Dendrobiums need your help!

[OnicheK]

Hello,

I noticed some spots on the leaves of some dendrobiums I have - they look as if some black liquid were spread on the back of the leaves. The spots don't seem oily and, at first, I didn't take them too seriously either.

But it is! To the one which suffered the toughest attack (a nobile-type hybrid), it begins to spread towards the pseudobulbs, as you can see in the images below.

I think it could be some fungus, but I have no idea what type and/or how to get rid of it. Other 9 or 10 dendrobiums have it (and one hybrid cattleya), but it only begins now: the leaves begin getting "dirty", but not the PBs for now. It's strange, because the affected leaves are not falling. They stay attached and with this type of spots that cover them more and more.

The infected plants got isolated, but I am not sure that I was in time to avoid further propagation.

What do you think it could be? And how could I treat those poor plants? Are they treatable or should I throw away all the plants that have it?

Should I spray all my plants with some fungicide? What type?

Thank you in advance,

O.

[camille1585]

I was tempted to answer botrytis, until I read that you say they are not oily! Is this spreading quickly? I think bacterial rot usually tends to spread more quickly than the fungal type. Hope other people can help!

And this is weird... I just saw your post on Orchidéefantome!! If you don't mind my asking, are you an italian who speaks french, or a french in Italy, or something else?

[Ross]

I would treat with a bacteriacide like Thiomyl or Physan 20. I think this is a rot agent.

[OnicheK]

Hello, Camille!

Thank you for your answer. I used to live in France, now I moved to Italy. You can write to me in English, French, Italian - feel free to choose

Orchid language would be best though

[OnicheK]

Thank you for your answer, Ross! Your answer gets me sad though and even more worried...

Well, let's hope for the best!

O.

[Leisurely]

If you can take a paper towel with soapy water and wipe the black off, it is sooty mold. I have two dendrobiums that exude a honey dew from the edges of the leaves. The sugary content of the honeydew grows a mold. It is completely harmless to the plant but looks very ugly if not washed off. If you can't wash it off then you should treat for fungus.