Source: NCDA&CS, 10/8/15

The emerald ash borer has become notorious in North Carolina. From its first appearance in the state in 2013, it has already left a trail of dead ash trees in its wake. And it continues to spread, prompting a statewide quarantine in September.  What are homeowners, landowners or land managers to do? There are three options for the urban or landscape/ornamental ash tree: remove the ash tree, replace the ash tree, keep the tree by treating it with pesticides to protect it from being attacked or rehab it following infestation.

Treating ash trees in the urban environment with insecticides is the best option for saving them from the emerald ash borer. Image background: Healthy ash trees protected with imidacloprid soil drenches. Image foreground: Untreated, declining ash trees that were eventually removed due to emerald ash borer infestation. (Image taken from Herms DA, McCullough DG, Smitley DR, Clifford CS, Cranshaw W. 2014. Insecticide options for protecting ash trees from emerald ash borer. North Central IPM Center Bulletin. 2nd Edition. 16 pp.)

For those interested in keeping their ash trees around, the N.C. Forest Service Forest Health Branch developed an Emerald Ash Borer Insecticide Guide. The guide was developed to assist even the newest of pesticide users with selecting and treating their ash trees, covering common questions from “is this tree even an ash?” to “how do I make the pesticide application?” The pesticides listed are registered in North Carolina and have been tested in field trials through universities and/or government agencies. The list was developed with assistance from the N.C. Department of Agriculture and Consumer Service’s Pesticide Section.

Homeowners may also decide to contact a certified arborist if they are uncertain about applying pesticides themselves or if their tree is large. Generally, it is worth hiring an arborist if one is dedicated to protecting ash trees larger than 20” in diameter, but arborists will serve any size tree.

To calculate your tree’s diameter, measure around the trunk of the tree (in inches) at 4.5 feet above the ground. Divide that number by 3.14, and that will give you your diameter at breast height, or DBH. DBH is directly associated with the amount of pesticide applied to the tree and is often referred to on the insecticide label.  A pesticide user will want to keep this number handy while measuring the chemical.

One common concern is cost. Will it be worth it? That is often a complicated question depending on many factors. There is an online calculator available through Purdue University that may assist in making the decision. After inserting the requested information, it will give you side-by-side comparisons of the cost to remove, remove/replace, and treat with different pesticides. The calculator is free, but users must register a user name and password. Generally speaking, however, the developers of the calculator assert that in most cases, it is more economical to protect ash trees with pesticides than it is to replace them.

For more information related to the research and science behind selecting an appropriate insecticide, the North Central Integrated Pest Management Center developed the publication Insecticide Options for Protecting Ash Trees from Emerald Ash Borer. It is an extensive guide that provides detailed answers to many common questions. Those interested in understanding more about insecticides for emerald ash borer are encouraged to consult this online publication.

For additional resources regarding ash trees in the urban environment, visit the N.C. Forest Service’s Managing Emerald Ash Borer in Urban Areas page. The Pesticide Guide is posted here, along with other tools to help in the identification and decision making process.

Lastly, the N.C. Forest Service continues to monitor the emerald ash borer. If you suspect you have the insect in an area not shown to be infested on the N.C. range map, please contact your local county ranger, call the NCDA&CS Plant Industry Division hotline at 1-800-206-9333, or email them at newpest@ncagr.gov.