327Journal of Arboriculture 29(6): November 2003
Hemlock woolly adelgid (HWA) is an introduced, piercing–
sucking insect that threatens forest and landscape hemlock
species (Tsuga canadensis, T. caroliniana) throughout most of
the tree’s geographic range (USDA Forest Service 2002). The
insect inserts its stylet into the xylem ray parenchyma cells of
hemlock to extract carbohydrates (McClure 1991). The tree’s
vitality depends on these carbohydrates because this cap-
tured energy is crucial for growth, maintenance, reproduc-
tion, defense, and storage (Shigo 1991). McClure et al. (1996)
have reported that dieback in hemlock may occur in 2 years,
affecting the lower canopy first, and moves upward, even
with HWA infestation distributed throughout the canopy.
For managing HWA infestations, three approaches are
available: foliar sprays, soil injection, and trunk injection. A
twice-yearly application of horticultural oil is the standard
treatment for HWA, but efficacy depends on thorough foliar
coverage of the contact insecticide and is subject to aerial
drift. Soil injection of imidacloprid eliminates the problem of
drift inherent in foliar applications, but leaching into the soil
profile is a concern in sensitive sites. Microinjection is the
most environmentally sensitive approach to pesticide
application, but wounding and the possibility of subsequent
girdling are of concern to the arborist. Arborjet VIPER
microinjection was designed to address the concerns of
environmental sensitivity and wounding of trees. It limits the
number of injection sites set circumferentially around the
trunk. The Arborjet VIPER system was selected for use in
therapeutic treatments in this study (Figure 1).
METHODS
Tree Microinjection
Twenty-four randomly selected hemlocks in Winchester,
Massachusetts, U.S., were microinjected between June 14
and August 1, 2002, for HWA management. Trees were
treated using 10% formulation of 1-[(6-chloro-3-pyridinyl)
methyl]-N-nitro-2-imidazolidinime (imidacloprid, 10%
Imicide HP, J.J. Mauget Co., Arcadia, CA) by trunk injection
into the active sapwood. Dosage was based on diameter at
breast height (dbh, 135 cm from soil level, using a Lufkin 6
m diameter tape). Mean dosage applied per 2.5 cm dbh was
2 mL. Mean dbh of microinjected
hemlocks was 41.3 cm,
and ranged from 18.8 to 85 cm. All the microinjected trees
were established urban forest trees.
Ports used in this study are cylindrical, barbed inserts
with rubber septa that were set circumferentially into the
trunk flare area. To place the ports, a portable 18.0 v Ryobi
drill (model# HP1802M) with a 0.74 cm brad-point bit was
EFFICACY OF ARBORJET VIPER
MICROINJECTIONS IN THE MANAGEMENT OF
HEMLOCK WOOLLY ADELGID
by Joseph J. Doccola
1
, Peter M. Wild
2
, Ilangovan Ramasamy
3
, Paulina Castillo
4
,
and Christine Taylor
5
Abstract.
Hemlock woolly adelgid (Adelges tsugae Annand) is an
introduced homopteran that infests native eastern hemlock (Tsuga
canadensis Carriere). It results in reduced tree vitality and, when
untreated, death. A state-of-the-art microinjection device employing
an air-over-hydraulic system was used to deliver a therapeutic dosage
of imidacloprid into the active xylem tissues of affected hemlocks.
Bioassays were conducted microscopically to determine HWA
mortality post-treatment. Injected trees had significantly (p < 0.05)
lower HWA populations compared to untreated controls; mean
mortality for injected trees was over twice that of noninjected trees.
The Arborjet VIPER system shows promise as a management tool in
the treatment of HWA.
Key Words. Adelges tsugae; Homoptera; Tsuga spp.; Arborjet
VIPER; imidacloprid.
Figure 1. The Arborjet VIPER injection device, equipped
with tree gauge to indicate injection pressure in the
sapwood, and top-mounted, 10 mL Dose-Sizer™ to
measure amount of formulation applied.
(14 pages)
(2 pages)
(24 pages)
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