How to Manage a Phyllosticta Infected Orchid

[aussieboy]

I’ve read from AOS that Phyllosticta is near impossible to erradicate from an infected orchid. As far as the title of this post goes, can you share your experience on managing the spread of this plant disease? if you own a collection of orchids, would you completely isolate an infected plant throughout its lifetime?

If water and humidity helps spores to grow on leaves, does watering the roots only a good idea to avoid the spread?

I own a vanda that is infected. Unknowingly it has Phyllosticta, I shared the water across my collection which caused the spread. Now I have a new set of seedlings that I don’t want to get infected.

[Shadeflower]

Phyllosticta is just a fungus.
It's true that fungusus are all around us at all times. Only hermetically sealed labs don't have any fungus but it's not really a big issue you are making it out to be. Fungus can grow on living tissue but strong orchids should not really be affected by a bit of fungus. It does seem to affect certain soft leaved bulb producing orchids like Oncidiums more than vanda's.
Funguses only grow in humid conditions which is the conditions orchid like but a big temperature differential between day and night, a gentle air flow to prevent stagnant conditions and some strong sun during the day will deter fungus from growing.

The worst is when a fungal infection infects plant tissue and is able to spread because once it infects a plant it has the perfect conditions to spread fast and the affected portion needs to be cut off and removed.

I have lost a few plants to fungal infections and you could argue I was keeping the orchids too wet which let the fungus spread but at the same time I know it has only happened to weak stressed plants. So I could blame the fungus and keeping the fungus away might help, sure but to me having healthy plants that can fight off fungus themselves is what ultimately gives them the best protection I think. Keeping orchid a bit dryier initially while they are stressed seems to help give them the best chances and giving orchids a good clean when it comes from a different greenhouse to wash off any fungal spores from the plant.

They always have fungal spores on them.

[estación seca]

There is a good article about this fungus on the Web page of the St. Augustine Orchid Society. It is also covered in Martin Mote's book Florida Vanda Growing: Month by Month.

[Ray]

Thiophanate methyl (Cleary’s 3336 or Thiomyl) should be effective against it.

It also wouldn’t hurt to disinfect the growing area with something along the lines of Physan, to eradicate fungal spores that are certainly well distributed at this point.

[Orchid Whisperer]

I agree with Ray's fungicide recommendation.

I would also add that you should provide soluble calcium and magnesium. Low concentration provided on a regular basis with routine watering. Gypsum (or plaster of Paris) and Epsom salts, a teaspoon of each to a gallon of water. Once dissolved, add a few ounces of that solution, per gallon, to your regular watering. The Ca and Mg help with disease resistance. The solution also provides sulfur.

Older plant leaves should be removed if they start yellowing and showing signs of Phyllosticta scarring. You see less scarring if the plants get the proper nutrients, the proper sunlight for the plant, fungicide treatment, and supplemental Ca and Mg.