Mechanical damage (mower, trimmer and tie wounds)

About

Bumps from mowers and whips from string trimmers strip bark at the base of young trees, and ties or wires left on too long cut into growing trunks. Repeated wounds can girdle and kill a tree.

Also called mechanical damage, mechanical injury, mower damage, mower blight, string trimmer damage, weed eater damage, girdling ties, root damage, physical damage

How to recognize it

Symptoms

Scraped, torn or missing bark at the base of the trunk, often in a ring at mowing height. Ties, wire or rope sink into a swollen ring of bark. Above the wound, leaves may thin and branches die back, and decay can follow.

Often confused with

Rabbits and mice also strip bark low on young trunks, mostly in winter under snow. Bark sunscald and frost cracks (see Winter injury) form on the south or southwest side, not all around the base.

Worse when

Grass growing right up to the trunk, young thin-barked trees (some maples and birches have bark less than 1/16 inch thick), and stakes, tags or ties left on after the first year.

How it spreads

It does not spread, but bark wounds let in wood-decay fungi.

When

All year; mostly the mowing season.

What to do, gentlest first

This is not an infection, so sprays for diseases won't help. Fix the cause below.

1. Mulch ring around trees Prevent

   Replace grass at the base with a ring of 2 to 3 inches of wood mulch over the root zone, so mowers stay away. Trim any grass near the trunk with hand shears, not a string trimmer.

   Keep mulch pulled back from the trunk itself.

2. Remove ties, tags and stakes By hand

   Take off nursery tags, twine and wire at planting, and remove stakes and ties after one year.

3. Let wounds close By hand

   Trim ragged bark edges cleanly and keep the tree watered and mulched. Trees can't heal wounds, but they wall them off over time.

   Don't paint or seal wounds. A tree wounded all the way around its trunk usually dies.

4. Trunk guards Barrier

   White, expanding trunk guards on young trees help them withstand bumps and also cut winter injury.

Plants it affects

Cherry (sweet and tart), Flowering crabapple, Japanese maple, Plum, Red maple, River birch, Sugar maple, Thornless honeylocust