WSU Extension


Caption: Oedema on geranium
Photo by: R.S. Byther
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Geranium : Oedema
(revision date: 4/23/2014)

Oedema is a physiological problem that occurs when the soil is warmer than the air, soil moisture is high, and relative humidity is also high. Lower transpiration rates coupled with increased water absorption causes cell pressure to increase, erupting epidermal cells and allowing inner cells to bulge and protrude. Symptoms usually occur on lower leaf surfaces and appear as watery blisters or galls, which eventually turn dark brown, yellow, or rust and give the appearance of a rust or bacterial infection. Cells die and discolor, giving the impression of a parasitic infestation. Insect feeding (especially aphids and thrips), mechanical injury, chemicals, and windblown particles produce a similar effect.
Management Options

Non-Chemical Management
  • Do not overwater.
  • Plant in well-drained soil.
  • Increase plant spacing to reduce humidity.
Select non-chemical management options as your first choice!

Chemical Management

None recommended

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Caption: Oedema on geranium
Photo by: R.S. Byther