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Geranium (Pelargonium spp.)- Oedema
Cause A physiological problem on many greenhouse plants including begonia. Out of dozens of samples there has only been one that was diagnosed with oedema by the OSU Plant Clinic. Oedema (edema) is more prominent when air temperatures are lower than soil temperatures, soil moisture is high, and relative humidity is high. Low transpiration rates with an increase in water absorption increase cell pressure, erupting epidermal cells and allowing the inner cells to enlarge and protrude. This protrusion kills the cells and discolors them (yellow, brown, or rust), giving the impression that a parasitic organism is involved. Light levels, low nutrition, and high soil moisture each contribute to oedema development. Brassica, Dracaena, Fatshedera, Peperomia, Pelargonium and Polyscias are also affected. Other plants that can be affected include camellia, eucalyptus, hibiscus, privet, schefflera, and yew.
Symptoms This condition is usually found on lower leaf surfaces. The first symptom is few or numerous watery blisters or galls. Blisters or galls can turn a dark brown-yellow or rust color and look like a rust or bacterial infection. Later the swellings become light brown or tan and corky in texture. Lesions may be concentrated near the leaf margin. They also can be lighter than surrounding areas of the leaf. The entire leaf may yellow and die.
Cultural control
- Do not overwater especially during overcast, cloudy days.
- Use a soilless mix that drains well.
- Do not use saucers on hanging baskets.
- Keep humidity low, by heating if necessary.
- Maintain higher greenhouse temperature.
- Check media pH, soil temperature and electrolyte concentration at regular intervals.
Reference Rud, N.A. 2009. Environmental factors influencing the physiological disorders of edema on ivy geranium (Pelargonium peltatum) and intumescences on tomato (Solanum lycopersicum). MS Dissertation, Kansas State University. 99p.