From: Rebecca Green
Dear Agatha, Hostas will grow almost anywhere. They will take full sun or shade. They don't need a lot of moisture, but will grow in boggy conditions just fine. Few things kill hosta. They are troubled by slugs in the shade though. Commercially available slug bates are effective. It sounds like where you live is an ideal environment for fungus. So perhaps your plants succumbed to a fungus disease. If fungus is a problem sprinkle your plants with sulfur powder.