Cause Sclerotinia sclerotiorum is a fungus that overwinters as small black structures (sclerotia) attached to decomposing infected plant portions. Sclerotia may survive more than several years. After a moisture-conditioning period of at least 70 days, they produce a small, stalked, cup-shaped fruiting structure (apothecium), which releases spores into the air. Spores may infect blossoms and senescing leaves. After colonizing, the fungus can invade healthy parts of the plant. Moist conditions within the plant canopy during bloom favor infection, as do rain, dew, and/or irrigation practices that keep foliage wet for long periods.
Other host plants include bean, carrots, pea, lettuce, potato, green pepper, cucurbits, parsnip, radish, other crucifers including canola, flower seed crops, and sunflower. Dandelion (Taraxacum officinale) is a very susceptible weed host.
Symptoms The disease is mainly on the lower portion of stems, producing a cottony white mold under wetter conditions or a light-brown appearance to the affected stem area. As the stems decay, small dark sclerotial bodies appear inside. Plants may die before seed harvest.
Cultural control
- Rotate using nonsusceptible crops such as grass or grains.
- Encourage maximum air movement between rows.
Biological control
- Bexfond at 7 to 14 fl oz/A for soil applications via drenches, in-furrow applications, drip irrigation, or sprays followed by irrigation. Reapply 3 to 4 weeks after planting. 4-hr reentry. O