Hard Black Spots on Cattleya Leaf

Flower Spotting

• Botrytis cinerea, or flower spotting, is a fungal disease that affects cattleya orchids. In addition to the formation of black spots on the plant, other symptoms include discolored spots of other kinds, often surrounded by a colorless or water-soaked area. This disease, like many fungal diseases, thrives in warm, moist areas and has the potential to kill the leaves and flowers of the cattleya orchid. Avoid over-watering the orchid and keep the planter or growing area free of debris that can house the fungi.

Tobacco Mosaic Virus

• Cattleya orchids suffer from tobacco mosaic virus, a variety of odontoglossum ringspot virus that affects orchids; it is a viral disease also known as diamond mottle, according to the University of California Davis Integrated Pest Management website. It causes brown or black flecks, spots or streaks to appear on the orchid. Viral diseases are not treatable; remove and destroy affected plants and replace the planter or soil they grew in to prevent the virus from spreading.

Leaf Spot Diseases

• A wide range of fungal leaf spot diseases affects cattleya orchids, from species of Cercospora to Phyllosticta; many of these fungal diseases start as light yellow, green or brown patches or spots in the leaves and grow into hard black or dark brown patches. This occurs as the fungi mature and begin producing spores for further growth. Prune severely affected leaves from the orchid and apply a mild fungicide to the cattleya plant.

Growing Conditions

• Certain growing factors make a cattleya orchid more likely to contract botrytis or diamond mottle and develop hard black spots that damage the appearance and longevity of the flower. Although orchids grow best in atmospheres of warmth and humidity, these factors also make it easier for fungi to grow; avoid watering the orchid too much to prevent excess water from building up in the planting area. Keep the planter free of debris, which houses pathogens as it rots. Clean all tools between uses to keep pathogens from spreading from one plant to another.