APPLICATION OF FUNGICIDES TO SOYBEAN FOR PLANT HEALTH BENEFITS

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APPLICATION OF FUNGICIDES TO SOYBEAN FOR PLANT
HEALTH BENEFITS
Donald E. Hershman Extension Plant Pathologist
University of Kentucky Princeton, KY
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Regional focus of talk
X
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Background

• Situation In 2003, Quadris (strobilurin) plus
  Warrior (synthetic pyrethroid insecticide )
  marketed for use on reproductive soybean as a
  means of increasing yield, but without any
  evidence of pest problems.
• In KY, about 20,000 acres were treated in 2003
  and 60,000 acres in 2004.
• Headline (a strobilurin) was labeled in early
  2005 and well over 100,000 acres were treated in
  KY this year.
• Plant Health and Soybean rust
• Use spread throughout the North Central region in
  2005 (7 million acres treated in U.S.)

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Fungicide Applications for Soybean Plant Health

• Strobilurin use in soybean where target diseases
  are not defined.
• Target enhanced plant health.
• Application target is R3 stage (beginning pod).
• Based on the assumption that full yield potential
  is rarely, if ever, realized in modern cropping
  systems.
• And that yield potential is lost due to
• Crop stresses and inefficiencies (non-optimal
  temperature, nutrients, soil water, etc.)
• Pests (ranging from hidden background levels to
  obviously damaging)

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Strobilurin Effects in Soybean

• Treated plants compensate for light to moderate
  stress conditions.
• more yield potential captured.

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Basis of Strobilurin Effect

• Stress-reducing physiological effects.
• Increased rate of photosynthesis
• Decreased respiration and ethylene biosynthesis
• Activation of non-specific plant defense
  mechanisms (e.g., H202)
• Improved nitrogen assimilation
• Controls some common fungal diseases.
• Brown spot
• Frog eye leaf spot
• Stem anthracnose
• Complexes of the above diseases, especially when
  present at low (background) levels.

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Greening Effect
NT
Quadris Warrior
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Strobilurin Yield Effects in Soybean

• Deep southern states have used fungicides for
  years due to consistently higher late-season
  disease pressure (especially frogeye leaf spot).
• Yield response to strobilurin in replicated plots
  and strip tests is highly variable.
• Negative to 20 bu/A

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On-farm strip trials across the U.S. in 2004 and
2005
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Yield Response to Headline by Location
source Marty Draper, SDSU
N35
N10 gt 4 bu/A 28
N10 lt untrt 28
N14 gt untrt lt 4 bu/A 40
Numeric response Relative advantage of
treatment Absence significant soybean disease in
all trials
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Yield Response to Headline by Location
N35
10/35 sites with significant economic response
(28.6)
Numeric response Relative advantage of
treatment Absence of significant disease in all
trials
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Frequency of observed significant economic yield
increase in Midwest Trials, 2005
Economic advantage associated with applying any
fungicide far from a sure thing.
Data source Marty Draper, SDSU
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Reasons for Variable Response

• Crops under varying degrees of stress.
• Good response
• Light/moderate stress (environment and/or
  pathogens sensitive to strobilurin)
• Poor response
• Little crop stress (optimal growing conditions)
• Overwhelming stress
• Due to environment and/or other pests not
  impacted by strobilurin chemistry

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Reasons for Variable Response

• Stress variation by region.

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Fungicidal Limitations of Strobilurins

• Less than optimal control
• Pod and stem blight, pod anthracose, Cercospora
  leaf blight
• Does not control
• Any viral, bacterial, or nematode diseases.
• Many common (and damaging) fungal diseases.
• Charcoal rot, Sudden death syndrome, Stem canker

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More Reasons for Variable Response

• Variable application timing.

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More Reasons for Variable Response

• Variable application and equipment technique.
• Improper droplet size, spray pressure and/or
  gallonage
• Results in differential coverage within canopy
• Variable levels of fungicide taken up by the
  plant results variable crop response to given
  stresses and/or disease.
• Different varieties planted
• Non-adapted varieties planted in some fields,
  adapted in some, and some marginal for area.
• Variable stress response in similar environment

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WHAT DO WE DO WITH THIS INFORMATION????
Target use in fields where probability of return
is greatest.
Avoid use in fields where probability of return
is low.
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RECOMMENDATIONS

• Targeted applications
• Fields that have a history of crop stress and/or
  target diseases.
• Fields planted to marginally-adapted soybean
  cultivars.
• Question use in historically high productivity
  fields.
• Use will always carry risk of no economic benefit
  due to lack of stresses or overwhelming stress.
• Any field could benefit, but no way at present to
  predict this this is where future efforts should
  be directed.
• Good soybean rust insurance?.....you decide.

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A WORD OF CAUTION

• Caution Insect populations may flair due to
  off-target kill of common entomopathic fungi
  (problems with flaring looper, aphid, and mite
  populations were noted some fields in 2005).
• Crop yields could be lower in treated fields than
  in non-treated fields if insect pressure is heavy.

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Yield from Efficacy Trials, WI
2 spotted mite infestation dry weather
significantly different (P0.05,
Duncans Multiple Range Test Data source Craig
Grau, Univ. of Wisconsin
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A WORD OF CAUTION

• Joe Q. Public is looking over our collective
  shoulders.

THANK YOU! ANY QUESTIONS?