Diseased Trees

Emerald Ash borer is a non-native insect from Asia that feeds on ash trees and disrupts the nutrients and water that flows through the tree, eventually killing it. Mendota Heights is within a Quarantine Area (Dakota County) of Minnesota. This means the movement of any ash wood, or regulated products of ash wood, is prohibited from a Quarantined Area to a Non-Quarantined Area.

Signs & Symptoms

Symptoms of EAB can be easily confused with other ash tree diseases, so it is best to consult a tree care professional if you think you have an infected ash tree. Here are some of the signs and symptoms to look for:

• Crown dieback
• Light patches of bark
• Epicormic sprouting, or new branch and leaf growth on the trunk of the tree or at the base, often excessively
• Vertical bark splits
• D-shaped beetle emergence holes
• S-shaped larval galleries under the bark of the tree
• Larvae (cream-colored, about 1.5 inches long) under the bark of the tree
• Adults (metallic green, usually under a ½ inch in length
• Woodpecker feeding

Prevention & Control

• Don’t move firewood! EAB can emerge from the infected wood for two years after cutting.
• Avoid removing, pruning, or cutting of ash trees during the active period (May 1 through September 30)
• Consult a tree care professional to decide if treating healthy, high-value ash trees with systemic insecticide is a workable option.
• Look for signs of EAB
• Remove infected trees and dispose of wood and debris properly, by sending them to the nearest Ash Tree Waste Disposal Site during the low-activity period (October 1 through May 1), and within your quarantine area.

Removal & Disposal

 After August 1 and before March 31, trees with EAB can be removed and transported within the quarantined area for disposal. There are several approved disposal sites within the area (listed below). Any transportation of EAB material outside of the quarantine zone must be chipped to less than 1”x1”x1” to effectively kill any EAB larvae.

Hire a reliable, insured, licensed arborist or tree service company if the tree is too large to remove yourself.

The wood does not have to go to waste. You can use it around your home in several ways, or even recover some of its value. Here are some of the ways you can use your dead ash trees:

• Lumber: Local mill operators are sometimes able to bring a portable sawmill directly to your property to be converted to lumber that you can use for a variety of projects. Milling is suited to trees killed by EAB, because the insect does not damage the interior part of the wood.
• Landscaping: The wood can be milled into timbers, or chipped for mulch for gardening and landscaping.
• Art or furniture: If you are a wood-worker, or are able to hire one, ash wood is a good substitute for oak, and can be made into a quality piece of furniture or artwork.
• Firewood: Wood from dead ash trees killed by EAB can still be used for firewood at the location where they were removed.

If you cannot find a way to use your dead ash wood around your home, there are a few options for disposal.

• Sell your ash wood to reputable buyer, such as a sawmill or other industry. Be sure to require a signed statement that all wood will be handled in a way consistent with the MDA quarantine regulations.
• Donate the wood. Your ash wood could make a difference in the community, by donating to local schools, parks, or community organizations. One such organization, Wood from the Hood, reclaims wood from all over the Twin Cities, turning wood that would normally be brought to a landfill, burned, or mulched, into quality and environmentally sustainable furniture, lumber, slabs, flooring, cribbage boards, growth charts, and more!
• If you are unable to use your ash wood, sell, or donate it, there are approved disposal sites within the quarantine area that accept ash wood. The entirety of Dakota County is designated as a quarantine area. The following is a list of some of the sites within Dakota County that accept ash wood.

Resources

If you suspect you have EAB infected trees on your property contact the Minnesota Department of Agriculture’s Arrest the Pest hotline a t888-545-6684  or email to report. Note the exact location of the tree and take a digital photo if possible.

• Ash Tree Management Policy (PDF)
• Right Tree/Right Location’ Guidance Document (PDF)
• How-To Planting Video from Tree Trust

Oak wilt is a deadly disease that affects all species of oaks (Quercus) found in Minnesota. Oak wilt infection spreads in two ways: sap beetles that carry the disease from fungal spore mats of infected trees to healthy trees, and below ground through root grafts (roots that have grown together). Oak wilt is caused by a non-native, invasive fungus called Bretziella fagacearum. The fungus infests the vessels of oaks that move water through the tree, eventually killing it.

Signs & Symptoms

Oak wilt is not easily identified without a lab test, particularly on white and bur oaks, and can be easily mistaken for other diseases such as two-lined chestnut borer, bur oak blight, and anthracnose. Some of the symptoms of oak wilt include:

• Rapid-leaf loss in mid-summer
• Leaf wilt starting at the edge of the canopy and moving inward
• Not all, but about half of infected red oaks produce fungal mats and pressure pads just under the bark of the tree, often causing the bark to crack

Prevention & Control

• Do not prune, cut, or remove live oaks during the High-Risk Zone (April 1 through July 15). The High-Risk Zone may occur earlier in the year with unusually warm spring temperatures. Use caution and only cut or remove hazard oak trees during the Low-Risk Zone (July 16 through November 1). If cutting, removal, or pruning must occur outside of the Safe Zone (November 1 through April 15), immediately apply water-based paint or shellac to the cuts or outer sapwood of the stump
• Do not move logs or firewood from oak wilt areas to areas where oak wilt is not present.
• Properly dispose of, or contain, infected wood. Options for on-site treatment include: debarking of the trunk, burying sections of the trunk or large branches, or cutting logs into firewood and stacking to allow for drying. During the High and Low-Risk Zones, firewood and cut branches should be covered with 4-6 millimeter clear plastic and sealed at the ground line
• For high-value trees, consider hiring a professional arborist to apply a fungicidal injection.
• Means of control include creating a barrier ring around diseased trees by trenching, or cutting roots to a depth of five feet or more (using a vibratory plow, trenching machine, or similar equipment).

Canopy die-back in Red Oak, (MN DNR)                

Bark cracking caused by pressure pads, (MN DNR)

More Information

For more information on the diagnosis, prevention, and treatment of oak wilt visit the Minnesota Department of Natural Resources website.

Dutch elm disease is caused by a fungi, and is spread by the elm bark beetle, and can also be spread to adjacent elms through root grafts. The elm tree tries to stop the spread of the fungus by producing structures to block the flow of water, which eventually kills the tree.

Signs & Symptoms

• ‘Flagging’, or when a single area or limb of the tree turns brown and/or yellow with wilting.
• Brown streaking in the sapwood, underneath the bark of the tree.

 Prevention & Control

• Once properly identified, remove infected trees and properly dispose of infected trees and wood.
• Any infected elm wood with bark intact; including dead, dying or weak elm trees, must be debarked, chipped, burned, or buried to ensure that the elm wood does not harbor beetles that can spread the disease.

More Information

For more information on Dutch Elm Disease (DED) visit the Minnesota Department of Agriculture website.

Report a Diseased Tree

If you think you may have diseased trees in your area, please email Krista Spreiter, Natural Resources Technician or by phone at 651-255-1123.

Other Diseases

Other diseases that can affect landscape trees and the urban forest:

Two-Lined Chestnut Borer

The two-lined chestnut borer is a native beetle that attaches weakened oak trees, and a disease that is often mistaken for oak wilt. These beetles seek out and lay eggs on weakened oaks in late May and June. The larvae then feed on the inner bark of live branches and stems throughout the summer. This feeding damages the nutrient and water-conducting tissues within the tree, causing the leaves to brown and wilt. When adults emerge in the spring and early summer, they leave d-shaped exit holes like those of the Emerald Ash Borer. This disease usually proves fatal, and the tree dies by the next summer.

The best management against Two-lined chestnut borer is keeping trees healthy. Healthy trees will fight off invading borers without intervention. Proper tree care such as appropriate watering, avoiding soil compaction, avoiding bark damage, and avoiding anything else that may cause tree stress.

Diplodia is a fungus that causes shoot blight, or dead branch tips, branch death, decreased growth, and sometimes fatality in several species of pine. The disease usually affects trees that are 30 years or older, and attacks trees that are already weakened. Symptoms usually start on the lower half of the tree and move upwards. Often all needles on the current season’s shoot die. Tiny black fungal bodies called pycnidia, or black spots, will appear at the base of the needle under the fascicle sheath.

Anthracnose is a common fungal disease that affects the following shade trees: Ash, Birch, Black Walnut, Butternut, Buckeye, Elm, Hornbeam, Maple, and Oak. It is caused by several different but closely related fungi. It is most common in cool, wet conditions, especially if these conditions are occurring at the same time as leaf growth. Anthracnose is not a significant threat, unless the tree is already under stress from other pests, diseases, or conditions.

Symptoms

• Tan or brown spots on leaves
• Curled or distorted leaves
• Leaf drop in spring
• Small brown to orange blisters on branches

Needle cast is a fungal disease of spruces trees that causes needles to turn brown and fall off. 

Symptoms

• Tiny black bumps can be seen under a microscope, arranged in rows on infected needles
• Brown to purple old growth
• Discolored needles fall in late summer or autumn
• Thinning needles near the trunk
• Dying branches

Prevent the Spread of Needle Cast

• Not planting Colorado Blue Spruce, as they are highly susceptible
• Plant spruce trees in areas with moist, well-drained soils and full sun
• Plant spruce trees grown locally, as they are likely to be best adapted to local conditions