Oedema on Geraniums
Oedema is not a disease, but a physiological disorder commonly seen on geranium, in particular the ivy geranium (P. peltatum). It primarily affects leaves, but it can also affect petioles and stems. High relative humidity and high soil temperatures favor oedema development. It is especially common in combination with overcast weather conditions. Under these conditions guard cells surrounding stomates on the underside of leaves swell with water. As pressure builds within the cells, the cells rupture. As the cells heal, brown, corky callus tissue is formed.
General recommendations for oedema control include the use of well-drained soil mixes, spacing plants to allow for good air circulation, watering plants in the morning and avoiding over watering in cloudy, cool weather. Avoid high soluble salts in the growing medium and maintain high nitrogen and iron levels in foliar tissues. Relative humidity in the greenhouse should be maintained between 60 and 70%.
Jean L. Williams-Woodward, UGA
Extension Plant Pathologist - Ornamentals
E-mail any questions or remarks to Jean L. Williams-Woodward