Oncidium with sun damage, black spots, ailing outer leaves
 

Hi everyone,

I have an oncidium that I recently got back after a long period in someone else’s care. It was under too-bright grow lights and received some burn damage, but was seemingly otherwise OK.

I’ve been keeping an eye on it and I suspect there’s also an infection. The spots seem to be worse, aren’t only adjacent to the lead burn, and two outer leaves are yellowing and very spotty.

Whatever this is, it seems pervasive in the plant. Most of my past issues have been solved by trimming an infected leaf. What’s the best way to treat this? When should I declare it beyond saving or not worth the risk to healthy plants in the house?

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Welcome to the Orchid Board!

I see a plant that didn't get enough water for a long time. Oncidiums like to stay evenly moist, and it is best if they never dry out. The moss is crisp dry. That works for some other orchids, like Cattleyas and Phalaenopsis, but not for Oncidiums. When they dry out the pseudobulbs develop wrinkles. Leaves take on a dull grey-green hue rather than being bright green. They get spots and horizontal wrinkles or pleats. New growths turn brown and die.

There is a chance the numerous fine black spots are damage from spider mites. Draw a tissue up the underside of the leaf from pseudobulb to tip, with a bit of pressure. If you see brown or red spots there are mites.

Fortunately these are tough plants that bounce back well when conditions improve. The older parts of the plant won't improve much, but new growth can be normal, and it may flower on the next growth.

To save typing, have a look at this recent thread:
Brassia orchid leaves turning yellow

Thank you for your response! I admit I’ve been neglecting that plant a little bit in quarantine. I’ve given it a good dip-watering and trimmed the worst leaves. Will continue to monitor.

I’m a little cornered that spotting seems worse than a reference photo I took about two weeks ago, given that it’s been in appropriate lighting for that time.

Many Oncidiums always have lots of spots. Onc. Sharry Baby is known for this. A drought-damaged plant like this may continue to develop spots until the plant becomes happy. The spots aren't related to light, they're related to insufficient watering and humidity.

Be sure you check for spider mites. They attack plants during periods of warm temperatures and low humidity. They prefer plants with soft, thin leaves, like Oncs.