After 40 years in the same house/same garden/same hostas coming up each Spring I have, this year, developed Southern Blight in virtually all (unconnected) parts of the yard. Neighbor not affected. Most hosta varieties showing symptoms of Blight. I had my lawn company spread mulch on all the beds about a month ago...could the Blight have come into my garden on it. The company says \"not possible\", they use a reputable supplier and no one else has complained. We have had some rain in St. Louis, but nothing with the weather (except for a late SPring) has been unusual. I do not know the ph of the soil.
Southern Blight Destroying Hosta
Certified GKH Gardening Expert
Fungicides are the only treatment for Southern Blight.
This link has more information for you.
You could contact your County Extension Office to see if others in your region are having issues with this disease. They may know the best product to use for your particular area.