Clover rot

Systematic position and nature: Sclerotinia trifoliorum is an ascomycete fungus within the genus Sclerotinia. As an obligate plant parasite, it targets various forage legumes. The pathogen persists in the environment primarily through sclerotia — dense, black, dormant fungal masses that can survive in the soil for several years, serving as the primary source of inoculate for subsequent crop cycles.

Diseases and host plants: The fungus is responsible for clover rot, a destructive disease characterized by the decay of the root crown and lower stems. Initial symptoms include a white, fluffy mycelial growth covering the infected tissues, leading to rapid rotting and plant death. Major hosts include red clover, white clover, alfalfa, and various other leguminous plant species grown in temperate regions.

Biology and lifecycle: The infection cycle is initiated when sclerotia in the soil germinate to produce apothecia. These structures release ascospores that are dispersed by wind to healthy hosts. Once the spores land on a host plant, they germinate and penetrate the tissue, forming a mycelial network that thrives throughout the cooler, moist periods of autumn and winter, often infecting the crown of the plant.

Conditions for development: Optimal conditions for Sclerotinia trifoliorum include moderate temperatures ranging from 5°C to 15°C and high humidity levels. Dense canopy structures, poor field drainage, and high soil acidity significantly increase the risk of disease outbreak. The pathogen flourishes where airflow is restricted, allowing the mycelium to spread rapidly between plants.

Damage and control measures: The economic impact is severe, often resulting in significant stand loss, reduced yield, and the need for premature reseeding. Control strategies focus on integrated pest management: implementing long rotations (at least 4-5 years without legumes), deep plowing to bury sclerotia beyond the reach of germination, maintaining soil pH via liming, and ensuring adequate plant nutrition to strengthen host resistance.

• Utilizing disease-resistant legume cultivars.
• Proper seed cleaning to avoid contamination.
• Managing field drainage to reduce humidity.
• Strategic timing of harvest and grazing to avoid canopy density.