I have recently had a phrag diagnosed with phytophthora. Aka plant killer. How can this be prevented in Phrags? Subdue and Truban are the best treatment. Can these be used on Phrags or will they kill a phrag?
You might consider treating your plants with Concentric Ag's Inocucor Garden Solution (to be renamed "Synergro" as soon as California registration comes through). It is a blend of several beneficial bacteria and fungi that populate plants and media, where they predate pathogens, secrete antibiotics to prevent future infection and hormones to stimulate growth. If you deflask seedlings, treating them will greatly enhance the survival rate.
I was approached by the company to carry it in 2014, so started using it on my own plants, and have not seen any disease or rot since. It is sold as a probiotic, registered as a soil and plant amendment, but can be a curative, as well.
It is effective on most plants - I'd say "all", but I haven't tried it on that many. A few non-orchid examples:
In PA, my wife planted New Guinea impatiens plants in our flower beds every spring, and every spring they succumbed to molds or mildew and were badly wounded. One spring, after Inocucor asked me to carry their product and sent me sample material, I tried spraying the plants once, immediately after planting. No molds or mildew that year, or any year after that when we repeated that regimen.
Also in PA, I had a 50' tall American Ash tree start losing its leaves in late May, and started seeing mushrooms forming a ring around the base. I mixed up about 15 gallons (using 2 liters) and poured it around the roots. No further deterioration al year, and the following spring it came back as if nothing had happened.
Here in NC, where we're learning all new diseases, a red, Japanese maple developed a fungus that made the leaves get brown tips and curl. One treatment from a hose end sprayer, wetting the plant and pretty well soaking the root system, and that stopped, and this spring it came back, defect-free.
I've taken to treating all plantings in the yard at least once a year, including some cycads. They have gotten Synergro and KelpMax about once every two months since spring, and the two, single-growth plants now have 5 and 3.
I suspect they're working on European sales, but some countries are more sensitive than others about importing live microbes.
There is another product, EM-1, that has contains only lactobacilli, making it less broadly effective, soI don't know if it's effective against fungi like phytophthora, but it's still a decent inoculant.