Sclerotinia Crown and Stem Rot
Symptoms:
- Initial symptoms are small, tan spots on leaves and stems that develop in the late fall in the Midwestern U.S.
- Infected leaf, stem, and crown tissues discolor, then become soft and stems wilt.
- In some cases, entire plants may rot, leaving minimal trace of the plant or pathogen.
- A whitish, cottony web-like growth can often be seen during wet conditions on stems and crowns of plants infected with Sclerotinia
- Spherical to cylindrical black bodies (sclerotia) about 1/8 inch to 1/4 inch develop within or on infected plant parts.
- Circular spotty areas in fields or entire fields may be destroyed.
Pathogen Involved:
- Sclerotinina trifoliorum (a fungal pathogen)
Time of Occurrence:
- Late fall to early spring
Conditions Favoring Disease:
- Cool, wet weather in the fall and winter.
Disease Management:
- Planting in spring or early summer in most parts of the U.S. will reduce disease incidence.
- Avoid planting in fall where this disease has been a problem. Late summer seedlings should be done as early as possible to enable plants to become well established prior to release of Sclerotinia spores in late autumn.
- Several alfalfa cultivars with moderate resistant to Sclerotinia are now available.
- Plowing may reduce disease by burying sclerotia and consequently reducing the number of apothecia produced from sclerotia.
- Use clean, sclerotia-free seed to establish new fields.