June 30, 2000

It's Back - Crown Rot of Hosta

I've avoided looking in the direction of my hostas since the onset of hot and humid weather. I decided to take a glance the other day and spotted the dreaded symptoms of crown rot - bronzing, wilting, and collapse of the outermost leaves. Inspecting the stems near the soil line revealed the white threadlike strands of the fungus and small tan sclerotia, resistant structures that resemble mustard seeds. The causal fungus, Sclerotium rolfsii, causes a decay of the stem near the soil line, allowing the leaves and petioles to be easily pulled from the plant.

Garden Lilies

White Mold on Ornamentals

White mold, caused by the fungus Sclerotinia sclerotiorum, is a serious disease problem on a number of different plant species. In Iowa, the best known host is soybean. However, many ornamental plants are also susceptible to white mold. The disease has recently been found on chrysanthemum and salvia samples submitted to the Plant Disease Clinic.

The disease is usually first noticed when the plant wilts. A fluffy white mold forms on the stem. Eventually, hard black sclerotia about the size of a sunflower seed can be found on the inside of stems and on the stem surface.