Purple Discoloration on Oncidium Sharry Baby Pseudobulb

[Ghosthunt64]

Hello, several weeks ago this odd purple blemish appeared on one of the pseudobulbs on a {little babby} division of Oncidium Sharry Baby ‘Sweet Fragrance.’ It doesn't seem to have developed much if at all in the past couple of weeks, and the new growth is growing pretty fast {for the size of the plant at any rate}. The blemish is neither soft nor wet. I'm worried it's something along the lines of Fusarium or a black rot but haven't found any descriptions or images that match this. Could anyone here identify it, and if so recommend a course of action? :thankx:

[Orchid Whisperer]

Fusarium causes plants to look as if they have experienced drought for months, meaning leaves and pseudobulbs look severely dessicated. Not just slightly in need of more water. I don't see any such signs in your plant. Is the discoloration in the pseudobulb closest to the viewer/camera in the top photo? (Photos are a little fuzzy, just making sure.). Purple coloration can happen due to a number of things, some benign or beneficial (such as improvement in light) or in response to cultural or environmental factors.

I do see some black dots. Those could be a fungal infection (common in Oncidium and relatives). Treat with a general purpose fungicide such as Cleary's (thiophanate-methyl), available online if not in your local garden center. Providing more calcium also can help plants resist diseases.

In recent years there has been a lot of hysteria on YouTube regarding Fusarium. Take that advice with a very large grain of salt, maybe an entire salt shaker. A few prior posters here on the subject of Fusarium have cut up entirely healthy plants looking for the dreaded "purple ring". Cutting should be a last resort. I would first look at:
1. Does the plant seem badly dehydraded? (Yours doesn't). Plants with Fusarium appear almost scorched.

2. If dehydrated, can dehydration be explained by another cause (root loss, poor watering, etc.)? Does correcting the problem improve the plant (do new growths grow properly when conditions improve)?

3. Seek out/bookmark the St. Augustine Orchid Society website, look for their pages on diseases and pests for Fusarium symptoms. There is also advice there about chemicals that may be used to control various diseases and pests.

4. If, after checking all other possible causes, you can't explain what you are seeing, except as Fusarium, go ahead and cut/check for the purple ring. It is possible to treat Fusarium, I have a Cattleya that had it about 20 years ago, after treatment and recovery, it grows and blooms well.

[Dollythehun]

Agreed with OW's advise. Please don't start cutting. My Oncidiums often have less than perfect foliage and pbulbs. They tend to look less than perfect. But I wouldn't worry about that spot unless it spreads rapidly or gets mushy.

[Ghosthunt64]

It's not the close one in the first image, it's the one in the back with the dark lower half. But, thanks for the comprehensive advice and I will probably fo a fungice treatment soon!

[fishmom]

Here's a link to the St. Augustine cultural information. It is beyond complete. I urge you to spend some time with it before you apply any chemicals to your plants.
Orchid Pests, Orchid Diseases