Species Specific Forum : Growing Orchids and Hybrids

[Rachel]

Hello Orchid Experts,

I would appreciate your help with a problem I've discovered.
I noticed some black spots under two of the leaves on my Dendrobium nobile today.

I wonder is this botrytis? I've read that botrytis appears on the flowers in certain Orchids (among which, Dendrobium) but my flowers are clear!!! If it is botrytis, what should I do? Should I remove the affected leaves? There seems to be an area of black underneath the main stem skin too. Is there any fungicide that you might recommend?

While I don't directly mist this Orchid, I do mist plants directly above it so it may be getting damp. I have isolated the Dendrobium nobile from other plants and am wondering what to do next.

Please help?


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Coming to the measured conclusion that the Hokey Pokey IS what it's all about.

[admin]

Hi Rachel, it looks like a fungal attack which is common on most plants during a cold snap. It's usually found where water has been during the cooler nights. Possibly the water from spraying has gone down into the leaf joint and it would settle under the leaf sheath, which you are referring to as the main stem skin. It's important to ensure that the plants are dry prior to night fall and that the temperature doesn't drop too low at night, this is what causes the bacterial fungus attack. It should'nt contaminate other plants nearby, they will get it if similar conditions get to them. Increasing air movement helps prevent it as well. Normally it wouldn't do much harm except badly mark the leaf, but that would drop anyway in the next 12 months. However, that particular leaf in the photograph shows it has settled on the stem and is protected by the leaf sheath, on some ocassions I have seen it not only mark the stem, but eat into it slightly causing a permanent mark. You can cut off the leaf then gently pull the leaf sheath of the plant by stripping it downwards then cleaning up the fungal attack with clean, tepid, fresh water.
Overall, it's unlikely to kill your plant but merely leave it disfigured.
During the cooler months, try to spray foliage early enough so that the plant is dry by nightfall, try not to spray so that it runs into the leaf axles, better to lightly mist plants several times per day rather than say, two heavy sprays. Try and ensure plants have good air movement 24 hrs per day. This should reduce the chances of bacterial attack, but may not elliminate it completely.
Bill.
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Earth is the insane assylum of the Universe.

[Rachel]

Hello Bill,

Thank you very much for your extremely informative and comprehensive reply, which has answered all my questions.
Tomorrow morning I will go about cleaning the leaf axles and removing the affected sheath as you have described.
Many thanks once again.

_________________
Coming to the measured conclusion that the Hokey Pokey IS what it's all about.

[Rachel]

Bill,
Just wanted to thank you again. The plant made a full recovery : )
_________________
Coming to the measured conclusion that the Hokey Pokey IS what it's all about.

[trey.sanders]

Hi Rachel

It's great to hear about peoples successes and where advice has worked.

Cheers
Trey

[admin]

HI Rachel, thanks for letting us know the plant has recovered. It's great, as Trey says, to hear of such success.
Bill.
_________________
Earth is the insane assylum of the Universe.