Disease of the Month - Algae and Biofilms in Greenhouses

  Hort Snacks - February 2017
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 Crops Affected: Range of greenhouse crops

Disease Cycle:


  • Primitive plants lacking roots, leaves and stems
    • Contain chlorophyll and photosynthesize
  • Grow on walkways, pots, growing media, greenhouse coverings, as well as under benches,
    • Can be a safety hazard, due to slipperiness
    • Compete with plants for nutrients
    • May form a water-impervious layer on the surface of growing media
      • May slow gas exchange in a growing medium, which slows root growth
    • Represent a food source for shore flies and fungus gnats
  • A layer or film of microorganisms which adheres to surfaces exposed to moisture (flowing liquids), and includes the formation of a matrix of substances which is resistant to being removed and/or killed by antimicrobial treatments
    • May form on surfaces (e.g. floors, benches) or within pipes, on hose ends, irrigation nozzles and emitters, tank walls, grow bags, etc.
    • May develop over hours and days to years
  • Represent a potential source of water-borne pathogens
  • Other organisms may attach to a biofilm over time
  • Reduce water oxygen levels, clog irrigation systems, potentially introduce pathogens to crops

  • Sanitize greenhouses regularly to remove debris, weeds or other nutrient sources
  • Ensure proper greenhouse ventilation and maintain some horizontal air flow
  • Avoid overwatering and standing water/puddling
    • Allow growing media to dry out prior to watering again
    • Design greenhouses (and maintain) to ensure floors drain and puddles do not develop
  • Avoid excess fertilization
  • Disinfect greenhouse surfaces regularly, using appropriate registered disinfectants and algaecides
    • Irrigation systems, including lines, will need to be cleaned out
  • Evaluate water sources and filter/treat accordingly
  • Treatments with disinfectants can remove a certain amount of biofilm layers, but may not be effective at completely removing a biofilm
    • Certain oxidation treatments can be more effective in reducing biofilms than things like bleach and acids; this includes ozone and chlorine dioxide
      • Treatments may not be compatible with actively growing plants
  • Ensure that water sources are treated properly prior to being introduced into the greenhouse system
An additional resource link:
Biofilm in the Greenhouse – Dramm.com article
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For more information about the content of this document, contact Robert Spencer.
This information published to the web on January 31, 2017.