Assessment and Etiology of Hickory Decline (NC-EM-07-01)
Preliminary Results
Jennifer Juzwik1, Stacey Olszewski1, Ji-Hyun Park2, Greg Reynolds1, Linda Haugen3
1 Northern Research Station, U.S. Forest Service, St. Paul, MN
2 Department of Plant Pathology, University of Minnesota, St. Paul
3 Northeastern Area State & Private Forestry, U.S. Forest Service, St. Paul, MN
INTRODUCTION
Results
Hickory decline (Carya sp.), particularly of “smoothbark” hickories, has recently been reported in several
states across the midwest (USDA Forest Service 2003 and 2004, Johnson et al. 2005, WIDNR 2005) (Fig. 1).
Widespread mortality has historically been linked to outbreaks of the hickory bark beetle (Scolytus quadrospinosus)
during or immediately after periods of drought (USDA Forest Service 1985). In the early 1990’s, a fungus
(Ceratocystis sp.) was linked to stem-discoloring and sunken cankers associated with beetle outbreaks (USDA
Forest Service 1994). Since then, two Ceratocystis spp. have been characterized, and those, along with other fungi
(Phomopsis, Armillaria), site factors such as soil fertility and land use, and the flatheaded woodborer (A. tiosus)
have all been associated with hickory decline. A re-examination of affected ecosystems is needed to determine
and/or clarify the extent of hickory decline and mortality and the associated climatic, biotic, and abiotic factors.
Site survey
100
A
80
Declining Trees %
• Oak-hickory-maple northern hardwood stands were found at all sites. Bitternut hickory (Carya cordiformis) accounted for 75% of the hickories, the remainder
were shagbark (C. ovata). Soils were sandy or silty loams, slopes of the sites ranged from 0 – 25% and elevation from 600 – 1861 ft.
• BA ranged from 51 – 114 ft2acre-1 (10 out of 14 sites considered “overstocked” with BA > 80 ft2acre-1).
• Decline severity (based on % crown dieback) was found to increase linearly with BA (r2 = 0.45) while incidence of mortality was highest at sites with
extremely low and high BA ( r2 = 0.67).
• Average decline frequencies for MN and IA were similar (45%) and higher for WI (65%) (Fig. 7).
• Similar levels of hickory mortality were found in IA and WI, ranging from 4 – 20%; higher levels were found in MN sites (6 – 89%).
• Severity of decline ranged from 21 – 95% across all sites; highest average values were recorded in MN (53%) and lower in WI (40%) and IA (30%) (Fig. 8).
• 12 out of 14 sites had adequate to high levels of hickory regeneration (200 - 2400 stems/acre for stems < 1-ft tall).
• Fungal cankers, Phomopsis galls, and hickory bark beetle (HBB) holes were the most common types of damage found (Fig. 9).
4 0
2 0
0
M in n e s o t a
A
B C D E F
W is c o n s in
G
H
I J
K
Io w a
L M N
S
Fig. 8: Severity of hickory decline by location
METHODS
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Site and Tree Data
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Wis con sin
Mic higan
Legend
Sites
State border
County border
Misso uri
0
65
130
260
390
Fig. 3: Adult
hickory bark
beetles
ke
rs
O
th
G H
C D E F
I
J
Io w a
K L M N
Fig. 7: Frequencies of declining (A) and dead (B)
hickories by location
T y p e
H ic k o r y b a r k b e e t le ( S c o ly t u s q u a d r o s p in o s u s )
H ic k o r y t im b e r b e e t le ( X y le b o r u s c e ls u s )
O a k b a r k b e e tle ( P s e u d o p it y o p h th o r u s m in u t is s im u s )
1 2 0
• HBB and/or their galleries were found at all sites (Fig. 10).
• Hickory timber beetle (Xyleborus celsus) was obtained from logs at 6 out of 14 sites.
• Oak bark beetles (Pseudopityophthorus minutissimus) were obtained from logs collected on the 25th of May in WI.
1 0 0
8 0
6 0
4 0
2 0
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M in n e s o ta
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B
C
D
Io w a
W is c o n s in
E
F
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S it e s b y S t a t e
Fig. 10: Predominant beetle species emerging from stem
sections of sampled declining trees
Fungi Associated with Declining Trees
• Ceratocystis spp. and Fusarium spp. were isolated from logs from declining trees infested with the hickory
bark beetle.
• Fusarium—positive log sections were commonly from trees infested with the hickory timber beetle.
• Fusarium spp. were more frequently obtained from sunken cankers on logs than were
Ceratocystis spp. (Table 1).
• Both fungi were obtained, in similar proportions, from annual, diffuse cankers.
Fig. 4: Hickory
bark beetle
galleries
• Small cubes of discolored wood underneath cankers were taken from each 2-ft log section (Figs. 5 & 6) and used to isolate for
suspected pathogens.
• Isolation protocol:
― Ceratocystis spp.: small wood cubes were placed in moist chambers for 10 days. Ascospore masses produced by perithecia
sporulating on cubes were plated onto MYEA + SS, and pure cultures obtained from the resulting isolates.
― Fusarium and Phomopsis: wood cubes were surface-sterilized with alchohol and flaming, small wood chips removed, and then
placed into petri dishes containing APDA. Cultures with characteristics of Fusarium and Phomopsis sp. were purified, identified to
genus, and stored at 40°C until species identification is made.
Discussion
Table 1: Frequency of fungal taxa isolated from stem sections
Sections
Type of Damage
Isolation Frequencies by Genus
Assayed
Ceratocystis
Phomopsis
(%)
(%)
Diffuse Stem Canker
78
46
29
0
Sunken Annual Canker
35
9
46
3
Globose Gall
13
0
0
15
SUMMARY
ONGOING WORK
• Additional sites will be surveyed and sampled mid-May to late July, 2008. These will include 2 more sites each in WI and IA, 3 sites in IN and OH, and 6 in NY.
Fig. 6: Sunken annual cankers (left) and exposed, discolored sapwood (right)
Fusarium
(No.)
• Several different types of damage were found on declining hickories (from most to least common): insect holes (associated with HBB, flatheaded woodborer, and ambrosia beetles), sunken annual and
diffuse cankers, Phomopsis galls, black leaf spotting, sapsucker and woodpecker damage, decay fungi, mechanical and fire damage, broken tops, and human-induced girdling.
• Incidence and severity of decline were positively correlated with basal area in our stands, in all but one site.
• Decline mostly affected trees > 5 inches dbh. Levels of regeneration observed at most sites were adequate for stand replacement.
• Hickory bark beetles and/or their galleries were found at all sites, exceeding occurrences of other damage on declining trees.
• Ceratocystis and Fusarium spp were both obtained from log sections from declining trees with hickory bark beetles and/or galleries.
• Fusarium spp. was more often obtained from sunken, annual cankers than Ceratocystis spp, but both fungi were similarly obtained from logs with diffuse cankers.
Ongoing Work
Fig. 5: Diffuse bark canker (left) and exposed,
discolored sapwood (right).
W is co n s in
A B
er
520
Miles
Insect Data Collection
• Two log sections from each declining tree were placed in insect emergence chambers.
• Total number and type of insects that emerged were recorded weekly over six weeks (e.g. Fig. 3).
• After six weeks, the bark on each log was removed and presence and type of galleries recorded
(e.g. Fig. 4).
C
an
1 4 0
Io wa
Indian a
M in n e so ta
s
Fig. 9: Average frequencies of stem damage types observed
Michigan
Illinois
40
4 0
Insects Associated with Declining Trees
Minne sota
• 14 sites in 13 counties across three states (IA, MN, and WI) were surveyed and sampled in the summer
of 2007 (Fig. 2).
• Total live stand basal area and number of hickory stems across four size classes were recorded at 9 fixed
radius plots (~1/15 acre) at each site.
• Frequencies of hickory decline and mortality (“decline” is defined as >20% crown dieback), decline severity
based on crown ratings, and evidence of damage on trees from fungi, insects, fire, or mechanical damage,
Fig. 2: Study site locations
were gathered at 30 point plots per site.
• Soil, topographical, and elevational data were gathered through use of GIS.
• At each site, four 2-ft long log sections were taken from each of three declining trees for insect and pathogen evaluation.
Pathogen Data
ap
60
6 0
No. of adults collected
Methods
8 0
Frequency of Damage (ave. %)
Severity of Decline (Ave. % crown dieback)
• Quantify relationships between decline incidence and severity and stand basal area, soil type, elevation, land use, and
drought history.
1 0 0
6 0
20
B
1 0 0
8 0
40
80
• Conduct field evaluations to determine the frequency and severity of decline and incidence of hickory mortality.
• Quantify relationships between decline incidence and severity and pathogen and/or insect presence.
60
0
10 0
Dead Trees %
Fig. 1: Declining
bitternut hickory in an
Iowa stand.
Objectives
RESULTS
(%)