Many of our remaining mature eastern hemlock trees are only alive today because they have received chemical pesticide treatments that have acted as an immediate life-support system. Chemical treatment is still the only completely reliable way to save an individual tree from mortality due to HWA (trees can still die due to other factors).
The good news is that chemical treatment is significantly cheaper than it was in the past, and we now have a better understanding of how to apply it, so you can get up to 5-7 years or longer protection from one application. One fairly large tree can be treated for less than $10. This remains the best option for most homeowners with a few dozen trees or less.
The neonicotinoids, imidacloprid (Merit and others) and dinotefuran (Safari), provide excellent control of hemlock woolly adelgid (HWA) when applied as a soil drench or soil injection. Both products are loosely bound to soil particles but are sufficiently water-soluble to be absorbed by tree roots following soil application.
Always make sure to follow state law and the chemical label when applying pesticides.
Detailed instructions for chemical HWA-control are available from the Hemlock Restoration Initiative “Info for Landowners” page.
Save Georgia’s Hemlocks (Note: the information on SGH’s page is directed towards GA residents; NC residents must follow NC laws regarding pesticide application–check the label!)
Although chemical treatments provide essential short-term HWA-control, they require repeated applications and are impractical in many situations. Therefore, other long-term options are being tested, evaluated and cautiously pursued. Learn about some of them here.