emerald ash borer afected tree

The Emerald Ash borer update

Agrilus planipennis Fairmaire

The Emerald Ash borer (Agrilus planipennis Fairmaire) continues to present problems for ash trees in North America. We’ve covered the facts about this pest in previous articles – please see: Emerald Ash Borer and 3 Tips to Detect Emerald Ash Borer – but we have some updates about recent advancements in countering this pest.


Biocontrol – aka biological control – Is a process by which predators, parasitoids, or pathogens reduce insect pest populations. These natural enemies can be manipulated by humans to make them more effective at reducing populations of certain pest insects.

The Emerald Ash Borer beetle

Primary predators of the emerald ash borer

Native woodpeckers are the primary predators of the emerald ash borer (EAB) in North America. Native parasitoids –  insects which feed on, and subsequently kill, their hosts – include the two-lined chestnut borer (Agrilus bilineatus) and bronze birch borer (Agrilus anxius), which are both related to EAB. Unfortunately, although woodpeckers and native parasitoids kill some EAB larvae, they have not been able to sufficiently suppress EAB populations to prevent trees from dying.

Scientists are currently searching for additional parasitoid species from the native range of the emerald ash borer in Asia to release in North America, with the goal of increasing the number of EAB eggs and larvae killed and slowing the rate at which ash trees are killed. 

In the last few years, the USDA has released stingless wasps – spathius galinae –  in EAB-infested areas. These wasps kill the beetles early in their lifecycle,  before they can devastate more trees in our communities, and the researchers are cautiously optimistic about the success of the project.

Insecticides to control the emerald ash borer

Several insecticide products are available to homeowners for control of emerald ash borer (EAB).  There are a number of factors involved in the correct use of these, however, including the tree’s location, value, and health. 

Research has shown that insecticide treatments are significantly more effective on EAB-infested ash trees with less than 50% canopy thinning.  Trees with greater than 50% canopy thinning should be removed and handled in accordance with local guidelines from your agricultural extension service. 

Insecticide treatment

Emerald ash borer insecticide treatment options available for use by homeowners are composed of acephate, imidacloprid, and/or clothianidin. These are usually applied in the spring as soil drenches around the base of the ash trees, and are suggested for use on trees that are less than approximately 47 inches (~120 cm) in circumference. 

It’s important to note that these should not be applied if flowering plants are present around the base of the tree, as the insecticide could move into the nectar of plants exposing it to pollinating insects. Also, insecticides containing imidacloprid have strict limits for the amount that can legally be applied per acre each year, making them unfit for use for treating multiple yard trees or for woodlots and forested areas.

Photo of tree afected by Emerald Ash Borer detail

Given the differences in application rates and restrictions on usage, your best option may be treatment by a tree care professional.  Besides being used as a drench, imidacloprid can also be injected into the soil by a professional using special equipment. 

Tree Implants are also available in retail outlets, but these require physically drilling into a tree during their application each year – a job best left to the professionals in order to avoid plant injury.

Let us help!

Our certified arborists can diagnose and treat the emerald ash borer, and offer safe options for treatment and/or removal of any diseased ash trees.  If your ash tree is showing any signs of decline, or you think it may have EAB, please contact our office as soon as possible.  If you think you’ve seen the emerald ash borer (EAB) or ash tree damage caused by an infestation, you can also report it to the USDA, or call 1-866-322-4512.

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