Twenty years ago predictions of the demise of our native Canadian (Tsuga canadensis) and Carolina hemlocks (T. carolina) from home and commercial landscapes turned out to be incorrect. The key reason was the effectiveness of the insecticide Imidacloprid®. This product is licensed by Bayer AG, and is found in a number of lawn and garden products, including Bayer Advance Garden Tree and Shrub Insect Control™ and Merit 75 WP.

Imidacloprid is a systemic insecticide. When properly applied to the soil near the hemlock trunks, it must be carried down into the soil and absorbed through the hemlock roots. The pesticide is applied to the soil Read and understand the easy package directions and watered in chemical within 24-36 hours. Do not expect rainfall to carry it down to roots.

There is even better news. Yearly applications is generally unnecessary. Imidacloprid appears to be more effective than the manufacturer’s recommendations. Hemlock adelgids do not destroy a hemlock tree or shrub hedge in 1-2 years. It may take 2-3 years before serious visual damage is observed.

Other insecticides labeled for use in the landscape may be sprayed to kill the crawler that hatches from the insect egg. Labeled products include Merit (imidacloprid), Talstar (bifenthrin), Onyx (bifenthrin), Astro (permethrin) and Safari (dinotefuran). Talstar is most widely used, providing excellent control any time through the growing season. Control from spraying Talstar has given two and sometimes three years of control. Do not spray trees if the material will drift into open water or other property.

Lastly, Safari 20 SG has slightly faster uptake by the tree as a soil drench or bark spray than products containing imidacloprid. Currently, it is sold only to state certified licensed landscape professionals.

All products are available at garden centers and farm supply stores.