White Mold of Perennials

by Dr. S. Nameth
OSU Department of Plant Pathology

White Mold of perennials is caused by the fungus Sclerotinia sclerotiorum. It causes a stem and based rot in a wide variety of herbaceous perennials. Initial symptoms are characterized by wilting of the affected plant. Closer observation of the base of the symptomatic plant will indicate a "water-soaked" or rotted appearance starting at the base and moving up the stem. In most cases the dense, white, fluffy growth of the pathogenic fungus can also be seen. In the advanced stages of disease development, the fungus will produce hard, black, overwinter structures called sclerotia. These sclerotia look like small bits of rat or mouse droppings and they appear around the base of the plant and also inside the pith of the plant.

Control of this destructive disease is difficult and relies highly on not spreading the sclerotia around from place to place via the moving of soil. Chemicals can be effective if used a protectant that will not allow the spores produced by the sclerotia to infect the flowers of the host plant. Infected plants should be removed from the bed and destroyed. Do not compost, as the sclerotia will survive and you will inoculate your soil when you amend it with the compost.

Fig. 1. Sclerotinia in pure culture. Note white color and the formation
of the sclerotia at the edge of the plate.

White Mold of Perennials

Fig. 1. Sclerotinia in pure culture. Note white color and the formation
of the sclerotia at the edge of the plate.

Fig. 2. Wilting of Rudbeckia infected with white mold.

Fig. 3. Base of Rudbeckia showing white, fluffy growth of the
fungus and the water-soaked lesion.

Fig. 4. Sclerotia and growth of fungus covering an infected tulip leaf.

Fig. 5. Sclerotia and growth of fungus on creeping phlox

Fig. 6. Fungal sclerotia located inside the stem of an infected plant.

White Mold of Perennials

Fig. 1. Sclerotinia in pure culture. Note white color and the formation of the sclerotia at the edge of the plate.

Fig. 2. Wilting of Rudbeckia infected with white mold.

Fig. 3. Base of Rudbeckia showing white, fluffy growth of the fungus and the water-soaked lesion.

Fig. 4. Sclerotia and growth of fungus covering an infected tulip leaf.

Fig. 5. Sclerotia and growth of fungus on creeping phlox

Fig. 6. Fungal sclerotia located inside the stem of an infected plant.

Fig. 1. Sclerotinia in pure culture. Note white color and the formation
of the sclerotia at the edge of the plate.

Fig. 3. Base of Rudbeckia showing white, fluffy growth of the
fungus and the water-soaked lesion.