Years ago when I had hundreds of iris, I did have trouble with botrytis and used Benlate which is now off the market. I still have most of a bag and so am treating my planted iris. I used to treat before planting. A disaster at a greenhouse caused it to be pulled, but from what I have read, it was a knee-jerk reaction. Appears might have been too strong an application. I have had a little soft rot but I think I was able to save those. I remember losing some Schreiners over the winter, but they may have been planted too late. Have lost only one that was planted early enough to survive. Am not sure what killed it as again it was over the winter. So far no rot of any kind in the two years since I started up again. But we are very dry here, so I don't have your problems. Annual precipation at the airport which is a bit dryer than at my house, 16.1 inches. We are the second driest state in the Union. I had a big clump of Pacific Panorama that got botrytis and I treated it in the ground and it completely recovered.
for all those who are suffering losses. May your 2016 bring better results.