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Remedy for Ash Trees Infested With Emerald Ash Borer

Leena Palande Jan 13, 2019
An ash tree damaged by the beetle called 'ash tree borer' (EAB) becomes brittle and hazardous to the public and property. The signs and symptoms of EAB infestation described further can help identify the disease.

Did You Know?

The hardwood obtained from an ash tree is tough but elastic. As it exhibits high strength and resilience, it is used to make tool handles, bows, hurleys, drum shells, guitar bodies, sports car frames, and baseball bats.
Ash trees belong to the family Oleaceae (Olive-tree like) and genus fraxinus. These medium to large deciduous trees are an important part of landscapes and can enhance the beauty of a garden or a street. About 70% of urban trees are ash trees.
Opposite branches, diamond-shaped ridges on the mature bark, and compound (pinnate, made up of several leaflets) leaves are the characteristic features of an ash tree. There are over 60 ash tree species; for example, black ash, blue ash, green ash, white ash (the largest of the family), European ash, manna ash, etc.
These trees are commonly found in Europe, Asia, and North America. However, they are becoming endangered, especially due to emerald ash borers and fungi like Gloeosporium aridum and Verticillium. Certain fungi can easily grow on wounded ash trees and can eventually kill them.
As the EAB creates thousands of wounds in a single ash tree, the chances of developing lethal canker diseases by the tree increase significantly. So, even if the EAB is controlled with insecticides, the tree may eventually die.
The emerald ash borer (EAB), the green menace, wreaked havoc in Michigan, Ohio, where it was first discovered in 2002. Millions of ash trees have died and 7.5 billion trees are at risk due to this pest.
Within just ten years, the beetle has spread to various other states and has attacked ash trees in the Midwestern, eastern, and southeastern areas of the U.S., and also trees in Ontario and Quebec, the eastern provinces of Canada.
If it continues to spread like this, within a decade or so, it will be able to kill all ash trees in the U.S.
A highly infested tree could be dead within a year. In less severe cases, without control measures, a healthy tree may die within five years, and all ash trees in that area may die within ten years of initial infestation.
The EAB first attacks green and black ash trees. Once they are dead, it attacks white ash trees in that area. A blue ash tree may show some resistance, but eventually, it would also succumb to the disease.

Emerald Ash Borer Disease

What is it?

The emerald ash borer (Agrilus planipennis) is a green beetle native to Asia and Eastern Russia. Outside its native range, it is an invasive pest. It was accidentally introduced to North America through solid wood packing material.
The adult has a distinctive dark metallic green color. It can be about one-half-inch long and about 1/8 inch wide. A female EAB can lay up to 275 eggs in one year. EAB population can spread over an area of 20 km within a year.
Predators and parasitoids native to North America have not been able to suppress EAB population. Identification of the disease through close observation allows for preventive measures.

Identification of the EAB Disease

'D-shaped' holes (about 3.5 - 4 mm wide, slightly larger than the size of the beetles, as the adults exit the tree) and S-shaped (zig-zag, winding tunnels, or serpentine galleries as the larvae feed between the bark and the sapwood) galleries underneath the bark.
As thousands of larvae burrow into the cambium layer of the tree, they destroy the vascular system of the tree. As a result, the flow of nutrients is interrupted. This brings about the death of the tree.
  • Notches on the sides of the leaves, as the adults feed on ash leaves.
  • Tree crown is thinned, it appears ragged.
  • As birds like woodpeckers feed on EABs, they may create holes in the bark. These holes can be seen surrounded by light-colored patches. Unnatural or increased woodpecker activity indicates EAB infestation.
  • Black and gray squirrels may leave ragged strips of barks near the S-shaped galleries, as they also eat EAB larvae. If the ash tree bark is falling off, it might be due to EAB infestation.
  • Vertical cracks (5 to 15 cm long) over larval galleries can be seen on the trunk as well as branches.
  • The bark over a larval gallery turns pinkish brown and dries.
  • As the branches begin to die, the foliage turns yellow, wilts, and falls off.
  • Sometimes, the tree under stress produces abundant seeds.
  • Epicormic shoots or suckers grow on the trunk and branches below EAB activity. Excessive sprouting from the base of the tree indicates EAB activity.


  • Emphasis is laid on natural biological control of EAB. Studies are done to see if native Asian wasps, who are natural predators of EAB, could be used to curb EAB population growth in US.
  • Three species imported from China are currently approved by the USDA for release: Spathius agrili, Tetrastichus planipennisi, and Oobius agrili. These three were successful in parasitizing EAB larvae one year after release. The researchers were happy to see that they survived the winter.
  • The USDA is also conducting studies to see whether Beauveria bassiana, an insect fungal pathogen, can be used to control EAB.
  • Specially designed traps can help catch the beetles.
  • Call a professional arborist to determine which trees can be protected, and which trees should be removed or replaced. The dead and dying trees should be taken down. This can help avoid potential hazard to persons and properties.
  • Annual application of Xytect 2x (active ingredient 'imidicloprid') or biyearly application of an injection which contains the active ingredient 'emamectin benzoate' have proven quite effective when used professionally and according to directions. The first one is applied as a soil drench (soil injection) while the latter is a tree injection.
  • You cannot use Xytect 2x for the trees that are situated near water bodies. A homeowner soil drench application is also available. TREE-├Ąge is another systemic pesticide that is injected into the trunk of the tree. It is effective for 2-3 years. A tree injection may wound the tree and a wound may lead to fungal infection and decay. So consult an arborist.
  • Treatment with TreeAzin, a systemic insecticide, could save some trees, if the damage by the emerald ash borer is noticed at early stage. This insecticide is produced from extracts of Neem Tree seeds (Azadirachta indica). It is injected into the base of ash trees, directly into the conductive tissues. It moves upwards with the flow of water and nutrients.
  • A biyearly application is recommended. It can be applied from mid May through August. It kills about 95% of EAB larvae and increases the chances of the tree surviving through an outbreak. It has been observed that TreeAzin reduces fertility and egg viability of adult female beetles feeding on treated trees. They produce mostly sterile eggs.


  • Even if an infested tree is cut down, EAB continues to live in the wood. Transport of unfinished wood products, such as firewood, should be avoided. This can help slow the spread of this pest. Ash firewood should not be moved within and out of the city. Buy and burn firewood locally.
  • Quarantines set up by local governments help prevent infested ash firewood, logs, or nursery trees from being transported.
  • Yard waste should be promptly set-out at the curb during your scheduled yard waste collection week. Instructions about wood movement and disposal are available on the web pages of respective cities. They should be followed strictly.
  • Homeowners should assess their trees and determine the level of infestation. They should report suspected outbreaks to the official agencies immediately. Early detection can help control the spread of the disease and also save some trees.
An effective insecticide may protect the tree form additional damage, but it cannot reverse the damage that has already occurred. As most insecticides need to be transported within the tree, a tree must be healthy enough to carry the insecticide up the trunk and into the branches and canopy.
Recovery is a slow process. And an ash tree is not treated with insecticides if EAB disease symptoms are not seen. Although very difficult, it is necessary to identify an ash tree that has only a few larvae, because early treatment is the only way to save the tree.