If that's what it is,
I live in Florida and get powdery mildew occasionally. Happens in Florida Especially with vine type plants. Its our no. 3 public gardening enemy i.m.o. (no1. Whiteflies, no. 2 tobacco hornworm) What I think you actually want is some liquid copper fungicide.
https://www.amazon.com/Southern-Ag-Liquid-Copper-Fungicide/dp/B0052NL4FK
The bottle gives you way more than you will need if you don't grow large scale. But should help control that mildew. Mix two teaspoons or so in a gallon of sprayer water and applied weekly till symptoms vanish. Could also be pest application residue they nursery you bought it from used.
Carefully check the label though. I've heard many similar chemicals have a 30 day waiting period from application to usable fruit. I am not sure this does. Best to find out before you apply though.
If you want cheaper miracle fruit seeds, try tradewindsfruit.com.
They sell the miracle fruit seeds you can try to grow. rock wool and a grow light with some light nutrients might help there.
Also, i.m.o. don't necessarily trust organic methods of pest control with some of the more prodigious gardening problems. Believe me I have tried with things like tobacco/green hornworm and its best to get rid of them right and dead, or else hunt and discover a hopefully provable alternative method (such as ph balanced Armor Si for whitefly control-this could be the gardening gold mine we've been looking for Florida. Instead of killing the whiteflies, you merely prevent them from being able to feed on the plant by strengthening the cell walls of the plant with Silica.) If you absolutely must use organic, then try Dr. Earth Final Stop, which has no application waiting period. I have tried it and can attest that it will not kill horn worms outright. But if it keeps them off your plants (and I can't say it doesn't because after first application I have not seen them reappear,) then have at it. Time will tell on that note. My tomatoes are still alive, at any rate.
-Key