The hemlock woolly adelgid (HWA), (Adelges tsugae), is an Asian-native sap-sucking insect that is killing eastern hemlock in the eastern United States. The adelgid was discovered in the 1950s in Richmond, Va. Since then it has spread quickly and now covers 40 percent of the native range of eastern hemlock, (Tsuga canadensis), in the U.S. If not controlled, the adelgid could wipe out eastern hemlock from many areas of the eastern U.S.

Feeding by the HWA causes premature needle loss and shoot dieback. Over a period of one to three years, crowns of infested trees thin noticeably. Some trees die in as little as four years.

Researchers are exploring the screening and release of exotic natural enemies from Japan and China, because few native natural enemies exist for this pest.

However, these programs are in their early stages of development. Presently, chemical control is the only solution for keeping infested trees alive until natural enemy populations are established. Moreover, chemical control might be the only option for homeowners who have hemlocks on their properties. In one experiment, two chemical formulations were tested to evaluate their control of the adelgid. The unpublished results are compiled by Jeffrey Fidgen and Scott Salom of Virginia Tech?EUR??,,????'?????<

The first was an experimental formulation of cyfluthrin, the second a commercially available formulation of imidacloprid (Pointer). Both products were injected into eastern hemlock in late spring 2004 with an Arbor Systems trunk injection system. A year later, adelgid populations on the cyfluthrin-treated trees were 64 percent lower than untreated trees, and 88 percent lower on the imidacloprid-treated trees.

Stay tuned to LSMP and landscapearchitect.com for more on current research involving imidacloprid and other pest treatments.

Interpreting the Results

Because scientific studies on imidacloprid involve different formulas, all studies are not created equal. A unique insecticide that works by disrupting bugs?EUR??,,????'?????<

Some formulas are sprayed, some are injected into the ground, others directly into tree trunks. Imidacloprid is even formulated into flea treatments that are applied directly to the skin of cats and dogs.