About a decade ago there were a lot of sickly looking or even dead ash trees in the Detroit, Michigan area. Ash is susceptible to a number of insects and diseases, some not easily diagnosed. Ash yellows, caused by a tiny organism called a phytoplasma, produces symptoms similar to those observed and, in the early 90s, widespread ash decline occurred across the Upper Midwest and Northeast. Multiple stressing factors were blamed. Not until 2002 was a beetle native to eastern Asia identified as the culprit. We know now it arrived at least ten years before being detected.
Emerald ash borer, Agrilus planipennis, probably entered the country in ash used in shipping crates or pallets. It infests only ash, Fraxinus spp., and resistance has not been observed in any of our native species. Although it seems counterintuitive for a forest insect to become established in an urban area, it is these areas along our coasts and the Great Lakes that receive goods transported from around the world. Organisms that infest solid wood packing material constitute an ongoing threat for introduction of nonindigenous and potentially invasive insect pests. At least eleven forest insect pests identified in the United States and Canada since 1990 are believed to have arrived this way.
Roughly one half inch long, the shiny, emerald green insect belongs to a group of beetles known as metallic wood-borers (Fig. 1). Adults emerge from the trees they fed in primarily during June and July. Emergence produces one sure sign of infestation, a small, one-eighth inch hole flattened on one side, or D-shaped. Sun loving, the beetles feed on ash foliage for a week or more before mating and laying eggs. Females produce fifty or more eggs, and lay them individually in bark cracks and crevices. They hatch within two weeks. Immature beetles or larvae are called flatheaded borers distinguishing them from roundheaded borers, cylindrical larvae of a different beetle group that often utilize the same food resource. The insect during this stage is flattened, whitish, and with distinct segmentation, tapeworm-like (Fig. 2). They feed on inner bark or phloem tissue. Phloem is living tissue responsible for moving the products of photosynthesis around the tree. Larval feeding tunnels called galleries curve and wind under the bark much like mountain roads until the tree’s translocation system is effectively severed (Fig. 3). When the tree is girdled, it dies, often in as little as two or three years following the first beetle bite.
In the core area, that region of southeastern Michigan where the beetle was first discovered, the dead tree total is estimated at 40 million. Numbers are mounting in surrounding states. Removals add hundreds of thousands as communities and forest owners seek to reduce losses, limit the numbers of beetles and limit the numbers of potential hazard trees.
As of October 2008, the emerald ash borer can be found in the following states; Michigan (2002), Ohio (2003), Indiana (2004), Illinois (2006), Maryland (2006), Pennsylvania (2007), Missouri (2008), Virginia (2008), West Virginia (2008), and Wisconsin (2008), and in two Canadian provinces; Ontario (2004) and Quebec (2008). On Dec. 1, 2006, the federal quarantine expanded to cover the entire states of Ohio, Indiana and Illinois in addition to the already covered lower peninsula of Michigan. Individual counties are quarantined in the other states. The more likely avenues of beetle movement, in addition to nursery stock, include green lumber and firewood. Because of difficulties with identification, movement of all hardwood firewood is regulated as are wood chips, whether composted or not.
Eradication efforts have largely been abandoned. A pilot study to reduce the beetle?s impact is ongoing in the Upper Peninsula of Michigan. Called "Slow Ash Mortality" or "SLAM" it involves a 4-faceted approach. Infested trees are removed. Trap trees serve as sinks, removed before beetle emergence, rather than as detection tools. Large diameter hosts are thinned out to reduce available breeding material and finally insecticides may be used to protect uninfested trees. Research is underway to identify effective lures to simplify detection. Control agents from areas where the insect is native have been identified. Resistance mechanisms are being investigated. All of these will take time to develop and incorporate into a management program.
For now, when the beetle arrives, the landowner has few options. Individual, high value trees can be protected with an insecticide. These treatments have to be repeated regularly and should a beetle tree be located within a designated area and an eradication cut performed, the treated tree would be removed. Removal and utilization of ash, particularly larger diameter ash from woodlots retards population buildup because the larger the tree, the more beetles that tree is capable of feeding. Ash value, already diminished, will probably continue to shrink. Once the beetle arrives in New York options available to the forest owner will also shrink due to quarantine. The picture is bleak. Emerald ash borer continues to devastate ash in this country and it is headed our way.
For the reader interested in additional information:
Much more extensive management recommendations for the forest owner in New York State can be found at http://www.dec.ny.gov/animals/7253.html as well as links from that site.
The author wishes to thank Therese Poland of the USFS for all her help and for supplying images. This article, presented here with revisions to provide more up-to-date information, first appeared in The New York Forest Owner 45(1): 16-17.