Invasive Tree Pests

Learn about Emerald Ash Borer, Asian Longhorned Beetle, and Thousand Canker Disease and other tree issues.

Emerald Ash Borer adult and gallery damage. Photo: Joseph O'Brien, USDA Forest Service,

Emerald Ash Borer adult and gallery damage. Photo: Joseph O'Brien, USDA Forest Service,

New invasive - Spotted Lanternfly

The Spotted Lanternfly is a plant hopper native to China, India and Vietnam, and has been introduced in South Korea and Japan. In Korea, where it was first detected in 2004, the Spotted Lanternfly is known utilize more than 70 species, 25 of which also occur in Pennsylvania, including cultivated grapes, fruit trees, and hardwood species. In the U.S., the Spotted Lanternfly has the potential to greatly impact the viticulture (grape), tree fruit, plant nursery and timber industries.

Entomologists in the PDA, entomology extension specialists in Penn State's College of Agricultural Sciences, Department of Entomology, Penn State extension educators, Pennsylvania Department of Conservation and Natural Resources entomologists, and USDA scientists will be collaborating to obtain answers to the many unknowns regarding this insect pest that is new to the United States.

It has appeared in parts of Berks, Montgomery, Bucks and Chester Counties that are now included in a quarantine area. State, municipal and local volunteer activities are aimed at limiting the spread and possibly eradication the insect while the infestation is still small.

Learn more at:

PDA Spotted Lanternfly page
Penn State Spotted Lanternfly information

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.
For advisories in Pennsylvania, visit the DCNR Advisories page

Insects and diseases moved with firewood include: Asian Longhorned Beetle, Emerald Ash Borer, Thousand Canker Disease and Spotted Lanternfly

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:

USDA BeetleBusters
Pennsylvania DCNR
ALB Host Trees

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:

Emerald Ash Borer Information site
If you see EAB, report it to PA Department of Agriculture 1-866-253-7189, or

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.

In Pennsylvania -
Pennsylvania Department of Agriculture
DCNR Thousand Canker Disease
Thousand Canker Disease

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.

For more information:
National Forest Service
PA DCNR Hemlock Wooly Adelgid page

Other Threats

Oak Splendour Beetle

Look at Potential Threats

The Nature Conservancy Gallery of Pests


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.

Fabrella Needle Blight of Hemlocks

Beech Bark Disease

Plum Pox Virus

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:

California Oak Mortality Task Force

For additional information on leaf-eating tree pests, please visit the Gypsy Moth page below.

 Return to Pest Pages

Gypsy Moth

— by Diane Oleson, M.S. — last modified March 5, 2012 11:12 AM

Gypsy moth is a cyclic insect that has been a problem in York county and will be again.

Invasive Plants

— by Diane Oleson, M.S. — last modified March 5, 2012 12:38 PM

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.

Aquatic Invasive Species

— by Diane Oleson, M.S. — last modified December 2, 2011 4:28 PM

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.

Native Alternatives

— by Diane Oleson, M.S. — last modified March 5, 2012 12:20 PM

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.

Home and Garden Pests

— by Diane Oleson, M.S. — last modified March 5, 2012 12:29 PM

Here are some unwelcome invasive guests common around the house or in your garden.