More than 20 million ash trees have died in the Midwest. They were killed by a half-inch-long, metallic-green beetle that tunnels underneath bark. The emerald ash borer, a beetle native to Asia, threatens to completely remove ash trees from U.S. forests.
This is not the first time our forests have been devastated. During the early 1900s, chestnut blight ravaged our forests by killing almost every chestnut tree, and in recent decades, Dutch elm disease has caused the widespread death of elms.
The emerald ash borer is only one example of many non-native insects that have invaded North American forests. These invasive species are efficient hitchhikers on a variety of wood packing and other plant materials. Increasing international trade has provided more opportunities for non-native insects to travel to places where they’ve never existed before.
The emerald ash borer was first detected in the U.S. in 2002 when large numbers of ash trees began dying in southeastern Michigan. The beetle had arrived several years before, probably by hitchhiking within wood crating or other wood materials in a shipment from Asia.
By the time the infestation was discovered, it was already too late to contain it. The beetle had spread across Michigan’s Lower Peninsula and into Indiana, Ohio and Ontario.
More recently, populations have been found near Chicago and in Maryland. In southeastern Michigan, where nearly all ash trees have been killed, communities and homeowners are struggling to deal with the costs of removing the many hazardous standing dead trees.
These beetles continue to spread across the Midwest. Humans unknowingly transport emerald ash borers when they haul infested ash logs, firewood or nursery stock, because the insects spend much of their lives hidden beneath ash bark.
The beetle’s worm-like larvae feed just under the bark and create wandering S-shaped tunnels that disrupt the flow of water and nutrients within the tree. When large numbers of larvae are present, they completely girdle and kill trees within one to three years. All ash trees—from small to large—are susceptible, even healthy ones.
Ashes, including white ash, green ash, blue ash and pumpkin ash, comprise about 3 percent of the trees in Missouri’s rural forests, and about 13 percent of the trees in our urban forests. In some places, they comprise as much as 30 percent of park and street trees. Cultivars of white and green ash are among the most commonly planted trees in urban landscapes.
Even before the emerald ash borer arrived, ash trees in the Midwest were battling native pests. It is common to see ash trees with symptoms of ash yellows (a disease) or ash decline, a condition caused by a variety of diseases or other stresses. Native wood-boring insects frequently attack ash trees stressed by injury, transplanting, soil compaction or poor tree location. All of these problems can result in branch dieback, sparse leaves and gradual decline of tree health over several years.
Because of these ongoing problems, it’s not easy to know if a tree has been attacked by the emerald ash borer. One of the most distinctive clues to look for is a 1/8-inch diameter, D-shaped hole in the bark that the adult emerald ash borer creates when it exits a tree.
Once an invasive insect species gains a foothold in North America, it can move by many pathways across the continent. Emerald ash borers traveled in firewood from Detroit to recreation sites throughout Michigan and nearby states. They hitchhiked in logs transported to sawmills and in nursery stock shipped from Michigan to Maryland.
Asian longhorned beetles, another non-native wood borer, traveled in firewood from infested trees cut down in Brooklyn to uninfested forests on Long Island.
Gypsy moths, which defoliate oaks, temporarily established themselves in northwestern Arkansas in the early 1990s, possibly after hitchhiking from the northeastern U.S. as egg masses attached to recreational vehicles. Aggressive action by state and federal authorities eradicated the gypsy moth population in Arkansas, but the infested area of the northeastern U.S. continues expanding westward and will eventually reach Missouri.
Asian longhorned beetle populations have been nearly eradicated in Chicago, and eradication efforts continue against populations in New York, New Jersey and Ontario. However, eradicating the emerald ash borer is very unlikely because of its wide distribution and the lack of effective means to detect and control it.
Insects are not the only forest pests that can be transported in firewood and other plant parts. Tree diseases such as oak wilt and Dutch elm disease can easily hitchhike, too, and are even more difficult to detect.
New national and international regulations specify treatments for solid wood packing materials that will reduce the threat of hitchhiking pests in international trade. Incoming cargo is examined for potential pests at U.S. ports by federal inspectors, although only a small fraction can be inspected because of the huge volume.
Working together, the Missouri Departments of Conservation and Agriculture, the U.S. Department of Agriculture and other agencies annually conduct surveys to detect new forest pests. Surveyors examine ash trees for evidence of the emerald ash borer at high-risk sites such as public and commercial campgrounds where campers bring in their own firewood. They also check ash trees in urban parks and streets, particularly where large numbers of ash trees have been planted since the mid-1990s. Nursery inspectors examine thousands of trees in Missouri’s commercial nurseries each year.
When harmful non-native plant pests become established in the U.S., the U.S. Department of Agriculture Animal and Plant Health Inspection Service and state departments of Agriculture are responsible for quarantines and eradication activities.
A federal quarantine is now in place to limit the spread of emerald ash borers. All ash nursery stock, logs and wood with bark attached, and all deciduous firewood is prohibited from being transported out of Illinois, Indiana, Ohio and Michigan’s Lower Penninsula, unless specific actions are taken to reduce the risk of the borers surviving in the ash material.
Operations to control isolated populations of emerald ash borers have been attempted at the edges of their known distribution. Treatments are expensive and involve cutting down all ash trees within an infested area and chipping them into one-inch pieces to destroy the borers and their food source. No insecticide treatments are 100 percent effective in eradicating an emerald ash borer population. Much research is underway to find better ways to detect and control emerald ash borers.
Many state and federal agencies are working together to protect our forest resources from these insect invaders, but they need your help. The most effective thing you can do to prevent the arrival of invasive forest pests is to avoid moving firewood long distances. Buying firewood from local sources supports local economies and reduces the threat of introducing new pests.
You can also help by keeping an eye open for new pests. The emerald ash borer has not yet been found in Missouri as of early 2007. But we need to be alert for its arrival. Areas where it is most likely to appear include campgrounds, homes or businesses receiving ash logs or firewood from outside Missouri, and residential or commercial sites where large quantities of ash were planted since the mid-1990s.
All of us working together can help keep the emerald ash borer and other invasive insects out of Missouri as long as possible. Reducing firewood movement and thinking about other ways that pests might hitchhike into our forests will go a long way toward preventing the arrival of the next new pest.
Is the tree an ash species?
Is the tree in poor health?
The following symptoms can be caused by native pests, emerald ash borers or other stresses:
Do you see any of the following?
It’s NOT Emerald Ash Borer if you see:
Check the links listed below to be sure.
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