Cistus Fungus

Aphids

• Aphids indirectly cause fungal infections of cistus through feeding on the plant's juices and excreting honeydew. Honeydew attracts flies and ants and can develop a fungus called sooty or black mold. Sooty mold does not infect the plant, but it can spread and block sunlight to the foliage, causing stunted growth and leaf drop. Spray aphid-infested cistus with a strong stream of water or apply horticultural oils or soaps to reduce the aphid population. Prune away areas infected with sooty mold and dispose of the cuttings away from the garden. Cistus leaves exude a substance called labdanum, which may also develop into sooty mold. Try an organic, sulfur-based product or a fungicide labeled for general purpose to treat leaf spot, powdery mildew and black spot.

Spore Migration

• Many fungi produce spores that travel on the wind, surf along on running or splashing water, such as rainfall and runoff, or hitch a ride into the garden on your shoes, hands or clothing. Fungal infections may cause spots on leaves, cankers or galls on woody areas of the plant, along with yellowing leaves, wilt and leaf drop. Since thousands of fungi species exist, the only sure method of identifying which one is attacking your cistus plant is to have a sample of infected plant tissue diagnosed by a professional. Most cooperative extension service offices can help with diagnosis. Once the diagnosis is made, look for a fungicide treatment specifically formulated for that fungus. Not all fungal infections are curable, and some can only be prevented, not treated. Spray plants at the rate and frequency recommended by the fungicide manufacturer.

Cultural Problems

• Over-watering cistus not only invites fungal infections, such as armillaria root rot, but can cause the plant's roots to drown and die. Cistus prefers dry growing conditions, with soil that drains fast and well. Cut back on watering and improve drainage. Rhizoctonia fungus is one of the few that thrive in dry conditions. Uncover the top of the cistus plant's roots to let them dry out.

Prevention

• Gather all weeds and plant debris from around the base of your cistus to eliminate hiding places for fungal spores. Take the detritus away from the garden and destroy it. Improve drainage, if necessary, and do not water the plants from overhead. Prune the foliage to improve air circulation; this helps the foliage dry out more quickly after rainfall. Do not over-water or over-fertilize. Wash your hands and disinfect all gardening tools between pruning cuts. A solution of one part water to one part bleach or full-strength liquid household disinfectant works well. If the cistus is severely diseased, consider removing it from the garden to prevent contamination of nearby plants.