Scouting for Soybean Diseases and Deciding on Fungicides

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As soybean fields are blooming, disease scouting needs to start to guide fungicide application decisions.

To determine if a disease will become a significant PEST, that will effect yield, four main factors need to be considered…

  • Pathogen presence – can be influenced by field history
  • Environment – the right conditions for disease to develop
  • Susceptible host – a variety that is susceptible to disease
  • Time – regarding the growth stage of the plant and when the disease develops

Scouting for and correctly identifying disease during soybean reproductive growth stages is critical to determine how necessary a fungicide application may be in protecting yield from disease. Some diseases have characteristic symptoms that are easily identified, where others may not be specific and may be mistaken for weather or chemical damage (see previous article Distinguishing Disease from Chemical Injury in Soybean). Pattern in the field where symptoms are being seen and entire plant samples should be examined and when needed can be taken to your local extension county agent for identification.

Some common soybean diseases found in Tennessee include Frogeye Leaf Spot, Septoria Brown Spot, Cercospora Blight, Anthracnose, Southern Stem Canker, Charcoal Rot, and Sudden Death Syndrome.  Descriptions of symptoms, pictures, and management options for these and other soybean diseases can be found on the mobile friendly field guide at Many diseases can be avoided by planting a disease resistant variety, regularly rotating to non-host crops, and when warranted fungicide applications can be applied.  The searchable variety database at can be used to look up disease ratings on varieties as well as yield response to fungicide in different environments (high, moderate, and low disease pressures). 

UT research has previously indicated that under circumstances of high disease pressure and conducive environmental conditions, timing a fungicide application at R3-R5 (beginning pod develop to beginning seed development) often provides the most consistent yield protection.

A foliar fungicide efficacy table (Soybean Fungicide Efficacy Table found at is developed by The North Central Regional Committee on Soybean Diseases (NCERA-137) and modified as needed by each state to provide information on foliar fungicide efficacy for control of major foliar soybean diseases. The table lists major soybean diseases and rates the different fungicides efficacy for each disease.

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