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From anthracnose to spongy moths to oak wilt, it often seems as though Michigan’s trees are under nonstop attack. But while local homeowners should certainly familiarize themselves with these pests and diseases, there’s one particularly destructive tree threat that deserves special attention.
Called the emerald ash borer (EAB), this introduced beetle has already reshaped Michigan’s tree canopy and wiped out millions of ash trees across the state.
We’ll explain everything you need to know about the emerald ash borer and lay out the best way to protect your trees.
Emerald Ash Borers: The Basics
Emerald ash borers are small beetles, measuring about one-half inch in length. As their name implies, their exoskeleton is bright, metallic green.
Adult EABs feed on the foliage of ash trees, but they don’t typically cause much real harm while doing so. In fact, they only feed on these leaves for a week or two before mating and then dying about six weeks later. It is the larval stage that causes the most damage.
After mating, female EABs begin depositing eggs in the crevices of ash tree bark. Larvae begin hatching from the eggs a short time later, at which time they tunnel through the bark of the trees, ultimately reaching the phloem, cambium, and xylem tissue.
While there, the larvae feed voraciously and create long, winding “galleries,” which cause damage to the tree’s vascular system. This prevents the tree from transporting nutrients from the leaves and water from the soil.
After pupating and turning into adults, the EABs tunnel through the outer bark, leaving D-shaped exit holes.
The History of the Emerald Ash Borer
Though a number of tree boring insects live in Michigan, the emerald ash borer is not native to our area (or anywhere else in the U.S.). Instead, they’re native to East Asia.
Unfortunately, Southeast Michigan is ground zero for the EAB, as the very first individuals found in the U.S. were spotted in Canton in 2002. Since then, the insect has spread aggressively throughout the Northeast, Midwest, and central United States.
In their natural homeland, EABs don’t reach the kind of high densities they do in the U.S. This is likely due to the parasites and predators that feed on the beetles in their native range, as well as the resistance some Asian ash trees have developed over time.
But when they arrived in the U.S., their population exploded, and they had access to an incredible supply of vulnerable ashes. This combination led to the outbreaks we’ve seen occur over the last couple of decades.
Is Emerald Ash Borer Fatal for Ash Trees?
Yes. Virtually every untreated native U.S. ash tree that develops a significant infestation will die. This highlights the importance of diligent monitoring and proactive treatments.
It also helps illustrate the extent of the problem. By some estimates, there are roughly 8 billion ash trees in North America, and they are all vulnerable to this pest. The widespread loss of an entire genus of trees would be catastrophic to not only natural forests but also urban tree canopies.
Some towns across Michigan and the rest of the country have already suffered from an almost complete loss of ash trees. This unfortunately mirrors earlier problems, such as chestnut blight and Dutch elm disease, which both had long-lasting ramifications.
Common Signs of Emerald Ash Borer Infestations
Emerald ash borers often cause trees to display one or more common signs and symptoms, including:
- Numerous D-shaped exit holes
- Dead branches in the canopy
- General canopy thinning
- Woodpecker damage
- Epicormic sprouting
- Serpentine galleries under the outer bark
If you notice any of these signs, it is important that you contact an ISA-certified arborist without delay. Prompt treatment provides the best opportunity to preserve infested trees, though success depends on the severity of the infestation and the tree’s overall condition.
Treatment Strategies for Emerald Ash Borer
Researchers are currently experimenting with a few different EAB treatments, including releasing wasps that may help control EAB populations. Some researchers are also investigating the potential role fungi may play in controlling EAB populations.
Scientists are also hopeful that “survivor” trees will be found, which can then be cloned to provide EAB-resistant cultivars in the future. You can even register survivor trees with the USDA if you have one growing on your property.
However, there’s currently only one way to effectively address EAB: systemic insecticides, preferably administered before any infestation occurs.
These insecticides are typically applied via soil drench, bark spray, or trunk injections. A few products are available to the general public, but for the best results, professional application is strongly encouraged. The three most commonly used insecticides include:
- Emamectin Benzoate: The most effective EAB treatment available, emamectin benzoate is a systemic trunk injection that should be applied every two to three years, preferably in the spring, after leaves have emerged.
- Azadirachtin: Another insecticide administered via trunk injection, azadirachtin is highly effective when applied annually and can provide effective protection with a two-year treatment cycle when EAB population pressure is low.
- Imidacloprid: A type of insecticide known as a neonicotinoid, imidacloprid can be administered via trunk injection or soil drench. Imidacloprid doesn’t always achieve the desired results, and as a neonicotinoid, it may harm beneficial, non-target insects.
- Dinotefuran: Also a neonicotinoid, dinotefuran can be applied as a basal trunk spray, soil drench, or trunk injection, though the results of the product have been mixed. Annual basal trunk sprays appear to be protective when applied at high rates.
Ultimately, the decision about which insecticide to use, the administration method, and the frequency of application should be made in conjunction with an ISA-certified arborist, like the pros at Longtree Tree Service.
Worried About Your Ash Trees? Longtree Tree Service Can Help!
Given the threat EAB represents, it is imperative that you take the steps needed to protect your ash trees. Whether your trees still look healthy, you suspect they’re currently under attack, or it’s time for another round of treatment, the professionals at Longtree Tree Service can provide the plant health care services you need.
From Farmington Hills to Southfield to Detroit, we proudly serve homeowners and commercial property managers across Southeast Michigan. Contact us today to arrange for a free evaluation and receive an itemized estimate for the services your trees need.
Sources & References
- Cary Institute of Ecosystem Studies – “8 Billion North American Ash Trees at Risk from Emerald Ash Borer”
This research feature details the immense ecological, economic, and cultural scale of the emerald ash borer (EAB) crisis across North American forests, emphasizing the catastrophic loss of native canopy diversity.
https://www.caryinstitute.org/news-insights/feature/8-billion-north-american-ash-trees-risk-emerald-ash-borer - Arbor Day Foundation – “Emerald Ash Borer Action Kit & Guide”
An educational campaign and preparation toolkit designed to help homeowners and communities identify native ash trees (Fraxinus genus), evaluate vulnerability, and execute proactive pest mitigation strategies.
https://www.arborday.org/planting-your-tree/emerald-ash-borer - USDA Forest Service (Northern Research Station) – “Ash Range and Monitoring Tools”
A technical data repository providing tools like the Northern Forest Futures database to help ecologists and land managers track ash mortality, document “lingering ash” resistance, and model future forest compositions.
https://www.fs.usda.gov/nrs/tools/ash - University of Wisconsin–Madison (Russell Labs) – “Signs and Symptoms of EAB”
A diagnostic field guide detailing the physiological indicators of an infestation, helping observers differentiate between general stress and definitive EAB markers like D-shaped exit holes and serpentine S-shaped larval galleries.
https://eab.russell.wisc.edu/signs-and-symptoms/ - Monitoring Ash (Ecological Research as Partners) – “EAB Distribution Map (US & Canada County-Level Data)”
A collaborative, real-time spatial mapping database that tracks the precise geographic spread and entry timeline of the emerald ash borer across individual counties and municipalities.
https://www.monitoringash.org/eab-distribution-map-us-and-canada-county-level-data/
