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