Symptom - White, cottony masses on branches especially near young tips –
An aphid-like insect, the hemlock woolly adelgid (Adelges tsugae) is by far the most serious pest of Canadian and Carolina hemlocks, killing whole forests of them from New England to North Carolina. Adelgids feed on the sap at the base of hemlock needles primarily on new twig growth. They usually start on the lower branches. Needles turn gray then yellow and then (drop)off. Branches die back, and growth is slowed. Typically, untreated trees die after 4 to 8 years, depending on their size, stress level, and location.
Trees of all sizes and ages are attacked. Adelgids reach maturity between late winter and early spring at the base of individual needles, covering themselves with white, cottony wax for protection. They lay brownish orange eggs under the cottony wax that hatch from February through June. Wind, birds and animals spread the eggs from tree to tree throughout the spring.
Important Tip - Avoid placing bird feeders in hemlocks, as birds pick up adelgid eggs and nymphs in their feathers and spread them to other trees. !
Do Not Fertilize - Because these pests thrive on trees rich in nitrogen, do not fertilize infested hemlocks. Research shows that twice as many adelgids survived on fertilized hemlocks as on unfertilized trees, and the survivors laid twice as many eggs.
Use Natural Insecticide - The newly hatched nymph stage is very vulnerable to control by sprays of natural products such as rotenone/pyrethrin insecticide, or neem oil soap. Time sprays between September and October to reduce potential impact on beneficial insects. Do not spray if temperatures are over 90° F. Thorough coverage is important, so use a compression sprayer to achieve good control.