We Get Cactus Fungus Questions
I spoke with someone from your store on the phone this afternoon about a problem with one of my cacti. They suggested that I email a closeup of the affected cactus. This yellowish covering is now over much of the surface area of the plant. I’d appreciate any suggestions for treating the problem. Thanks,
It does indeed look like a fungal infection of “Rust”. Your plant should be treated with a fungicide as soon as possible. Under normal situations I would recommend spraying the plant with a 1-2% Neem Oil solution, an effective, natural fungicide that has limited toxicity to humans and pets and I think you should start with it. Spray liberally with Neem to the point of run off and keep your plant out of direct light for a few days. Reapply after a week. It may take several treatments to kill off the fungus. There will be scaring of the plant tissue, but the orange should fade. Neem Oil is available in 100% that you mix yourself or a ready to use diluted spray, either one will work.
Unfortunately it may be that your plant is so infected with rust, that you may need to resort to something nastier to save your plant. But the systemic fungicides should only be used at last resort and handled with extreme caution, they are designed to cross the cell barrier and do not
care if it is a plant’s cell or your skin cell. If you go that route use chemical resistant gloves and follow the directions completely. Systemics are dangerous and like I said only to be used at last resort.