Clover rot

Clover rot is a destructive plant disease caused by the fungal pathogen Sclerotinia trifoliorum. This fungus is a specialized parasite that primarily attacks leguminous crops, with red clover being particularly susceptible. Other hosts include alfalfa, various vetches, and occasionally other members of the Fabaceae family.

The characteristic symptoms of the infection often appear during cool, moist periods in late autumn or early spring. A dense, white, cottony mycelial growth develops on the crown and the base of the stems. As the infection progresses, the tissues soften and decay, leading to the collapse and death of the plant. Infected patches of the field typically show a sudden, circular thinning of the crop stand.

Environmental conditions are crucial for the development and spread of the pathogen. The fungus thrives in cool temperatures combined with high humidity. It survives in the soil as sclerotia, which are hard, black, resting structures. Under favorable conditions, these sclerotia germinate to produce apothecia, which release ascospores that travel via wind to initiate new infection cycles on the foliage.

The harmfulness of this disease is significant, as it can cause complete loss of legume stands, especially in dense, high-yielding fields. Beyond the immediate loss of forage biomass, the disease degrades the quality of the harvested feed. If not managed properly, the buildup of sclerotia in the soil creates a long-term problem for subsequent legume crops in the rotation.

Management and prevention strategies focus on breaking the pathogen's life cycle:

• Implementing long-term crop rotations, keeping leguminous crops out of the field for at least 4 to 5 years;
• Employing deep plowing to bury infected plant debris, preventing the development of apothecia;
• Avoiding excessive nitrogen fertilization that promotes lush, soft growth susceptible to infection;
• Ensuring the use of high-quality, clean seed that is free from sclerotia contamination.