The fungus Pythium, which is commonly found in the soil, can infect geranium root and stem tissue and cause plant death. Wet, poorly drained soil favors disease development. Infected plants are usually stunted.
Leaves turn a yellow or brown color, wilt, shrivel and eventually die.
Lower leaves often show symptoms first. In early stages of the disease, plants may show recovery at night, but wilt again the following day. To diagnose Pythium root rot, dig an unhealthy plant and wash the soil from the roots. Diseased plants will show rotted, brown roots. Often the outer layer of root tissue is missing and few roots are present.