Like bwaynef said, county extension to diagnose soil sample is great if this is happening a lot, and like guywires said, emergency repot some. Plants in stress give off signaling hormones from their roots that opportunistic bacteria/fungi can likely smell we don't even know what's going on with soil science anymore getting so complicated. The good news is we do know some pathogens and and we know effective treatment if identified.
I would do a soak, put the plants in the kiddie pool like mentioned, and instead of the recommended drench do 1/2 dose (because they are sitting in the water) A FEW kiddie pools if you have lots of plants. Don't mix the healthy with quarrantine plants.
Largest consideration how much money/time to spend 'fixing' and what plants get first treatments.
I would do a soak, put the plants in the kiddie pool like mentioned, and instead of the recommended drench do 1/2 dose (because they are sitting in the water) A FEW kiddie pools if you have lots of plants. Don't mix the healthy with quarrantine plants.
Largest consideration how much money/time to spend 'fixing' and what plants get first treatments.