Transcript the PowerPoint Presentation

Asian Soybean Rust
Gregory Shaner
Dept Botany and Plant Pathology
Purdue University
Revised: 1/30/2006
Two species of rust fungi infect
soybean


Phakopsora pachyrhizi
 Asian Soybean Rust
 Extremely damaging
 First reported in continental U.S. in Nov
2004
Phakopsora meibomiae
 Known for many years from subtropical
Americas
 Not as aggressive
 Not known in U.S.
Continental
U.S. - 2004
Hawaii
1994
Paraguay - 2001
Brazil -2002
Argentina - 2002
Uganda - 1997
Zimbabwe - 1998
S. Africa - 2001
Australasia 1902 through the
1960
How did Phakopsora pachyrhizi get
to the U.S.?


Most likely hurricane winds in autumn of 2004
 South America
 Central America
Land bridge
 Gradual movement from South America to
Central America, Mexico, southern U.S.
 Short-distance movement on susceptible plants
Soybean rust is a foliar disease



Fungus infects mainly leaf blades
Infections may also occur on leaf
petioles and pods
Most pustules are on the underside of
the leaf
Tan and Red Brown reactions to
Phakopsora pachyrhizi
(USDA-APHIS Web site)
Rust can reduce yields 10-80%




Premature defoliation
Poor pod filling
Smaller seed
Rusts are obligate parasites, so
they do more than just remove
photosynthetic leaf area
Disease triangle
Pathogen
Host
Environment
Pustule from primary infection
Soybean rust is a polycyclic disease
About 9 days
are required for
an infection to
mature into a
pustule
Spores from primary pustules cause
more infection
Pustule
numbers
increase
exponentially
These infection cycles begin whenever
conditions allow spores on leaves to
germinate and penetrate
Under favorable conditions, pustules
develop on all leaves
When infections become old, leaf tissue
dies
Spore production in soybean rust
pustules
Day 1
Day 6
Day 13
Day 27
Soybean rust can develop very rapidly
Winter survival of soybean rust




This is the bottleneck
Rust fungi do not persist in crop residue
Soybean rust is not seed borne
It survives on green host plants
 Unlikely to survive the winter in most
U.S. soybean areas
 Probably will survive the winter on the
Gulf Coast or Caribbean
The soybean rust fungus has a
broad host range


Phakopsora pachyrhizi is known to
infect 35 species of legumes in addition
to soybean
Among these are several weeds and
crops grown in the U.S.

Most of these other host species occur in
the South
Possible hosts of soybean
rust in Indiana
Kudzu with
soybean rust
Cultivated Crops:
Soybeans
Korean and Japanese
clover
White clover
Kidney beans
Garden pea
Ornamental plants:
Hyacinth bean
Wild hosts:
Kudzu
Crown-vetch
Yellow sweet clover
Soybean
rust on
kudzu
www.planthealth.info
Epidemiology scenario


Overwintering in
South
Annual migration
of spores into
Midwest
•Damage will depend on:
•How early spores arrive from South
•How favorable local weather is for spread
36.8%
10.5%
6.1%
7.6%
7.4%
5.2%
Weather that Favors Rust



Summer climate in Midwest will probably be
generally favorable for rust
Temperatures from 59 to 82 °F
Dew for several hours is sufficient for
infection
Management of soybean rust



Resistant cultivars
 This would be the desirable approach, but
there are none
Cultural practices
 Tillage, rotation, date of planting will not
likely have any effect
Fungicides
 There are several effective fungicides
Resistant cultivars



USDA has been screening germplasm in a
containment facility and in other countries
So far, not much resistant germplasm has
been found in Glycine max
Some germplasm lines have partial
resistance
 It’s not known if this resistance is
sufficient to provide protection
Fungicides



Fungicides will be the only control option for
several years to come
Effective fungicides currently fully labeled:
 Chlorothalonil (Bravo, Echo 720)
 Azoxystrobin (Quadris)
 Pyraclostrobin (Headline)
Topsin M, also labeled for use on soybean,
does not control rust
Fungicides approved under
Section 18





Myclobutanil (Laredo)
Tebuconazole (Folicur, Orius, Uppercut)
Propiconazole (Tilt, Bumper, Propimax)
Propiconazole + Trifloxystrobin
(Stratego)
Tetraconazole (Domark)
Systemic vs. non systemic
fungicides





Most fungicides that are, or will be, labeled
for soybean rust are systemic
They are absorbed by plant and move in
transpiration stream (toward leaf tips)
Products differ in degree of systemicity
These products may show some curative
activity
Non systemic fungicides provide a protective
barrier on the leaf surface
Types of fungicide action



Protectant
 Applied before disease onset
 Kills spores as they begin to infect
Curative
 Can kill established infections before
symptoms appear
Eradicant
 Inhibits development of an established,
symptomatic infection
 May have antisporulant activity
Effects of fungicides on rust development
Spore
germination Penetration
Mycelial
growth
PreSporulation
sporulation
Chlorothalonil
Triazoles
Strobilurins
Highly effective
Little or no effect
Strobilurin plus triazole:
Twin biochemical modes of action
Strobilurin
Inhibits electron transfer
Fungal cell
in cytochrome bc1 complex
of mitochondria. Therefore,
disrupts energy production
by the fungus.
Powerful preventative action
Triazole
Inhibits sterol biosynthesis.
Sterols are important
components of the cell
membrane.
Good curative activity
...... also of benefit for
resistance management
Soybean rust fungicides: Biokinetics (bioassay)
Alto (cyproconazole)
Folicur (tebuconazole)
10 x 5 microlitre droplets (1.9 g ai/ha = 0.027 oz av ai/A; assumed spray volume of 200 l/ha = 21.4 US Gal/A)
applied to all leaflets in zone between the two white lines 1 day before inoculating lower leaf surface
Opus (epoxiconazole)
Untreated
An effective fungicide product is
only part of the story


Application must be timely
Good coverage is important
 This includes getting fungicide down
in the canopy
 By the time pustules break out on
infected leaves, one or more leaves
will have formed above
Application timing


Fungicides work better as protectants than as
therapeutics
First spray should be applied before
incidence exceeds 5%


This means only a few pustules at mid-canopy on
no more than 1/20 of the plants
If application is delayed until most plants
have rust, control will be unsatisfactory

Incubation period is what can trip you up
Application technology





Droplet size <220 m (“fine” to
“medium”)
60 drops per cm2 of leaf (387/in2)
Nozzles 1 ft above canopy
15 to 20 gpa spray volume
5 gpa for aerial application
Spraying conditions

Don’t spray when:
 Temperature is above 86 °F
 Relative humidity is below 55%
 Wind speed is greater than 5 mph
Will more than one application be
needed?


Rust may start before plants have
produced all their leaves
 A plant at R1 has developed only half
its nodes
New growth won’t be protected
Should growers scout their
fields?



Initial infections may be focal
 These may be overlooked
Sentinel plots may be used
 Several plots in each state
 Sown 2 wk before normal sowing time
 Monitored twice weekly for rust
Once rust is found, a general alert will be
issued
Diagnosis and detection



Early infections can be difficult to see
Sporulation is on underside of leaf
Several look-alike diseases
 Bacterial pustule
 Bacterial blight
 Brown spot
Rust on
trifoliolate
leaves
Five days after infection
Soybean rust lesions on leaves, seen with
backlighting
Nine days after infection
Twenty-five days after infection
Bacterial pustule may be
confused with soybean rust
Bacterial blight is another rust look-alike
Lesions produced by Pseudomonas savastanoi pv glycinea.
These may superficially resemble rust, but inspection with a hand
lens will reveal the difference.
Brown spot
Common in Indiana
Appears soon after plants
emerge
Spots don’t reach upper leaves
until late in the summer
Who is looking for rust?



Scouting activity in Indiana will begin in the spring
Plant pathologists at Purdue and county extension
educators will be looking for soybean rust
First detection of rust will also depend on others
 Soybean growers
 Crop advisors
 Seed company staff
 Crop certification inspectors
 Survey entomologists
First detectors


Purdue has a program to train “first
detectors”
This is coordinated through the Plant
and Pest Diagnostic Laboratory (PPDL)
What to do with a suspect
sample


Take sample to County Extension Office
Submit sample to the Purdue Plant and Pest
Diagnostic Laboratory (PPDL)
 County extension offices have submission
forms
 Flatten symptomatic leaves between
pieces of dry paper and double-bag in
plastic
 Exact location of field is critical
Web site


There are several Web sites about
soybean rust
The Purdue Plant and Pest Diagnostic
Laboratory Web site has current
information about soybean rust and
links to other authoritative sites
 http://www.ppdl.purdue.edu
Conclusions





Rust will be a serious soybean disease in
Indiana, but not necessarily every year
Rust can be controlled
Fungicides will be the first line of defense
Ultimately, resistant cultivars will probably be
developed
Purdue CES is working with other
governmental and commodity organizations
to provide accurate and timely information
about this disease