Forest Pests: Insects, Diseases & Other Damage Agents

Hemlock Woolly Adelgid Georgia Forestry Commission Forest Health Monitoring Factsheets Written by Terry Price, Georgia Forestry Commission Adapted for the web by the Bugwood Network

Adelges tsuga

The hemlock woolly adelgid (HWA) is a sucking insect that attacks Eastern and Carolina hemlock trees. This insect is native to Asia where it does very little damage to the hemlock species there. It was first observed in North America in the 1920's in Oregon and British Columbia. It was later discovered in Richmond, Virginia around 1950. Since that time is has spread into 14 states on the eastern seaboard from Georgia to New England.

The HWA has spread west and south into Georgia from North Carolina and South Carolina. It is present in Rabun, Towns, Habersham, White and Union Counties. The heaviest infestations are found in the Chattooga, Little Tennessee, Tallulah and Hiawassee watersheds and in the headwaters of Brasstown Creek in Union and Towns Counties. Other watersheds with lighter infestations are the Soque, Chattahoochee and Nottley.

In the United States there are very few natural enemies of the HWA. For this reason, the Connecticut Agricultural Experiment Station in Windsor, CT in 1992 began studying the coccinellid beetle Sasajiscymnus tsugae, a natural enemy of the HWA in China. Initial results of this investigation concluded that S. tsuga showed promise as a natural control enemy of the HWA in the United States.

Fourteen releases of S. tsuga (28,700 beetles), two releases of the predator Scymnus sinuanodulus (450 beetles) and one release of Laricobius nigrinus occurred in northeast Georgia in 2004.

Feeding from the HWA causes the needles to dry, turn grayish green and drop from the tree. This can occur within a few months. In subsequent years dieback of major branches occur and eventually the entire tree dies. Infested trees can be identified by the white fibrous egg sacs on the undersides of the branches (Figure 1). This material is present during the winter months, which is the ideal time to survey for the HWA.

Figure 1 photo by Robert L. Anderson

The Georgia Forestry Commission surveys for the HWA each year and assists Clemson University and the USDA Forest Service with predator beetle releases in the general infested areas. Currently the HWA is present in 5 Georgia counties, which are Rabun, Towns, Habersham, White and Union. Areas to be receiving predator beetles in 2005 are the Chattooga Watershed in Holcomb Creek and downstream of Burrells Ford on the stem; Tallulah River Watershed in the headwaters above Lake Burton; Hiawassee River headwaters in the Swallow Creek drainage, Mill Creek, Corbin Creek and High Shoals Creek; and the headwaters of Brasstown Creek.

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