Disease of the Month - Edema

  Hort Snacks - February 2019
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 Causal Organism: N/A

Crops Affected: potatoes, cruciferous vegetables (cabbage, etc.) greenhouse vegetables, etc (depending on the disorder)

Disease Cycle:

  • Caused by differences between daytime soil temperature and moisture levels and night-time temperature and moisture levels
    • Days with warm, wet soil followed by cool and saturated night-time air
  • Water uptake by the roots is rapid and exceeds the rate of transpiration
    • Cells under the surface of the leaves are stimulated to enlarge and divide, creating enough pressure to rupture the surface layers of leaf tissue
    • Injury to the epidermal layers by blowing sand or feeding insects (e.g. thrips) can increase the problem
  • In greenhouse situations, poor ventilation can slow transpiration while root pressure remains high
Edema on greenhouse cucumber
Photo by Richard Nemeth

  • On cabbage, small, wart-like growths or bumps that develop in varying densities on the either interior or exterior surfaces of several of the outer leaf layers of cabbage
    • May grow together – irregularly shaped elevated areas
    • Growths may split and turn whitish – creates a crystalline appearance (initially)
    • Turn brown and corky
  • In greenhouse crops (tomato), leaf tissues may become waterlogged, resulting in raised, blister-like growths on upper or lower leaf surfaces; fruit may also develop edema
  • Avoid over-irrigation when day and night temperatures differ greatly
  • Ventilate greenhouses properly and regulate watering in situations when humidity may build up
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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, 2019.