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 HWAand 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)
Are some eastern hemlocks resistant to HWA?
Todd CaswellRichard
CasagrandeLaura IngwellBrian MaynardEvan Preisser Laura Radville
Preisser et al. (2008) sampled 142 hemlock stands in 2005
“Potentially resistant hemlock”
In FOREST stands with ≥95% mortality
Mature (>10 m) trees Appeared relatively
healthy largely free of HWA and elongate hemlock
scale
INNATE OR
ENVIRONMENTAL?
Evaluating hemlock resistance
1. Propagate cuttings2. Grow under identical conditions3. Infest with HWA under controlled
conditions
CT sample sites
Burnham Brook, CT
Lyme, CT
Madison, CT
Rooting hemlocks Two variables: time of season and hormone
treatments
Propagation bed
January 2006 cuttings
Spring 2006root ratings 0-3
Results of 2006 winter cuttings (number rooted/number treated)
SITE CODEHORMEX
451:1 DIP 'N
GROW1%
KIBAHORMODIN
3 CONTROLAA 0/18 12/18 2/18 0/10 0/18
BB 1 11/17 14/17 6/17 8/17 1/17BB 2 9/15 8/15 5/15 10/16 2/12M 1 2/14 6/15 0/15 0/15 NAM 2 5/7 4/7 5/7 0/7 NAOL 1 3/7 1/6 2/6 0/6 NAOL 2 0/17 3/17 0/17 0/16 NA
Totals 30/95 48/95 20/95 18/87 3/47
% Rooted 31.58% 50.53% 21.05% 20.69% 6.38%
13.93 35.89 31.920.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
45.00
0 1 2
Treatment
Mea
n %
Roo
ted
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
Rooted cutting in June
HWA inoculation
Inoculated plant
2006 HWA results
0
20
40
60
80
100
# se
ttled
HW
A/c
uttin
g +/
- SE
5 5 5 4 42 23
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
2009 HWA inoculation results
2010 HWA inoculation results
0
2
4
6
Resistant Control
HWA
craw
lers
/cm
)
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