Round fungus spots attacking my Paphs. If some of you have insights on a durable solution.

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treefrog

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Matoury - FRENCH GUIANA - FRANCE
Hi everyone, for the last two years, I've been struggling with what appears to be a fungus attacking the leaves of my Paphiopedilums. I live in the French Guiana Amazon and the climate is very humid! I grow all orchids under a 50% shade house and my shade house is quite ventilated. However, each rainy season, observe a recrudescence of these very annoying round brown spots appearing on my plants. I don't believe the climate here is much more different than the one in Malaysia, Thailand, Borneo, etc from which most of my multi paphs are coming from (roth, lowii, haynaldianum, philippnensis, etc.)

I've been applying both soft treatments (cinnamon and copper) and harder one (Prochloraz and Benomyl) but while it stops the attack for about a week or two, it always comes back.
Here are a few pictures to better illustrate my problem (note that the white stuff topping the media is dolomite, following @Roth advice for better tropical culture).
I thought that maybe some of you that grows their Paph in more tropical climates might have encountered this 'fungus' before and would have good advice on how to resolve this issue: changes in culture, more adequate fungicide, or even beneficial bacteria/fungus, etc?
Many thanks in advances for your input!
Cheers,
Math

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Instinctively it looks to me as if it comes from the water. The spots look dry!?
Droplets stand on the leaves. Perhaps the water is not 'clean' enough? You could try disinfecting the water first. It might also help to water the plants for a while directly on the substrate and not from above. If that solves the problem I'd guess the cause is in the water (germs etc.).

You can also see from the community pots that some are infected and others are not. Perhaps the leaves of the infected plants are wider and at a different angle so that the (infected) water remains there for longer/forms larger drops.

Just an observation.

I don't have such problems. I use a terrarium, unventilated, 75-80% rH, with a lot of sphagnum on the bottom. However the high humidity may encourage the problem because it could promote the present infection. But its certainly not the main cause.
 
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I have this exact same problem even thought my Paphs are in an exceedingly well ventilated area. It seems to strike at random, most of my plants aren't affected.
 
I have a sangre de grado tree in Tarapoto I could use to collect the sap. However, I would very be interested in identifying this pathogen and learn about ways to prevent it. I use both city treated tap water and the water I collect from the mountain creek next to my greenhouse. The problem arised with both water sources unfortunatly.
 
The pathogen is in the immediate environment. Well, it’s likely in the entire environment around you, but if you periodically disinfect the shade house structure, benches and floor, and kill it in/on your plants, splashing rain drops will have less of a chance of spreading it back to the plants.
 
The pathogen is in the immediate environment. Well, it’s likely in the entire environment around you, but if you periodically disinfect the shade house structure, benches and floor, and kill it in/on your plants, splashing rain drops will have less of a chance of spreading it back to the plants.
I wonder if some preventive probiotic treatments (Bacillus or Trichoderma) would be a solution here.
 
Instinctively it looks to me as if it comes from the water. The spots look dry!?
Droplets stand on the leaves. Perhaps the water is not 'clean' enough? You could try disinfecting the water first. It might also help to water the plants for a while directly on the substrate and not from above. If that solves the problem I'd guess the cause is in the water (germs etc.).

You can also see from the community pots that some are infected and others are not. Perhaps the leaves of the infected plants are wider and at a different angle so that the (infected) water remains there for longer/forms larger drops.

Just an observation.

I don't have such problems. I use a terrarium, unventilated, 75-80% rH, with a lot of sphagnum on the bottom. However the high humidity may encourage the problem because it could promote the present infection. But its certainly not the main cause.
I have this same thing. But, never water from above, always water the medium.
 
The pathogen in your photos is a common infection on wild orchids, at least in the Peruvian Amazon. And like in your observation it can be one plant and not on others next to it.
I saw the same problem on a group of paths I had growing in the garden under trees receiving full rain. Never any problems until I moved them under a roof. Then various plants presented with the problem.
Ugly but never killed a plant.
 
I wonder if some preventive probiotic treatments (Bacillus or Trichoderma) would be a solution here.
Probiotics may very well help, but rather than picking a specific one and hoping it works, you’d do better to try a multi specific one with broader-spectrum effects.
 
As a basic preventative cleary and azoxystrobin together as a drench stops most leaf fungal issues...

Should be mentioned the probiotics are not thoroughly tested on orchids and considering theres no regulations on them as far as I am aware, I wouldn't trust the purity of the products. Its very possible a blend could contain a mildly pathogenic strain that slows growth
 

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