By Marcia Anderson
I was recently in a conference of Certified Tree Experts representing many northeast and north-central states to discuss the invasion and progressive devastation of our nation’s ash trees by the emerald ash borer.
Yes, we have another pest focused on annihilating our community forests. Think back. First, it was Dutch elm disease. Later, chestnut blight, the gypsy moth, followed by the Asian longhorn beetle. Now, the emerald ash borer (EAB) is here. While common in urban landscapes across much of the continental U.S., native ash trees (Fraxnus sp.) have little natural resistance to this most recent pest. In addition, EAB, which is native to Asia, has no natural enemies in the U.S.
A major problem with an emerald ash borer infestation is that most people do not see it coming, and by the time the trees begin to show signs of decline, it is too late. The really bad news is that 95% of ash trees hit with EAB will be dead within five years. The only way to save your favorite ash tree is to prepare and be proactive in your response.
Range. Ground zero for the EAB invasion was near Detroit, Michigan in 2002. EAB has already swept through the Midwest and devastated almost every ash tree in its path. In Ohio, nearly all ash trees (over 20 million) suffered close to 100% mortality. EAB is now present in 34 states and 2 Canadian provinces. In infested areas, 90-100% of ash trees will be dead within 4-5 years.
How does EAB kill trees? EAB attacks ash trees of all sizes. EAB starts with large trees, but then goes down to smaller ones, devouring the insides of every ash tree in its path. EAB first attacks stressed trees, such as those with a portion of bark removed. The females lay 30+ eggs in the cracks of bark, beginning toward the top of the tree. The eggs hatch and the larvae bore in and feed on the phloem that conducts nutrients throughout the tree. Gradually, the infestation moves into the inner layers of the tree. The larvae spend one or two years feeding inside the tree before emerging as adults in the spring. If you see the adults exit holes at eye-level of a tree trunk, the infestation is heavy and has probably been there for several years. Symptoms that aid in early detection are yellowing or orange tinged leaves, loss of leaves in the canopy, sections of death in the canopy and eventually a weak, dying tree.
How does EAB spread to other areas? EAB is often found near highway rest stops. As a matter of fact, as I was driving through Pennsylvania to New Jersey in November, one landed on my car’s windshield at a rest stop. It was the first time I had seen one, and marveled at its small size and metallic green color. EAB’s are carried along railroad and other transportation thoroughfares, wherever ash trees or wood are transported. Adult EABs can hitchhike on truck beds, barges, and cars. Utility workers are often the first to find them in newly infested areas. Female beetles can disperse up to three miles from the source tree.
EAB is coming to an ash tree near you. New Jersey, New York, and the New England states are now the latest targets of this pest. According to the New York State Department of Environmental Conservation, less than 5% of the state’s 900 million ash trees are currently infested. However, because black and green ash are keystone species in the regions’ wetland ecosystems, their loss could mean the loss of the entire ecosystem. In New York and New Jersey’s hardwood forests, one in every 10 trees is an ash. The entire state of New Jersey is under an EAB quarantine and under federal and state regulation to minimize the spread to non-infested areas. All ash wood must remain in municipal boundaries unless it is chipped or the bark removed.
Strategies to hamper the spread of EAB. 1) First and foremost quarantine all ash wood, including firewood. 2) Replace ash trees with a diameter of 12” or less. If your community decides not to treat, figure that those ash trees will die, and become hazardous. Do you remove the trees now or later at a higher cost? 3) Remove infected trees – they are already hazardous. Dying trees dry out very fast and become unpredictable because they can crack and fall, even on calm, clear days. Removals should begin with the largest ones first. What to do with all of that ash wood? Chip or kiln dry the wood, which kills the bugs. Ash makes good pellets for wood burning stoves and can also be used in industry, furniture, and baseball bats.
Management options. An Integrated Pest Management (IPM) program for trees helps to create a healthier environment by reducing both pests and unnecessary pesticide use. IPM stresses the use of monitoring, maintenance, and sanitation. The use of pesticides, when needed, is also part of the IPM toolbox. Treating proactively for EAB falls into this “when-needed” category, in lieu of removing all of your ash trees.
If your trees are within 10-15 miles of known infestations, they are at risk. Success in treatment is ultimately determined by both the tree’s health and in initiating treatment before EAB has begun its demise. By the time people notice thinning in the canopy, EAB has already caused considerable damage to the vascular system of the tree. Even large ash trees can be protected from EAB by treating with systemic insecticides. Milwaukee saved most of its trees by treating because they decided that it was more economically beneficial than removal and replacement. Considerations in every town and situation are different.
There are three options for urban ash tree management: Removal and replacement; treatment with insecticides until they can be removed; and treatment with insecticides for the duration of the infestation. New York State and the North Central IPM Center offer good publications that describe the insecticide options for protecting ash trees from EAB. While some options are available to homeowners, others require professional application.
Dr. Jason Graboski of Rutgers University says that the states on the front lines, such as NJ, NY, MD and those in New England can benefit from the lessons learned by MI, OH, IN and PA. He shared with us information from the New Jersey EAB webpage that both informs residents and tracks EAB sitings across the state. New York also has an EAB website with reference maps. In addition, there is a national Emerald Ash Borer Information Network with detailed information for the entire U.S.
About the Author: Marcia is with EPA’s Center of Expertise for School IPM in Dallas, Texas. She holds a PhD in Environmental Management from Montclair State University along with degrees in Biology, Environmental Design, Landscape Architecture, and Instruction and Curriculum. Marcia was formerly with the EPA Region 2 Pesticides Program and has been a professor of Earth and Environmental Studies, Geology, and Oceanography at several universities.