Black spots on Oncidiums

[jmrathbun]

Can you tell from the attached photo what's eating my Oncidiums?

[Alice-NJ]

It seems that no one has replied to your post, so I'm going to offer the bit of information that I have on oncidiums. The word is that oncidiums suffer from dark spots which do not cause much harm, but whether or not the spots on your plant are the type that is referred too, it's hard to tell. If no one more knowledgeable replies to your question, you might try to do some research on this condition.

[raybark]

One theory I have heard is that of the buildup of salts exuded through the leaf stomata, resulting in some localized toxicity.

I have no idea if that has any validity, but I have noticed over the years that it is 1) common, 2) only an aesthetic issue, as the plants don't seem to "mind" it, and 3) reduced in occurrence when the RH % is kept high.

[amendazn]

The chat is that oncidiums ache from aphotic spots which do not could cause abundant harm, but whether or not the spots on your bulb are the blazon that is referred too, it's harder to tell. If no one added abreast replies to your question, you ability try to do some analysis on this condition.

[jean2]

These black spots are caused by Botrytirs it's a kind of fungus. Low air circulation and too much moisture cause this problem, increase the air circulation and reduce the humidity.

[raybark]

Originally Posted by jean2

These black spots are caused by Botrytirs it's a kind of fungus. Low air circulation and too much moisture cause this problem, increase the air circulation and reduce the humidity.

Hi Jean. Do you know that for a fact or have some reference to back that up? I don't mean to be "challenging", it's just that I've never heard that explanation for oncidiums, and it doesn't jive with my own observation. If that's the case, it lends a whole new series of approaches to preventing it.

Sure, Botrytis cinerea has been known to produce black spotting on blossoms under moist, stagnant conditions, but the "oncidium spotting" I've seen tends to occur in drier environments.

[richardb]

I agree with Ray that the spots are unlikely to be botritys on Oncidiums. There is no element of "dusty" or "decaying" around the spots.
I have this regularly and always understood that it is cultural. Ray says salts from the stomata, but the stomata are under the leaves. Another explanation is too hot or airless. Zygopetalums get black spots sometimes too, but like Oncidiums do not seem to mind.
Richard

[otis226]

I've read that misting the Oncidium alliance can cause back spots on foliage. Seems to be true for a new Aliceara I just got, but I'd bow to Ray's and others experience, for sure.
Tony

[erna]

Originally Posted by raybark

Hi Jean. Do you know that for a fact or have some reference to back that up? I don't mean to be "challenging", it's just that I've never heard that explanation for oncidiums, and it doesn't jive with my own observation. If that's the case, it lends a whole new series of approaches to preventing it.

Sure, Botrytis cinerea has been known to produce black spotting on blossoms under moist, stagnant conditions, but the "oncidium spotting" I've seen tends to occur in drier environments.

I agree with you.
I have several Oncidium and the spotting is certainly not caused by botritys. As a matter of fact it occurs naturally in some Brassia.
erna