Since its discovery in 2009, the emerald ash borer (EAB) has spread dramatically (Figure 1) within the Commonwealth. This spread will continue through short-range dispersal flights of the insect and long distance transport of infested wood, primarily firewood. Naturally, those in EAB-infested areas wonder how long they should apply preventive treatments to protect valuable ash trees. At this point, the threat in infested counties remains high and protection should continue.
The consensus of EAB researchers in states that have had infestations longer than Kentucky suggests that treatments may be needed for 5 to 7 years after the population peak. Some Kentucky counties are probably near their peak, but it is difficult to know for sure. Beetles will continue to emerge from infested trees and disperse to find surviving ash trees, although numbers of both diminish over time. Variables in the equation include the number of stems in the county and those in landscapes. Information on the numbers of ash stems per county (pre-EAB) is available here. Numbers range from 6.8 million (Henry County) to 38,000 in Martin County. Ash trees in wooded areas will provide sources of beetles until the population crashes from an unsustainable number of host trees.
The most conservative protection strategy at this time is to continue one of the recommended treatment alternatives for 4 to 6 more years. These include:
1) An annual soil drench of imidacloprid,
2) An annual trunk spray of dinetofuran, or
3) Alternate year injections of emamectin benzoate.
These can be adjusted if a more accurate assessment of the local EAB situation becomes available.
There are no EAB assessment tools, such as an efficient beetle trap, to monitor populations. Any reduction in an existing control program must be made by trial and error. The main alternatives would be to reduce the treatment rates (drench or trunk spray) or extend the treatment interval (trunk injection) to once every 3 years. Full treatment could be resumed if evidence of crown dieback or woodpecker activity point to EAB activity.
By Lee Townsend, Extension Entomologist