Moving to Dade County after living in Florida my entire life has brought change abounding! I have experienced many novel things in my new home that I never would have experienced through my upbringing in Florida. One of those was the snow day we recently had, which included my first time ever sledding! Another was watching trees lose their leaves and become bare during the winter. Those are deciduous trees, but another of my favorite new things is a species of evergreen trees I didn’t see much of in Florida. The Eastern Hemlocks I come across in Dade County are beautiful!
Unfortunately, Eastern Hemlocks are at high risk of becoming infected and killed by the hemlock woolly adelgid (HWA). HWA is an invasive insect native to Japan that found its way into the United States in the 1950s. The insect feeds off the tree’s needed energy reserves and can ultimately lead to the death of a once large, healthy hemlock tree.
You can easily detect HWA infestations by their white, woolly-appearing egg sacs and visible crawlers on branch tips. If a hemlock tree in your yard or pasture has branches with graying foliage, this may indicate an infestation. If you notice this gray/white appearing foliage now, in early spring crawlers will be present and feeding at the base of the branch needles. There is ongoing research into other ways of battling this insect, but as for now, insecticides are necessary to save infected Eastern Hemlocks.
There are four main options of insecticide active ingredients to suppress HWA: bifenthrin, dinotefuran, imidacloprid and thiamethoxam. The most commonly used and effective active ingredient is imidacloprid. Imidacloprid works systemically and is thus, I think, the most convenient way you as a homeowner can treat your infected hemlocks. Systemic poisons are ones that get inside a plant and work from within, and to use your flowable formulation imidacloprid insecticide (Imidacloprid 2F), you pour it into the soil around the base of the infected trees. This should be done according to the dosage recommendation on the label for the brand of Imidacloprid 2F insecticide you choose.
Once you have read the label and determined the dosage recommendation for a soil drench of the insecticide, you can prepare the soil for application. To do this, use your feet, hands or a shovel to brush away the top layer of soil around the trunk of the tree, about 12-18 inches from the trunk. Be sure to do this around the entire base of the tree. Next, pour the prepared solution evenly around the entire perimeter of the trunk of the tree. Be sure to do this without pouring the solution directly on the trunk. Be sure your solution application is within 18 inches of the trunk, where you removed the top layer of soil. After application of the solution, the top layer of dirt you brushed aside can be brushed back over the drenched soil.
Treatment of HWA infected hemlock trees with imidacloprid insecticide should protect them for five years. Please note that soil applications should NOT be made within 10 feet of a pond, lake, wetland or stream channel. Soil applications are most effective when the soil is moist, but not saturated. Therefore, soil applications are not recommended immediately after rainfall or in a drought.
As for when to treat hemlocks for HWA, right now is a great time of year.
If you have any further questions, please feel free to reach out to me by calling our office at (706) 657-4116 or emailing me at firstname.lastname@example.org.
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Agriculture and Natural Resources Extension Agent
UGA College of Agricultural & Environmental Sciences
Dade County Extension