To determine if a tree has been attacked, University of Illinois Extension horticulture educator Martha Smith suggests the following steps.
First, identify the tree. Emerald Ash Borer attacks only members of the Fraxinus genus, or true ash. On true ashes, buds, leaves, and branches form directly opposite one another on the twig or branch. If they do not, the tree is not a true ash and the EAB cannot attack it. The most common types of ash in Illinois are green, white, blue, black, and pumpkin ash. Some names are misleading -- for example, mountain ash is not a true ash. It is a member of the Sorbus genus and cannot be attacked by EAB.
Second, start to look for signs of decline, starting in the upper third of the tree canopy. If the tree looks unhealthy, look for D-shaped holes about the size of a BB. Anything round or larger has not been caused by EAB.
If bark on the trunk is splitting, lift it and look underneath. Snake-like tunneling under the bark may indicate the presence of EAB. Young sprout growth clustered at the base of the tree may also indicate EAB.
University of Illinois Extension has a handy checklist that can be used for identifying the tree and determining if EAB is present. The checklist and other information on managing this pest is available for downloading at http://web.extension.illinois.edu/fmpt. The document is also available from local U of I Extension offices. Due to the volume of contacts, U of I Extension will not conduct site visits.
University of Illinois recommends starting insecticide treatments only when your tree is within 15 miles of an EAB infestation, or if you are within a county that is quarantined. It may be more cost effective to replace a small or struggling ash tree than to pay the cost of ongoing treatments. In addition, trees in poor health are not likely to respond well to treatments. Do not treat trees showing more than 50 percent canopy decline; these ash trees are unlikely to recover even if treated.
For information on EAB in Illinois, including quarantine maps, visit www.illinoiseab.com.