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Brown Stem Rot

 
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Brown Stem Rot

Stem Symptoms of Brown Stem Rot

Split soybean stem showing brown stem rot.
Split soybean stem showing brown stem rot.

  • Brown stem rot (BSR) infection causes vascular and pith tissues to turn brown to reddish brown (pith discoloration is a characteristic/distinguishing symptom)
    • Split stems longitudinally to inspect for brown stem rot
    • Check at and between nodes near the soil line
  • The height of internal stem discoloration is a measure of brown stem rot severity
    • When disease is severe, discoloration is continuous from the base of the plant upwards
    • When disease is less severe, discoloration only occurs at nodes, with healthy, white tissue between nodes

Disease Facts

Mature soybean stem infected by brown stem rot.
Mature soybean stem infected by brown stem rot.

  • Caused by Phialophora gregata, a fungus that survives in soybean residue
  • Widely established throughout the north-central U.S., where soybeans are its only host
  • There are 2 known strains - strain A is highly aggressive, and strain B is mild
  • Fungus infects roots early in the season, but symptoms of vascular system damage usually appear in midsummer, during reproductive development
  • Fungus is not carried with seed, and minimal amounts of inoculum are carried with soil adhering to farm equipment

Conditions Favoring Disease Development

Higher temperatures inhibit brown stem rot.

  • Brown stem rot development is greatest between 60 and 80 F
    • Higher temperatures inhibit brown stem rot - little or no disease develops above 90 F
  • Severity and incidence of brown stem rot is greatest when soil moisture is near field capacity, which is also optimal for crop development
    • Symptoms worsen if disease development is followed by drought stress during pod fill
  • Severity increases when soil pH is near 6.0 and is less severe at pH of 7.0 or greater
  • Brown stem rot may be more severe in fields where SCN is also a problem

Phialophora gregata Disease Cycle

  • Survives in infected soybean residue left on soil surface
  • Pathogen does not produce survival structures - survival is totally dependent on soybean residue
  • Fungus can continue to reproduce throughout the winter, influencing inoculum levels in the spring
  • Conidia (spores) are produced in late spring
  • Infection of new soybean crop occurs through roots (by growth stage V3) and progresses to stems
  • Infected stems become inoculum source for next disease cycle

Impact on Crop

  • Brown stem rot infection progresses from roots to vascular system (water and food-conducting system) of soybean plants
  • Infection causes a gradual disruption of the vascular system
  • Premature plant death may occur, especially if heat and drought stress impacts badly diseased plants
  • Degree of yield loss depends on environmental conditions, variety and fungal strain
    • Brown stem rot strain A causes more damage and may reduce yields up to 40% when severe
Foliar symptoms of brown stem rot.
Foliar symptoms of brown stem rot.
 

Management

  • Select Resistant Varieties: PioneerĀ® brand soybean varieties have been continually improved for resistance to BSR
    • Screening potential new varieties in areas of high brown stem rot incidence is key to variety improvement
    • DuPont Pioneer rates its varieties and makes rating available to customers
    • For fields with a history of brown stem rot problems, plant a variety with a rating of 6 or higher
    • Your Pioneer representative can help you select varieties with appropriate BSR resistance and other important traits
  • Crop Rotation: Effective in reducing disease inoculum - 2 years away from soybeans is more effective than 1 year
  • Tillage: Some tillage may be necessary to bury infected residue - the rate of inoculum decline is directly related to the rate of soybean residue decomposition
  • Manage SCN: Plant varieties resistant to both sudden death syndrome (SDS) and soybean cyst nematode (SCN)
  • Sanitation is not needed: Minimal amounts of inoculum are carried with soil adhering to farm equipment

Field comparison of variety susceptible to brown stem rot and brown stem rot-resistant variety

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The foregoing is provided for informational use only. Please contact your authorized Pioneer sales professional for information and suggestions specific to your operation. Product performance is variable and depends on many factors such as moisture and heat stress, soil type, management practices and environmental stress as well as disease and pest pressures. Individual results may vary.

PIONEERĀ® brand products are provided subject to the terms and conditions of purchase which are part of the labeling and purchase documents.