| If the rot is on the leaves cutting it off is the best treatment. If it gets into the rhyzone it is lost. If rot has gotten into the psuedobulbs and rhyzone cut off the bad bulb and take one good growth off as well. You have to stop the spread. The only chemical traments are very dangerous chemicals and expensive. For Pythion fungus, which this sounds like, Subdue works at $300 a quart and if it is fusarium then Heritage at about $500 a pound. As I said the best treatment is a pair of scissors. Be sure to clean the cutting instrument with each plant and wash your hands after handling each plant.
You can sterilize with bleach or better is pool algaecide (which is the same chemical as physan). I am surprised to se so much rot in only three days of rain. Here in SW Florida rain can be every day for months and while I get some phythion fungus it is only on a small percentage of my nursery. You may have started with only a small infection and spread it with your hands or splashing water from plant to plant. Morelikely, it may have spread in the move to the new home in boxes or vans rather than the rain. | 
