Emerald Ash Borer: Treat It or Remove It?

Michigan is where EAB started. If you still have an ash standing, here is how to decide what to do with it.

Emerald ash borer was first found in Canton, Michigan in 2002. Southeast Michigan is ground zero, and two decades later most untreated ash in Metro Detroit is dead or dying. If you still have one standing, you have a decision to make and the clock is not on your side.

How to tell if your ash has it

• Canopy thinning from the top down. The upper third goes bare first while the lower branches still leaf out.
• D-shaped exit holes, about an eighth of an inch across. Round holes are a different insect. D-shaped means EAB.
• Epicormic sprouts, meaning shoots coming straight out of the trunk and base. That is the tree panicking.
• Woodpecker damage, called blonding, where birds strip outer bark chasing larvae and the trunk looks pale and patchy.
• S-shaped galleries under the bark. Peel a piece of loose bark and you will see winding tunnels packed with sawdust.

Treat it or remove it

The honest rule of thumb used by most Michigan arborists: if the canopy has lost more than about 30 percent, treatment is a waste of money. The vascular system is already too damaged to move the insecticide where it needs to go.

If the canopy is still mostly full and the tree is worth keeping, meaning it is a good specimen in a good spot, emamectin benzoate trunk injection is effective and lasts two to three years per treatment. Budget roughly $10 to $20 per inch of trunk diameter, so a 20 inch ash is $200 to $400 every two to three years, indefinitely. Do the math against removal cost before you commit, because treatment is forever.

Why dead ash is dangerous to leave standing

This is the part people underestimate. Ash does not decay like other hardwoods. It goes brittle fast, often within two to three years of death, and it fails without warning. Branches snap in still air. Climbers will not climb a dead ash, which means the removal now requires a bucket truck or a crane, which means your $1,200 removal is now a $2,500 removal.

Every year you leave a dead ash standing, it gets more dangerous and more expensive to take down. There is no scenario where waiting saves you money.

What we see across Metro Detroit

Sterling Heights, Warren, Clinton Township, and Livonia subdivisions built in the 1970s and 80s were planted heavily with green ash because it was cheap, fast growing, and tolerant of clay soil. Those neighborhoods lost their entire street tree canopy. Detroit and Southfield have large numbers of standing dead ash on residential lots. Oakland County communities with tree ordinances, including Birmingham, Novi, and Farmington Hills, generally allow dead or hazardous tree removal without the usual permit hurdles, but check before you cut.

What to plant instead

Do not replace an ash with another ash. Good Michigan replacements that handle clay soil and urban conditions: swamp white oak, hackberry, Kentucky coffeetree, American hornbeam for smaller spaces, and tulip poplar if you have the room. Avoid Bradford pear, which splits, and avoid Norway maple, which is invasive here and shades out everything under it.