How to Kill Fungus on Cactus

Remove the infected pads or leaves with a pair of sharp pruning shears. This helps prevent the fungal infection from spreading to the rest of the cactus. Place the infected pads in a plastic bag and dispose of it in the trash.

Transplant the cactus after removing all of its infected pads. Use a clean pot that has not been exposed to fungal spores. Use pasteurized soil. If you cannot find any cacti potting soil labeled “pasteurized,” make some yourself. Slightly moisten the potting soil, place it in an open plastic bag and microwave it for about four minutes.

Keep the pads and leaves of the cactus dry. Some lesions, particularly those caused by the fungus Phyllosticta, may fall off when the cactus is no longer excessively moist. Keeping the plant dry will help prevent future fungal infections. Water the soil around the plant's base, but do not splash water on the cactus itself. Watering in the early morning will allow the plant to dry out throughout the day.

Apply a fungicide like thiophanate methyl to outdoor cacti during a rainy season. This may help prevent the development of new fungal infections. The amount to apply may vary between brands, due to varying concentrations. Follow your selected product's directions.

Remove the entire plant if it is heavily infected to prevent the fungus from spreading to other cacti. Place the cactus in a plastic bag and dispose of it.