Univ. Vermont

(Entomopathogenic Fungii)

$34,514

Univ. N. Carolina

(Native Predators)

$30,000

VPI and State Univ.

(Native Predators)

$35,000

NE Forest Exp. Sta.

(Predators from China)

$20,000

$59,462

CT Agric. Exp. Sta.

(Predators from Japan)

$15,000

$60,000

$85,000

NJ Dept. of Agric.

(Rearing Methodology)

$15,547

$34,315

$50,000

SUBTOTALS:

$15,000

$50,000

$110,061

$128,901

$135,000

GRAND TOTAL:

$438.962

1. Finch-Pruyn Company – NY based timber company (also provided $10,000 to the National Arbopretum in support of hemlock genetic resistance research)
2. USDI Geological Survey – Biological Resources Division
3. USDA Forest Service – Forest Health Technology Enterprise Team
4. USDA Forest Service – Special Technology Development Program
5. USDA Forest Service – Cooperative Suppression Program 

The Effects of Predators on the Hemlock Woolly Adelgid in North Carolina and Virginia

Matthew S. Wallace and Fred P. Hain
North Carolina State University Department of Entomology

Cage exclusion experiments were performed to determine any predator effects. Both Virginia sites had no visible predator effects but their was evidence for a predator effect at Hanging Rock State Park in North Carolina. The most abundant predators at this site were chrysopids so they may be having more of an effect on adelgids than previously anticipated. The cecidomyiid is probably not a significant predator of adelgids at the Virginia sites because it is not synchronous with the adelgid life cycle. The highest cecidomyiid densities were in late June (0.02/cm) which is after most of the sistens nymphs have hatched and the progediens adults are starting to die off. However, the generally high diversity of native predators may warrant research that studies interactions with any introduced foreign predators. Fred Hain (919) 515-3804; Fax: (919) 515-7273; Email: fred_hain@ncsu.edu

To date, approximately 54 species of lady beetles have been collected from hemlock infested with Adelges tsugae in Yunnan, Sichuan, and Shaanxi Provinces in the Peoples Republic of China. Twenty-one of these species have been described as new to science (Yu and Montgomery, in press).

Three of these species have been imported for further evaluation in the U.S. Forest Service Quarantine Laboratory in Ansonia, CT. Scymnus sinuanodulus has now been reared through two complete generations in the quarantine laboratory. It is a univoltine species that lays eggs during the spring that hatch after about 10 days and complete development in 40 days. Adults can live two or more years. Field observations and laboratory evaluations indicate that its host range is restricted to adelgids with a preference for hemlock woolly adelgids over adelgids on pine. Over 4,000 of this species were reared in the laboratory this past year. S. camptodromus egg laying begins in the spring and continues into fall; however, the eggs have an obligate diapause and must overwinter before they will hatch. This behavior has made rearing difficult and this colony may be discontinued. A third species, S. ningshanensis was collected from Shaanxi, the northern-most province, and appears very promising for the northern range of hemlock woolly adelgid in the eastern U.S. Michael E. Montgomery (203) 230-4331; Email: mem1023@aol.com; or Wenhua Lu (203) 735-8495; Email: wenhua@uriacc.uri.edu

In 1988, the NJDA, supported by funds from the USFS and NJDEP, Bureau of Parks and Forestry, established eleven permanent study plots (PSP) in native hemlock stands throughout northern New Jersey. The plots, which were divided into three subplots, consisted of those which were lightly or heavily infested with HWA and noninfested. Data which is collected each year from each subplot includes percent of new growth, HWA population levels, age, other pest insects attacking the trees and DBH. In 1990, one plot was dropped from the program and two additional plots were added. In 1994, crown ratings were included in the data collection and transects using compass bearings have been established in each hemlock stand containing the PSP’s in an effort to gain a more accurate picture of tree mortality throughout the stand. It wasn’t until 1992 that tree mortality became evident; but since then, plots which were heavily infested when established in 1988 are declining rapidly and are now showing an average of 50-80% mortality. This year, Pseudoscymnus tsugae was released in six of the PSP’s set up in 1988. Besides the six PSP’s, releases were made in eight additional hemlock stands.

In May 1997, the laboratory received 100 adult P. tsugae from the Connecticut Agricultural Experiment Station (CAES). The primary objectives of the predator production program were to establish a back-up colony to the CAES’s colony, develop an efficient mass production technique and to provide predators for inoculation of HWA infested areas in New Jersey. A total of 600 beetles was produced before the HWA went into summer dormancy in July. Those beetles were to be used to initiate the mass rearing program once the HWA became active in the fall. When the HWA resumed activity, the beetle responded and production increased. With beetles being produced at a level of between 5,000 and 7,000 per week by early winter, a dependable storage method needed to be developed to hold the surplus adults for spring release. The storage method adopted for adult beetles was highly successful allowing the laboratory to hold adults up to five months with no losses. By July 1998, the laboratory was able to produce 85,000 adult P. tsugae. Of those, 75,000 were released in New Jersey, 5,000 were sent to the CAES and 5,000 were held as rearing stock.

Since production hinges on field collected host material, the laboratory has been evaluating various alternative methods for laboratory rearing. To that end, we are now growing hemlocks in containers from bare root 4-inch seedlings to 18-inch plants in one year and have 2,000 potted hemlocks in various stages of growth. Very early work to inoculate those plants with HWA has begun and will be an important focus of our work when the adelgid emerges from aestivation in October 1998. Robert Chianese (609) 530-4192: Email: agpchia@ag.state.nj.us; Daniel Palmer Email: agppalm@ag.state.nj.us; and Mark Mayer Email: agpmaye@ag.state.nj.us

From a sizeable bank of field-collected pathogens, researchers at the University of Vermont have made significant progress developing isolates for use against HWA. Thousands of symptomatic adelgids were collected from hemlocks in MA, CT, NJ and VA. Each was cultured in the laboratory and fungal isolates recovered and identified. None of this research could have been done without the diligent assistance of Charlie Burnham, MA, George Koeck, NJ, Tim Tigner, VA and David Orwig, CT.

First, each fungus was tested for pathogenicity against a laboratory culture of aphids. Previous research had shown that the aphids responded in a manner identical to HWA. From these results scientists were able to select a dozen isolates representative of several genera for direct testing on field-collected HWA. This research was recently completed in VA and results are extremely promising. Three isolates have been chosen for further development.

Information is already available on how to mass-produce each isolate for operational use, data is now needed to characterize the physiology of these isolates to facilitate timing of field applications. Of equal importance is data on how they perform in conjunction with HWA predators such as Scymnus sp. and Pseudoscymnus tsugae. No single approach is the answer to management of HWA. But if each is used in a total IPM program chances of successful management of this serious pest will be enhanced. Now, Vermont researchers propose to test these insect-killing fungi operationally, and to conduct trials to determine their compatibility with these tiny predatory beetles. Previous links with companies that produce fungi for use against other economically important insects will aid in developing effective formulations for use of these pathogens in forests and urban communities. It is anticipated that this research will be closely aligned with other efforts conducted by the HWA Working Group throughout the region. It is also expected that this work will assist future research in biological control using entomopathogenic fungi in a large-scale forest situation. Bruce L. Parker (802) 656-5440; Fax: (802) 658-7710; Email: bparker@zoo.uvm.edu

Drs. Mark McClure and Carole Cheah, assisted by Robert Ballinger, Beth Beebe and Mary Klepacki, and in cooperation with Dr. Tim Tigner of the Virginia Department of Forestry, conducted studies in 1997 at three sites in Connecticut and one in Virginia to evaluate the ability of Pseudoscymnus tsugae to reduce local densities of hemlock woolly adelgid. Adelgid egg masses on tagged tips were counted in spring in separate, but similar, release and control areas and on control tips prior to bagging for exclusion of predators in the release site. Between 2,400 and 3,600 adult beetles were then released at each site. Sites were visited monthly thereafter for foliage inspection and dispersal monitoring. In spite of a much cooler spring than usual, reproduction in the field was observed with larvae being recorded from July to mid-September. Adults were found in early October on infested, non-release hemlocks in the release area, up to 102m away. All sites were revisited in the fall when counts were made of developing adelgid nymphs on new and past year’s growth on tagged tips in both the release and control areas. The results showed remarkable short-term impact on adelgid densities by P. tsugae. Adelgid densities within bagged controls were very similar to densities in control areas indicating the minor role of native predators and cage affects. Comparison of these control densities with those of release branches indicated an average depression of 63 (47-83)% reduction of adelgid densities on new growth. Between 62-87% reduction in adelgid densities was noted on older growth. On April 30, 1998, an overwintering adult was found in the Virginia release area (elevation >2000 ft) subject to ice storms. Overwintering adults were also recovered easily at two of the Connecticut release sites on May 7, 1998, but not at the third site which had a much older and heavier infestation with declining tree health.

Current studies are investigating the long-term ability of P. tsugae to disperse from a central release tree and to suppress adelgid populations following a single release of 10,000 adult beetles in a relatively isolated 10-15 acre stand of recently infested hemlock. In spring 1998, sites were established in Connecticut, Virginia and New Jersey, the latter in cooperation with Mark Mayer and Dan Palmer of the New Jersey Department of Agriculture. At each site, adelgid egg masses were counted on the release tree and on trees at 50m intervals along 200m transects prior to beetle release. Establishment, reproduction and distribution of P. tsugae and adelgid population suppression along the transects and adjacent trees will be followed during the course of this and subsequent seasons. Tree health is also being rated according to the system developed by Dr. Tigner in 1997.

Thus far, laboratory and field studies have determined that P. tsugae possesses many attributes of a successful biological control agent including an ability to significantly reduce adelgid densities on release branches during the year of release. However, even though P. tsugae has overwintered successfully for three years in Connecticut and Virginia, beetle numbers in spring are too few to indicate sustained attack on adelgid populations. Studies during the next two years will determine if an initial release of a much larger number of beetles will affect long term control of hemlock woolly adelgid, and if P. tsugae will be a solution, or even a part of a solution to the adelgid problem. Mark McClure (860) 683-4979; Fax: (860) 683-4987; Email: mmcclure@caes.state.ct.us

Zilahi-Balogh, G., S.M. Salom, and L.T. Kok: Laricobius nigrinus (Coleoptera: Derodontidae) adults were collected at the Lost Lake Conifer Seed Orchard owned and operated by Western Forest Products Ltd., near Victoria, BC, in March 1998 and a colony was established on Adelges tsugae (Homoptera: Adelgidae) (HWA) at the quarantine facility at the Prices Fork Research Center of Virginia Tech. L. nigrinus was reared in environmental chambers on eastern hemlock in ventilated plastic containers containing sterilized moistened peat between 13 and 15°C, 85-95 RH and 12:12 L: D photoperiod. L. nigrinus successfully mated, oviposited and developed on a diet of A. tsugae indicating it is a suitable host.

As biology of L. nigrinus has not been described previously in the literature, development is described from laboratory observations. Eggs were laid singly in the woolly ovisacs in the spring. Egg development was between 9 and 11 days between 13 and 15°C. Time from egg deposition to adult emergence ranged from 56 to 63 days between 13 to 15°C. Four instars were determined from head capsule measurements. All life stages of L. nigrinus were observed to feed on HWA. First and second instar larvae fed only on eggs of HWA, while third and fourth instars and adults fed on all life stages of HWA. Mature fourth instars migrated to the soil to pupate. Emergent adults stayed in the soil and exhibited negative phototaxis. From this behavior we believe they are summer aestivating. At present we have an F1 generation of L. nigrinus that is summer aestivating. Host preference and suitability studies will be conducted in spring 1999 when these adults begin reproducing in the lab. Scott Salom (540) 231-4029; Fax: (540) 231-9131; Email:salom@vt.edu

Cunningham A., S.M. Salom and L.T. Kok: Primary focus of research in 1998 was in studying the feeding habits of A. obliterata and H. axyridis on Adelges tsugae (hemlock woolly adelgid, or HWA). This included a complete account of the voracity of H. axyridis on HWA in the egg, adult, and developing nymph stages, and initial work on its voracity on green pea aphids (Acyrthosiphon pisum). Adult beetles consumed as many as 98 HWA eggs in a 24-hour period and over 40 adults or developing nymphs. Initial work was also done in analyzing the short-term diet preferences of H. axyridis. Though studies are incomplete, initial results indicate that pea aphids are preferred slightly, though H. axyridis tends to attack the first prey encountered regardless of species. A survey was undertaken to analyze the increased number of H. axyridis larvae found on HWA populations in the spring. The survey showed populations of over one larva per infested branch in early May, tapering off toward zero in late June.

The European ladybird Aphidecta obliterata was recommended for evaluation as an HWA biocontrol agent due to its preferences to prey on adelgid hosts. Encouraging initial voracity results were found with Aphidecta obliterata imported from British Colombia (consuming more than 35 HWA eggs per 24 hours), although rearing methods must still be perfected. From three adults obtained in mid-spring, mating was observed and viable eggs were laid at 18°C at a 12:12 (L:D) photoperiod. No eggs were produced by colonies obtained in the summer, possibly indicating that eggs are normally laid only in the spring. In late summer, during the aestival diapause of HWA, eastern spruce gall adelgids were successfully substituted as a foodsource for A. obliterata, which consumed as many as 45 individual adelgids per 24 hours. Scott Salom (540) 231-4029; Fax: (540) 231-9131; Email:salom@vt.edu

Salom, S.M., J.W. Neal, and W.T. Mays: We are attempting to determine the influence of temperature and photoperiod on initiation and duration of aestival diapause in HWA sistens. The goal is to identify conditions in which HWA can be continuously reared without the constraints of a 4-month diapause. We can report on two experiments completed and an ongoing 3rd experiment.

Diapause 1997: All sistens exposed to a photoperiod of 16:8 (L: D), at 12, 17, and 22°C, went into aestival diapause. At the 12:12 photoperiod, only adelgids preconditioned at 12 and 17°C, and kept at those temperatures through the sistens lifestages, developed with a reduced occurrence of diapause. At 12°C, over 40% molted at least once within 24 days. At 17°C, duration of diapause lasted 3 months as opposed to 4 months documented in field studies. These data were a first indication that aestival diapause is not obligative, but rather induced by environmental cues.

Diapause 1998 - Experiment 1: All HWA progrediens were reared at 12°C treatments and three photoperiods (12:12, 11:13, and 10:14). Maintained under the same conditions, no sistens entered aestival diapause. 100% of all 1st instar sistens molted within 49, 63, and 63 days at 12:12, 11:13, and 10:14 (L:D) photoperiods, respectively.

Development progressed more quickly at 12:12 than at the other two photoperiods, taking only 63 days to go from settled 1st instar nymph to adult. Time of development was lengthened with a decrease in photoperiod.

Diapause 1998 - Experiment 2: Sistens, preconditioned as progrediens at 12 and 14.5°C, are currently being evaluated at these temperatures and three photoperiods (12:12, 13:11, 14:10). In addition, another group of

adelgids in which progrediens developed outdoors and were moved in to 12 and 14.5°C chambers prior to sistens egg hatch are also being tested. Data from the preconditioned group is similar to data collected in 1997, where ca. 50% of the sistens molted and the rest are in diapause. The difference here is we are getting development at a warmer temperature of 14.5°C. All sistens that came from outdoor developing progrediens are aestivating. This confirms pre-conditioning of progrediens is essential for initiating diapause in the sistens stage. Scott Salom (540) 231-4029; Fax: (540) 231-9131; Email:salom@vt.edu

CHEMICAL CONTROL OF HWA

The Kioritz® is a hand-held soil injector made for injecting fertilizer and systemic pesticides into the root zone of trees and shrubs. The injector holds up to 90 ounces of solution and weighs approximately 6 lbs. The injector tip is placed 3-8 inches deep in the soil around the base of the plant and the dispensing knob is struck with the hand to deliver the required amount of solution around the targeted plant. The Koritz® advantage is that it requires no power spray equipment and a fraction of the water is used for making soil injection treatments as compared to conventional power soil injection treatments.

Imidacloprid, the active ingredient contained in Merit®, is a systemic chloronicotinyl insecticide used for control of insect pests in turf and ornamentals. Soil applications of imidacloprid can be used to control a wide range of tree and shrub pests including HWA and scale insects. Imidacloprid translocates systemically and its mode of action is by ingestion when applied as a soil application. The Kioritz® is not intended to replace conventional treatment methods such as power spraying or power soil injection, but it does offer lawn/landscape professionals and arborists another option for treating trees and shrubs. Bruce Steward, Bayer Corporation (610) 925-0472; Fax: (610) 925-0473

HEMLOCK GENETICS

Researchers at the U.S. National Arboretum are attempting to develop hemlocks resistant to HWA by crossing the susceptible eastern native hemlock species, T. canadensis and T. caroliniana with the reportedly more resistant Asian speices, T. diversifolia, T. chinensis, and T. seiboldii. Suitable parent trees were identifed at the U.S. National Arboretum, Washington, DC, the Morris Arboretum of the University of Pennsylvania, Philadelphia, PA, and recently at the Orland E. White Arboretum, Blandy, VA. Over 2000 seedlings have been generated from controlled pollinations. Morphological traits have been of limited use in identification of putative hybrids. Both molecular and biochemical approaches are being utilized to develop rapid and accurate screening techniques of large numbers of progeny. DNA sequence data derived from cloned Randomly Amplified Polymorphic DNA (RAPD) bands have been used to generate species-specific PCR primers that are being used to test paternity in selected crosses. Frank S. Santamour is pursuing biochemical research to verify the basis of resistance/susceptibility. The USNA team has received two grants through the FHTET and includes: Alden M. Townsend; Susan E. Bentz (plant breeding); Margaret R. Pooler (molecular); Frank S. Santamour, Jr. (biochemistry); Floral and Nursery Plants Research Unit, U.S. National Arboretum, Washington, DC. S.E. Bentz (301) 344-4113; Email: sbentz@ars-grin.gov

FOREST HEALTH

Dave Orwig, Matt Kizlinski and David Foster of the Harvard Forest in Petersham, MA, have initiated a study in central Connecticut examining the timing, magnitude, and duration of N cycling changes in six hemlock stands infested with HWA vs. two uninfested control stands. Closed-top soil cores are being examined for N analysis, pH, texture, and gravimetric soil moisture. In addition, ion exchange resin bags are being used in situ to monitor N availability and bags located out of plot will be examined for potential nitrate export. Soil temperature is being monitored at two depths at various locations within each site and hemispherical photographs will be used to calculate the degree of canopy openness and to create an index of light availability. The 1998 data will be used as baseline information for comparison with future data as the stands continue to deteriorate.

Our landscape level project has continued in the summer of 1998 and we now have extensive forest composition data from 116 mapped hemlock stands located within a 6000 km² transect that stretches from Long Island Sound to the Massachusetts border. Data includes hemlock mortality, degree of HWA infestation, average hemlock crown vigor, hardwood composition, humus depth, hemlock size and density info, and sapling and seedling information. All information is currently being incorporated into a GIS analysis of landscape-level, biological, edaphic, and historical factors that control the HWA-induced damage patterns observed in hemlock.

The initial stand-level results examining mortality, microenvironmental changes, and seedling dynamics were published in the Journal of the Torrey Botanical Society 125:60-73. (Forest response to the introduced hemlock woolly adelgid in southern New England by David A. Orwig and David R. Foster.)

David Orwig (978) 724-3302 ext. 250; Email: orwig@fas.harvard.edu

We are currently improving the methodology that we developed to monitor hemlock condition in the New Jersey Highlands (for a summary see Royle, D.D. and R.G. Lathrop, 1997. Monitoring hemlock forest health in New Jersey using Landsat TM data and change detection techniques. Forest Science 43(3):327-335). We are incorporating multiple years of Landsat TM imagery and topographic data derived from a digital elevation model (DEM) to quantify the extent, severity and rate of hemlock defoliation from 1984 to the present. Our mapping and monitoring efforts will be extended throughout northern New Jersey, the Hudson Highlands of New York State, and the Delaware Water Gap National Recreation Area (DEWA) along the PA/NJ border. In cooperation with the National Park Service and the USGS Biological Resources Division, the operational efficacy of the improved methodology will be tested in DEWA and in the Shenandoah National Park in Virginia.

We will be using the resulting hemlock condition maps and a GIS to investigate the effect of site moisture on defoliation by HWA at the sub-stand level. Variables related to site moisture include soil characteristics, percent slope, aspect, and landscape position. Denise Royle (908) 932-1582; Email: royle@crssa.rutgers.edu

We have completed our study of the impacts of adelgid infestation on light availability and nitrogen (N) cycling rates in hemlock-dominated forests in Connecticut and Massachusetts. Data were colleceted at six formerly hemlock-dominated sites spanning a continuum from 0% to 100% mortality. Adelgid-induced hemlock mortality led to increased light availability and increased hardwood seedling regeneration (mostly black birch) within six to ten years after the onset of hemlock decline. Differences in soil organic matter, total soil carbon (C) pools, and total soil nitrogen (N) pools between impacted and non-impacted sites were not associated with hemlock decline. However, N cycling rates increased dramatically with adelgid-induced hemlock mortality, suggesting that a pulse of nitrate leaching from soil is likely in areas experiencing adelgid infestation. A manuscript with results from this study is currently in review and should be published before the end of 1999. Jennifer Jenkins (610) 975-4032; Email: jjenkins/ne@fs.fed.us

Within DEWA, hemlock is common on relatively cool, moist sites, and many of the largest stands occur on steep slopes surrounding cascading streams. These "hemlock ravines" are highly valued because of their distinctive aesthetic, recreational and ecological qualities. In 1989, HWA was detected within the Park. At the request of the National Park Service, the Biological Resource Division of the USGS conducted a comparative study designed to determine the potential long-term consequences to aquatic communities of the suspected transition from hemlock-dominated forests to mixed hardwood forests. We conducted a landscape analysis of the Park using Geographic Information Systems (GIS), and used the results to select 14 hemlock and hardwood site pairs that were similar in topography (i.e. slope, terrain shape, aspect, light levels) and stream size, but differed in forest composition. This paired watershed approach provided a powerful means to discern the influence of hemlock forests on stream communities. This study would provide an aquatic perspective on what we stand to lose in terms of biological diversity, should hemlock forests die.

We collected a total of 178 aquatic invertebrate species in DEWA streams. We found streams draining hemlock forests supported more aquatic invertebrate species than streams draining hardwood forests. Approximately 17% of the invertebrate species were either strongly or moderately associated with hemlock, and three species were found only in streams draining hemlock forests. In addition, the trophic composition of aquatic invertebrate communities was different between forest types suggesting that ecosystem function may also be disrupted by changes in forest composition. Specifically, streams draining hemlock forests had a higher proportion of predators and lower proportion of grazing invertebrates than corresponding hardwood forests. Similarly, fish trophic structure differed, with streams draining hemlock supporting a significantly larger number of predators. In contrast, fish diversity was higher in streams draining hardwood forests though two species, brook trout and creek chub, were more common in streams draining hemlock forests. Evidence to date suggests hemlock may modify the stream environment by creating a larger variety of microhabitat types and/or a more stable thermal and hydrologic regime. Based on these results, we predict a significant decline in average within-site and park-wide diversity should widespread hemlock mortality result from the HWA infestation. Craig Synder (304) 724-4468; Email: craig_snyder@usgs.gov; Robert Ross (717) 724-3322; Email: ross@epix.com

The hemlock woolly adelgid (Adelgid tsugae) (HWA) was first detected in Shenandoah National Park in 1988 along the Thornton and Frazier Hollow drainages by trail maintenance personnel. Coincidentally, this was a time of successive droughts. Indeed, the hemlocks (Tsugae canadensis) were affected in that initial period by HWA, hemlock borer (Melanophila fulvoguttata), and root rots. The result in those early years was the quick fading and death of many individuals. Though the heightened borer activity faded away with resumption of normal precipitation in following years, the presence of HWA quickly grew widespread within the Park. Overall health of hemlocks has increasingly deteriorated.

Park managers initiated a detection survey in 1990/91 to determine the HWA distribution. The findings were dramatic. All 94 of our hemlock study sites throughout the Park contained HWA. Detection sampling was dropped after 1991, yet annual hemlock crown health monitoring was continued during the years 1992-1996. Protocols were recommended by John (Rusty) Rhea; adapted from maple crown health (USDA-FS FPM, Region 8). This is an excellent, relatively inexpensive method to gather an extensive overview of tree and stand health. It has provided valuable trending or indexing of our hemlocks. On the down side, it is indirect to the question whether HWA is the morbidity cause. Rather, crown health can be considered the composite of impacts from drought, other weather/climate, air pollution, acid deposition, site disturbances, and general insects and disease.

Again in the 1997 field season we combined stand health monitoring with direct observations for the presence of HWA. This was accomplished by examining one live hemlock for HWA on every 10 live/dead trees surveyed for crown condition. Because it is difficult to reach and assess twigs from upper branches, most insects we observed were from suppressed trees within reach from the ground. Of the 94 areas visited in 1991, 78 were revisited in 1997. These observations for HWA presence helped us create some initial findings and confirm earlier anecdotal ones as follows:

• HWA was detected in 91% of the areas. This is down from 100% in 1991.
• Of 557 hemlocks observed for HWA, 34.8% had heavy infestations, 20.5% medium, 25.5% lightly infested, and 17.1% had no evidence.
• The heaviest infestations seemed to occur at lower elevations. The heaviest HWA infestations were at Pass Run along US Hwy 211, Brokenback and Cedar Runs on the east side, and Riprap Hollow on the west side.
• The areas absent of HWA appeared to be in our highest elevation sites, particularly in the central part of the Park (also generally highest). These included Millers Head Trail, the Appalachian Trail between Big Meadows Campground and Fisher’s Gap, and Meadow School Road and Mill Prong Trails, just off Skyline Drive.
• Confirming the phenomenon of lower elevations having greater chance for current HWA infestations were our stands that follow drainages over extensive elevation drops. These include Piney River, Limberlost/White Oak Canyon, Lewis Falls, Staunton River, Devil’s Ditch, South River, and the North Fork Moormans River.

The first year we observed the elevation differential of HWA infestation was in 1997. We wondered at first whether this was a short-lived occurrence based on a specific weather event. However, in 1998, John Young (USGS – Biological Resource Division, Leestown, WV), found that subsequent statistical analysis of our annual crown health surveys indicates this as a longer-term trend. We know that upper elevations are not immune to HWA infestation, as indicated by 1990/91 field data. Yet, several areas once infested have lesser infestation levels at this time; and Young’s work indicates this elevational difference is significant. We believe this is due to late winter/early spring cold snaps that destroy HWA when they become less protected from cold weather.

In spite of this area of hope, parkwide hemlock crown health is deteriorating. Note Table 1 statistics. Recognizing this, we have doubled our protection efforts, expanding both the number of trees we treat and the number of applications per year. As with other land ownerships, our operational treatment is limited to those areas we can reach from roads and load-bearing trails with hydraulic spray equipment. We use insecticidal soap and horticultural oil in those settings. We are also preparing to reach other hard to reach high-value individuals using systemics such as AceCaps® and Merit 75WP® on a case by case basis. Our objectives in HWA suppression are to: (1) preserve a wide range of seed source for future re-establishment; (2) preserve individuals in historically important cultural sites; and (3) preserve individuals in highly prized recreation areas.

Table 1. Hemlock Crown Health Data for Shenandoah National Park, Virginia*

1990-1991

77.4

12.9

2.1

2.1

5.4

1992

21.0

56.0

18.3

2.2

2.5

1993

13.3

39.2

42.7

4.0

0.8

1994

1.1

24.3

64.3

9.2

1.1

1995

4.8

27.9

54.4

7.6

5.3

1996

8.3

25.9

43.0

19.1

3.6

1997

9.9

26.9

39.3

8.8

15.0

James Akerson (540) 999-3496; Email: james_akerson@nps.gov; Gary Hunt (540) 999-3490; Email: gary_hunt@nps.gov