Seed Crop, Crucifers-Sclerotinia Stem Rot

[includes arugula, broccoli, broccoli raab, Brussels sprouts, cabbage, cauliflower, Chinese broccoli, Chinese cabbage, collard, kohlrabi, kale, mustard, radish other than daikon, rape, rutabaga, and turnip]

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 turns 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 non-susceptible 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 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.
  • Rovral 4 Flowable 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. Washington (SLN WA-960027) and 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 at 11 to 14 oz/A has a special label for Sclerotinia control in seed crops in WA only (SLN WA-020016). Begin at early bloom and repeat on 7- to 10-day intervals. Preharvest interval is 7 days. 12-hr reentry.