Landscape Architect Articles

LCN April 2006 Tree Care03-30-06 | News

Micro Injection for Hemlock Woolly Adelgid

By Erik Skindrud, regional editor

J.J. Mauget capsules containing the imidacloprid formulation Imicide are one approved treatment for hemlock woolly adelgid.

The hemlock woolly adelgid (pronounced ah-DEL-jid) is a small, aphidlike creature that is wreaking havoc on eastern hemlock forests from Connecticut to Georgia. Hemlocks in manmade landscapes are also at risk.

With the pest moving westward into Tennessee (and elsewhere) at a rate of about 20 miles a year, forest managers are creating a five-year plan to combat the insect. Arborists and maintenance people in charge of urban landscapes also need to be vigilant, and should be aware of a number of options if the pest is detected.

Forest managers are releasing thousands of beetles in an attempt to slow and halt HWA?EUR??,,????'???s advance. If detected on private or municipal property, the technique known as micro injection gives managers a way to attack and slow the pest in individual trees with a minimum risk to the environment.

It can take six to 10 years for hemlocks to decline and die from HWA, so the researchers think it likely that imidacloprid can slow the progression of adelgid infestation. Still, the chemical is best seen as a treatment, not a cure. Eastern hemlocks make attractive trees, shrubs and hedges in ornamental landscapes. This specimen is on the campus of Murray State University in Murray, Ky.

According to a Virginia Tech study micro injection treatments using the Imicide brand imidacloprid formula have proven effective against HWA. Results showed a clear reduction in adelgid populations in treated trees (a 52 percent reduction three months after one treatment and an 87 percent reduction a year after two treatments). Another technique (using Kioritz soil injectors and imidacloprid) gave trees ?EUR??,,????'??similar protection?EUR??,,????'?? from the pest, the study concluded.

Interestingly, overall tree health remained unchanged for all trees in the study, treated or untreated. While this sounds disappointing, the researchers attribute the finding to the fact that trees in the study were evaluated for just three years.

The Virginia Tech team also evaluated possible environmental harm from imidacloprid. While very small concentrations were recorded in nearby ponds and streams, the researchers did not consider the treatments to pose a risk, except, perhaps, in areas with ?EUR??,,????'??rocky well-drained soil.?EUR??,,????'?? The team did not treat trees within 50 meters of streams or lakes.

As always, users should follow manufacturer instructions when using imidacloprid or any insecticide treatment.

The hemlock woolly adelgid is an Asian native that showed up in the eastern U.S. in the 1950s. The insect is seen here with its whitish-waxy cover scraped away.