Cause Sclerotinia sclerotiorum is a fungus that overwinters as small black structures (sclerotia) attached to decomposing pods and stems in soil. Sclerotia may survive 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 senescent tissue such as blossoms and leaves or may germinate and colonize plant debris. After colonizing, the fungus can invade any part of the plant with which it comes in contact. Moist conditions within the plant canopy favor infection, as do rain, dew, and/or irrigation practices that keep foliage wet for long periods.
Other host plants include bean, hop, pea, lettuce, carrots, flower seed crops, green pepper, parsnip, potato, sunflower, radish, other crucifers including canola, and cucurbits. Dandelion (Taraxacum officinale) is a very susceptible weed host.
Symptoms The disease is mainly on aboveground parts, producing a cottony white mold. As cabbage leaves decay, small dark bodies appear in the mold. Finally, the mold is replaced by numerous hardened sclerotia that gradually change from white to black.
On seed crops, stem attacks cause severe losses. Diseased tissues eventually bleach white, giving the disease its name "white blight." Sclerotia that are black on the surface and white inside, associated with this bleached tissue, are diagnostic.
- Rotate using non-susceptible crops such as grass or grains.
- Encourage maximum air movement between rows.
- Fontelis at 16 to 30 fl oz/A on 7- to 14-day intervals. Do not make more than two (2) sequential applications before alternating to a labeled fungicide with a different mode of action (non-Group 7). Preharvest interval is 0 days. 12-hr reentry.
Reference Purdy, LH. 1979. Sclerotinia sclerotiorum: History, diseases and symptomology, host range, geographic distribution and impact. Phytopathology 69:875-880.