Diagnose orchid problem

OR_KIDSeptember 4, 2012

I'm looking for a diagnosis of what is wrong with my Lori's Star Dedrobium. It appears to develop brown spots on the new leaves emerging from new spikes. If I don't cut off the area of the leaves affected by these spots the whole leaf turns yellow and falls off.

The spots first appear on the underside of the leaves then spread out laterally and on the top of the leaf. Older leaves seem to be affected differently developing spots too but the leaves do not yellow and fall off.

It appears some of my other orchids have this blight too...but are affected differently (and not as bad)

So I have two questions:

1. What am I dealing with?

2. Can I get rid of it, and if so how?

If it is a fungus it appears I will need some sort of systemic treatment (ie that is absorbed into the plant via roots or leaves). I've tried sulphur and sulphur based fungicides to no effect. I live in Canada in the Maritimes. Is there anything I can purchase off the shelf?

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arthurm(Sydney, NSW AUST)

You have a Formosum Type Dendrobium which under some growing conditions are considered difficult.
Fungus spots may be an indicator that the plant is not happy. If your conditions are not too bad you could try using one of preventative treatments such as echo oil which is based on Canola Oil that puts a preventative film on the leaves to stop the fungus getting in. Once those black scars are there, they are forever even if the fungus is stopped from spreading.

    Bookmark   September 4, 2012 at 4:41PM
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Thanks arthurm

I'm wondering if the fugus is already in the plant. perhaps it's not so clear from this image but it looks like the three newest leaves on one of the new canes are yellowing and drying out?

    Bookmark   September 4, 2012 at 8:25PM
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arthurm(Sydney, NSW AUST)

Sorry, i am not an expert on fungus, but from my experience it is more likely to attack on dewy autumn nights when the fungus spores can penetrate the leaf surface. Ditto, if the plant is growing in unsuitable conditions and its natural resistance is weakened.
When i said that those Formosum Types Dens are difficult I was referring to here. latitude 33S. Over 1000 orchids exhibited by members of a local orchid society in the last year and nil Formosum Type Dens.
Check the net for culture notes to see if your conditions are close to those recommended. The plant doesn't look in bad condition but take note that i have tried to grow these beauties several times and they died Sigh!
Hopefully, someone with more success will answer your question

    Bookmark   September 5, 2012 at 3:28AM
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