The most common problem with hemlocks is infestation by an insect called hemlock woolly adelgid (Adelges tsugae). If you see deposits of white, cotton-like masses on between the needles, then this is most likely the problem. This disease is hard to cure but it can be controlled, particularly if it is caught early. For the home gardener the best treatment is to spray with natural insecticides such as pyrethrin or neem oil sprays. Use a compression sprayer for efficient application. September and October are the best times to apply the sprays.  For serious problems in large trees a certified arborist should be consulted.

To keep hemlocks healthy, it is helpful to apply mulch around the tree. Also, water them well during a dry summer. Do not use fertilizer with a high nitrogen content as this just encourages the growth of tender new leaves that are susceptible to infestation.

Other problems with hemlock are root disease and hemlock rust.

For tips on a variety of gardening topics, see our Plant Information Guides.
- Courtesy of NYBG Plant Information Service