I think my orchids have black rot. Why? And what do I do?
Answer from Don Ghiz
If you ask a hundred peeps how to grow Cattleyas, you’ll get 100 answers, all different. But to me, black rot is a sign of too much water or not drying out enough between waterings. We tend to love our plants to death. LOL.
Black rot is a fungus and spreads very fast. If I see it, and not as often as people who water more than me, I cut to clean green and then put cinnamon or fungicide on the cut.
One more point, if I may. Cattleyas should be planted in the smallest pot they will fit in. Otherwise the center of the plant and bark stay too wet, causing scale and rot issues. Let them dry out until you think they’re dying and then a good watering. They bloom better, too, if stressed.
Answer from Jay Balchan
If you grow Cattleyas like I do, one of the most devastating diseases you can get in your growing area is black rot. I do not know the scientific name for this bacteria, but it is the fastest spreading rot I have ever seen, and once it gets into the pseudobulbs of your Cattleya, the plant is pretty much compost. This rot usually forms on a leaf after a heavy rain. For me, growing in a greenhouse, I can get this rot on plants that sit under my roof vents when the rain is hard enough to blow in and drip on leaves. Black rot is exactly as the name says. It is black in color and quite soft. The “good news” for this type of rot, if there is any, is that it is easy to spot and that it usually (but not always) forms on the “meat” of a leaf and not in the crown or axis of the leaf.
When you see this rot you MUST TAKE IMMEDIATE ACTION. Trust me, if you wait even a day, that rot will have already gotten down into the pseudobulbs and all is most likely lost. The only cure for this is to remove the infected area by a wide margin. You cannot treat this rot with cinnamon or other topical treatments. When you do cut the leaf off, cut at least 1 inch beyond any rot you can see. If you have 2 inches to spare on the leaf, take the extra inch.
Losing one leaf is far better than losing the plant. After cutting the leaf, I always treat with a topical powder fungicide. Cinnamon would be the greener option, but it is not as powerful. If the rot has gotten into a pseudobulb, then you need to go at least two bulbs back and cut the plant. Even then you are likely to have a poor outcome. You can sometimes see the rot as a small dot/circle of dark tissue in the middle of the pseudobulb. But even if you can’t see it, it can still be there.
Just remember to take action immediately if you see this type of rot on your plants. If you put off treatment for even one day, the whole plant is a goner.