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.
Unfortunately Sclerotium rolfsii is capable of causing disease on many different perennials, vegetables, and annuals. Control of crown rot consists primarily of careful inspection before planting and sanitation measures that prevent the spread of the fungus to other plants.
A bulletin on crown rot, SUL 8 Crown Rot - A Serious Disease of Hosta and Other Ornamentals, is available at county extension offices or through the Extension Distribution Center on the Iowa State University campus. The bulletin describes and pictures disease symptoms, signs of the fungus, the disease cycle, and control strategies.
This article originally appeared in the June 30, 2000 issue, p. 83.