Look for cotton swab-like cushions at the base of needles on hemlock. These are the female ovisacs of the Hemlock Wooly Adelgid (HWA). Newly hatched crawlers will be emerging from these sacs to feed on the hemlock foliage from now until June. Use, insecticides, insecticidal soap, or insecticidal oil sprays from mid-May through June to kill the eggs and immature crawlers of this pest.
The Elkington Lab at UMASS reports that recent surveys reveal that cold temperatures may have killed up to 90% of this hemlock pest during the winter. If true, this will be a great relief to this amazing but besieged conifer. However, UMASS preaches caution by recommending that any plants with known HWA infestation be monitored for potential problems.
Crawlers will be active at this time and are vulnerable to applications of dormant oil. However, the temperature must be above 45ᵒF for the latter to be effective.