The Minnesota Arborist “Most Wanted” List

The following “Most Wanted” list of tree killing culprits describes the species responsible for the deaths of thousands of Minnesota trees annually. If you see evidence that any of these offenders have victimized the trees on your property, immediately contact a Minnesota certified arborist to minimize the spread of their damage.

Emerald Ash Borer This assailant is an invasive species that is native to Asia. The mature adult beetle has a dark metallic-green hue and is about 1/2 inches long. As their name implies, they destroy ash trees. Catastrophic damage to the tree is done by the larvae of the beetle as they relentlessly bore into the tree to find and feed upon the nutrient-rich layers beneath the bark. All species of ash tree are susceptible. Symptoms of an infestation are:

• D-shaped exit holes in the bark created by adult beetles after they hatch • S-shaped tunnels under the bark produced by the larvae as they bore and feed • Increased woodpecker activity on the tree • Branches dying in the upper canopy • Sparse leaves in the upper canopy

If any of your trees are infested with the emerald ash borer, you need to take immediate action to keep the infestation from spreading to other ash trees. Contact a certified arborist to learn what your options are and begin an appropriate method of treatment.

Forest Tent Caterpillars Every 5 to 10 years an outbreak of these creepy diminutive defoliators occurs. In central and southern Minnesota they are highly attracted to basswood and oaks, and in northern Minnesota their preference is birch and aspen. When an outbreak occurs, masses of these caterpillars can defoliate entire trees. At the height of an outbreak the caterpillar population can reach four million caterpillars per acre! For people who live and vacation in forested areas these tiny intruders are an extreme nuisance. Aside from defoliating acres of trees they cluster in the thousands on tree trunks, branches, and buildings. When bothered or provoked they ooze slimy black goo that can permanently stain cloth or painted surfaces. As they dine in the branches above they rain their filthy excrement on everyone and everything below. There's nothing you can do to prevent an outbreak, but fortunately, damaged trees usually fully recover within a year or two.

Gypsy Moths Be especially on the lookout for this suspect as it has already been found in parts of Minnesota. The caterpillars of the Gypsy Moth are ravenous leaf eaters that can defoliate entire trees. After repeated seasons of defoliation a tree will die. These caterpillars aren’t picky eaters either. Although they prefer aspen or oak, they will gladly dine on over 500 types of trees! There are protective measures you can take to prevent their spread. When you travel, inspect your vehicle and any goods you're transporting for their egg masses. When you camp use only local firewood, but if you do bring your own firewood use all of it and make sure it is completely burned. Contact a certified arborist for programs and more information to help prevent their spread.

Pine Bark Beetles Red pines are susceptible to pine bark beetles during times of drought. Evidence of an infestation manifests as orange and brown needles on most branches with few or no new shoots or needles developing on the bud tips. If you feel you have a tree that is infected the best help you can give your tree is by ensuring it is well watered. However, you should contact an arborist to examine the tree and determine whether it should be cut down and properly disposed of. Your arborist will also be familiar with techniques to reduce the spread of this pest.

Two-Lined Chestnut Borers Two-lined chestnut borers attack all species of oak trees, though they prefer red oak. Most often they infest weakened oak trees. Symptoms of an infestation generally appear in mid-July and are indicated when the leaves on infested branches are small, sparse, and discolored. The leaves on healthy branches stay green. The best prevention against this pest is to keep your trees healthy.

Conclusion The best defense against these suspects is prevention. However, if you see evidence of these tree killing critters in your yard, take action immediately. A certified arborist can help you keep your trees healthy and take measures to prevent the spread of an infestation and transmission of infection to healthy trees.

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