Hi-Yield Captan 50W Fungicide is considered rainfast after having dried completely. This normally takes at least 2 hours.
Unfortunately, Hi-Yield Captan 50W is not labeled to be used on tomatoes. You can use something like
Unfortunately, Hi-Yield Captan 50W Fungicide is not labeled to treat Bearded Iris Rhizome nor any type of rotting.
We recommend getting in touch with your local extension office to get a positive identification and what the source may be for it.