Recognizing and Identifying Soybean Rust

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Recognizing and Identifying Soybean Rust
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Two planting dates no obvious symptoms
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An apparently disease-free field
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Soybean rust infection in the lower canopy
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Defoliation can occur quickly
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Any of various hand lenses are critical to field
identification
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Infected tissue on the underside of a leaf
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Transmitted light through a rust infected leaf
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Progression of leaf symptoms
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Early symptoms
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Pustules magnified on a disecting stereo
microscope.
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The top surface of a soybean rust infected leaf
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The bottom surface of the same soybean rust
infected leaf
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Plastic bags can help preserve samples and force
the pustules to sporulate.
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A spore shower from the leaves above
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Watch for rust in Alternative hosts Weed hosts -
Kudzu
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Alternative Weed Hosts - Kudzu
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Similar Diseases

• Soybean rust
• (Phakopsora pachyrhizi)

• Wheat leaf rust
• (Puccinia triticina)

• Corn rust
• (Puccinia sorghi)

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Alternative hosts Common bean
Alternative hosts Common bean Uromyces
appendiculatus on Phaseolus vulgaris near Capitan
Miranda, Itaipu, Paraguay
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Alternative hosts Common bean
Alternative hosts - Uromyces appendiculatus on
Phaseolus vulgaris and Phakopsora pachyrhizi on
soybean near Londrina, Paraná, Brazil
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Potential Difficulties for Initial Identification
of Rust in North America

• Scouting may not be sufficient in all areas of
  the country.
• Initial infections may not be recognized.
• Other diseases have similar symptoms
• Bacterial blight and Bacterial pustule.
• Septoria brown spot and Downy mildew.
• Producers willingness to adopt fungicide use.
• Fungicide availability.
• Ability to treat required acres (aerial and
  ground application).
• Large farm sizes in parts of the country.
• Lack of understanding of fungicide mode of
  action.
• Skeptisism about rust risk.

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Recognizing soybean rust

• Look for necrotic spots on leaflets?
• Large necrotic areas indicates advanced disease!

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Recognizing soybean rust

• Look for chlorotic (yellow) spots?
• Indicates early infection it is difficult to
  see rust!

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DownyMildew
Potentially confusing diseases
A
C
B
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SeptoriaBrown Spot
Potentially confusing diseases
A
B
C
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Bacterial Pustule
Potentially confusing diseases
A
B
C
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Bacterial Blight
Potentially confusing diseases
A
C
B
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Recognizing soybean rust

• Hold leaves up to the light.

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Rust Management

• Early detection and rapid response will be
  critical.
• Watch for a National Alert system to track
  soybean rust.
• Listserv
• Media releases
• Etc.
• Website postings with daily records of rust
  distribution, and severity based on field
  surveys, monitoring plots, and observations of
  First Detectors
• Training for First Detectors and other ag
  professionals is critical to good data feeding
  into the communication system!
• Check with your local state extension specialists
  for specific management recommendations for your
  part of the country.

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Planting dates and fungicide application
Soybean rust defoliation on three planting dates
with (foreground) and without (background)
fungicide at EMBRAPA near Londrina, Paraná, Brazil
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Severe symptoms just before leaf drop
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Prepared as a training aid for the National
Plant Diagnostic Network by Martin A.
Draper Loren J. Giesler Extension Plant
Pathologist Extension Plant Pathologist South
Dakota State University University of
Nebraska-Lincoln May 2004 Thanks to the
following image contributors Albert
Tenuta Douglas J. Jardine Ontario Ministry of
Food and Agriculture Kansas State
University Anne Dorrance Laura Sweets Ohio
State University University of Missouri