Geraniums (Pelargonium spp.) are shrub-like perennials that bloom with pink, red, coral or purple flowers that often grow in clusters. The roundish foliage is wavy and lobed. Geraniums prefer warm, sunny weather and well-drained soil. A fungal disease causes geranium plants to yellow.
Geraniums are susceptible to root rot caused by the phythium or rhizoctonia fungi. The presence of the soil-borne fungi in planting area at seeding time causes seeds to rot before germination.
Initial symptoms of disease include the yellowing of all above ground plant areas. Infected geraniums have stunted growth and start to wilt. There are brown to black lesions on plants near the soil line. Wet, humid weather leads to the appearance of gray or white, web-like growth on plants. Roots of infected plants develop water soaked, glassy lesions.
Plant geraniums in well-drained soil and do not over-water. Avoid excessive use of high-nitrogen fertilizers. Obtain disease-free plants from reliable sources. Chemical control options include the use of fosetyl-al fungicide.