Hemlock Woolly Adelgid

Asked February 11, 2014, 1:31 PM EST

Last year I contacted the extension center in Scranton regarding an infestation of Hemlock Woolly Adelgid, I got an answer and I got information of this pest. what I did not get is how to kill it, I wish it can be as simple as giving me a name of a product that I can get at home depot or Lowes or etc. I can not afford a person or company to came and treat my bushes, I have to do it my self Please I want to save my beautiful bushes in my backyard. Thanks Jose Zambrano

Lackawanna County Pennsylvania

1 Response

This insect is manageable in the landscape and nursery if found early and treated. Forest trees pose a different challenge and thus are almost impossible to treat effectively or economically. Many of those may be lost in time. The best overall strategy is to be aware of its signs and to monitor for it on a regular basis. Once found, there are a couple of options.

  • Horticultural oil sprays work extremely well when and where they can be properly utilized. It is important to thoroughly apply the oil throughout the tree. Homeowners can treat their own hemlock shrubs and hedges with this product. Large trees will need to be sprayed by a professional arborist with the proper spray application equipment. A dormant oil spray can be applied while the plant is dormant and the correct weather conditions prevail, generally late March into April. Dormant oils must be applied before the buds open and when there will not be freezing temperatures for 24 - 48 hours after application in order to reduce injury to the plants. Do not spray on cold days. Temperatures of at least 45 degrees F. are recommended. However, avoid overcast or wet days which greatly slows the drying time of the oil.
  • Horticultural oils can also be applied at the "summer" rate during much of the growing season. Again, avoid cool, overcast days or hot and humid days. Oil sprays are used for established populations of the HWA but offer no preventative benefits if the adelgid isn't present. Hemlocks infested with the HWA should be treated with oil sprays both at the beginning of the growing season and then once again towards the end of summer to insure proper control. Smaller hemlocks (shrubs) may only require one application. Once under control, continue to monitor for future re-infestations and then treat once found.
  • Imidacloprid (e.g. Meritâ„¢) is also effective against the HWA. It works best as a systemically applied pesticide either through the soil or by injection into the trunk. For soil application, there is a homeowner version of this product or it may be applied by a professional. When soil applied, it may require 8-12 weeks before the insecticide is up in the tree and coming into contact with the adelgid. When trunk injected (by a professional) the translocation time may only be 3-5 weeks. However, more than one application may be needed in a growing season. If a tree has been infested for several years, imidacloprid may not work well since the host's vascular system may have been greatly compromised and the product won't move through the tree to where it is needed. Some general use chemical pesticides are also listed for the HWA and can be applied as a foliar spray. However, many of these will not be effective against the egg stage, while horticultural oil kills all life stages of the HWA, including the eggs.