Note: the crowns appear alright atm, it is affecting the outer leaves and probably the roots. I bagged them and they have perked up temporarily. I am not expecting the improvement to last.

I have no idea and i'm looking for a different way to disinfect pots myself, at the moment I just bleach them for an hour or more and then wash with dr.bronners sal suds detergent.

I don't know if there is a cure for phytopthora.... (for root rot) I've heard hydrogen peroxide and i'm about to try neem - I've got a philodendron moonlight and geraniums plants also showing root rot although I don't think it's phytopthora although the philodendron is strange... anyway i'm about to try neem oil as a root wet ... at 1 percent... I've no idea if it works or not. (the hydrogen peroxide did not work..the ones that were healthy stayed healthy and the sickening ones died)

my advice though is to cut leaves off the suspect plants... and replant as soon as possible... even then it might be too late since the fungus is already in the 'blood'.

maybe some kind of fungicide will help but I've no experience.

oh ... and keep every tool used absolutely sterilized ... I've been using a lot of rubbing alcohol on scissors/knives as well as bleaching and washing all pots....

also isolate suspect plants if you can... if it is possible it can be transmitted from plant to plant by fungus gnats or on the air as fungus spores....then better safe than sorry.

all the best.

I did treat one of them with hydrogen peroxide, for the sake of experimenting. Then I put it in an area with good air circulation. I wont be sad if i lose these guys but it is my fault they got sick. I delayed much-needed repotting, and let the soil dry too much between waterings. None of my better-cared-for babies (the ones in the right size pot) got sick, even though they were directly next to these ones.

It has taught me a lesson in repotting. It's not good to procrastinate.

The one I treated with hydrogen peroxide was not as far gone. But we will see if it shows any signs of improvement. From what I have seen, it is always fatal. But I havent seen it a lot.

I don't know if it is Phytophthora or not. I just call it "rot."
I have repotted, scraped and treated with cinnamon but I haven't had much success saving any plant after it has seriously started to rot.
I had a bit of luck with leaves taken from rotting plants. I am then very careful about cold/wet conditions of the leaf culture but even that is dicey as the leaf may be infected/affected.
Prevention seems to be the only "cure."
I get rot in cold, wet soil with a usual component of low humidity.
Best of Luck! If you do anything and it seems to be effective, make a note of it and post it for others to try.