Rust causes brown pustules surrounded by yellowed tissue on the leaves. Plants may bloom prematurely, have small flowers, and die early. Use proper plant spacings and resistant varieties. No controls are listed.
Anthracnose attacks the leaves and stems in late summer. On older stems the spots are sunken, oblong, yellowish-green to gray with a narrow brown border. On the leaves, the spots are yellowish green turning dirty white with a narrow brown border. When the stem is girdled the plant dies. Destroy infected plants and use wider spacings. No controls are listed.
Gray mold causes flower spikes to wilt and light brown areas form on the lower stem of the flower cluster. Infected plants break over below the flowers. The disease is worse in wet weather. Cut off infected flower stalks and keep beds free of debris. Sprays of benomyl will control this disease.
Stem rot can be detected by the presence of cottony growth on stems of infected plants near the soil line. Infected plants die and should be destroyed.