Black Rot
By Andrea Peck
Leave it to the orchid to be dramatic—even when ill.
Not long ago, I was having trouble with my orchid. It had not flowered in a long, long time. Its roots were flinging themselves into the air as if they were howling in protest. My expectations had sunk to survival mode. I just wanted it to stay alive. In a last desperate attempt to save it, I decided to repot it.
And, as I've been known to do in fearful situations, I went one step further and opted to repot it myself. Despite my lack of any experience whatsoever in orchid repotting this seemed like a reasonable endeavor. I held my breath and bought the special soilless mix. Then, I bought a special pot with holes in it. For a while, things went swimmingly. In other words, my repotting did not kill it. I moved it to a new home on the kitchen table—an area with bright, indirect light. It soon grew two nice green leaves. Things were looking good.
Then, alas, trouble—in the form of a bit of translucent mottling-- reared its head. It appeared innocuous, so I ignored it. If I remember correctly, it looked like a large water spot, which it probably was. I'd put my orchid out in the rain thinking only of free water.
Not long thereafter doom set in.
Doom in the form of an inky mass, jet black and seeping. It was as if the hand of evil was wrenching the leaf into a one-dimensional abyss. I found out that the heinous black spot had a name: black rot. A simple name reminiscent of a toothless pirate or slippery wraith.
Black rot is caused by two fungi, Pythium ultimum and Phytophthora cactorum. Apparently these two fungi are only able to survive in wet conditions. The spores of the fungi are made of zoospores which are mobile in water—and capable of infiltrating the leaf. Once it has its hooks in the leaf, the spore develops a vegetative mycelium, which allows it to proliferate throughout the leaf. This is when the leaf begins to show the characteristic black blemish.
This plant disorder is serious. If left untreated, the zoospores will cavort gleefully right down to the root of the plant. Once that happens your orchid is ‘nevermore.'
Preventing death is easy if you catch it early. Use a knife or scissors that are disinfected. Then cut off all infected tissue. If the problem is severe, this may mean cutting into the pseudobulb or even the rhizome. Once you have removed the infected portion, treat the ‘wound' with a fungicide. Interestingly, cinnamon is recommended by the American Orchid Society. You can even use cooking oil to make a thin paste with the cinnamon. Sounds tasty.
Prevention is pretty simple: keep standing water off of your orchid and allow the plant plenty of air circulation to minimize a buildup of moisture.
Well, that's it. I'm off to take my own advice with a pair of sharp scissors, a dash of cinnamon and a bit of olive oil.