S OY B E A N D I S E A S E M A N A G E M E N T
CPN-1006
Stem Canker
Introduction
Stem canker is a disease of soybean in the United States
and Canada where infections occur primarily on the
lower portion of the stem. Multiple fungi in the genus
Diaporthe cause the disease. However, identifying and
managing stem canker is similar regardless of which
fungus is involved.
Symptoms and Signs
Often, the first symptoms of stem canker are dead plants
with dried leaves still attached to petioles late in the
season. Diseased plants usually occur in patches within
fields (Figure 1). Initial symptoms typically appear on
the lower third of the stem shortly after flowering
(growth stage R1).
The lesions start as small, reddish-brown spots at the
base of a branch or leaf petiole and then expand to form
slightly sunken cankers that are reddish-brown with
reddish margins (Figure 2). Cankers may remain on one
side of the stem and can extend over several nodes or
girdle the stem, killing the plant (Figure 3). In some
cases, Diaporthe fungi cause top dieback by forming a
dark brown canker on the upper four to six internodes,
which kills only the top of the plant (Figure 4).
Figure 1. When stem canker appears in a field, you will see dead plants
with their leaves attached.
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Stem Canker
Diaporthe fungi may also be associated with gray streaking
in the lower stem and taproots. Interveinal foliar chlorosis
and necrosis may occur as a result of a toxin the fungus
produces, but it is difficult to distinguish foliar symptoms from several other soybean diseases that cause
similar symptoms (see Diseases with Similar Symptoms,
page 4).
Disease Cycle
Figure 2. An example of the reddish-brown stem canker lesions on the stem.
The fungi that cause stem canker survive in residue or in
the soil for several years. Seed can be infected, but
fungal spores from infested residue are usually the
primary source of the fungus. Several weed species also
serve as hosts, including black nightshade, curly dock,
morningglory, and others. However, many of these weed
hosts do not show symptoms of stem canker.
The fungus produces spores during rainy weather, which
then splash onto plant tissue. Infection occurs during the
early vegetative stages of soybean growth, although
cankers are not visible until the plant enters reproductive
stages. Secondary spore production on infected plant
tissue can occur, but later infections will not have as
great an impact on disease development.
Infection can occur over a wide range of temperatures,
but the fungus requires extended moist periods to infect.
Disease can develop to epidemic levels when rainy
weather persists during the early vegetative stages of
soybean growth.
Disease Diagnosis
Figure 3. Cankers may extend over several nodes on the stem.
Figure 4. Top dieback occurs when cankers form on upper stem nodes.
Soybean Disease Management
Several other soybean
diseases can cause similar
symptoms, which can
make diagnosis difficult
(see Diseases with Similar
Symptoms, page 4).
Cankers may be isolated
between nodes, or extend
from a node to the soil
line (Figure 5). Plants
infected with the fungus
that causes stem canker
typically do not have
interior taproot discoloration. You may need a
laboratory diagnosis to
Figure 5. Stem canker can be
distinguish stem canker
difficult to diagnose because lesions
from other diseases.
often extend below the soil line.
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Stem Canker
Yield Loss and Impact
Yield loss from stem canker can approach 50 percent on
susceptible cultivars under favorable conditions. Stem
canker can cause premature death of soybeans in large
areas of the field (Figure 6). These plants often have
fewer and smaller seeds.
Figure 7. Severe stem canker may require several management techniques,
including planting resistant varieties, rotating crops, and tillage.
Figure 6. Severe stem canker infestations can cause premature death and
yield loss.
The impact on yield is greatest when plants are infected
early in the vegetative stages and weather is conducive
for disease development. Infections that occur during
reproductive stages often affect yield less. Soybeans
with partial resistance to stem canker must be infected
very early in the season for extensive yield loss to occur.
Management
The best way to manage stem canker is to plant resistant
soybean varieties. Consult your seed dealer to obtain
current information about varieties with stem canker
resistance.
Rotating crops to a nonhost may reduce the amount of
inoculum available to infect the next soybean crop.
Soybean rotations to nonhosts such as corn, wheat, and
Soybean Disease Management
sorghum are recommended for at least two years after a
severe disease infestation (Figure 7). If stem canker is
severe, avoid rotating the field with alfalfa, which is also
a host.
Evaluations for stem canker control indicate that fungicides may not be effective when susceptible cultivars are
used. However, fungicides can manage stem canker in
cultivars with moderate resistance. Apply sprays during
early vegetative stages.
Fields under minimum or no-till production are at
higher risk for stem canker development because they
have more crop residue. Incorporating infested crop
residue into the soil will reduce the survival rate of the
fungus and the amount of fungus available to infect the
next soybean crop. You can further reduce disease
development by planting fields with a history of stem
canker last.
Fields high in soil organic matter or with high fertility
are also at increased risk for disease. Maintain adequate
fertility to reduce disease impact.
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Stem Canker
Diseases With Similar Symptoms
Table 1. Symptom expression on roots, stems, and leaves for stem canker, brown stem rot, Fusarium wilt,
Phytophthora stem rot, sudden death syndrome, tobacco streak virus, and white mold on soybean.
Disease
Roots
Exterior Stem
Interior Stem
Leaf Symptoms
stem canker
healthy
dark red-brown canker
at node that can extend
over several nodes;
lesions often not
entirely around stem
brown stem rot
healthy
healthy
brown discoloration in
pith (center of stem)
interveinal chlorosis
and necrosis
Fusarium wilt
brown vascular
tissue
healthy
brown vascular tissue
leaves yellow
and wilt,
remain attached
Phytophthora stem rot
root discoloration
dark brown lesion
beginning at the
taproot and extending
up several nodes on the
stem and surrounding
the entire stem
brown internal
discoloration on plants
at any stage
leaves yellow
and wilt,
remain attached
sudden death
syndrome
root discoloration
and rotting; internal
browning of tap root
healthy
brown or gray
discoloration in below
outer stem layer but
pith is white
interveinal chlorosis
and necrosis of
leaves, leaves drop
after death
healthy
dark red-brown canker
at node(s) -not always
present
brown discoloration
of the pith at node(s)
healthy; bud
proliferation and
plants stay green
after maturity
healthy
white cottony mold
stuck to lower stem,
black, hard sclerotia
may be present
black sclerotia
embedded in
stem tissue
leaves wilt and
turn grayish green
between veins,
remain attached
tobacco streak virus
white mold
(Sclerotinia stem rot)
discoloration or
browning near lesion
interveinal chlorosis
and necrosis,
typically leaves
remain attached
to plant
Brown Stem Rot (BSR — Phialophora gregata)
The foliar symptoms of brown stem rot (BSR) include yellowing
and necrosis between veins. The stem symptoms include brown,
discolored pith tissue, especially near the nodes of soybean stems
(Figure 8).
How to distinguish BSR from stem canker:
Stem canker’s foliar symptoms may be similar to those of BSR,
so the real difference is visible in the stem. Split the plant stems
to confirm the discolored piths that are characteristic of
BSR-infected plants.
Figure 8. Stems infected with brown stem rot have brown discoloration and
disking in the pith.
Soybean Disease Management
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Stem Canker
Fusarium Wilt (Fusarium oxysporum)
Fusarium wilt-infected leaves turn yellow, die, and remain attached
to the stem (Figure 9). Plants affected by Fusarium have brown
vascular tissue in the roots and stems, which cause plants to
eventually wilt and possibly die (Figure 10).
How to distinguish Fusarium wilt from stem canker:
Plants with Fusarium wilt have brown vascular tissue in the roots
and stems — plants with stem canker do not. Also, plants with
Fusarium wilt do not show external decay or stem lesions above
the soil line.
Figure 9. (Top) Plants with Fusarium wilt will die prematurely and retain
leaves, similar to stem canker.
Figure 10. Brown discoloration in the lower stem is indicative of
Fusarium wilt.
Phytophthora Root and Stem Rot (PRR — Phytophthora sojae)
Phytophthora root and stem rot (PRR) occurs in wet, waterlogged,
compacted soils. Symptoms of this disease generally appear
during or shortly after waterlogged soil conditions.
How to distinguish PRR from stem canker:
The stems of Phytophthora-infected plants have a characteristic
dark brown lesion on the outer stem tissue that continues from
the roots up to the third or fourth node (Figure 11).
Figure 11. Long brown lesions that continue from the roots to the middle of
the stem are characteristic of Phytophthora root rot.
Sudden Death Syndrome (SDS — Fusarium virguliforme)
Sudden death syndrome (SDS) occurs in wet, compacted soils.
SDS symptoms are expressed as yellowing and necrosis between the
veins of leaflets during the soybean plant’s mid- to late reproductive
stages. The veins of symptomatic leaves will remain green.
How to distinguish SDS from stem canker:
SDS-infected plants will not have a stem lesion as stem
canker-infected plants do. As the foliar symptoms of SDS progress,
the leaflets will eventually curl or shrivel and drop off with only
the petiole remaining (Figure 12), instead of remaining attached
and dead as they do with stem canker.
Figure 12. Brown to gray discoloration in the lower cortex of the plant
indicates infection by the fungus that causes sudden death syndrome.
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Stem Canker
Tobacco Streak Virus (TSV)
Tobacco streak virus (TSV) causes bud blight, leaf and flower
bud proliferation (Figure 13), green stem disorder, and
sometimes a lesion or blotch near the nodes (for example,
red node). The internal stem tissue of infected plants also can
be brown near the nodes.
How to distinguish TSV from stem canker:
Stem canker will not cause bud proliferation. TSV lesions near
the node are much smaller than stem canker lesions.
Figure 13. Bud proliferation is very common in plants infected by tobacco
streak virus.
White Mold (Sclerotinia stem rot — Sclerotinia sclerotiorum)
White mold (Sclerotinia stem rot) is typically more of a problem
in years when conditions are rainy and cool during flowering.
Lesions develop on the nodes and expand up the stems. Infected
leaves often die and remain attached to the stem.
How to distinguish white mold from stem canker:
Sclerotinia-infected plants can be identified by the presence of
white fungal growth on the outside of the stems (Figure 14).
In addition, the white mold fungus produces sclerotia that are
hard and black.
Figure 14. White fungal growth and black fungal sclerotia are present on
plants affected by white mold.
Find Out More
Reviewers
To learn more about stem canker, visit the visit the NCSRP
Soybean Research Information and Initiatve (SRII)
website (www.soybeanresearchinfo.com) or consult your
land-grant institution. Other publications in the Soybean
Disease Management series are available by visiting the
SRII website or your land-grant institution’s website.
Emmanuel Byamukama, South Dakota State University
Anne Dorrance, Ohio State University
Doug Jardine, Kansas State University
Dean Malvick, University of Minnesota
Sam Markell, North Dakota State University
Adam Sisson, Iowa State University
Laura Sweets, University of Missouri
Authors
Kiersten Wise, Purdue University
Carl Bradley, University of Illinois
Martin Chilvers, Michigan State University
Loren Giesler, University of Nebraska
Febina Mathew, South Dakota State University
Daren Mueller, Iowa State University
Damon Smith, University of Wisconsin
Albert Tenuta, Ontario Ministry of Agriculture and Food
Soybean Disease Management
Photo Credits
All photos were provided by and are the property of the
authors and contributors except the cover photo and
Figures 4, 7, and 8 by Craig Grau, University of Minnesota;
Figure 10 by John Kennicker, Iowa State University;
Figure 13 by Gary Munkvold, Iowa State University; and
Figure 9 by Alison Robertson, Iowa State University.
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Stem Canker
Acknowledgments
The Soybean Disease Management series is a multi-state
collaboration sponsored by the North Central Soybean
Research Program (NCSRP). Learn more about the
NCSRP at www.ncsrp.com.
This publication was developed by the Crop Protection
Network, a multi-state and international collaboration of
university/provincial extension specialists and public/
private professionals that provides unbiased, research-based
information to farmers and agricultural personnel.
This project was funded in part through Growing Forward 2
(GF2), a federal-provincial territorial initiative. The
Agricultural Adaption Council assists in the delivery of
GF2 in Ontario.
The authors thank the United Soybean Board and Grain
Farmers of Ontario for their support.
Design and production by Purdue Agricultural
Communication.
This information in this publication is only a guide, and the authors assume no liability for practices implemented based on this information.
Reference to products in this publication is not intended to be an endorsement to the exclusion of others that may be similar. Individuals
using such products assume responsibility for their use in accordance with current directions of the manufacturer.
May 2015
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©2015 by the Crop Protection Network. All rights reserved.
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Stem Canker
The Crop Protection Network is a multi-state and international
collaboration of university/provincial extension specialists and
public/private professionals that provides unbiased, research-based
information to farmers and agricultural personnel.
Soybean Disease Management
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