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Emerald Ash Borer: Now What?

July 18, 2006

The emerald ash borer has been detected in Illinois, both in Lily Lake in Kane County and in Wilmette in northern Cook County. This was to be expected because the geographic distribution of this insect has increased substantially throughout Michigan, Indiana, Ohio, and Canada. The emerald ash borer is an invasive species, and Illinois has been the recipient of other invasive insect species, including the gypsy moth, Asian longhorned beetle, Japanese beetle, pine shoot beetle, and banded elm bark beetle. One of the major concerns is the future of planting ash trees in landscapes. First of all, ash trees have been the staple of the nursery industry for decades because they are able to survive in a wide variety of soil types and site conditions. Second, ash trees are easy to propagate and are an inexpensive landscape tree. As such, ash trees have been extensively planted within municipalities and urban environments. However, this had led to the practice of over-planting with one particular tree species. Historically (and we should learn from the past), problems have been encountered through the wide-scale use of one plant type (= monocultures), which has led to the demise of some of our most beautiful trees. For example, monoculture plantings of American elm resulted in these trees succumbing to attack from the Dutch elm disease. Recently, honey-locust trees, which have been extensively planted throughout the United States, are experiencing problems associated with diseases.

The bottom line is that it is important to plant a diverse assortment of plant material to increase genetic diversity, as opposed to switching from one monoculture to another. A mixture of plant species is much more restrictive to the natural spread of insect and disease pests because tree species vary in their susceptibility to different pest complexes.

It is important to realize that this insect is likely to travel on its own about one-half mile per year, although it is capable of flying about 5 miles. At that rate, it would take a very long time for this insect to move throughout the state even if regulatory control measures are not very effective. This insect is much more likely to move large distance with the aid of people. The movement of firewood appears to be the most likely avenue of long-distance movement by emerald ash borer.

An item to consider is the preventive treatment of ash trees. Application of imidacloprid (Merit) into the soil within 2 feet of the trunk has been found to provide protection to ashes for about a year after application. In fact, protection is heightened by two successive years of treatment. Higher levels of control have been obtained with the IMA-jet formulation of imidacloprid by Arborjet. It is likely that an infestation will be present in an ash tree for a couple of years before dieback, emergence holes, and other symptoms become apparent. As a result, we are in agreement with other states in recommending preventive treatments only on ash trees in the same county or within 10 to 12 miles of an infestation. Ohio State University has an excellent synopsis of emerald ash borer treatment options at http://ashalert.osu.edu/latestnews.asp?id+497.

Author: Phil Nixon Raymond A. Cloyd


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