Emerald Ash Borer & Thousand Canker Virus

Asked October 13, 2013, 1:35 PM EDT

I am confused about recommendation for prevention of this borer. I read in the Denver Post that "no action at this time" was recommended, but I have been getting unsolicited proposals from several tree companies, including Swingle, for doing trunk injections.

Also, is there any update on the Thousand Canker virus that was reputedly impacting Black Walnut trees, with no mitigation in sight.

We have mature trees of both varieties.

Denver County Colorado

3 Responses

Emerald Ash Borer (EAB) was found in a couple of Ash trees in Boulder at 30th and Valmont. These have been the only ash trees infested to date in CO, and were likely the result of someone bringing infested ash firewood from the Midwest into the area.
At this time there is NO need to preventively treat ash trees in Denver. If you lived at 24th and Valmont in Boulder, the value of preventive ash treatments would be much higher!
In Denver it's probable that no preventive treatments are needed or recommended anytime in 2014.

"Making any treatment for EAB when it is not present is also unjustifiable from any perspective. Yet we are already seeing in many areas the unleashing of some intense marketing to get homeowners to get in EAB treatment programs. Marketing being done in areas where there is zero risk of any significant EAB infestation in 2014 (Denver, Fort Collins……….) This marketing could be considered unethical and harmful. And its harm is not just to the homeowners who are duped into paying for something they do not need (yet) but to the industry. Emerald ash borer is not here yet, although it will be a few years from now. And when it does get here then you will have to decide what to do. “But right now, make a note of what company is knocking on your door. A few years from now, when you have to decide to treat your ash tree or remove it, you likely will need to hire a company to help you out. There will be many good ones to choose from. But to make the choice a bit easier, remember the name of that company knocking on your door selling you a service in 2013 (or 2014, 2015…) that was unneeded and inappropriate. And then hire someone other than that company.” Whitney Cranshaw, Professor/Extension Specialist, Entomology Colorado State University

Watch for further news reports or contact Colorado State University Extension in 2014 for any updates on EAB.

Keep in mind that lilac-ash borer is already well-established in Denver; it damages drought-stressed, marginally maintained ash trees, particularly 'Autumn Purple' ash. So, water the rooting area of your ash tree during dry warm snowless periods Oct-Apr, in addition to "normal" seasonal watering Apr-Oct.

Thousand Cankers Disease (TCD) of walnut: This is a fungal disease vectored (spread) by walnut twig beetle. Much more info at:

Robert, thanks, you verified my suspicion re the ash issue. But, regarding the Thousand Canker prevention... do you think I am wasting money having annual trunk injections to thwart the insect that spreads it?

Yes, you may be wasting money.....There's no real effective insecticide options. Imidacloprid (Merit) is not very effective. Plus there's the issue of what insecticide can be legally used on a nut-bearing (edible) crop, whether you intend to eat the black walnuts or not.
Some individual black walnut trees may have some genetic resistance to Walnut Twig Beetle and TCD. Susceptible black walnuts may not show symptoms until a few years after initial infestation by WTB. See also: