How to Treat Hemlock Diseases

Hemlock trees are generally disease resistant with a few exceptions.

The hemlock tree is a common, decorative, landscaping tree in North America. This needle evergreen grows between 40 and 70 feet tall on average and prefers cool, moist, well-draining soils. The hemlock is susceptible to certain diseases and pests, the most common of which is the hemlock wooly adelgid. Fortunately, hemlock diseases are easy to treat.

Things You'll Need

• Pruning shears
• Pesticide
• Fungicide

Instructions

1. Inspect the branches and trunk, looking for signs of disease. Weak or wilting branches, damaged bark, insect larvae and fungus are signs. Look also for excessive needle loss and cotton tuftlike masses on the underside of foliage, which are common signs of the hemlock wooly adelgid.

2. Examine the hemlock's roots, another area of the tree where disease shows itself. Look for fungus, white or blackened roots, and roots that appear dead. These are signs of annosus root disease, which is common in Western hemlocks.

3. Prune any diseased branches. Using wood-alcohol sanitized, sharp, pruning shears, remove branches that appear weak or wilted. Cutting the branches at 45-degree angles encourages regrowth. Pruning prevents the spreading the disease to other parts of the tree.

4. Apply pesticides if your hemlock tree suffers from pests or fungicide if it's a fungal problem. Use 75 percent water-soluble powdered imidacloprid spray to eliminate hemlock wooly adelgid. Using safety goggles, gloves and a facemask avoids contact with chemicals.

5. Continue monitoring your hemlock, checking for signs of disease periodically throughout the year. Check regularly for hemlock wooly adelgid pests, which typically lay their eggs between March and June.

References

• United States Department of Agriculture: Pest Alert - Hemlock Woolly Adelgid
• University of Connecticut: Tsuga Canadensis
• Ohio Department of Natural Resources: Hemlocks At Risk