Cause Sclerotinia sclerotiorum is a fungus that overwinters as small black structures (sclerotia). 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 a healthy 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, 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 aboveground parts, producing a cottony white fungal growth. As leaves decay, small dark bodies appear in the fungal growth. Finally, the fungal growth 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.
Cultural control
- Rotate using nonsusceptible crops such as grass or grains.
- Encourage maximum air movement between rows.
Chemical control
- Cannonball WG (Group 12) at 7 oz/A on 7- to 10-day intervals. May be applied the day of harvest. 12-hr reentry.
- Carboxamide (Group 7) formulations are registered for use.
- Endura at 7 to 9 oz/A on 7- to 14-day intervals. Preharvest interval is 14 days. 12-hr reentry.
- Fontelis at 16 to 24 fl oz/A on 7- to 14-day intervals. Preharvest interval is 3 days. 12-hr reentry.
- OSO 5% SC (Group 19) at 3.75 to 13 fl oz/A on 7- to 14-day intervals. Can be applied the day of harvest. 4-hr reentry. O
- Switch 62.5WG (Group 9 + 12) at 11 to 14 oz/A on 7- to 10-day intervals. Do not make more than two (2) sequential applications before alternating to a labeled fungicide with a different mode of action. Preharvest interval is 0 days. 12-hr reentry.
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
- Serenade Opti at 14 to 20 oz/A on 7- to 10-day intervals. Applications can be made up to and the day of harvest. 4-hr reentry. O
- Stargus at 6 to 8 fl oz per 1,000 ft row as an in-furrow treatment, 3 to 4 quarts/A as a soil drench (drip or chemigation) on 10- to 21-day intervals, or 2 to 4 quarts/A as a foliar spray on 7- to 10-day intervals. Preharvest interval is 0 days. 4-hr reentry. O
- Taegro 2 at 2.6 to 5.2 oz/A on 7- to 14-day intervals can suppress soilborne diseases. 4-hr reentry. O