Emerald Ash Borer Outlook 2015  

The most severe emerald ash borer (EAB, Figure 1) attacks in Kentucky are focused in the triangular area bounded by Louisville, Lexington, and northern Kentucky.

Figure 1. Emerald ash borer. (Photo: Lee Townsend, UK)

Figure 1. Emerald ash borer. (Photo: Lee Townsend, UK)

Distribution of Kentucky Infestations

The following map (Figure 2) indicates the known distribution of the EAB in Kentucky based on trap captures, confirmed samples, and a recent survey conducted by UK Ag & Natural Resource and Horticulture Extension agents.

EAB has been detected in counties depicted in green; however, the infestations are low and may be limited to specific parts of those counties. Counties colored in yellow have moderate infestations, while EAB is widespread with significant ash mortality evident in red counties. There have been no confirmed findings from counties in white.

Figure 2. Known emerald ash borer infestations (color code: green- present at low level; yellow – moderate; red – high; white - not detected).

Figure 2. Known emerald ash borer infestations (color code: green – present at low level; yellow – moderate; red – high; white – not detected).


Kentuckians who are living in counties where EAB has been detected should determine the numbers and sizes of ash trees on their properties and decide on a course of action. Managing Emerald Ash Borer: Decision Guide is a good tool to use.  In general:

Ash trees can be saved if they are:

  • Healthy and growing vigorously with 75% or more of their leaves.
  • Valuable to the homeowner and are showing little outward sign of EAB infestation.

Ash trees should not be saved if they are:

  • Unhealthy with less than 50% of their leaves.
  • Planted on poor growing sites.
  • Not important to the landscape.
  • Showing crown dieback, woodpecker damage, bark splits, and/or water sprouts at base of tree.
Figure 3. Emerald ash borer-infested ash showing crown dieback and shoot growth from lower trunk. (Photo: Lee Townsend, UK)

Figure 3. Emerald ash borer-infested ash showing crown dieback and shoot growth from lower trunk. (Photo: Lee Townsend, UK)

Ash trees probably will need to be protected for at least 7 to 10 years. However, this will vary due to a variety of factors, including the local intensity of EAB activity and number of ash trees in your area. Numbers of ash stems in counties can be found at http://pest.ca.uky.edu/EXT/EAB/Ashnumbers.pdf

Treatments for homeowner use

Homeowners can treat trees with a diameter of less than 20 inches (about 60-inch circumference) measured at 4 1/2 feet above ground level. Twelve-month tree and shrub products containing the active ingredient dinetofuran or imidacloprid can be applied annually in mid- to late March as granules or soil drenches according to label directions.  A thorough discussion of control decisions and alternatives is available in Insecticide Options for Protecting Ash Trees from Emerald Ash Borer.

Treatments for commercial applicator use

Tree care professionals can be hired to treat trees with diameters greater than 10 inches, or to protect smaller trees, as well. Commercial pesticide applicators can use products and application methods that may allow treatment at 2-year intervals, rather than annually. Be wary of people coming door-to-door offering to treat landscape trees. Commercial applicators must be certified and licensed by the Kentucky Department of Agriculture.  Ask to see their pesticide certification card and obtain a written estimate of costs and warranty of proposed work.

Winter Hardiness and Degree Days

The EAB is a hardy insect that spends the winter as a full-grown larva in a cell formed in the outer sapwood. It is unlikely that our 2014-2015 winter has directly caused EAB mortality. The larvae will pupate in a few weeks and begin to emerge after about 500 degree days (base 50) have accumulated in your area.

You can find the current accumulation and daily predictions for the nearest weather station by going to the UK Ag Calculating Degree Days Web site and selecting “Corn Growing Degree Day Calculator/Forecaster” listed in the left-hand menu. From the drop-down list, select the nearest weather station; leave the Biofix Date as Jan 01, 2015; choose “Daily” under GDD Accumulations; select “Screen” for the Output Destination; and click on “Submit Choices.”

Running the model today (March 3, 2015) indicates that 31 degree days (base 50) have accumulated since January 1.  Based on historical weather data, the total should reach 500 by about May 13. That date will change based on actual temperatures. As long as the soil is not frozen or saturated with water, it is better to treat for EAB with an insecticide drench too early, than too late. Allow at least a month for an imidacloprid treatment to be picked up by the roots and distributed throughout the tree; dinetofuran probably requires 2 to 3 weeks.


By Lee Townsend, Extension Entomologist


Posted in Forest Trees, Landscape Trees & Shrubs