Asian Soybean Rust -
Frequently Asked Questions V:
Monitoring, Tracking, and Scouting
Author: David Holshouser, Extension Soybean Specialist, Tidewater Agricultural Research and Extension Center; Elizabeth Bush, Special Research Associate, Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech; Pat Phipps, Extension Plant Pathologist, Tidewater Agricultural Research and Extension Center; and Erik Stromberg, Extension Plant Pathologist, Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech
Publication Number: 450-305, posted March 2006
How important is scouting for Asian soybean
rust (ASR)?
Scouting for ASR on a nationwide basis is probably
the most important aspect of managing the disease.
If scouting is effective, the rust can be tracked as it
moves through United States soybean-growing regions.
Scouting locally is also important because ASR
could leapfrog areas as it moves north, and without a
coordinated survey in Virginia, early infection could
go undetected. Virginia plant pathologists and agronomists
use tracking and forecast information to determine
when fungicide applications to control diseases
should begin in Virginia, the class of fungicide that
should be applied, and if scouting should be intensified.
This is critical for controlling a disease such as
ASR that develops very rapidly under favorable environmental
conditions.
When do I need to start scouting for ASR
and how should I scout fields?
Scouting is key to ASR control, since this disease progresses
very rapidly and the presence or absence of the
disease will determine which class of fungicide to use.
Scouting should begin when the first true leaves appear.
This is an excellent time to check stands and monitor
for other problems, in addition to ASR. Scouting
intensity should increase as plants enter reproductive
stages and continue through full-pod (R1 through R6)
stages.
Scout fields at least every other week during vegetative
stages and weekly from R1 (beginning flower)
stage through the late R6 (full-pod) stage. Do not just check the perimeter of fields. Walk fields in a ‘W’ pattern.
Depending on field size, check six to ten locations
within each field. Make sure to scout shady parts of
the field, low-lying areas, areas near bodies of water,
and any site where high moisture conditions will be
favorable for disease development. Also scout areas
with any suspicious yellowing. After rainy periods, or
when disease forecasts and tracking data indicate that
the movement of ASR into Virginia is likely, increase
scouting frequency and intensity.
Use a 20X hand lens to check leaves of differing ages
on plants (i.e. leaves from the plant bottom, middle,
and top). Pay particular attention to the lower main
stem leaves, where initial infections usually begin. In
the early stages of the disease, yellow flecks or tan to
brown or reddish-brown pinpoint spots appear on the
upper leaf surface. Hold leaves up to the sky to backlight
them for visualization of early and hard-to-detect
symptoms of ASR. In later stages of the disease, powdery,
pale brown pustules that contain the urediniospores
form on the undersides of leaves.
It is difficult to positively identify ASR in the field so
laboratory identification is necessary. If ASR is suspected,
collect ten to 20 symptomatic leaves and place
them in a sealable plastic bag. Keep leaf tissue from
damage or drying out during transport to a Virginia
Cooperative Extension office or plant diagnostic lab.
Keep the tissue in a sealable plastic bag in a refrigerator
if the sample cannot be transported or mailed right
away.
Soybean producers using an early soybean production
system (e.g. early-maturing cultivars planted in
April) should begin intensively scouting fields in June
when flowering begins. For May-planted and traditionally
used maturity groups, intensively scout from July
through September. For double-crop soybeans, begin
intensive scouting in late July to August, and continue
through mid- to late October.
Can soybean rust be diagnosed in the
field?
No. Current technologies only allow qualified individuals
to give a preliminary diagnosis in the field using a
20X or more powerful hand lens. Positive identification
of ASR must be made by trained plant pathologists in
a laboratory. There are other soybean foliar diseases
that may be mistaken for ASR. Bacterial pustule, for
example, is easily mistaken for ASR. Product development
for a serological test, suitable for use in the field,
for ASR is ongoing and it is possible that this product
may be available sometime in the future.
Is Virginia cooperating with other states
to track and monitor ASR?
Virginia is part of a nationwide monitoring, tracking,
and forecasting system. Scouting for ASR will
take place in Virginia and all other soybean producing
states. The public can access scouting information at
the USDA Soybean Rust Information Site (www.sbrusa.
net). At this website, one can observe where scouting
has occurred, where ASR has been found, and see
county-specific scouting recommendations and disease
management information.
Does Virginia have a soybean rust monitoring
program?
The Virginia Soybean Aphid and Rust Monitoring
Program was initiated during the summer of 2004,
expanded in 2005, and will continue. Scouts monitor
commercial soybean fields and smaller soybean plots
containing multiple maturity groups. These fields and
plots are located throughout all soybean-growing regions
of Virginia and are scouted on a weekly basis.
Scouts collect suspect ASR-colonized leaf samples for
examination at the Tidewater Agricultural Research
and Extension Center. Final diagnosis of suspect ASR
samples is made by plant pathologists. Results of the
monitoring program are uploaded to the USDA soybean
rust information site and are also available at the
Asian Soybean Rust website at Virginia Tech (www.
ppws.vt.edu/ipm/soybeanrust/index.htm).
If we need to apply fungicides before rust
arrives, why is scouting on my farm or in
Virginia so important?
ASR will most likely move from south to north.
Therefore, Virginia may actually be more dependent on
North Carolina scouts than those in Virginia. However,
spore deposition may not occur in a linear fashion from
south to north, but leapfrog over areas due to climatic/
weather patterns and events. Additionally, Virginia is
a component of the nationwide scouting system and
scouting in Virginia is a critical component of the
ASR detection system. The presence or absence of rust
within a region will determine whether a preventative,
curative, or premix fungicide should be used.
Does Virginia’s soybean rust monitoring
program include spore trapping?
Yes. Traps are located in or near sentinel plots and are
sampled once per week.
What are spore traps?
Urediniospores are the principal fungal structures responsible
for spread of ASR. Therefore, the ability to
detect these spores is important for early detection.
Spore traps are small devices used to collect spores at
strategically placed locations throughout the country.
The type used in Virginia is a passive-design trap that
samples air like a weather vane, where the opening to
the trap is pointed towards the wind and any material
in the air is then captured onto a glass slide coated with
petroleum jelly. Traps are located in or near sentinel
plots and are sampled once per week. Slides are express-
mailed to a scientist at a university lab for identification.
The presence of rust spores does not mean the ASR
is in the area and present on host plants. At this time,
spores cannot be positively identified as ASR spores.
Therefore, at this time, the procedure must be considered
experimental. Confirmation of ASR can only be
accomplished with laboratory identification of the disease
on leaves.
If rust spores are detected in one of Virginia’s traps,
the sentinel plot and surrounding soybean fields will
be vigorously scouted. Leaves will be collected and
brought back to the laboratory for a thorough evaluation.
How will I know when and if I need to treat
my fields?
To determine fungicide application recommendations,
Virginia Cooperative Extension specialists in agronomy
and plant pathology will be observing forecasting
models, tracking rust movement through the United
States, and evaluating leaf samples submitted by the
Virginia Soybean Aphid and Rust Monitoring Program
and other first detectors.
After soybean rust is confirmed by Virginia Tech plant
pathologists, they will notify all pertinent Extension
agents, certified crop advisors, and other first detectors.
Information and recommendations will be distributed
by the Internet, mail, mass media, etc.
Check the Asian Soybean Rust home page, www.ppws.
vt.edu/ipm/soybeanrust/index.htm, or hotline, (757)
657-6450 x103, frequently for on the status of ASR in
Virginia and up-to-date fungicide recommendations.
Other ASR resources:
Asian Soybean Rust website at Virginia Tech -
http://www.ppws.vt.edu/ipm/soybeanrust/index.htm
USDA Soybean Rust Tracking site -
http://www.sbrusa.net/
North American Plant Disease Forecast Center-
http://www.ces.ncsu.edu/depts/pp/soybeanrust/
The Southern Plant Diagnostic Network -
http://spdn.ifas.ufl.edu/soybean_rust.htm
Related Publications
Asian Soybean Rust - Frequently Asked Questions
I: Background and General Information, Virginia
Cooperative Extension publication 450-301
Asian Soybean Rust - Frequently Asked Questions
II: Identification, Biology, and Ecology, Virginia
Cooperative Extension publication 450-302
Asian Soybean Rust - Frequently Asked Questions
III: Control with Fungicides, Virginia Cooperative
Extension publication 450-303
Asian Soybean Rust - Frequently Asked Questions
IV: Cropping Systems and Cultural Practices,
Virginia Cooperative Extension publication 450-304
Asian Soybean Rust - Frequently Asked Questions
VI: Sprayer and Nozzle Technology, Virginia
Cooperative Extension publication 450-306
Acknowledgments
The authors would like to express their appreciation
for the review and comments made by Ames Herbert,
David Moore, Mike Parrish, and Wade Thomason.
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