Blisters on the petals of orchid. Blister on spruce needles. Oedema appears as small, sometimes corky blisters which form on the lower leaf surface. These blisters may eventually harden to form white, tan, or brown wart like corky bumps on the lower leaf surface. As injury continues, leaves turn yellow, droop, and fall off.
Plants become spindly and cease growth.
Oedema is most prevalent in the late winter especially during extended periods of cool, cloudy weather. It is likely to develop when the soil is warm and moist and the air is cool and moist. This environment results in rapid water absorption from the soil and slow water loss from the leaves. These conditions are most frequently encountered in greenhouses or indoor situations rather than outdoors. Geraniums, rhododendrons, begonias, pansies, violets, and certain fleshy leaved plants such as jade and peperomia are particularly sensitive to conditions which lead to the development of oedema although almost any broadleaved plant may be affected.