Emerald ash borer in Minnesota

Emerald ash borers generally have a one-year life cycle that can extend to two years in a vigorously growing tree.

• Adults emerge from ash trees any time from late May to August.
• After feeding on leaves, adults mate and females lay eggs on the bark or in small cracks.
• Eggs hatch in seven to ten days.
• The larvae tunnel under the bark of ash trees and feed until fall.
• The fully grown larvae live through the winter in chambers constructed under the bark.
• They transform into pupae in early spring.

• EAB larvae create winding, S-shaped galleries in the outer sapwood and in the tissue (phloem) that carries food from the leaves to the rest of the tree. 
  • Not all galleries in ash are caused by EAB.  See also Recognizing insect galleries in ash trees. 
• These tunnels girdle the trunk and branches, interrupting the flow of water and nutrients.
• The S-shaped galleries become visible if you remove the bark on the trunk.
• Adults emerge in spring creating small, one eighth-inch D-shaped exit holes. These holes might not be visible right away.

Trees are often killed in about four years, although it can take as little as two years. When trees are first attacked by EAB, the symptoms are hard to notice.

• During the second year, woodpecker pecks and thinning foliage begin to be apparent.
• By the third year, woodpecker activity is more common and canopy thinning is more pronounced.
• You may see vertical bark cracks due to the tree trying to heal over old galleries.
• Although woodpecker activity and vertical bark splits are not always caused by EAB, they are common symptoms in EAB infested ash trees.
• By the fourth year, the canopy has seriously declined and may even be dead.
• You may see leafy sprouts, especially along the lower trunk.
  • This can happen as a response to emerald ash borer tunneling.
  • This typically occurs when trees are almost dead and does not automatically indicate EAB.

There are other problems that can cause an ash tree to decline. Go to What's wrong with my plant? for help in diagnosing an ash problem.

Consider the distance to current known infestations

• If your ash tree(s) is within 15 miles of a known infestation, it is at a higher risk of being attacked by EAB (see Minnesota Department of Agriculture EAB status map).
• If your tree(s) is beyond 15 miles from any known infestation, you do not need to treat it until EAB is confirmed in your area. The further your ash is from a known occurrence of EAB, the less likely that it will become infested.

Consider the health of your ash tree

• The tree could be protected if it still has most or all of its canopy.
• If it has lost half of its canopy or more, it is in poor health and treatment might not be effective.

Consider the tree's importance to you

• If it is a valued tree, you may want to protect it.
• Healthy, mature trees improve the attractiveness of a landscape, raise property values, help reduce energy costs, and decrease stormwater runoff.

Effectiveness of pesticides

• The pesticides available for treating EAB have been shown to be effective in protecting ash in University research trials.
• Trees do not build up resistance because of the pesticide applications and need to be treated on a regular basis (every one to three years depending on the pesticide that is used).

Treatment guidance for homeowners

• Some products are available to residents so they can treat ash themselves.
• Homeowners should only treat trees smaller than 15 inches DBH.
  • Measure the distance around the trunk at 4.5 feet above the ground and divide it by three to get Diameter at Breast Height (DBH).
• For specific information on pesticides available for homeowners when treating EAB, see Emerald Ash Borer: Homeowner Guide to Insecticide Selection, Use, and Environmental Protection.

Treatment guidance for professionals

• Ash trees larger than 15 inches DBH are generally best treated by a professional arborist.
• For specific information on EAB pesticides available to professional arborists, including application methods, rates, and timing, see Insecticide Options for Protecting Ash Trees from Emerald Ash Borer (PDF).

CAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Remember, the label is the law.

• This is a valid option when faced with the risk of EAB.
• The larger the tree, the more expensive it is to remove.
• It is easier and less expensive to remove the tree while it is alive.
• Once an ash tree is dead, the branches become brittle making it much more challenging and dangerous to cut down.

You may want to hire a professional arborist to remove your trees.

• Be sure to ask for certificates of insurance and local references.
• Get at least two estimates and do not rush into a decision because you are promised a discount.
• See How to hire a tree care professional.

Consider other woody plant options that are available to Minnesotans. When there are more diverse types of trees in the urban landscape, neighborhoods can tolerate future pest problems better.

If you already have an ash tree in your yard and it is healthy, there is no reason to remove it. As long as it is a low-maintenance plant, keep it in your landscape. We strongly recommend not to plant additional ash.

Good options for replacing ash trees in Minnesota

Here are seven native tree species to consider for replacing your ash. Each species has its own unique characteristics and is adapted to different sites.

American elm (disease-resistant varieties)

Best reason to plant: You’ll bring back a charismatic tree to Minnesota’s landscape.

Research and testing have provided a number of disease-resistant elm trees. These elms have been planted widely across Minnesota. 

• They tolerate wet conditions. 
• They require full sun for the best growth. 
• Valley Forge and Princeton varieties are most similar to native American elm and have the classic vase-like form when mature.
• Hybrid Asian elms tend to be shorter in height compared to other varieties and grow well on tough sites. 

Consult your tree or nursery supplier for suggestions on the right variety for the qualities that you want in an elm.

Aspen

Best reason to plant: You want to maintain trees in an ash woodland.

All of Minnesota’s trees in the Populus genus — quaking aspen, big-toothed aspen, and balsam poplar — may be good alternatives in woodlands formerly dominated with ash.

• Quaking aspen is the most common tree in Minnesota, making it a good choice to replace ash.
• Balsam poplar may do well in wetter soils, while quaking and big-toothed aspen may do better on drier sites. 
• Aspen sprouts without using seeds. It is often one of the first species to come back to an area after a timber harvest or fire.
• Forest managers in northern Minnesota have been successful with planting cuttings from balsam poplar in black ash wetlands.  

Northern white cedar 

Best reason to plant: You want a conifer that’s characteristic of the Minnesota Northwoods.

• Northern white cedar can form dense stands and survives well in moist soils. If you’re looking for an ornamental variety, it is sold under the name arborvitae. 
• Northern white cedar trees will attract wildlife, especially white-tailed deer. Cedar is one of the most heavily browsed tree species by deer.
• Protect seedlings with fencing around trees or groups of trees. 
• Deer may congregate in stands of cedar in the winter to avoid heavy snow depths in other open areas, such as those with deciduous trees.  

Swamp white oak

Best reason to plant: You want to plant a tree that’s predicted to do well in Minnesota’s future climate.

• Also known as bicolor oak, this species can tolerate heavy and wet soil, which makes it a good replacement for black ash.
• While native only to southeastern Minnesota, swamp white oak is known as a climate change "winner" and has been planted with success in research trials in northern Minnesota.
• Swamp white oak does not grow as tall as bur oak and white oak, two similar species.
• The tree is less susceptible to oak wilt fungus than red oak.
• The acorns on this tree will attract a number of wildlife species. 

Hackberry

Best reason to plant: You want a hardy shade tree that can survive a tough environment. 

• Hackberry is a hardy tree that can grow in harsh urban environments.
• It can survive heat and drought or wind and ice, making it suitable for Minnesota’s climate.
• In its native habitat, it can be found in floodplains and along rivers in the central and southern portions of the state.
• Its corky bark sets hackberry apart from other trees in Minnesota. Birds and other wildlife will be attracted to its berry-like fruits. 

Silver maple

Best reason to plant: You want a fast-growing tree that provides a lot of shade.

• Silver maple is one of the fastest-growing maples.
• It is common in southern Minnesota and grows into the north-central part of the state, typically along rivers.
• Silver maple is widely planted as a shade or ornamental tree. Its leaves are dark green on top and “silvery” on the bottom, giving the tree its name.

River birch

Best reason to plant: You want a stately tree for your yard in the Twin Cities Metro or Blufflands. 

• River birch is adapted to warm climates as far south as Florida.
• It can thrive in floodplains and near stream banks that are sometimes flooded.
• The river birch can be a single- or multi-stemmed tree, making it a great tree to consider for the landscape around your home.
• Its copper-colored bark makes it stand out from other common trees. 

Diversifying your yard or woodland with a variety of species will help your landscape survive future insect and disease outbreaks.   

Many municipalities maintain a list of suggested replacement trees for ash, so check with your local city or county’s forestry division. Consult an arborist or forester for more advice to make sure you plant the right trees in the right spot. 

If you have a forest with ash trees in it, Managing Ash Woodlands has practical and timely ash management recommendations for woodland owners.

See Replacement trees for ash woodlands with emerald ash borer.

Management today can help prepare your forest for a healthy future.