Lighter spots on top of leaves, dark bumps on bottoms of leaves

[reptilegrrl]

Most of my oncidiums have something like this on one leaf or another, and so I figured it was probably normal, but I haven't seen it mentioned anywhere or in photos.

I took a photo of my big oncostele. This is the only plant where the issue seems more intense at the center of the leaf.

The top of the leaf appears to have some slight spotting- lighter spots scattered around the leaf. The bottom of the leaf has many dark spots as are typical of onc-type orchids, but in most cases they correspond somehow with the light spots on top. And in the center of the leaf, beneath the largest light spot, there is a hard, dark-ish, irregular bump. All of my onc-types have something like this, but none as big as this one, and none that seem to affect the top of the leaf. Is this a disease?

I do not share water and this orchid came from a source different from my others. ALso, there's no evidence of pests on this or any of my orchids.

[Orchid Whisperer]

Photos are sort of fuzzy and dark, but I'm guessing scale insects (underside of leaves). The yellowing on the top of the leaf, with insects below, it a common symptom.

If you just have a few, a Q-tip or paper towel moistened with rubbing alcohol usually removes and kills them. You should inspect any tight/hiding places on the plant for possibly more scale.

If you confirm that you have scale (those raised bumps wipe off with a paper towel) and find that you have a lot of scale, you should get a systemic insecticide with imidocloprid, use once a week for 4 weeks.

[reptilegrrl]

No scale. The black spots look like the typical oncidium "freckles", and are slightly raised. I did go over the leaf with an alcohol wipe to no effect.

[reptilegrrl]

Here is a better pic. The issue is concentrated nearer to the tips of the leaves than to the base.

[reptilegrrl]

is it possible for it to be scale but not react to alcohol? Some of the dark spots are pits, some of them are raised and feel hard. I looked at them under a magnifying glass as well, but they are so tiny, like pinpricks, that this didn't do much. I also notice it is most prevalent on the leaves that get the most light.

[Orchid Whisperer]

It could be the normal Oncidium spotting, but a few spots are diamond-shaped, possibly Guignardia? (fungus)

When I've had plants with Guignardia, or typical Oncidium spotting, I find that merely increasing calcium helps a lot. Either gypsum, or calcium nitrate, should help, a teaspoon of gypsum (or quarter to a half teaspoon Ca nitrate) should do it. The latter is a fertilizer, so skip regular fertilizer the week that you use.

[reptilegrrl]

I mist this plant with a spray bottle twice a day, sometimes 3x if I am around and the day is dry. This plant also sits directly beneath an led plant light. Could either of those be part of the problem?

---------- Post added at 07:22 AM ---------- Previous post was at 07:01 AM ----------

Also thanks for the calcium tip. Would calcium carbonate be okay?

[Orchid Whisperer]

American Orchid Society advises against water on the leaves for Oncidiums Spotted Oncidium Leaves

I'm not sure the leaves are bruised by water as they state, but it might encourage fungus.

You have some spots that are bumps, others that are not. If the bumps can't be wiped off, they must not be scale. Not sure what it could be.

[reptilegrrl]

I don't water from above, but I mist my orchids pretty thoroughly. Without misting my humidity these days is around 52, with misting I can get it to the high 50s or low 60s. I will scale back the misting and see if that helps. I'm very glad it's not scale.

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[Leafmite]

I find that adding Calcium helps my orchids resist fungus and bacterial issues. Calcium Carbonate is often used in agriculture for plants so it should work very well.
Misting works well as long as the air-circulation is very good but if the water sits on the leaves too long, it can encourage fungus or bacterial growth. The Calcium, though, should help the new growth be more resistant.

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