Help with dendrobium.

[moniluhum]

Just found these spots on leaf of dendrobium. Also saw black areas on base of some the leaves. Is this fungal?If so what is best fungicide. Looked up st augustine orchid society, but could not find one that best describes this ailment.

[WhiteRabbit]

[NYCorchidman]

No need to spray anything hardcore as the black stuff is harmless. (in picture 2).
It is very common when orchids are grown under high humidity like greenhouse setup. Almost all my nobile hybrids come with them on their 'armpits'.
It is called sooty mold and they like to grow on plant exudates.

The other one, the dark spot, are they first and last photo of the same leaf??

The reason I ask is the first one shows the light halo around the spot, which worries me as this is something serious.

Regular spots without halo are usually harmless as long as they don't spread.
It is most often caused by either sunburn or bacterial attack.

[moniluhum]

The two pictures of the spots are of the same leaf. You mentioned bacterial attack. Is that something you need to treat?

[NYCorchidman]

As long as it is not growing in number or size, you should not worry about it.
It usually is just one time thing.

But with the halo around it, you want to keep a close eye on it. I call that they mystery ring disease and once you see it happen, then there is no stopping it.

[moniluhum]

I have already cut the affected leaf. Would it be alright to say use a fungicide to prevent any potential afflictions
Also, if you are treating a plant how soon can you remove the plant from quarantine?

[NYCorchidman]

Nobiles are pretty much disease free given the right culture. Strong light and lots of water is all they need.
I wouldn't spray healthy plant for preventative measure as doing so is one, not necessary, two can weaken the plant.

Your second question is for a while new thread. lol

Spraying sick plant takes at least a few weeks. You want to spray at recommended frequency, and then you want to make sure sick plants are healthy again.