Emerald ash borer was confirmed in Madison in late 2013. More than a decade on, most ash trees that were never treated are dead or dying. If you still have an ash, the decision in front of you is a simple one, and it should not be put off: protect it, or take it down while that is still a safe job.
The arrival is over. What is left is the clean-up, and a shrinking number of trees still worth saving.
Emerald ash borer is a metallic green beetle from Asia, about half an inch long. The adults do little harm. The larvae feed under the bark, carving tunnels through the layer the tree uses to move water and sugars. Enough larvae, and the tree is girdled from the inside. Untreated, it usually dies within a few years of being attacked.
The beetle was first found in Wisconsin in 2008 and was confirmed in Madison, in an ash near Warner Park, in late 2013. By 2024 the Wisconsin DNR had confirmed it in all 72 counties. The quarantines that once tried to slow it are gone: the federal one ended in 2021 and Wisconsin rescinded its own in 2023, because there was nowhere left to protect. Foresters expect the great majority of untreated ash trees in Dane County to die.
The City of Madison chose to protect a large share of its public ash, and treats roughly 10,000 street and park trees by trunk injection. On private property the decision belongs to each owner. If you have an ash and have done nothing so far, you can safely assume the beetle has found it.
Two questions to answer before anything else.
Branches and buds grow in opposite pairs, directly across from each other. Few other Madison trees do this: maples, dogwoods and buckeyes are the main ones. The leaves are compound, with five to eleven leaflets on a single stalk. Bark on mature trees has tight, interlacing ridges in a diamond pattern. Green and white ash were planted by the thousand as street and yard trees. Mountain-ash is not a true ash and is not affected.
The crown thins from the top down. Leafy sprouts break out along the trunk and main limbs. Woodpeckers strip the outer bark to get at the larvae, leaving pale blond patches that show up well in winter. Look closely for D-shaped exit holes about an eighth of an inch across, vertical bark splits, and, under loose bark, winding S-shaped tunnels packed with fine sawdust.
Stand back, look at the whole crown against the sky, and pick the closest description.
Treatment works, and it is a commitment. It is worth being clear about both.
The treatment with the best record is a trunk injection of a systemic insecticide, given through small ports drilled at the base of the tree. The tree carries it up into the crown, where it kills larvae feeding under the bark. Protection lasts two to three years and then has to be repeated, for as long as you want to keep the tree. Stop treating, and the beetle returns.
It makes sense when the ash is healthy, with most of its crown intact; when it is well placed, shading the house or anchoring the yard; and when losing it would change the property. A large, sound ash is a valuable tree, and tree preservation is the right instinct when the tree can repay it.
It does not make sense when the crown is already half gone, when the tree has structural defects that would justify removal anyway, or when it is crowded against a building or under wires.
In Wisconsin, anyone applying pesticides for hire must be certified by the state Department of Agriculture, Trade and Consumer Protection. Treatment is a job for a certified pesticide applicator, ideally an ISA Certified Arborist who can judge whether the tree is worth treating in the first place. Products sold to homeowners for pouring around the base of the tree work only on smaller trees and have to be applied every year. We do not treat trees. We will tell you honestly which side of the line yours is on, and if it is the wrong side, the removal is ours.
Of all the dead trees a crew deals with, ash is the one nobody wants to find three years too late.
Most dead trees stand for years and come apart gradually. Ash is different. The wood dries quickly once the tree dies and becomes brittle. Large limbs break off on calm days. Trunks snap partway up. The root collar decays and whole trees go over.
For a tree crew the consequence is simple. A living or recently dead ash can be climbed, roped and taken apart in the usual way. A long-dead ash cannot: no climber should tie into it, and no rigging point in it can be trusted. It has to be taken down from a lift, or lifted out in pieces by a crane, which takes more equipment, more room and more planning. On a tight Madison lot that can be the difference between a morning’s work and a job that needs the street closed.
So the honest advice is the same for every untreated ash: decide now. If it is going to be removed eventually, professional tree removal is safer for the crew, gentler on the yard and simpler in every way while the tree is still alive. See our tree removal page for how the work is done, and stump grinding for what happens afterward.
An ash between the sidewalk and the street belongs to the City, which decides whether to treat or remove it. If yours looks untreated and unwell, report it to Urban Forestry at 608-266-4816. Do not arrange treatment or removal yourself. Our terrace tree guide explains why.
An ash coming down is also a chance to do better than the last generation of planting did.
Ash is good firewood and good lumber. With the quarantines lifted there is no legal barrier to keeping or using it, but the state still asks people to buy and burn firewood locally, because firewood carries many pests besides this one. Keep it for your own fireplace, have the brush chipped for mulch, or ask whether a trunk is big and sound enough to be worth milling.
Madison lost its elms to one disease and then planted ash in their place. The lesson is variety. The City’s own foresters now aim for no more than 10 percent of any one species, 20 percent of one genus and 30 percent of one family across the city, and at least three species on every block. The same thinking works in a yard.
Whatever you choose, plant it in spring or fall, a few feet away from the old stump, with the root flare at ground level and mulch 2 to 4 inches deep, kept off the trunk. Water it deeply once a week for the first few summers. Tree planting done well is the best tree care there is, and healthy trees are the ones that survive the next pest.
This guide is general information from a tree service, not legal advice, and ordinances change. Before you act on anything here, check the primary sources, or ask the agency directly.
Yes. It was confirmed in Madison in late 2013 and is now found in every Wisconsin county. Most untreated ash in Dane County are dead or dying. The City protects about 10,000 public ash trees by trunk injection; private ash trees are their owners’ responsibility.
Not if the crown is still mostly full. Treatment works well on ash that have lost less than about a third of their canopy. Once about half the crown is gone, the tree can no longer move the insecticide to where it is needed, and removal is the realistic choice.
Look for branches and buds in opposite pairs, leaves made of five to eleven leaflets on one stalk, and bark on mature trees with a tight diamond pattern of ridges. Mountain-ash, despite the name, is not a true ash and is not attacked by emerald ash borer.
A crown thinning from the top down, leafy sprouts on the trunk, pale patches where woodpeckers have stripped the bark, D-shaped exit holes about an eighth of an inch wide, bark splits, and S-shaped tunnels packed with sawdust under the bark.
Ash wood dries and turns brittle unusually fast once the tree dies. Limbs and even trunks snap without warning, often on calm days. A climber cannot trust it to hold a rope, so dead ash has to come down from a lift or by crane. It is safer for everyone done early.
You can keep it. Wisconsin rescinded its emerald ash borer quarantine in 2023, but the state still asks people to buy and burn firewood locally, because firewood moves many pests. Use ash firewood on your own property, or have the wood chipped for mulch.
All guides, or go straight to a service: tree removal, tree trimming and pruning, stump grinding, stump removal, emergency tree service.
Tell us what you’re looking at and we’ll call to set a time to walk the yard. If a tree is down or hanging, call instead.
