Kentuckians living in counties where emerald ash borer (Figure 1) has been detected should determine the numbers and sizes of ash trees on their properties and decide which trees, if any, should be protected. Managing Emerald Ash Borer: Decision Guide is a good tool to use in the evaluation process.
Homeowners can use 12-month tree & shrub products containing the active ingredient dinetofuran or imidacloprid that are labeled for emerald ash borer (Figure 2) control. These products must be applied annually and can protect trees with a diameter of less than 15 inches (about 45-inch circumference) measured at 4.5 feet above the ground.
Arborists or certified tree care professionals can be hired to treat ash trees with diameters greater than 15 inches. They can use products and application methods that are not available to homeowners, and these products can be applied at 2-year intervals rather than annually. Applicators must be certified and licensed by the Kentucky Department of Agriculture. Before hiring an applicator, ask to see their pesticide certification card. In addition, obtain a written estimate of costs and warranty of proposed work. A thorough discussion of control decisions and alternatives is presented in Insecticide Options for Protecting Ash Trees from Emerald Ash Borer.
It is likely that ash trees probably will need to be protected for at least 7 to 10 years before treatments can be reduced or stopped. However, this will vary due to a variety of factors, including the local intensity of emerald ash borer (EAB) activity and number of ash trees in your area. Numbers of ash stems in counties can be found at in the Ash Stem Numbers document.
Ash trees can be saved if they are:
- Healthy and growing vigorously with 75% or more live foliage.
- Valuable to the homeowner, and trees 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 sites or not important to the landscape.
- Showing crown dieback, woodpecker damage, bark splits, and/or water sprouts at base of tree (Figure 3).
EAB is a hardy insect that spends winter as a full-grown larva in a cell formed in outer sapwood. The winter of 2015-2016 should have had no adverse effect on EAB mortality. 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 Insect Degree Day Calculator/Forecaster. Select the weather station nearest you and use the European Corn Borer (Base 50F, Biofix Date Jan 1) with the output sent to your screen.
Running the model today (March 1) for central Kentucky shows that 62 degree days (base 50) have accumulated since January 1. Based on historical weather data, the total should reach 500 by about May 15. Based on this, soil drenches should be applied in late March.
Things to remember about soil treatments:
- Do not treat if soil is frozen or saturated with water.
- Clear away mulch before treating and replace when finished.
- Place the treatment directly on the soil around the base of the tree.
- Water the treatment in if the soil is dry.
- Allow a at least a month for an imidacloprid treatment to be picked up by roots and distributed throughout the tree.
- Do not treat near roots of plants that attract pollinators.
By Lee Townsend, Extension Entomologist