See:
Rose (Rosa spp.) and hybrids - Armillaria Root Rot
Fir, Douglas and True - Armillaria Root Rot
Notes: Armillaria root rot is a problem mostly in the forest. It could also be a problem in the landscape if bushes are planted in new home sites recently cleared of native vegetation. Armillaria occurs on the roots of many different plant species. The fungus can live many years as a saprophyte in soil, on infected stumps, roots, and other organic matter. Diagnostic mycelial fans can be observed between the bark and wood of the root crown. Mycelial fans are thick, white layers of fungus that adhere to the inner root bark and/or the wood beneath the bark. Avoid wounding roots and overwatering in landscape settings. Removing soil in a 3-ft radius around the crown and main trunk root area will help to minimize conditions that favor the fungus. Remove severely infected plants and destroy them, being careful to remove small roots from the soil. Then replant with resistant species.