3-4 years. The eastern black walnut (Juglans nigra) which is native to our area is especially susceptible. Both the beetle and the fungus are specific to walnut trees of various species, and usually kill the tree within three years of infection. Branch mortality, numerous small cankers on branches and the bole and beetle activity are the primary symptoms.
TCD has been confirmed in Bucks County, PA.
Hemlock Wooly Adelgid
Hemlock wooly adelgid (Adelges tsugae) kills or weakens hemlocks by sucking sap from the undersides of branches at the leaf base. The Elongate hemlock scale (another invasive species) frequently attacks hemlocks weakened by the adelgid. The combination can accelerate or increase tree mortality.
Look at Potential Threats
Insects are not the only invasive problems trees face. Nor are they the only type of invasive species. here are some pathogens that can affect trees.
Sudden Oak Death
Sudden Oak Death (SOD) is a disease of oaks caused by Phytophthora ramorum. So far, it is only established on the west coast, but has been intercepted in Pennsylvania in a tray of nursery stock. For more information, including information for nurseries, visit:
For additional information on leaf-eating tree pests, please visit the Gypsy Moth page below.
Return to Pest Pages
Gypsy moth is a cyclic insect that has been a problem in York county and will be again.
Many of the plants we see in our yards are not native to the mid-Atlantic region. Some of these plants are not good neighbors, and refuse to stay in our yards, with disastrous consequences.
Invasive species are not restricted to the land. Many invasive species that are problems in our water bodies are also part of our homes, as pets; in ponds or water gardens; or are moved via our recreational activities.
Consider the use of native plants in your yards and gardens instead of non-native plants. Here are resources to assist gardeners in making more eco-friendly selections.