Emerald ash borer is and has been a problem for quite some time now. We have established populations of EAB (emerald ash borer) in many areas of the Central Great Plains and Midwest. It is here to stay, and we must learn the best management practices if we are to see any ash trees survive. Living here in Northeast Kansas, I have seen a slow progress of the pest across the state, but it is here.
Managing EAB is the only treatment possible, as it is too late to eradicate this insect. But what can we do to manage our woodlands, urban forests, and landscapes to prevent total devastation of our ash trees? Once we know the history of EAB and its identification, treatment options, and how to determine if a tree is worth saving, we can determine the best management practice.
History of Emerald Ash Borer
EAB is an exotic, wood-boring beetle from Asia, that was first discovered near Detroit, MI in the summer of 2002. It has been conjectured that the beetle may have arrived as early as 1998 in the area. Since then, it has traveled swiftly through the Central US, into 35 different states. It is likely that some of the spread is due to movement of firewood for camping, across state lines.
Emerald ash borer can be found in Alabama, Arkansas, Colorado, Connecticut, Delaware, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Nebraska, New Hampshire, New Jersey, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Vermont, Virginia, West Virginia, and Wisconsin.
The range of native ash trees spreads across the United States and Canada, with 18 species. Here in Northeast Kansas and Southeast Nebraska, we are concerned with just 2 species of ash, green and white. Green ash has been planted in landscapes and parks throughout the region, because it is a quick grower that provides good shade. White ash has purple-orange fall color and a rounded habit, making it a prominent street tree in many towns.
Since its introduction into the United States, EAB has killed millions of trees and cost millions to homeowners and cities for removal and treatment.
Identification of Emerald Ash Borer
The emerald ash borer (EAB) adult is a small, shiny green beetle, 10 to 13 mm in length. They can be difficult to distinguish between other similar wood-boring beetles in the same family. Rule of thumb is that if they are found in or under an ash tree, it is likely EAB. But if you are uncertain, please call your local extension office or Grimm’s Gardens for help.
Life Cycle of EAB
The adult female beetle lays 40 to 70 eggs in the crevice of ash trees. Once the eggs hatch, the larvae chew into the tree and begin feeding in both the phloem and cambium layers, disrupting the flow of water throughout the tree. As they feed, the larvae form S-shaped galleries which are filled with the frass (excretions) of the larvae. These S-shaped galleries are a good identification clue for EAB.
The larvae feed for 1-2 years before pupating into adults while in the tree. The adult insects overwinter inside the tree and begin to emerge in late spring or early summer, through a D-shaped hole. They then fly to new trees to repeat the process.
Determining if Your Ash Tree is Worth Saving
Now that we have looked at the characteristics of EAB, we need to look at the trees that are vulnerable. There are 3 species of ash native to Kansas, and just 2 in Nebraska. However, they have been planted throughout our cities, parks, golf courses, and landscapes. The determining factors for deciding on tree protection are as follows.
- Proximity to infested trees.
- Is your tree already infested?
- Is your tree healthy?
- Location of the tree may determine importance.
- Cost of Removal
How Close is Your Tree to Ash Trees Infested with Emerald Ash Borer?
One of the determining factors to deciding tree protection is how close your ash tree is to EAB quarantine zones or infested trees. In Nebraska, treatment is recommended on valuable trees within 15 miles of infested trees. However, we know that EAB can be in a tree for up to 3 years before major damage is noticed, so I think a distance of 30 miles would be wiser.
Is Your Ash Tree Already Infested with EAB?
If you live within the 30 mile range, and you have an ash with signs of canopy dieback, then you should consider treatment. If your tree is a valuable tree worth saving that is. Trees with less than 50% of canopy dieback can be treated effectively for emerald ash borer. However, if EAB has been present in a tree for 2-4 years before significant damage is seen, the tree will be unlikely to stage a comeback.
How Healthy is Your Ash Tree?
There are many other things that can impact the health of your tree. Knowing if there are other issues can help with determining whether or not to treat an ash tree for emerald ash borer. The following visual symptoms may impact the health of your tree.
- Circling or girdling roots
- Branch dieback
- Storm damage
- Improper pruning cuts
- Holes or hollows
- Mushrooms growing on limbs or the trunk
- Wounds from mowers, trimmers, or animals
- Leaf diseases
If your tree has 1 or more of the above symptoms, it may be advisable to consider treatment or removal, if your live within 30 miles of an EAB infestation.
Where is Your Ash Tree Located?
If you have an ash tree that is not valuable as a shade tree or specimen tree, it may not be worthy for treatment. Trees growing near sidewalks, which may affect root growth and viability, are considered potential hazard trees, and should not be considered for treatment. Additionally, ash trees under or near power lines, growing within 20 feet of a building, or leaning over a structure should not be considered for treatment.
Trees that you should consider for treatment include the following.
- Trees that shade homes or building on the west or south side and are more than 20 feet away.
- Specimen trees that represent a different species than those that are native.
- State or National champion trees.
- Trees that are very healthy.
Would it Cost More to Treat the Tree, or Remove it?
Some ash trees, over the course of their lifetime, would cost more to treat with an insecticide, than would to remove the tree and plant something else. If you can get a service estimate from a qualified applicator, such as Grimm’s Gardens, then you can determine the cost of tree treatment over a lifetime, versus cost to remove and replace.
For example, a young tree, planted within the last 5 years, will end up costing thousands to treat over the course of 50 years. But removing that tree at an early age, and replacing with something different, would cost far less than either the treatment or the future removal cost.
Treatment Options for Emerald Ash Borer
There are generally 2 areas of options for treatment, one for professionals, and one for homeowners. A limited number of insecticides are available to homeowners, and are often not as effective. When picking a professional, look for a certified arborist with insurance.
Treatment Options for Homeowners
For small, young trees on the outside of the recommended treatment distance, the following options are available to homeowners.
Soil Drench with a Systemic Insecticide
This treatment is applied around the base of the trunk in October or November to protect the tree for 1 year following the treatment. This application can be difficult to get even results, spread around the root sections of the tree. There is potential for contamination of water supply or lakes if the application is done during a rainy period.
Trunk Spray with an Insecticide
This application is done using an application of an insecticide such as Spinosad, Imidicloprid, or Bifenthrin directly onto the bark of the tree to prevent hatching larvae from penetrating the trunk. This method is effective at prevention, but can become costly as it will need to be applied monthly during the months of May, June, and July, when the beetles are flying and laying eggs. Some of these insecticides are also dangerous for homeowners to apply without Personal Protective Equipment.
Treatment Options for Professionals
The above listed options can also be applied by a professional with a Commercial Pesticide Applicator’s license. When choosing a company, such as Grimm’s Gardens, be sure they have proper certifications for spraying chemicals. The following is the best treatment for your ash tree.
The use of a trunk injection of Emamectin Benzoate is effective for prevent 85-95% of canopy dieback when the pressure of emerald ash borer is high in the area (15 to 30 miles). This application must be done by a professional. While injection does involve drilling holes in trunk, they are small and cause much less damage than EAB itself. Applications last for 2 years, making it more efficient than other sprays.
Emerald ash borer continues its westward journey through the Great Plains states and will soon be threatening the whole country. By following our best management practices for determining if our ash trees are worth saving, we can maximize effort and minimize costs. Save one tree at time!