Help Stop Insect & Disease Invasions

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.

Tree City USA is supported by the USDA Forest Service Urban and Community Forestry Program.