It's a war zone out there.
The larvae of emerald ash borer feed in the phloem and outer sapwood of trees. The beetle apparently has a one-year life cycle.
In the Midwest and northeastern U.S., city foresters, arborists and tree care service providers are currently on the front lines. They have some weapons in their arsenal, but the victories are few and far between. The costs to fight the battle are great, but the costs to ignore the enemy are worse. The enemy is swift, the enemy is smart, the enemy can multiply, and the enemy is hungry.
This enemy is the emerald ash borer (EAB), a mean, green, ash-eating machine. The pest initially appears unthreatening, but packs a monstrous bite. Once it infiltrates an area, EAB causes damage so rapidly, professionals can barely keep up. It doesn't help that it's hard to spot initial infestations in healthy ash trees. Even professionals sometimes miss them. By the time insect damage is recognizable, many EABs are spreading havoc on nearby ash. And then they will eat through every native ash species in its path until they're gone.
The threat shouldn't be downplayed, says Deb McCullough, a professor of forest entomology at Michigan State University in East Lansing, Mich. Michigan was where the invasive beetle was first detected in the U.S. in 2002. "Once the beetle enters a typical residential neighborhood, if no one does anything to stop it, within 10 years the ash trees are dead and need to be removed," she says.
What's lost in addition to a stand of old, sturdy, shade-producing ash trees? All the benefits they provide. Researchers predict the economic loss in treatment and removal of the trees over the next 10 years to be in the billions. And, that doesn't include the loss of stormwater infiltration, energy conservation, carbon sequestration and other benefits these trees deliver. Researchers say those benefit losses shouldn't be ignored - water and air-conditioning bills have already risen in areas of Michigan and Ohio that have lost a considerable chunk of ash trees.
What can a tree service provider do in the fight against EAB? Join the war, researchers urge. New treatment options, diverse planting plans, and economic treatment and removal staging can make fighting EAB a real possibility.
When EAB first arrived in the U.S. - supposedly in ash wood that stabilized cargo ships or crated heavy consumer products from Russia, China, Japan or Korea - the infestation probably started with a small number of beetles. By 2002, when EAB was first detected, many trees in southeastern Michigan were already dead or dying. Native ash trees had little or no resistance to EAB, and natural enemies had little effect on high EAB populations, so infestations spread as people moved contaminated ash nursery trees, logs or firewood into uninfested areas.
In many parts of the country, ash is considered a fairly dominant tree species. In urban areas, ash trees can comprise 5 to 40 percent of municipal trees, McCullough says. The beetle feeds on the tree's vascular system, cutting the tree off from nutrients and water and causing the tree to slowly suffocate. The bug tends to start feasting closer to the top of a tree, then works its way down, which is one reason it's hard to detect. All 16 native ash species are vulnerable to EAB, and larvae have been found in trees as small as 1 inch in diameter.
Today, EAB infestations are present in 15 states (Michigan, Illinois, Indiana, Iowa, Kentucky, Maryland, Minnesota, Missouri, New York, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia and Wisconsin) and Canada.
When left to its own devices, EAB was initially seen moving less than 1 mile per year, explains David Shetlar, professor of entomology at The Ohio State University. Shipments of ash nursery trees and logs are now regulated and transporting firewood outside of the quarantined areas is illegal, but moving infested firewood remains a problem.
Since then, researchers have found the local spread of infestation is much greater. Based on his experience watching EAB spread in Michigan and Northwest Ohio, Dr. Dan Herms says if an ash tree is within 15 miles of an infestation point it should be considered at risk. "This is a function of how hard EAB is to detect, especially in low infestations," says Herms, a professor in The Ohio State University's department of entomology. "When delineating infestations, we've learned almost every time that EAB is always more widespread than we think."
Since their discovery in southeast Michigan in 2002, the EAB has destroyed millions of ash trees in the Midwest. Note the severity of the tunneling created by their larvae.
Herms saw EAB's spread in Toledo, Ohio, firsthand. The initial attack was slow. "It took more than 10 years for ash trees to go from 0 to 30 percent mortality," he explains. "But as the beetle multiplied, ash tree deaths went from 30 to 99 percent in just three years. People are fooled into thinking they can keep up with it in the beginning, but once it reaches an inflection point it goes very rapidly."
As EAB settles into an area and populations multiply, small trees can die in one to two years, and large trees in three to four years, McCullough says. The website www.EmeraldAshBorer.info estimates EAB has already affected 50 to 100 million ash trees and threatens to kill most of the 7.5 billion ash trees throughout North America.
Why should tree care professionals stay educated on EAB? Because "this is a critter that we won't stop," Shetlar says.
The situation sounds extremely dire, but researchers have made strides in understanding EAB, and there has been much learned over the last three to four years that makes implementing a plan to fight the pest a real possibility. "We can absolutely do something to fight EAB," McCullough insists.
First, professionals in and near EAB zones can get a jump on the pest by taking tree inventories at their clients' properties. Create public awareness by educating customers who have ash trees and are near infestation areas, Herms suggests.
Then, come up with economical plans for staging treatments and removals where EAB is a problem. At Michigan State, McCullough has participated in a study due out early this year simulating how EAB populations will grow and spread and how trees will decline. "If you do nothing, those trees are dead in 10 years," she says. "But we're finding if you treat just 20 percent of the trees each year, after 20 years you can actually save 99 percent of your ash trees."
This is possible now, because "we know more about the insect, we have better products to control it, and we have better methods of using those products," McCullough says.
On large commercial sites or in municipalities, cost has been a great concern for city foresters and property managers. While it typically costs $700 to $800 to remove a tree, it costs $3 to $4 per diameter inch to treat a tree, McCullough says. While the high cost of removal is a one-time charge, with treatment, a property owner must factor in treating ash trees yearly or biyearly until EAB populations diminish and healthy ash trees can survive less frequent treatments. After seven or eight years, the cost of treatment can exceed the cost of removal, Shetlar says.
But when including benefit losses, protecting individual accent or critical trees in the landscape may be worth more than their removal and replacement costs, Shetlar adds. "Losing a large, old ash tree means losing all of its benefits, something you can't instantly get back," explains Steve Frank, a professor and extension specialist in entomology at North Carolina State University, Raleigh, N.C. "You can't gain 50 years of growth in less than 50 years."
It's easy to see how the emerald ash borer acquired its name. However, it's the larvae of the insect that creates the damage
McCullough's research has looked into pricing a treatment strategy for a small percentage of trees each year, and the findings are significant. "If you had EAB and started treating the trees four years after the beetle got established (because no one finds it right away), you would pay approximately $365,000 for treatments and removing a few of the trees that you couldn't save," she says. "If you didn't treat the trees, let them die and just planned on removing them, you would pay $2 million within two years in removal costs. Even if gas prices were to go up and treatment costs altered slightly, the difference is still significant." (For more on effective treatment strategies, see "Insecticide Options for Protecting Ash Trees from Emerald Ash Borer" at www.emeraldashborer.info/files/Multistate_EAB_Insecticide_Fact_Sheet.pdf).
Many residential communities treasure their beautiful shade-producing ash trees (left). But like the American chestnut tree that succumbed to an invasive species more than 50 years ago, the days of the ash tree as a street tree appear to be over as evidenced by the image on the right.
When it comes to planting new trees or replacing lost ash trees, researchers encourage landscape designers and architects to focus on species and age diversity. "The lessons have been learned with Dutch elm disease, chestnut blight and now EAB," Frank says. "If one tree is too heavily represented, it could be at risk for the next invasive species to enter the country." (For some recommended alternatives to ash trees in the Midwest, visit www.emeraldashborer.info/files/e2925.pdf.)
In the meantime, other things are being done to try and fight EAB. Biological controls are continually being studied, though there is no scientific evidence yet that EAB populations are impacted by these predators.
While Asian ash trees aren't encouraged as replacement species yet since they aren't as desirable as North American white or green ash trees, researchers are studying what makes Asian ash naturally resistant to EAB. They're hoping to breed them with North American ash trees to create a more desirable and resistant species.
Ultimately, "the problem won't go away," McCullough says. "Sure, you can plan to cut down ash trees as they die. This will work for a year or two, but then you won't be able to keep up with it and these dead trees will become unsafe, creating situations for potential law uits. You can't sit around and ignore it."
Professionals must get informed, educate their customers and implement service strategies to fight. "If you're in this industry, I don't see how you cannot learn about EAB," Herms says. "The demand for service will increase, whether it's for treatment or removal. You'd be doing yourself and the industry a disservice if you didn't educate yourself and your customers about EAB."
Nicole Wisniewski is a 15-year green industry veteran and award-winning journalism and marketing professional. She is currently a senior project manager in The Davey Tree Expert Co.'s marketing/corporate communications department. Visit her blog at www.mybiggreenpen.com or reach her at firstname.lastname@example.org.