Fungal Leaf Spot

Leaf-Spotting is caused by Cercospora sp. a genus of ascomycete fungi. There are several species that cause fungal leaf spot; however, leaf spot on orchids is predominantly caused by Cercospora angreci.

Symptoms: Leaf spot appears as small, mostly circular, spots on leaves that grow (enlarge) with time. The color of the spots can vary from green to brown, often with purple margins. As the infection progresses the leaves may become yellow and fall.

Cercospora "spores" are dispersed by water or wind and germination only occurs in humid conditions during late spring and summer. Moisture encourages the growth of the fungus and therefore the more moisture the worse it gets. Good air circulation helps to reduce the "moisture" on the leaves after watering.

Treatment is difficult because the cercospora "fungu's" can live in ground residue. Only Copper fungicides are effective, other fungicides can slow down but not erradicate the fungus.