Emerald ash borer damage can be easy to miss at first, especially in a mature yard where a tree’s upper canopy is difficult to inspect from the ground. The insect is small, but its larvae feed beneath the bark and interrupt the flow of water and nutrients that an ash tree needs to survive. By the time a tree looks severely thin or begins dropping large limbs, the infestation may have been present for some time.
Early recognition gives property owners more choices. It can help them protect a valuable ash, make a safer removal plan, avoid moving infested material, and pay closer attention to nearby trees. The key is knowing which signs point specifically to emerald ash borer and which may be caused by drought, disease, storms, or ordinary seasonal change.
Start by confirming that the tree is actually an ash
Before looking for insect damage, make sure the tree is an ash. Ash trees usually have compound leaves, meaning several leaflets grow from one main leaf stem. The leaflets are commonly arranged in pairs with a leaflet at the tip. On the twig, branches and buds are generally positioned directly opposite one another, rather than alternating up the stem. This opposite branching pattern is a useful feature because many common landscape trees have alternate branching.
Mature ash bark often develops a pattern of interlacing ridges that can resemble diamonds, although bark varies with age and species. Seeds may appear as flat, winged samaras that hang in clusters. Leaf shape and bark alone can be confusing, so it helps to examine several features together. If identification remains uncertain, a local tree professional can distinguish ash from lookalikes before decisions are made about treatment or removal.
Understand what happens beneath the bark
Adult emerald ash borers lay eggs in crevices of ash bark. After hatching, the larvae tunnel into the layer beneath the bark where the tree moves water and sugars. Their feeding creates winding galleries and damages the tissues responsible for transporting resources between roots, trunk, branches, and leaves. As this damage accumulates, portions of the canopy become stressed and eventually die.
This hidden feeding explains why the earliest symptoms can be subtle. A tree may still leaf out in spring and look reasonably full from a distance while the infestation is progressing in its trunk or main branches. It also explains why surface sprays or casual home remedies are not a reliable response to a suspected infestation. A useful assessment considers the condition of the entire tree, the extent of canopy decline, the site, and the practical options available for that specific ash.
Look for small D-shaped exit holes
One of the clearest signs of emerald ash borer is a small, distinctly D-shaped exit hole in the bark. These openings are left when adult beetles emerge from the tree. The flat side of the “D” is an important detail. Other insects can leave round, oval, or irregular holes, so it is worth looking closely rather than assuming that every small opening is evidence of emerald ash borer.
Exit holes may be found on the trunk, major limbs, or upper branches, and they can be difficult to see on rough bark. Use binoculars to inspect higher areas rather than climbing or leaning a ladder against a questionable tree. Holes alone do not tell the full story, but D-shaped openings paired with canopy thinning, bark damage, or woodpecker activity make emerald ash borer a much stronger possibility.
Check for galleries when bark has already loosened
When bark naturally separates from a declining ash, the wood beneath may reveal pale, serpentine galleries that twist back and forth. These tunnels are made by larvae feeding under the bark. Their winding pattern is very different from a clean crack in wood or a simple scar caused by mechanical damage. Galleries often become wider as the larva grows.
Do not pull bark from a healthy-looking tree just to search for galleries. Removing bark can create wounds and may obscure useful evidence. Instead, inspect areas where bark is already loose, broken, or has fallen away naturally. If a downed branch or section of bark is available, its underside can offer a safer opportunity to look for tunnels. Photographing what you find can also help a qualified inspector evaluate the symptoms.
Watch the canopy for thinning that begins at the top
Emerald ash borer commonly causes thinning and dieback in the upper canopy first. Twigs may produce fewer leaves, leaves may appear smaller than usual, and some upper branches may remain bare while lower sections still leaf out. Over time, dieback can move downward as the tree loses its ability to supply water and energy to more of its crown.
Canopy decline is not exclusive to emerald ash borer. Dry weather, compacted soil, root injuries, fungal disease, construction activity, and other pests can all affect leaf density. What makes the pattern more concerning is a combination of upper-canopy thinning with other ash borer indicators. Compare the tree with nearby ash trees, and look at it from several angles over the growing season rather than judging its health from one quick glance.
Notice new shoots on the trunk and lower limbs
A stressed ash may produce clusters of new shoots along its trunk, large limbs, or near the base. These are often called epicormic shoots or water sprouts. They are the tree’s attempt to keep making leaves after its normal canopy has been compromised. On an ash with other symptoms, this sudden growth can be an important warning sign.
New shoots are not automatically proof of infestation. Pruning, storm damage, excessive shade changes, and other stressors can prompt the same response. Still, a tree that has a thin crown, dead upper branches, and abundant sprouts on the trunk deserves closer inspection. The tree is signaling that its normal structure is under strain, even if the exact cause needs confirmation.
Take woodpecker activity seriously, but not as a diagnosis by itself
Woodpeckers often search infested trees for larvae beneath the bark. Their feeding can leave patches where the outer bark has been chipped or flaked away, sometimes producing a lighter, speckled appearance across the trunk and branches. This is sometimes referred to as woodpecker flecking. It can be especially noticeable in winter, when leaves no longer block the view.
Woodpeckers feed on many insects, so their presence does not prove emerald ash borer. A single pecked area may simply reflect normal wildlife activity. However, extensive flecking on a tree that is confirmed as ash, especially when accompanied by exit holes or crown dieback, is a reason to investigate further. Treat it as one piece of evidence rather than the final answer.
Separate ash borer symptoms from common lookalikes
Broken branches, sparse foliage, and bark cracks can have many causes. A storm-damaged tree may lose limbs without showing galleries or D-shaped holes. Root problems can lead to a generally weak canopy, while leaf diseases may create premature discoloration or leaf drop without damaging the trunk’s transport tissues. Seasonal stress can also make one year’s growth look less vigorous than expected.
Look for patterns rather than relying on one symptom. Emerald ash borer is most strongly suggested by a confirmed ash tree with several signs that fit together: upper-canopy dieback, epicormic shoots, D-shaped exit holes, serpentine galleries, bark splitting over galleries, or notable woodpecker feeding. If there is uncertainty, avoid making irreversible decisions based only on a thin canopy or a few holes of unknown origin.
Inspect safely without creating a new hazard
Never climb a declining ash or work beneath dead limbs. As emerald ash borer damage progresses, branches can become brittle and fail with little warning. Dead wood may be held in place temporarily by surrounding branches, then fall during wind, rain, or ordinary tree movement. Keep children, pets, vehicles, and outdoor seating away from areas below a tree that is shedding limbs or showing significant canopy loss.
A ground-level inspection can reveal a great deal. Walk around the tree, inspect the trunk base and major branch unions, and use binoculars for the upper crown. Note dead branches, bark splits, holes, sprouts, and areas of woodpecker activity. A few clear photos taken from the same locations over time can document whether decline is stable or advancing. If the tree is near a house, driveway, sidewalk, utility line, or neighboring property, a professional assessment is particularly important.
Decide quickly when the tree may still be worth protecting
Not every infested ash has the same outlook. The tree’s size, overall condition, location, canopy loss, and importance to the landscape all matter. Trees with limited visible decline may have more management options than trees with extensive dieback and major structural defects. A timely inspection can help clarify whether protection is practical or whether the tree has reached a stage where safety should take priority.
For local guidance, an Ottawa County aborist can evaluate the tree in person and help distinguish a potentially manageable infestation from a tree that has become a removal concern. An on-site review is valuable because it considers factors that photographs cannot always show, including trunk condition, deadwood distribution, root-zone stress, access for equipment, and targets beneath the canopy.
Use pruning for safety and structure, not as a substitute for assessment
Pruning can remove dead, broken, rubbing, or hazardous branches and can make a declining tree safer in the short term. It may also improve access for a closer inspection. But pruning does not eliminate emerald ash borer larvae inside the trunk, and aggressively cutting back a stressed ash can create additional strain. The amount and timing of work should suit the tree’s condition and the immediate safety needs of the site.
When dead limbs are present over frequently used areas, a qualified tree pruning service can address those hazards while preserving sound portions of the tree where appropriate. This is especially useful when a property owner needs help deciding which branches are actually dangerous and which are simply lower-vigor growth. Proper pruning also avoids unnecessary wounds and poor cuts that can complicate recovery or future management.
Protect nearby ash trees from overlooked stress
If one ash is suspected or confirmed to have emerald ash borer damage, inspect other ash trees on the property and nearby landscape. Trees at different stages of infestation can look very different. One may have obvious dieback while another appears healthy but has early signs hidden in the upper branches. Mapping the location and apparent condition of each ash makes it easier to prioritize next steps.
Good growing conditions do not make an ash immune to emerald ash borer, but reducing avoidable stress helps trees cope with challenges. Avoid damaging roots with soil disturbance, keep mulch off the trunk, prevent repeated impacts from lawn equipment, and pay attention to irrigation needs during dry periods. Broader tree health care can also help identify compaction, nutrient issues, disease concerns, and other conditions that may be contributing to decline or affecting management decisions.
Handle removed wood responsibly
Firewood, logs, branches, and bark from an infested ash can carry pests to new locations. Moving that material farther than necessary can create a problem beyond one yard. Follow applicable local and regional guidance for handling ash wood, and ask the company performing the work how material will be processed, transported, or disposed of. Do not assume that a piece of wood looks safe simply because no insect is visible on its surface.
Keeping material management in the plan is part of responsible tree care. It is easy to focus only on the standing tree, but cleanup choices matter too. If an ash must be removed, discuss the full process before work begins: site access, protection for turf and nearby plants, wood handling, stump options, and how remaining ash trees will be monitored afterward.
Build a simple monitoring routine for the growing season
A practical monitoring routine does not require specialized equipment. At the start of the growing season, take a few wide photos of each ash from consistent viewpoints. Check leaf density in the upper crown, note new dead twigs, and look for sprouts on the trunk or base. Later in the season, repeat the photos and compare changes. During leaf-off periods, examine branch structure and woodpecker flecking more easily.
Write down what you observe, including which side of the tree shows symptoms and whether nearby ash trees show similar changes. This record makes it easier to communicate with a professional and prevents memory from filling in gaps. More importantly, it turns a vague concern into an informed decision. Spotting emerald ash borer damage early will not make the issue disappear, but it can give homeowners time to protect healthy trees, reduce hazards, and respond before decline becomes an emergency.