Emerald Ash Borer

Tim Iverson

(7/2016) The Emerald Ash Borer, or EAB, is a little green beetle about the size of a penny. While diminutive in denomination their impact is anything but. This lean green eating machine is working its way across the eastern half of the United States in a marathon buffet fashion. Worse yet, this gluttonous spree is going unchecked because it’s a non-native invasive species without any natural predators in North America. This epidemic is placed on par with the Chestnut Blight of the early 20th century, which virtually eradicated the American Chestnut within its native range. We’ve already lost more than 50 million Ash trees in the 10 years since the EAB’s arrival, and it threatens the remaining 8.7 billion remaining Ash trees.

In the summer of 2002 the Emerald Ash Borer made its first appearance in North America in Michigan and Ontario, Canada. Originally hailing from Asia the EAB was likely transported accidentally in wooden packing material aboard cargo freighters. It didn’t take long for the EAB to latch onto the land of the free. Over the past 14 years the beetle has spread voraciously across much of the eastern United States, and now has active infestations in 27 states (including Maryland) and two Canadian provinces.

Adult Emerald Ash Borers lay eggs in the outer layers of bark. The larvae chew their way through the phloem and cambium. These are the layers of a tree responsible for transferring nutrients and water throughout the tree. The larva will feed on these layers for several months and generally overwinter here. The following spring the larva will pupate and emerge as adults in May or June. The adults make a direct line to the canopy of the tree and begin consuming the leaves. Small trees can die from this type of infestation within a season or two, while it generally takes larger ash trees 3 to 4 years of sustained infestation before death occurs.

In most places Ash trees comprise between 10 - 20% of urban forests. A 20% loss would cause a rise in the urban heat island, decreasing air quality, and depreciate the general appearance of an area. Invasive plants would likely be the first in the ecosystem to fill these vacant spaces. Commercially, Ash is commonly used for baseball bats, guitar bodies, furniture, and flooring. Ash is one of the most commercially viable trees in North America. The environmental and economic losses would be significant.

In Asia, the Emerald Ash Borer is little more than a nuisance pest. Natural resistance from native Ash trees and predators, like parasitic wasps, keep the population under control so that the EAB doesn’t do catastrophic damage. North America lacks these natural checks and balances so the devastation from the Emerald Ash Borer has been significant here. The US Department of Agriculture has identified four separate parasitic wasp species that have been approved for release in the United States. Biological control agents, or using natural predators, has been successful in controlling other invasive species. Large scale releases of one species of parasitic wasp have been occurring regularly in Michigan since 2009. This species is reported to be achieve a 90% parasitism rate within its natural range. Hopefully similar success rates will occur in North America.

Maryland hasn’t been exempt from the verdant villain, and the town of Thurmont recently became an unwilling host too. Early this past spring Maryland Department of Natural Resources (MD DNR) identified several trees within Thurmont Community Park that were displaying symptoms of an infestation. Upon further review all 276 Ash trees within the park showed some level of infestation and damage from the EAB. While treatment plans do exist they are very costly and often are not entirely effective - only prolonging the life of the tree before an inevitable demise from infestation. MD DNR officials are working closely with city officials and crews to assess trees for removal and replacement. By prioritising the severity of infestation officials can focus on staggering the removal process. Jim Humerick, Chief Administrative Officer for Thurmont, said, " We are closely monitoring the existing trees and will not remove them until absolutely necessary. This will provide us with a window over several years to transition gradually rather than losing all the trees at one time."

Chemical treatment is usually only effective as a preventative measure, but once a tree has been infested it will generally only prolong the life of the tree for a short time. DNR currently has a 50/50 funding match for chemical treatments available to municipalities, governments, and conservation lands. Newly planted Ash trees or currently unafflicted trees can be treated to repel any future attacks by the EAB. In an attempt to prevent or slow the advance and spread of the EAB there is both a Federal and a State quarantine and ban on transporting firewood across state and county lines.

It remains to be seen how this will all unfold. Are we doing enough or will the Ash go the way of the American Chestnut? Can we even prevent the ultimate demise at all? Researchers seem to think so, but it all comes down to prevention and timely response to infestation at this point. Average citizens can do their part by buying locally sourced firewood to prevent further spread and transmission of the pest, but the rest is up to chemical treatments, predators, and effective policy.