Ask Mr. Smarty Plants

Shasta daisy, Leucanthum vulgare x superbum is native to Turkey, Russia and Europe. The Lady Bird Johnson Wildflower Center is dedicated to the use, care and propagation of plants native not only to North America but to the area in which they are being grown.

Since we have no information on this plant in our Native Plant Database, we will try to find some information on the fungal root rot, itself. From the NGA Garden Shop website, we found the information that Shasta daisies need full sun and well-drained soil. You didn't say how long you had been raising the flowers or what your soil is, but if you have a clay soil, or poorly draining soil, these plants either need compost worked into their soil for drainage, or a raised bed. If they are in shade or part shade, that just encourages the fungus even more. From the University of Illinois Extension website, we obtained this information on Armillaria Root Rot. While this article emphasizes fungal attacks on woody plants, trees and shrubs, it points out that herbaceous blooming plants can also be affected.

We would suggest you contact the University of Illinois Extension Office for either Grundy or Will counties.  If this is an ongoing problem in your area because of the soils, they should have some advice to offer you. Or maybe just sympathy. We are sorry, too.