Scouting for Soybean

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Scouting for Soybean
Rust
Lisa M. Behnken
Regional Extension
Educator, Crops University of
Minnesota Extension Service, Winter 2005
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Soybean Rust Workshop Brazil Feb 12-24,
2005 International Agtivities
My Sponsors MN Soybean Research Promotion
Council U of MN Extension
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Equator
Itacoatiara
Campo Novo
Uberlandia
Rondonopolis
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South America vs MN or Midwest U.S.

• Brazil/South America
• Tropical
• Year round supply of rust spores in many
  locations
• Extended planting and harvest season
• 60 inches of rain
• Determinate type soybeans
• R1 soybeans almost full canopy

• United States/MN
• We have winter
• Spores will need to blow in from the south every
  season
• Tight planting and harvest window
• 30 inches of rain
• Indeterminate soybeans
• R1 soybeans small, no canopy yet

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Extended Planting (Sept March) and Harvesting
Season in Brazil
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Clouds of dust filled with rust spores behind the
combines
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Soybean Growth Differences Brazil vs. MN

• Determinate type varieties most of vegetative
  plant growth completed by R1 stage. Plant adds
  only 1-3 more trifoliolates once flowering
  begins. (Photoperiod insensitive)
• Indeterminate varieties (planted in most of US
  and in our area) plant continues to put on many
  more trifoliolates once flowering begins.
  (Photoperiod sensitive)

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EMBRAPA, BRAZIL, Feb 2005
Determinate type Soybeans
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Rochester, MN July 8, 2004
Indeterminate Soybeans
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August 2, 2005Rochester, MN
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Why Is Scouting Important?

• Our Best Tool for Managing Soybean Rust
• Prevents us from Jumping the Gun
• Identify the problem early
• Choose the right fungicide
• Apply fungicides at the right time
• Evaluate coverage and performance of fungicides
• Evaluate disease development based on weather,
  growing conditions, and fungicide application
• It Works!
• Brazilian farmers depend on it!

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SCOUTING More important than ever!

• Most Critical Period is R1-R6
• R1 R2 5 days
• R2 R3 10 days
• R3 R4 9 days
• R4 R5 9 days
• R5 R6 15 days
• Total 48 days from R1 to R6
• Protection time depends on fungicide used,
  weather, and soybean growth 7-21 days

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R1 Stage One open flower at any node on the main
stem
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R6 Full Seed Stage Pod containing green seeds
that fill pod cavity at one of four uppermost
nodes
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Scouting for Soybean Rust
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• Focus on
• Early planted fields with early maturing
  varieties
• Low lying or protected fields with prolonged dew
  periods (overlaps in planting)
• Fields with early canopy closure
• Check other known hosts - legumes
• Intensify efforts scout every 3 days
• Continue to scout after fungicide applications.

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Scouting Continued.

• Examine
• Leaves in the Lower Canopy first use stick
• Look for early chlorotic spotting
• Examine about 50-70 leaves/50 acres
• Use 15 to 20x hand lens to ID pustules
  and spores released from pustules
• Put sample in plastic bag, blow some air into it
  and seal. Check for pustule/spore development.

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Use a stick to push the soybeans back. Examine
the lower canopy
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Hold the leaf up to the sun. Look for lesions on
the leaf
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Draw a circle around the lesion
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Put the 20X hand lens up to your best eye.
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Pull the leaf towards the hand lens. Examine the
lesions.
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What Does It Look Like?

• Symptoms
• Begins on lower leaves as small gray lesions on
  underside of leaves
• Chlorotic spots- visible on upper and lower
  leaves
• Lesions change from gray to tan
• Lesions enlarge and form a blisterlike pustule at
  center, usually on underside of leaf
• Spores released from pore formed at tip of
  pustule

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Early Soybean Rust
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Chlorosis, or yellowing may be visible On upper
leaf surface. No halo
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Soybean Rust Closeup
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Lesions on lower leaf surface
Photos Courtesy USDA-ARS FDWSRU
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Soybean Rust Closeup
5x
40x
Pustules on lower leaf surface
Photos Courtesy USDA-ARS FDWSRU
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Rust Spores
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Lesions color change

• Resistant to rust
• Red-brown (RB) reaction, lesions may or may not
  develop into sporulating pustules
• Killed rust
• red-brown lesions also appear after fungicide
  applied
• Fungicide Effectiveness
• Red-brown lesions indicate fungicide
  effectiveness and if there is a need for
  additional fungicide applications
• Susceptible Alive
• Tan lesions that develop into sporulating
  pustules

C. STONE
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High levels of infection leaf drop, pod and
seed abortion Clouds of spores produced
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Note skips near power lines
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SOYBEAN RUST
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www.soybeans.umn.edu
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Acknowledgements

• Reid Frederick and Mo Bonde, USDA-ARS, Fort
  Detrick, Maryland
• Glen Hartman and Monte Miles, USDA-ARS,
  University of Illinois
• Jim Kurle and Seth Naeve, University of Minnesota
  
• Marty Draper, South Dakota State University
• X.B. Yang, Iowa State University
• Craig Grau, University of Wisconsin
• Roger Borges, University of Wisconsin
• Jose Tadashi Yorinori, EMBRAPA, Brazil
• U of MN Regional Extension Educators and IPM
  Specialists
• Eric Rund, International AGtivities