Progress 03/01/03 to 02/28/06
Outputs
Imidacloprid application methods and timing were compared for efficacy against the hemlock woolly adelgid in forests. The methods compared were (1) soil injection near the trunk, (2) soil injection dispersed throughout the area under the canopy, (3) soil drench near the base of the trunk, and trunk injection with the (4) Arborjet, (5) Wedgle, and (6) Mauget systems. The applications were made in the fall and the following spring. Adelgid populations on the hemlocks were assessed in the two successive falls following the treatments. Relative to the untreated control trees, all the soil applications resulted in population reductions, but none of the trunk injections did. Fall and spring treatment efficacy did not differ. There were no statistical differences among the soil treatments; reductions by the soil treatments were between 50 - 100% (avg. 80%) by the first fall and 83 - 100% (avg. 98.5%) by the second fall. Analysis of imidacloprid residues using ELISA found
residues in sap, needles and twigs one month to 3 years following application, but sample variance was high within treatments. A laboratory dose-response bioassay using excised, adelgid-infested hemlock branches with cut ends immersed in serial dilutions of imidacloprid determined the median lethal concentration to be 300 ppb, based on an exposure of 20 days. A high degree of suppression of the adelgid on forest trees was associated with residues in hemlock tissue greater than 500 ppb and 120 ppb 1 and 2-years after soil treatment, respectively. A single soil application of imidacloprid at the lowest labeled rate in 1999 reduced adelgid populations by 80% 7 years later. Analysis of covariance for a dose-response study in PA determined that there is an interaction between dosage and tree dbh, implying that larger trees require a higher dosage to accomplish the same degree of control. Leaching studies for imidacloprid using the organic matter matrix found in the surface layer under
forest hemlocks demonstrated that there is little risk of imidacloprid leaching when the active ingredient is placed in this layer.
Impacts
My research demonstrating shallow subsurface placement of imidacloprid to be the most effective treatment for control of hemlock woolly adelgids is being used by forest managers throughout the adelgid-affected states. Forest managers and arborists have discontinued using the ineffective devices, and the insecticide treatments reflect my research results. Examples are treatment protocols for the Forest Pest Management Division of the Pennsylvania Department of Natural Resources and protocols used in the Greater Smoky Mountains National Park. To date, PA has treated nearly 15,000 hemlocks with a cumulative 200,000 inch dbh (A. Sior, pers. comm.). Adoption of these methods is expected to provide the best treatment effect, thereby minimizing the number of required treatments and total quantity of insecticide required to maintain the health of the valued hemlock trees. The Smoky Mountain National Park has committed to spending $450,000 per year for insecticide treatments to
control hemlock woolly adelgid, and personnel there have calculated the benefit to cost ratio to be 8.82, not including the cost savings from not having to remove hazardous dead trees from heavily traveled portions of the park (Tom Remaley, GSMNP, pers. comm.). US EPA has approved a special local needs label for imidacloprid to be used in the Southern Appalachians at up to 1.2 lb a.i. per acre, a 3-fold increase over previous agronomic field use limits. Best management practices (written by Bayer in collaboration with USDA FS, university scientists, and me) have to be followed by applicators.
Publications
- Cowles, R. S., M. E. Montgomery, and CAS-J Cheah. 2006. Activity and residues of imidacloprid applied to soil and tree trunks to control hemlock woolly adelgid (Hemiptera: Adelgidae) in forests. J. Econ. Entomol. 99: 1258 - 1267.
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Progress 01/01/05 to 12/31/05
Outputs
Imidacloprid application methods and timing were compared for efficacy against the hemlock woolly adelgid in forests. The methods compared were (1) soil injection near the trunk, (2) soil injection dispersed throughout the area under the canopy, (3) soil drench near the base of the trunk, and trunk injection with the (4) Arborjet, (5) Wedgle, and (6) Mauget systems. The applications were made in the fall and the following spring. Adelgid populations on the hemlocks were assessed in the two successive falls following the treatments. Relative to the untreated control trees, all the soil applications resulted in population reductions, but none of the trunk injections did. Fall and spring treatment efficacy did not differ. There were no statistical differences among the soil treatments; reductions by the soil treatments were between 50 - 100% (avg. 80%) by the first fall and 83 - 100% (avg. 98.5%) by the second fall. Analysis of imidacloprid residues using ELISA found
residues in sap, needles and twigs one month to 3 years following application, but sample variance was high within treatments. A laboratory dose-response bioassay using excised, adelgid-infested hemlock branches with cut ends immersed in serial dilutions of imidacloprid determined the median lethal concentration to be 300 ppb, based on an exposure of 20 days. A high degree of suppression of the adelgid on forest trees was associated with residues in hemlock tissue greater than 500 ppb and 120 ppb 1 and 2-years after soil treatment, respectively. Although precise relationships between residues and efficacy are elusive, soil application of imidacloprid resulted in chronic exposure of adelgids to imidacloprid in tissues and their population suppression for more than 2 years following application. Graduate students = 0
Impacts
My research has demonstrated that the most effective treatment of hemlocks for control of hemlock woolly adelgids results from shallow subsurface placement of imidacloprid. Results from this study are being used by forest managers throughout the range for hemlock woolly adelgid infestations in the east. Forest managers and arborists have discontinued using the ineffective Wedgle device, and most of the insecticide treatment efforts for hemlocks are using soil-based application of imidacloprid. For example, treatment protocols for the Forest Pest Management Division of the Pennsylvania Department of Natural Resources are specifying treatment of hemlocks with shallow soil injection, and trees in the Greater Smoky Mountains National Park are being treated with a shallow soil drench of imidacloprid suspension. Adoption of these methods is expected to provide the best treatment effect, thereby minimizing the number of required treatments and total quantity of insecticide
required to maintain the health of the valued hemlock trees. The Smoky Mountain National Park has committed to spending $450,000 per year for insecticide treatments to control hemlock woolly adelgid, and personnel there have calculated the benefit to cost ratio to be 8.82, not including the cost savings from not having to remove hazardous dead trees from heavily traveled portions of the park (Tom Remaley, GSMNP, personal communication). In 2005, Pennsylvania was committed to a similar expenditure for chemical control in its state parks.
Publications
- No publications reported this period
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Progress 01/01/04 to 12/31/04
Outputs
A 7 x 2 factorial imidacloprid efficacy study was conducted at several forest sites in CT. The 7 treatments consisted of 3 types of soil application, 3 types of trunk injection, and an untreated check. The 2-level factor was application timing: either in the fall or the spring. Moderately infested, vigorously growing trees were chosen at least 50 m apart to avoid root overlap and treatment contamination. Insecticides were applied between October 1-29, 2002 and between May 28-June 6, 2003. Kioritz-injected imidacloprid at a rate of 1 gram of active ingredient per inch DBH was applied to the soil as two treatments: either close to the base of the trunk or dispersed within the dripline. Bayer Advanced Tree and Shrub Insect Control (68 ml of product per inch DBH, equivalent to 1gm a.i./DBH, as above) was diluted in 3.8 liters of water and drenched outwards from the trunk of the tree to a distance of 45 cm. Trunk injection applications were made with the Mauget Imicide,
the Wedgle system Pointer (with the new 12% a.i. formulation), and the Arborjet system following the recommended method for each manufacturer. Cold temperatures during the winter resulted in mortality in surrounding untreated trees of 85-95%. Therefore, mortality was not evaluated for the overwintering generation but delayed until July 7-15 when following (progrediens) had developed. The soil applications, especially the fall applications using the Kioritz injector, gave the greatest mortality. The trunk injection methods were ineffective. Evaluations of adelgid populations on treated trees in December 2004 confirmed that chemical control with soil injection is very long-lasting, whereas the numbers of adelgids found on trunk-injected trees were no different from the untreated checks. A follow-up study in Pennsylvania is now investigating whether reduced dosages of imidacloprid (0.125, 0.25, 0.5 and 0.75 g active ingredient per inch DBH) can result in significant reductions of hemlock
woolly adelgid populations.
Impacts
Forest managers are adopting soil application of imidacloprid for controlling hemlock woolly adelgid and for preserving the health of hemlock trees in highly valued stands. They are also avoiding the use of ineffective trunk injection techniques. My data were used by USDA Forest Service personnel to dissuade private companies from injecting imidacloprid into the trunks of every hemlock in the Smoky Mountains National Forest, a proposal that would have cost several million dollars.
Publications
- Ward, J. S., Montgomery, M. E., Cheah, C.A.S.-J., Onken, B. and Cowles, R. S. 2004. Eastern hemlock forests: guidelines to minimize the impacts of hemlock woolly adelgid. USDA For. Service Publication NA-TP-03-04. Northeast Area State and Private Forestry, Morgantown, WV.
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Progress 01/01/03 to 12/31/03
Outputs
A 7 x 2 factorial imidacloprid efficacy study is in progress at several forest sites in CT. The 7 treatments consist of 3 types of soil application, 3 types of trunk injection, and an untreated check. The 2-level factor is application timing: either in the fall or the spring. Moderately infested, vigorously growing trees were chosen at least 50 m apart to avoid root overlap and treatment contamination. Insecticides were applied between October 1-29, 2002 and between May 28-June 6, 2003. Kioritz-injected imidacloprid at a rate of 1 gram of active ingredient per inch DBH was applied to the soil as two treatments: either close to the base of the trunk or dispersed within the dripline. Bayer Advanced Tree and Shrub Insect Control (68 ml of product per inch DBH, equivalent to 1gm a.i./DBH, as above) was diluted in 3.8 liters of water and drenched outwards from the trunk of the tree to a distance of 45 cm. Trunk injection applications were made with the Mauget Imicide, the
Wedgle system Pointer (with the new 12% a.i. formulation), and the Arborjet system following the recommended method for each manufacturer. Cold temperatures during the winter resulted in mortality in surrounding untreated trees of 85-95%. Therefore, mortality was not evaluated for the overwintering generation but delayed until July 7-15 when following(progrediens) had developed. The soil applications, especially the the fall applications using the Kioritz injector, gave the greatest mortality. All the trunk injection methods were ineffective. Mortality will be evaluated again in December and the following Spring. Anticipating the effect of winter mortality on evaluation of of the treatments, we used an immunological method to measure imidacloprid residues (EnviroLogix ELISA test kit). Single branches of 45 cm length were cut from fall-treated trees between May 2-6 and all study trees on July 7-15 and August 20-27, 2003. Sap was extracted at the field site using a pressure chamber and
200 p.s.i. nitrogen. Volumes of 250-700 microliters were obtained for each sample with 100 microliters required for imidacloprid determination. The ELISA assay of sap indicated that soil-based application of imidacloprid resulted in good mobilization and persistance in branches. With the Mauget system injections, a relatively short-lived peak of imidacloprid was found in the branch sap. Residues from the other two trunk injections were not detectable. Detected concentrations for all treatments were low, <20 ppb. Graduate Students=0
Impacts
Forest managers may adopt soil application of imidacloprid for controlling hemlock woolly adelgid and for preserving the health of hemlock trees in highly valued stands (such as trees near picnic areas and along streams important for spawning fish).
Publications
- No publications reported this period
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