Seed Crop, Crucifers (Brassica and Raphanus spp.)-Sclerotinia Stem Rot

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. On seed crops, stem attacks can cause severe losses.

Host plants include bean, pea, lettuce, carrots, potato, sunflower, flower seed crops, crucifers, and cucurbits. Dandelion (Taraxacum officinale) is a very susceptible weed host.

Symptoms The disease is mainly on aboveground parts, producing first a water-soaked appearance followed by a cottony-white mold, unless conditions turn hot and dry. In seed crops, the stem is more commonly affected and infected plants can be scattered through a field, including field edges. Diseased stem 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 On seed crops of broccoli, Brussels sprouts, cabbage, cauliflower, Chinese cabbage, collard, kale, kohlrabi, mustard, rutabaga, and turnip, the most effective control is aerial fungicide sprays.

  • Fontelis (Group 7) at 16 to 30 fl oz/A on 7- to 14-day intervals for leafy and root brassicas and can be used for those seed crops produced in Oregon. 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.
  • OSO 5% SC (Group 19) at 3.75 to 13 fl oz/A on 7- to 14-day intervals for leafy brassicas and can be used for those seed crops produced in Oregon. Can be applied the day of harvest. 4-hr reentry. O
  • Priaxor Xemium Brand (Group 7 + 11) at 6 to 8.2 fl oz/A for leafy brassicas and can be used for those seed crops produced in Oregon. Do not make more than one (1) application of any Group 11 fungicide
  • Rovral 4 Flowable (Group 2) at 2 to 4 pints/A in 20 to 100 gal water is labeled for Alternaria on crucifer seed crops and will also control Sclerotinia diseases. Apply once petals start to fall and monthly for two (2) more applications if needed. An appropriate spreader-sticker is recommended. For seed production only in Oregon (SLN OR-130001) only. Not labeled for use on canola/rapeseed. Do not feed treated crop to livestock or graze treated area. Check label for crop rotation restrictions. 24-hr reentry.
  • Switch 62.5WG (Group 12 + 9) at 14 oz/A on 7- to 10-day intervals beginning at bloom for seed crops in Oregon (SLN OR-160001) and Washington (SLN WA-020016). Preharvest interval is 7 days. 12-hr reentry.