Emerald Ash Borer
Emerald ash borer (EAB) (Agrilus planipennis) is a wood-boring beetle from eastern Asia that can kill our
native ash trees: green ash (Fraxinus pennsylvanica), white ash (Fraxinus americana), and black ash (Fraxinus nigra). Mountain ash is not a true ash and is not affected by EAB.
EAB has devastated ash trees in Michigan and other states, resulting in the loss of all ash trees in
some communities. It was found in St. Paul in 2009 and since then state and local agencies have been monitoring and aggressively reacting when it is found.
What Should Residents Do About EAB?
- Keep an eye out for EAB signs and symptoms when you’re driving, biking, or walking in Maplewood.
- If you suspect an ash tree has EAB, follow the MDA’s Does My Tree Have EAB checklist (PDF). If it is pretty clear the tree may have EAB, contact Maplewood Public Works at 651-249-2400 or the state’s Arrest-A-Pest email or hotline at 888-545-6684.
- If you are considering preventative treatment with chemicals on a tree on your property, carefully evaluate the pros and cons.
- Observe the firewood and ash quarantine.
- Avoid pruning ash May through September, when the beetles are most active.
Canopy dieback of an ash tree
Maplewood’s Approach to EAB
In 2011, Maplewood City Council approved an EAB Management Plan. There are about 2035 ash trees on our city boulevards and at city parks. This does not include ash trees in naturalized areas or on private land. If EAB plays out here like it has in other states, we could lose all ash trees in the city.
Maplewood’s EAB Plan includes monitoring and detection, education and outreach, strategic removal, and replanting. Strategic removal may include: 1) removing all infected ash, 2) removing ash in poor condition prior to infection, and 3) removing healthy ash where it will help slow the spread of EAB through the community.
There are insecticides available that kill EAB and can save an ash tree. However, for environmental and financial reasons, the city’s EAB Plan does not support the use of pesticides on ash trees on city-owned land. Thus, residents that wish to apply a chemical treatment to a boulevard ash tree are not allowed to do so.
Signs of Emerald Ash Borer
Emerald ash borer (Agrilus planipennis) is a wood boring beetle related to bronze birch borer and twolined chestnut borer. The adult EAB is not more than ½ inch long and is an iridescent green. It is unlikely to be seen because it feeds in a tree’s canopy and can be confused with more common green insects.
A new EAB infestation is difficult to detect. By the end of the second year of infestation, dieback in the crown begins. By the third year, there is little foliage in the crown, and dieback is very noticeable.
- Crown dieback from the top
- New shoots or growth at the lower trunk
- D-shaped exit holes
- Bark splitting
- Serpentine shaped galleries formed under bark
- Extensive woodpecker damage
When the pupa becomes an adult and leaves the tree, the make a D-shaped exit hole. If the bark is pulled back, the wood behind the exit hole will reveal the galleries the larvae made while feeding. The splitting of bark can indicate an infestation. As an infestation grows, the tree responds by sprouting additional branching on the trunk. Also, woodpeckers are drawn to the larvae, and the sign of woodpecker feeding is another sign of EAB infestation.
How Emerald Ash Borers Kill Ash Trees
Eggs of EAB are laid on bark. After 7-10 days, the eggs hatch and the larvae tunnel under the bark into the phloem and xylem-tissues in the tree that transport water and sugars. As the larvae feed and grow, they etch galleries in the tissues that stop the flow of water and nutrients. When the tree is riddled with chambers, it can no longer function, and it dies. Trees infested and re-infested with emerald ash borer are likely to die in two to four years.
The larvae feed until fall, and overwinter in the tree. In early spring, the larvae pupate, then emerge from the tree as adults between late May to August. The new adults lay eggs in summer, and the cycle continues.
Unhealthy ash are especially attractive to adults laying eggs, but as EAB populations grow, healthy ash trees are also used. EAB has been found in ash trees as small as one inch in diameter.
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Can an Individual Ash Tree Be Protected from EAB
Pesticides may save an ash tree if applied prior to EAB infestation or in an early stage of infestation. Deciding to use an insecticide to save an ash tree from EAB requires serious thought. The insecticides available for EAB are not selective for the beetle and can kill or impact many of the insect species that feed on the tree. The effectiveness of the chemical, potential to harm other organisms, size of the tree, amount of infestation, season of application and other factors need to be weighed. Treatments will need to be repeated every two to three years. For guidance on pesticide use for EAB, see Emerald Ash Borer: Homeowner Guide to Insecticide Selection, Use, and Environmental Protection and other links below.
If you decide to use an insecticide on a tree on your property, please use the trunk injection method, which injects the product directly into the tree. You will need to hire a professional tree care company that is a licensed pesticide applicator to do this type of application. The city strongly discourages the use of insecticides applied as a soil drench. When pesticides are applied to the soil around a tree, they can negatively invertebrates and can easily end up in streams, lakes, and wetlands where they impact aquatic insects.
Firewood & Ash Quarantine
Ash wood and firewood in Hennepin and Ramsey Counties is under quarantine and cannot be moved out of the county. To help slow the spread of emerald ash borer, the Minnesota Department of Agriculture has quarantined four counties: Ramsey, Hennepin, Houston, and Winona. The following items may not be moved out of the quarantined counties without a permit:
- All parts of ash tree
- Ash chips and mulch
- Firewood from hardwood (non-conifer) trees
- Untreated ash lumber with bark attached
On its own, EAB moves about ½ mile a year from an infestation area. But insects in infested firewood or nursery stock can travel hundreds of miles in a day. The first step to managing EAB is to not take ash wood away from where it has grown.
Ash wood can be taken to the Ramsey County compost sites that accept brush. See link below for hours and locations: