Distribution and Impact of Sirococcus Shoot Blight
of Eastern Hemlock
Isabel A Munck, USDA Forest Service , Northeastern Area State and Private Forestry, Forest Health Protection
William Ostrofsky, Maine Forest Service
Denise Smith and Glen Stanosz, Department of Plant Pathology, University of Wisconsin-Madison
INTRODUCTION
PRELIMINARY RESULTS
Sirococcus fungi infect several conifer species killing and
deforming new growth. Damage is more noticeable in
regeneration but lower crowns of mature trees are also
affected. Sirococcus shoot blight can become widespread and
cause tree mortality if weather conditions are favorable. In
2009, eastern hemlock was confirmed to be a new host of the
pathogen Sirococcus tsugae. This pathogen causes defoliation
and shoot blight of an ecologically invaluable resource
(Figs.1&2) already threatened by exotic insect pests hemlock
woolly adelgid (HWA) and elongate hemlock scale (EHS). The
geographic distribution, impact, and epidemiology of this
newly described disease of eastern hemlock are unknown.
Thus, the specific objectives of this project are to:
• 39 of 41 FIA plots had seedlings with Sirococcus shoot blight symptoms
• In contrast, only 4 of the FIA plots were infested with both EHS and HWA,
3 plots were infested with HWA only
• 71% of seedlings had Sirococcus shoot blight symptoms
• Shoot blight severity varied from 1 to 75% of shoots affected, but for
most seedlings blight severity was limited to < 10% of shoots. Similarly,
defoliation was limited to < 25% of the crown for most seedlings (Fig. 4)
• For some locations disease symptom can be quite severe, with mean
blight severity, or percentage of shoots affected, in the 26-50% range
• Blight severity was correlated with hemlock seedling and tree density.
Crown defoliation was correlated with hemlock tree density, basal area,
and Sirococcus shoot blight severity (Table 1)
• Of 41 samples collected from FIA plots 17 produced Sirococcus spores, 15
samples yielded cultures, and 13 were positive with PCR (Fig. 3)
• In permanent plots, disease symptoms appeared in mid-June and
progressed until the third week of July. On average, 11-25% of the shoots
were blighted and 1-10% of the crown was defoliated during both 2011 &
2012 (Fig. 5)
A
METHODS
B
Acknowledgements
The authors wish to thank Wayne Searles, Justin
Williams, Maria Vasta & Michael Simmons for
field assistance, Randy Morin & Liz LaPoint for
FIA plot assistance, & Rebecca Lilja for the map.
Figure 2. Progression of Sirococcus shoot blight
from (A-F). Current year shoots emerging next to
infected previous year shoots (A). Current year
shoots become droopy (B) and are killed as the
summer progresses (C-E). Infected seedlings can be
severely defoliated (E & F).
A. 6/17/11
Delineation of geographic range: From June-August 2012, 41
plots on public lands with eastern hemlock regeneration
established by the USFS Forest Inventory and Analysis
Program (FIA) were surveyed (Fig. 3).
At each plot, 20
seedlings defined as trees taller than 1 ft but smaller than 1
inch in diameter at breast height were sampled along
transects or quadrants. Shoot blight severity and defoliation
were assessed on a 0-5 scale for each seedling (Fig. 4).
Pathogen identification: Samples from each plot were kept
cool and shipped overnight to UW-Madison. Upon arrival,
samples were placed in moist chambers to facilitate fungal
sporulation and obtain pure cultures. The pathogen was
identified using DNA-based techniques.
Long term monitoring: Five permanent plots (each with 20
trees) were established in the USFS Massabesic Experimental
Forest (MEF) during the summer of 2011 will be revisited to
determine year-to-year variation of disease severity and
crown defoliation. Samples were also collected each month
from permanent plots established in 2011.
B. 6/20/11
C. 7/6/11
Figure 3. Distribution of FIA plots sampled and
positive confirmation of S. tsugae. Most plots had
symptomatic seedlings but samples collected after
8/8/12 did not yield positive results.
Figure 4. Sirococcus shoot blight severity and crown defoliation of hemlock seedlings.
A
60
Disease Severity
Crown defoliation
A
N=40 plots
AB
A
AB
40
BC
B
20
C
CD
C
D
C
0
0
5
0
0
1-1 11-2 6 - 50 1 - 75 76-10
2
5
0
CONCLUSIONS
• Sirococcus shoot blight is
widespread and can be severe in
some locations
• Disease symptoms are associated
with greater tree & seedling density
suggesting that thinning dense
stands would reduce conditions
favorable to disease development
• For positive diagnoses, samples
should be collected from the end of
June to the end of July
D. 7/10/12
5
0
0
0
5
2
1
0
5
7
1
1
11 26 - 51 76Percentage of crown affected
Percentage of diseased shoots
Figure 5. Disease progression in permanent
plots at the MEF.
Percentage of symptomtic shoots
1. Delineate the geographic range of Sirococcus shoot blight
of eastern hemlock in New England and New York (NYS)
2. Verify the association of the pathogenic fungus S. tsugae
with widely observed shoot blight symptoms
3. Quantify incidence, severity, and impact of the disease on
eastern hemlock regeneration
4. Monitor changes in disease impact over time.
Percentage of trees
Figure 1. FIA plots sampled. Eastern hemlocks
often grow at the borders of streams and are
valued riparian habitat (A), collection of field data
in Maine (B).
20
18
N =5 plots (20 seedlings per plot)
B
16
14
B
12
10
8
6
4
A
2
June-20-11
July-6-11
July-21-11
Sampling Date
E. 7/21/11
F. 1/26/12