Help Stop Insect & Disease Invasions
Tree City USA Bulletin #56—Abridged VersionDownload This Page (PDF)
The cast of infamous and unwelcome insects and diseases is constantly changing, but the USDA Forest Service annually monitors about 20 of the more serious forest pests. Here are five that have been introduced and are destroying urban trees.
Emerald Ash Borer
First reported in Detroit in 2002, this shiny green beetle is only about 1/3-inch long in the adult stage. It targets all ash trees, with a preference for green ash, white ash and blue ash in that order. Tens of millions of ash trees in urban and forested settings have been killed and the insect is spreading.
Recognition: Sudden fading of an ash tree’s crown in summer. D-shaped holes where the adults emerged. Direct observation of the adults feeding on leaves.
Asian Longhorned Beetle
This infamous pest was first observed in the Brooklyn, New York area in 1996. However, it is believed it arrived there in the 1980’s, probably in solid wood packing material. It is a huge insect that bores into a wide variety of hardwood trees. These include its favorite—maples—as well as willows, horsechestnut, elms, birches, poplars, mimosa, hackberry, ashes, London plane and mountain ash.
Recognition: It is the large, 3/8-inch exit hole that gives away this invader, often before the tree even shows signs of declining because of the tunneling activity. The adult is spotted black and white and is about 1-inch long with antennae that spread up to 3 inches. They usually feed on the midrib of leaves.
Hemlock Woolly Adelgid
Shady hemlock groves are dear to the hearts of many who enjoy our eastern forests. Hemlocks also add beauty to parks and home landscapes. Unfortunately, this species is attractive to a tiny, white insect introduced from Asia. Decline and mortality in hemlocks began to appear in Connecticut, New Jersey and Virginia in the late 1980’s and is being spread by wind, birds and at least in one case, on nursery stock.
Recognition: Large numbers of fluffy white specks that line twigs at the base of leaves on a hemlock is a sure giveaway that the tree is infected by mature hemlock woolly adelgids. Immature stages are more difficult to detect because they are smaller than the diameter of a leaf and dark colored.
Sudden Oak Death
We have lived with oak wilt disease in eastern forests for years and have developed a number of preventative methods. Now there is a west coast disease that kills western oak species in the red oak group and can damage the foliage of many others, such as California bay laurel, Douglasfir and coast redwood. The disease was discovered in the 1990’s and spreads by infected nursery stock, wind-blown rain and contaminated irrigation water.
Recognition: This one requires laboratory analysis for positive identification. However, the diagnostic symptoms on susceptible species are red-brown to black cankers and seepage on the lower trunks.
Thousand Cankers Disease
Eastern black walnut trees are the victim of this fungal disease. Mortality in black walnuts growing in the western states was at first attributed to drought but a new fungus, Geosmithia morbida has now been identified as the culprit. Unfortunately, the disease is spreading eastward into the native range of black walnuts.
Recognition: Crown dieback and thinning in walnuts. Removal of bark will reveal the cankers but laboratory cultures in agar and microscopic examination is necessary to positively identify the disease. The insect that carries the disease (vector) is smaller than a pencil point and difficult to detect. Sometimes there is seepage from the tiny hole it makes as it enters the tree.
What You Can Do
There is a role for everyone to help fight against the spread of insects and diseases that destroy trees. Whether you are an individual working alone or a member of an organized group, there is a need to heighten awareness about pests, be on the watch for invaders, and know who to contact for help or to report findings.
Learn More About Insect & Disease Pests
Whether working alone or as part of an organization, a first step is to become knowledgeable about the pests that threaten tree species in your area. An excellent guide to this information is an annual publication produced by the USDA Forest Service titled Major Forest Insect and Disease Conditions in the United States. For more about this publication as well as links to specific websites about the major pests, see the supplemental materials for this bulletin. There are also workshops conducted in many communities. Your state forester, County Extension Office or local branch of Master Gardeners would be a starting point to see what might be available.
Include Monitoring and Information as a Tree Board Activity
Tree boards can expand their responsibilities by providing information about pests and pest control through local media, workshops, publications and information booths at public events. Also, ordinances can be reviewed to assure content that allows for inspection and control of infected trees on private property as well as in rights-of-way and on public land. Suggested language for a section on “Tree Protection” can be found in Tree City USA Bulletin No. 6. Another activity potentially spearheaded by tree boards and/or the urban forester is to include pest monitoring as part of the tree inventory with a goal of using this information to guide future management decisions. IPED, part of the i-Tree suite of programs, is a free inventory tool to make this job easier.
What to Do if you Find Something Suspicious
- Carefully compare the symptoms or actual insect with photos in reference materials.
- Collect samples. The insect is best, properly euthanized and contained in a tight container such as a pill box. Chewed leaves, bark samples, etc. may also be helpful. In the case of diseases, the collected sample should be contained in a tightly sealed plastic bag or other container.
- Take photos of the infected tree, both distant and close-up, and note exact location and date.
- Describe the extent of damage, position on the tree(s) and other helpful observations.
- Submit your findings to a specialist such as your local county or state Extension specialist, state forester, certified arborist or consulting forester.
Help is Available
For examples of volunteer organizations that monitor invasive pests, obtain a complete edition of bulletin #56 from the Arbor Day Foundation. For additional sources of information and assistance, view the supplemental materials for this bulletin.
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