My Orchid Cactus Has Black & Brown Spots

Light Exposure

• Brown or black spots on orchid leaves could mean overexposure to light and sun. According to the University of Florida Extension, orchids need only partial shade to stay strong, and anything more than that can cause sunburn, which occurs when the sun scorches droplets of water on the leaves. Move the plant into an area with less direct sunlight, and turn off any lights near the plant to avoid any possibility of further overexposure. When orchids are outside, black spots may occur when the environment is hot and dry, and the spots will disappear when the weather improves around them.

Petal Blight

• A disease that affects only the petals of various plants, including orchids, is petal blight. The disease starts off with small, water-soaked spots on the petals that are slimy when touched. As the disease progresses, the spots merge together and the petal collapses. To prevent the disease from spreading further, remove all dead flowers from the orchid. Use a fungicide that contains chlorothalonil and mancozeb as their active ingredients. When treating, it is best to spray potted orchids outside, so as not to get any traces of the chemical in the home.

Leaf Spot

• Various fungal pathogens cause leaf spot for orchids and other flowers and plants. When the disease begins, you will see irregular or unusual shaped spots on the leaves. Choose a fungicide made for houseplants to control the disease and apply it every seven to 14 days, or as directed on the bottle. Remove all infected leaves, using cutting tools that are sterilized before and after use.

Bacterial Soft Rot

• Orchids are affected by bacterial soft rot down near the soil line, where brown and black lesions attack the plant's tissue. Most likely culprit for this disease is too much water surrounding the base of the pant and not enough drainage. Plant your orchids in well-drained, coarse potting soil, and place them in indirect sunlight. It's best to remember that orchids won't survive in regular potting soil.