Hello Jabeck42 (only this showed up -- our apologies that we don't have your name, too!),

Thank you for contacting Ask Extension about your ash tree and protecting it from the EAB. We are attaching a CSU Fact Sheet # 5.626: Insecticides Used to Control Emerald Ash Borer on Residential Shade Trees. We've also included a registration link to a webinar being given tomorrow (highly recommended!). The webinar will be recorded in case you cannot watch it tomorrow.

The information below is from our CSU Master Gardener Horticulture Specialist, Entomologist, Lisa Mason.

Webinar description and link:

Emerald ash borer (EAB), an invasive beetle deadly to all ash trees is slowly spreading throughout Colorado. Join us for a webinar on May 2^nd at 6pm to learn more about where EAB has been confirmed in Colorado, how to identify an ash tree, signs and symptoms of EAB and lookalikes, what options are available for homeowners, and how to hire a contractor. This webinar is hosted by Colorado State University Extension in partnership with the City of Littleton. Registration available here: https://col.st/Z2gUn

Q+A document: https://files.arapahoeco.gov/Open%20Space/Our%20Work/EAB_FAQ_Final.pdf

Here is a compilation of answers from a few different questions:

Imidacloprid

Soil drenches for emerald ash borer (e.g. imidacloprid) are most effective when they are applied shortly after budbreak in the spring. Are you applying the soil drench yourself or hiring a professional? A few tips: For soil drench insecticide to be effective (regardless if you or a professional applies it), the soil must remain moist to allow the roots to pick up the insecticide. The soil should be kept moist for at least 2-3 weeks after application to help the roots uptake the insecticide and move it throughout the tree.

A few things to consider with imidacloprid:

• The product binds to organic matter. If you have grass, mulch, or flowers under the tree, the product will bind to mulch, and the grass/flowers will uptake the product leaving less of the insecticide for the tree. You’ll want to remove any organic matter from the base of the tree.


• If you have plants that flower, per the label you can’t apply the product because it will harm bees and other beneficial insects.


• Consider the slope of your landscape. You don’t want run off after application.


• When applying do-it-yourself insecticides, be sure to read the label and follow the directions explicitly for effectiveness and safety.


• The product will not work in dry soil. Since imidacloprid moves through the tree slowly, keep the tree well-watered so the tree can move the product throughout the tree.

Emamectin benzoate

Research has shown that emamectin benzoate can actually last up to 3 years. It is labeled for 2 years since that's very effective if applied correctly. To learn more about the research about lasting 3 years, I recommend reading page 14-15 of this PDF (or page 13-14 if you go based on the page numbers in the bottom corners of the pages).

The decision to treat every 2 or 3 years is a personal decision based on financial considerations, and the homeowner's peace of mind. Some homeowners prefer the guaranteed treatment every 2 years. Some would rather save money and resources, and treat every 3 years.

The game-changer with emamectin benzoate is that you can treat your ash trees AFTER emerald ash borer (EAB) has infested your tree, as long as your trees are healthy and haven't lost more than about 30% of the canopy. This allows homeowners time to make the decision on when to start treatment.

Be sure to keep your tree well-watered for a few weeks after the injections! Since EAB treatments are systemic, the roots need to be able to uptake the product and distribute it throughout the tree. A well-watered tree will be able to do this more efficiently.

Emamectin benzoate is most effective when it's applied mid-to-late spring just after the tree has leafed out.

When Hiring a Tree Care Professional

• Ask for credentials. Arborists should be certified through the International Society of Arboriculture, have a current State of Colorado Pesticide Applicator License and should be insured.  The ISA link (www.treesaregood.org) provides a list of certified arborists by city/zip code.

• Ask for a specific contract of work and customer references.

• Do your research and get quotes from multiple companies.

• Some municipalities like the City of Littleton have a list of certified tree care companies approved to work within the city.

EAB Insecticide Options:

https://extension.colostate.edu/docs/pubs/insect/05626.pdf

Sincerely,

Anne C, Becky C

Hello Anne and Becky!

Hi Jason,

Here is the link to the webinar recording:  https://youtu.be/_dtztXtau1U

Also, to follow up to original question (not sure it was directly answered): Imidacloprid (the active ingredient of Bayer Advanced Trees and Shrub) available to consumers it NOT strong enough to treat large trees. The rate of imidacloprid must be doubled in trees with the diameter of over 15 inches to provide control, and that formula is not allowed for consumer purchase. Since you do have a large tree, to ensure it's survival, I would consider hiring an arborist. 

To help with the financial cost, you could use emamectin benzoate, and only treat the tree every 3 years. This insecticide is labeled for treatment every 2 years, but we have plenty of research to demonstrate it can treat your tree for 3 years. All other insecticides need repeat applications once per year. 

Please let me know if you have any other questions! 

Thanks,

Lisa

Lisa Mason
Horticulture Specialist, Entomologist
Colorado State University Extension, Arapahoe County