Micro Injection Tool: From Efficacy and Duration of Trunk-Injected Imidacloprid in the Management of Hemlock Woolly

By Joseph J. Doccola, Eric J. Bristol, Samantha D. Sifleet, Joseph Lojko and Peter M. Wild, ArborJet Inc.

Injection capsules like these are applied at a rate based on the tree?EUR??,,????'???s diameter and the chemical treatment. This tree has more than 30 capsules attached?EUR??,,????'??+the manufacturer says that permanent damage is avoided if holes are limited to 1/2 inch deep. The capsules should be removed no more than three days after application. Photo courtesy of Tree Tech

An aphid-like sucking insect, the hemlock wooly adelgid is wreaking havoc on the eastern hemlock tree. If no effective countermeasure is found, the tree could join American chestnut and elm tree as an extinct species. To prevent this, scientists are scrambling to perfect chemical treatments and to discover biological-control species that will prey on the adelgid.

The ArborJet Tree I.V. method uses a slender needle, eliminating the need to drill holes. Rubber gloves make the treatment look like a hospital medical procedure?EUR??,,????'??+they are suggested to avoid absorption of insecticide through the skin. Photo courtesy of Great Smoky Mountain National Park, www.forestryimages.org

Scientists have already developed effective treatments using Imidacloprid, the synthetic-nicotine insecticide trademarked by Bayer. Various formulations of the chemical can be injected into a tree?EUR??,,????'???s roots via the ground, or directly into a trunk by micro-injection.

Recently, technicians working for the Massachusetts-based company ArborJet ran a study to evaluate the efficacy of micro-injected Imidacloprid.

A cordless drill, a urethane-tipped mallet and a tape measure are all it takes to effectively administer insecticide using the capsule method. Chemical-resistant gloves are recommended for workers. Photo courtesy of J.J. Mauget

The study found that the insecticide does not provide a quick cure, but can help an infected tree resume growth after two injections over a year or more. Several other studies suggest that other Imidacloprid formulations can be effective too.

?EUR??,,????'??Hemlock woolly adelgid (Adelges tsugae) (HWA) is an introduced piercing, sucking insect that affects hemlocks by extracting carbohydrates from the xylem ray parenchyma cells. Left untreated, HWA will result in reduced shoot growth, branch dieback, and ultimately tree death. In this study, the insecticide formula, called IMA-jet (5% Imidacloprid), was applied by trunk microinjection with the Arborjet Tree I.V. Sixteen randomly-selected HWA-infested hemlocks were treated in 2002 and 2003 and eight trees were selected as untreated controls.

ArborJet?EUR??,,????'???s Tree I.V. method is seen here attached to multiple trees in a city park. Because the equipment is valuable, application is often begun in the morning so the bottles, tubes and injectors can be removed and stored before nightfall. Photo courtesy of Tree Tech

?EUR??,,????'??Treatment with stem-injected Imidacloprid did not provide a quick knockdown of the HWA, but required time (at least one year). In the year after a second treatment, we observed sufficiently high HWA mortality for hemlock to resume growth. We have a high degree of confidence that a repeat treatment increased the levels of Imidacloprid for the duration of efficacy observed. We recommend an increased dose for trees in the 30 to 59 cm size class and larger, and for an increased level of efficacy to extend the injection interval (to once every 2 years), and to limit the number of wounds a tree receives. The new rate recommendations are reflected on the IMA-jet label revised in 2006. (See the label for precise dosage guidelines).

A Mauget capsule is employed in the war against emerald ash borer in Michigan. Used with a cordless drill, the capsules are a convenient and time-efficient method for treating large numbers of trees. Photo courtesy of David Cappaert, Michigan State University, www.forestryimages.org

?EUR??,,????'??These results demonstrate that hemlock trees with active hemlock wooly adelgid infestations can be successfully treated using Imidacloprid.?EUR??,,????'??