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Hemlock Woolly Adelgid Identification and Control

Hemlock Woolly Adelgid Identification and Control


  • Extremely devastating hemlock pest introduced in the 1920’s in Pacific Northwest from the Orient.
  • Hemlock woolly adelgid (HWA) reported in Henderson and Transylvania counties since 2002.


  • Egg laying begins in February, older nymphs secrete fluffy white mass for protection while sucking sap from hemlock needles. A second generation occurs in July and produces fluffy white mass in October.
  • Wind, birds, and animals disperse insect.


  • Look for fluffy white mass on the base of needles. Mass is present throughout the year, but most prominent in the late spring.
  • HWA feeding restricts nutrients to the foliage causing discoloration and eventual leaf drop.
  • Tree usually starves to death within 3 to 5 years.



  • Foliar spray treatment of horticultural oil and /or insecticidal soap. Best time is in August through mid-fall or late-May through mid-June. Avoid drift to open water such as streams and ponds. Should be applied with high pressure sprayer to get complete coverage.
  • Soil drenches or injections of Imidacloprid. These include Merit® or Bayer Advanced Garden Tree and Shrub Insect Control®. Do not use in areas near streams and ponds.
  • A professional and licensed applicator can make these treatments if you prefer. (See applicator list.)

Beneficial Insects

  • Two tiny lady beetles show promise of being good biological controls for the HWA.
  • Research laboratories in SC, TN, and NC are rearing these beetles; unfortunately, they are difficult to rear due to they require a large food supply and exact environmental conditions.
  • Beetles are being released on public lands such as Pisgah National Forest, but are currently unavailable for homeowner use.


  • Managing landscape site conditions to reduce stress often can reduce infestations.
  • New planting sites should be loose, moist, and well drained.
  • Older trees should be watered adequately to reduce water stress.


  • Check on-site and surrounding trees regularly.
  • Inspect trees before purchase.
  • Clip and burn or treat infected branches.
  • Do not transport infected branches.
  • Do not put bird feeders in hemlocks.

For more information on HWA, visit the following web sites:
US Forest Service

Save Our Hemlocks

For more information on imidacloprid, see: Imidacloprid

Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. For assistance, contact an agent of the North Carolina Cooperative Extension Service in your county.

North Carolina State University and North Carolina A&T State University commit themselves to positive action to secure equal opportunity regardless of race, color, creed, national origin, religion, sex, age,or disability. In addition, the two Universities welcome all persons without regard to sexual orientation. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

Prepared and edited by Diane Ashburn (1) and Cliff Ruth (2)

1.Diane Ashburn is an Extension Agent in Henderson County, NC with responsibilities in Urban Horticulture.
2.Cliff Ruth is an Area Extension Agent based in Henderson County, NC with responsibilities in Commercial Horticulture.

Page Last Updated: 1 decade ago
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