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Hemlock woolly adelgid resistance E. Preisser, B. Maynard, R. Casagrande. No reported resistance in Tsuga canadensis or T. caroliniana. Western hemlock. W. hemlocks resist eastern HWA and E. hemlocks resist western HWA. Mountain hemlock. Difficult to grow in northeast.
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Hemlock woolly adelgid resistanceE. Preisser, B. Maynard, R. Casagrande No reported resistance in Tsuga canadensis or T. caroliniana
Western hemlock W. hemlocks resist eastern HWA and E. hemlocks resist western HWA
Mountain hemlock Difficult to grow in northeast
Chinese and Japanese hemlocks are HWA-resistant (But poor choice for landscape or forest)
Todd Caswell Richard Casagrande Laura Ingwell Brian Maynard Evan Preisser Laura Radville Are some eastern hemlocks resistant to HWA?
In FOREST stands with ≥95% mortality Mature (>10 m) trees Appeared relatively healthy largely free of HWA and elongate hemlock scale INNATE OR ENVIRONMENTAL? “Potentially resistant hemlock”
Propagate cuttings Grow under identical conditions Infest with HWA under controlled conditions Evaluating hemlock resistance
Rooting hemlocks Two variables: time of season and hormone treatments
Results of 2006 winter cuttings (number rooted/number treated)
2007 rooting results Treatment 0 = ControlTreatment 1 = 1:1 ratio of Dip ‘n Grow to water Treatment 2 = 1:2 ratio of Dip ‘n Grow to water
Mark Mayer’s NJ “bulletproof stand” Courtesy of Mark Mayer
2007 sample sites100 cuttings each from • 6 CT Trees • 5 NJ Trees (Mark Mayer) • 2 PA Trees (Scott Stitzer) • 1 MD Tree (Dave Mausel) • 4 Control Sites (MA, NY) 18 Trees (1800 cuttings)
2007 rooted cuttingsheld for testing in spring 2009 • Allow additional time to recover from rooting and outgrow field environmental effects • Provide 12 months of growth under standardized conditions • Improve timing of plant growth and HWA inoculation
HWA inoculation tests – 2009 • Inoculate all rooted cuttings with HWA in early spring • 3 groups: control, resistant, and cuttings from western hemlocks • Assessed HWA settlement and survival
2010 HWA inoculation results 6 4 HWA crawlers/cm) 2 0 Resistant Control
Progress towards providing nurseries with plants • Planning third large-scale test of HWA resistance in spring 2011 • Carried out large-scale grafting experiment in 2010 – results in summer 2011 • Set up ‘hemlock hedge’ of resistant trees for cuttings and assessment of growth form and HWA resistance