How to Read the Signs
Ash trees have a way of looking fine from a distance while quietly struggling beneath the surface. That's part of what makes catching problems early so important, especially in South Dakota where emerald ash borer pressure has been steadily spreading across the region.
A few things worth watching for: thinning or dying branches at the top of the canopy, sometimes called dieback, are often one of the first visible clues. You might also notice bark that looks split or S-shaped galleries just underneath if you peel a small section back. Sprouts shooting up from the base of the trunk or along lower branches can signal the tree is under stress. Woodpecker activity, particularly heavy pecking on the upper trunk, sometimes points to borer activity below.
Not every struggling ash is beyond help. Timing matters quite a bit, though. Trees that have lost a significant portion of their canopy may be past the point where treatment is practical. An arborist can assess what you're actually dealing with before you commit to a course of action.
What to Watch For
Spotting trouble early gives you more options. Here are the signs worth paying attention to:
- Thinning canopy at the top. The upper branches lose leaves first. If the crown looks noticeably sparse compared to previous years, that's worth a closer look.
- S-shaped galleries under the bark. Peel back a small section of loose or damaged bark and you may see winding, serpentine tunnels just beneath the surface. These are feeding paths left by emerald ash borer larvae.
- D-shaped exit holes. Small, flat-sided holes about the size of a pencil eraser appear where adult beetles have emerged. They're easy to miss but distinctive once you know what to look for.
- Vertical bark splits. The outer bark may crack or pull away from the trunk in strips, often revealing discolored wood underneath.
- Epicormic sprouting. Clusters of small shoots pushing out from the base of the trunk or along lower branches are a stress response. The tree is essentially trying to compensate for what it's losing above.
- Woodpecker activity. Heavy, repeated woodpecker damage on the upper trunk is a practical signal. Birds go after the larvae beneath the bark, so concentrated pecking often means something is already living there.
- Yellowing or early leaf drop. Leaves turning yellow or falling before autumn arrives can point to a tree under significant stress.
None of these signs on their own confirm the problem, and some can overlap with other issues. A certified arborist can assess what's actually happening and help you decide whether treatment is still a realistic path forward.
Triage: How Soon Should You Act?
Some situations can wait a few weeks. Others need attention within days. Knowing the difference helps you make a practical decision rather than a rushed one.
Start by looking at the tree's position. An ash showing signs of decline near a structure, a parked vehicle, or a path people use regularly deserves a closer look sooner rather than later. Weakened trees can drop large limbs without much warning, and ash trees affected by emerald ash borer often deteriorate faster than they appear to from the ground.
Next, consider how far along the decline looks. Early signs, like thinning canopy or sparse leafing in spring, suggest there may still be a treatment window. More advanced symptoms, like significant bark loss, heavy woodpecker activity across the upper trunk, or branches that are already dead and brittle, point to a tree that has moved past the point where treatment is likely to help.
Timing also matters for treatment itself. Trunk injections and soil treatments work best when applied during specific periods in the growing season, so a tree that looks manageable now could move out of the treatment window if you wait too long.
A qualified arborist can assess the tree's condition directly and give you a realistic picture of what options remain. That assessment is worth getting before the decision gets made for you.
The Value of an Inspection
A proper assessment of an ash tree usually starts with a visual inspection of the bark, canopy, and trunk. A certified arborist will look for the telltale signs of Emerald Ash Borer activity: S-shaped galleries under the bark, small D-shaped exit holes roughly the size of a pencil tip, and canopy dieback that often begins at the top and works downward.
Beyond the visible signs, the arborist will consider how much of the canopy has already been lost. That number matters a great deal. A tree that has lost a significant portion of its canopy may not respond well to treatment, while one caught earlier in the process has a better outlook.
You'll also get a sense of the tree's overall structure and root health. A weakened ash can become a hazard over time, so the assessment isn't just about the pest. It's about the whole picture.
What you walk away with is a clearer understanding of where your tree stands and what your realistic options are. That might mean a treatment plan, a removal recommendation, or simply a timeline for monitoring. Either way, the assessment gives you something concrete to work with rather than leaving you guessing.
Common Questions
What does early emerald ash borer damage actually look like?
The first signs are easy to miss. Look for small D-shaped exit holes in the bark, roughly the size of a pencil tip. You may also notice thin, winding lines just beneath the bark if a section peels away. These are feeding galleries left by larvae. Canopy thinning, particularly at the top of the tree, is another early indicator. Catching these signs before significant dieback sets in gives treatment more of a chance to be effective.
My ash tree is losing bark in patches. Should I be concerned?
Peeling or splitting bark on an ash tree is worth taking seriously. Woodpeckers are often drawn to trees infested with emerald ash borer larvae, and their feeding activity can strip away bark in noticeable patches. The woodpecker activity itself is not the problem. It is a signal that something is happening underneath. If you are seeing this alongside canopy dieback or yellowing leaves, having an arborist assess the tree sooner rather than later makes sense.
How much canopy loss is too much for treatment to work?
This is one of the more important questions to ask before committing to a treatment plan. Once an ash tree has lost roughly half of its canopy, treatment becomes significantly less reliable. A tree with heavy dieback may not have enough healthy tissue left to distribute and benefit from treatment. An arborist can assess the extent of decline and give you a realistic picture of whether treatment is still a practical option or whether removal is the more sensible path.
Can an ash tree look fine on the outside but still be in trouble?
Yes, and this is part of what makes emerald ash borer infestations difficult to catch early. The larvae feed beneath the bark, disrupting the tree's ability to move water and nutrients, often before any obvious external symptoms appear. By the time crown thinning or branch dieback becomes visible, the infestation may already be well established. If you have ash trees on your property and EAB has been confirmed in the broader area, having them inspected proactively is a reasonable step.
When in Doubt
If your ash tree is showing signs of stress, or you simply want to know where it stands before making any decisions, a professional assessment is the right place to start. An experienced arborist can evaluate the tree's condition, identify whether emerald ash borer or another issue is involved, and walk you through realistic treatment options based on what they actually find. That kind of on-site evaluation takes the guesswork out of it. Some trees respond well to treatment when caught early enough. Others are too far along. Either way, knowing the full picture helps you make a decision you feel confident about rather than one made under pressure.