ISSUE 6   June 18, 2009


With the recent discovery of emerald ash borer (EAB) in St. Paul, Minnesota, many people in North Dakota are already asking how they can protect their own ash trees from this devastating pest. With perfect timing, a group of university researchers have published, "Insecticide Options for Protecting Ash Trees from Emerald Ash Borer." This 14-page document is available on-line at:  

The guide covers many topics including available insecticides, delivery systems, and their effectiveness. There are many more insecticide options for professionals – including trunk injections and soil injections – than for homeowners. Some of the key points outlined include:

  • Insecticides can effectively protect ash trees from EAB. However, experiments have repeatedly shown that treatments that work at one site, in one year, may not work at a different site or during a different year.
  • Imidacloprid formulations for homeowners (Bayer Advanced™ Tree & Shrub Insect Control and other generic formulations) can be applied only once per year. Because of the variability in university studies with larger trees (>15-inch diameter), homeowners wishing to protect larger trees should consider having them professionally treated.
  • Unnecessary insecticide applications waste money. If EAB has not been detected within 10-15 miles, your trees are at low risk.
  • Trees that are already infested and showing signs of canopy decline when treatments are initiated may continue to decline in the first year after treatment, and then begin to show improvement in the second year due to time lag associated with vascular healing. Trees exhibiting more than 50 percent canopy decline are unlikely to recover even if treated.
  • Emamectin benzoate is the only product tested to date that controls EAB for more than one year with a single application. It also provided a higher level of control than other products in side-by-side studies.
  • Soil injections should be no more than 2-4 inches deep, to avoid placing the insecticide beneath feeder roots.
  • To facilitate uptake, systemic trunk and soil insecticides should be applied when the soil is moist but not saturated or excessively dry.
  • Xytect™ soil treatments are labeled for application at a higher maximum rate than other imidacloprid formulations, and the authors recommend that trees larger than 15-inch DBH be treated using the highest labeled rate. Merit® imidacloprid formulations are not labeled for use at this higher rate. When treating larger trees with Merit® soil treatments, best results will be obtained with two applications per year.
  • Treatment programs must comply with any label restrictions on the amount of insecticide that can be applied per acre in a given year.
  • For more information on emerald ash borer, go to:  If you intend to use pesticides always read and follow the label. If you suspect that your ash trees may be infested with EAB, contact Dave Nelson, ND Department of Agriculture (701-328-4765), Sarah Tunge, ND Forest Service (701-228-3700), or Joe Zeleznik, NDSU Extension Service (701-231-8143).

    Joe Zeleznik
    Extension Forester

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