Disease of the Month - Edema

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