Tree Killers in Our Yards

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Published on: May. 2, 2007

Last revision: Nov. 30, 2010

saw, only slower.

Look for Damage

The most obvious sign of tree injury is missing bark at or near the ground line, where the string flays the tree or the lawn mower deck bumps it. Sometimes you can see one or several spots where the wood is worn bare.

Damaged trees usually show signs of stress, including leaves turning color too early in the year, leaves drying up in the summer and areas barren of foliage. The degree of stress is proportional to the number of xylem, phloem and cambium cells that have been destroyed. In most cases, highly stressed trees will die.

Preventing Damage

This type of injury is 100 percent preventable by simply keeping lawn mowers and string trimmers away from trees. Also, do not use trees as pivot points for mowers or allow pet chains to rub against them.

If a strip of taller grass and weeds around the tree trunk bothers you, either hand-trim it carefully or keep a weed-free zone around the tree with mulch or herbicide. Keeping the area clear of grass and weeds has the added benefit of removing competition for nutrients and moisture.

Use care when applying herbicides, especially around thin-barked trees. Don’t allow the herbicide to get on the bark. Use a shield if necessary.

Mulching is more effective if you kill grass and weeds below it with herbicide first. Place 2–3 inches depth of mulch around each tree as far out as you want to go. Mulch should not touch the tree trunk. Think doughnuts—with a hole in the middle for the tree trunk. A publication on proper mulching is available from Conservation offices and online at www.missouriconservation.org/317.

You can also use ground cover barriers to keep grass and weeds from growing next to the tree. Covers that let oxygen and water penetrate through to the root system are better than those that do not, such as black plastic. Make a slit in the cover to place it around the tree. Don’t let it touch the tree trunk. Put mulch on top of the cover to make it look nicer and to help hold the cover in place.

You can further protect a small tree with a 6- to 12-inch-long piece of plastic irrigation pipe. Slit it along its length to allow you to fit it around the trunk. Keep it loose enough that it doesn’t affect growth. Remove it or replace it with a larger size as the tree gets bigger.

If Your Tree is Injured

Stop further damage! Protect the tree, and make sure whoever cares for your lawn understands how easy it is to damage bark.

Nothing you can put on the tree’s wounds will fix the damage. However, trees are not defenseless. They grow over wounds, compartmentalizing them. The tree then attempts to restore or replace connections between the roots and the branches.

If the bark is gone from more than 50 percent of the circumference of the tree, it’s usually best to remove the tree. Chances of recovery are slim, and the tree will be susceptible to falling, especially during storms.

If less than 25 percent of the circumference of the tree is affected, it will likely recover. If the bark is missing from 25–50 percent of the tree’s circumference, watch the tree for health issues like rot or branch dieback. A little time may help you to make the decision whether to keep or remove the tree.

Be sure to water damaged trees. Aim for a thorough soaking of the ground below the tree, whether by natural rainfall or supplemental watering, every 7–10 days during the growing season. Hopefully, there will be enough xylem left to transport sufficient water from the roots to the leaves.

Trees are living organisms. They look strong and invincible, but they are more easily killed than many people believe. Don’t be a tree killer. Be careful with your lawn mower and string trimmer. Make it a policy to avoid hitting trees with them.

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