LEXINGTON, Ky. — Since the first discoveries of emerald ash borer in Boone, Jessamine, and Shelby counties in 2009, this invasive insect has spread through normal dispersal flights and the inadvertent movement of infested wood. Tunneling beneath the bark by the larvae (Figure 1) has caused extensive ash mortality. The extent of the destruction can be seen in Figure 2.
Figure 2. Extent of emerald ash borer-induced ash decline in Kentucky based on aerial and ground surveys as of 2017. (Map provided by A. Nielsen, Kentucky Division of Forestry)Here are some considerations concerning emerald ash borer (EAB) management in Kentucky based on the map zones.
Red Zone
For the past few years, the high-risk areas have been those shaded red in Figure 2. While the potential for infestation still exists, most of the unprotected ash trees in those areas have died, so the endemic EAB population is probably relatively low. Unfortunately, there is no trapping information upon which to base relative assessments of the EAB population.
Management Options in the Red Zone
The most conservative course would be to maintain full protection for another 2 to 4 years. Alternately, a moderate course of action would be to continue protection, but reduce the rate of insecticide applied (use half- or 2/3- label rates, for example) or to extend the interval between applications (for example, from alternate years to every 3rd year).
Under these strategies, watch tree crowns for wilting or dieback that could indicate some borer activity. Normal treatments can be resumed if this occurs.
Risk of Infected Trees and Affect on Wood Value
Dying and dead ash trees are dangerous. Canopies of ash trees after early to intermediate EAB infestations often suffer dieback resulting in substantial accumulation of deadwood. EAB-infested ash branches or stems may fail prematurely and without warning during windy conditions, pruning, or tree removal. More information on the risk is available in Effects of Emerald Ash Borer Infestation on the Structure and Material Properties of Ash Trees (ISA).
A variety of insects, including ambrosia beetles, attack standing dead ash trees. Their activity can affect potential uses and value of the logs. See 2018 White Paper on Ambrosia Beetle Damage to Dead Ash in KY: Prevalence and Economic Impact to Loggers in Northern Kentucky (UK Forestry) for more information.
Yellow Zone
It is likely that EAB populations are increasing in areas shaded in yellow where EAB mortality is assessed as sporadic.
Management Options in the Yellow Zone
Populations in these areas are probably increasing, so it is time to begin preventive treatments for trees that warrant protection. Several systemic insecticides are available that provide effective protection, even for large trees. Homeowners can protect desirable ash trees with diameters of 20 inches or less at 4.5 feet above ground level (DBH) using a soil drench containing the active ingredient imidacloprid. Mid-March to mid-April is a good time to apply this treatment, which must be repeated annually. Tree care professionals have products and techniques that can protect larger diameter trees and allow applications at extended intervals.
White Zone
Lack of detected EAB activity in this area does not mean there are no active infestations. The borer may be present for 3 to 4 years before infestations reach detectable levels. For example, infestations around Evansville, Indiana are a potential source of beetles for the Owensboro area (link to Indiana map) .
What to Look For
Symptoms of EAB infestation include crown die back, epicormic shoots, splitting bark exposing serpentine galleries, and D-shaped exit holes. See examples here
Management Options in the White Zone
Best actions for tree in the white area are to
1) Check landscapes for ash trees and
2) Determine whether to follow a protection program when the EAB appears.
Management Decision Guide
Follow this link to an EAB decision guide. There is no need to begin a preventive borer control program until active infestations are found within 15 miles of your location.
Click here to visit the University of Kentucky Pest News blog.
— Lee Townsend, University of Kentucky Extension Entomologist
For more news from Kentucky, click here.