Do I need Fungicide on My Soybeans?

042913_2028_HaveILostAn2I have had some questions from growers this winter about planting untreated soybeans in an effort to reduce costs.  While you can get away with planting soybeans without fungicide, there are factors to consider to maximize your success.  The following information comes from Anne Dorrance at Ohio State University.

It is true that soybeans do not always need a fungicide seed treatment.  However, on soils with poor drainage where replanting is relatively common, replanting costs today are much higher than the estimates of $80/acre from 10 years ago. Basically seed treatments are an insurance policy to protect that young seed/seedling until it is out of the ground and growing.  Here are some things to consider when deciding to leave out seed treatments.

  1. Does the farm have a history of replanting?  If so, no question, use fungicide seed treatments.  Even at the older estimates of replanting associated costs, one replant will pay for more than 10 years of a seed treatment.
  2. How well does the field drain?  Farm drainage system has not been updated or field is slow to drain after heavy rains.  More often than not, seed treatments will protect the seed and have added yield benefits compared to non-treated seed.  All of the soil borne pathogens that can infect soybean require high moisture.  With a properly designed, well maintained drainage system, the amount of time a field is saturated is greatly reduced.  If the system is poor, old, or not functioning well, the time the field is saturated is much longer, which amounts to more seeds/seedlings becoming infected when those heavy rains do occur.
  3. Are you reducing seeding rates in 2015?  This is another place where seed treatments are beginning to play a larger role, with reduced seeding rates, every seed becomes important and seed treatments can have a large contribution to maintaining early plant populations.  In some seed treatment studies, the treated seed is emerging at rates greater than 90%, compared to non-treated seed which may be less than 50% depending on field conditions.
  4. Is there a field history of phytophthora?  Phytophthora causes early season damping-off.  While most varieties have varying levels of natural resistance, seed treatments often supplement the natural resistance until the soybeans are up and out of the ground.
  5. What are the soil conditions and are you planting early?  The cooler and wetter the soil, the longer the seed/seedling will sit below ground.  This gives these soil borne pathogens more time to feed.  For those first planted fields, seed treatments can provide protection, especially when it can take 2 to 3 weeks for them to emerge.

There are some field conditions when a seed treatment is not needed.

  1. Planting into warm, well-drained soil.  Those perfect planting conditions when the seed will probably emerge 3 to 4 days after you plant it probably do not need fungicide.
  2. No heavy rains are predicted for the region for the 2 weeks following planting.  The plants can germinate and emerge before any hard, compacting rains can occur.

With the trend to planting early into less than ideal conditions, seed treatments provide a form of insurance to help ensure good establishment.  While treated seed is not always necessary it is important to know the risk factors and manage them accordingly.