Treating Ash Trees

Asked October 13, 2016, 11:56 PM EDT


I have a lovely ash tree in my front yard. We would like to keep it healthy and defended against the ash beetle. How can we do that? Do we need to hire a pro? How often does it need to be treated? And any other question that I should have asked :-)

I'm sure you are not allowed to recommend specific companies to do the work, but please tell me what to look for in their treatment plan, and what questions to ask the prospective arborist.


Jim Hulings

Larimer County Colorado trees and shrubs

1 Response

Hi Jim,

Thanks for your question. The first thing that's important is that the emerald ash borer has not been found outside of Boulder County. It was found in both Longmont and the Gun Barrel subdivision this summer, but (as of today) is still in the Boulder area.

It's good that you're thinking about your ash tree and making a plan. It's important to consider all options. Not every ash tree is worthy of treatment. However, it sounds like your tree is healthy, in good condition and has no other predisposing stress factors. It's important to keep the tree healthy and continue to care for it...including watering during fall and winter. While emerald ash borer doesn't target sick trees specifically, this will help with other stress-related problems (like lilac-ash borer, twig dieback, etc.).

Right now, we are not suggesting that people treat their trees for EAB if you live in Larimer County. However, the choice remains yours. It also depends on where you live...if you're in Berthoud or south Loveland, treatment will likely be recommended sooner than if you're in north Fort Collins. It will depend on where the insect is found in the county.

Depending on the size of your tree, homeowners have the option to treat themselves. The product you can use is imidacloprid, which is a yearly application. If the tree is greater than 12" at diameter at chest height (measured by doing the tree's circumference and dividing by three), then treatment must be done by a professional. We cannot recommend specific companies, but go with a company that has the proper license to apply pesticides and is a certified arborist through the International Society of Arboriculture (ISA).

The most effective treatments are either soil-applied or trunk injections. Treatment, depending on the chemical, will need to be applied every year to every two or three years. Cost will vary. The chemicals used for treatment include imidacloprid, azadirachtin, emamectin benzoate and dinotefuron. Imidacloprid and dinotefuron must be applied annually; azadirachtin may last two years; emamectin benzoate may last up to three. Both azadirachtin and emamectin benzoate require drilling holes into the base of the tree for application. Dinotefuron is a trunk drench or soil drench; imidacloprid is generally a soil drench.

There is a ton of information where you can become more knowledgeable about this pest and the treatment options (so you're ready to make a decision when the time is necessary). The first is the publication from CSU (see page 11 for the treatment options and their details).

The other is the Colorado emerald ash borer website, which is the most up-to-date:

Please let me know if you have other questions.