Pacific Northwest 1998 An Online Guide to Plant Disease Control

FactSheets offer superior print quality for the page you are currently viewing. Using Microsoft's Internet Explorer has given best printing results.
Glossary
Guide Home
Search

OSU Extension Office
 
Broccoli (Brassica oleracea) -- Downy Mildew (Staghead)
 
Cause: Peronospora parasitica, a funguslike microorganism that overwinters in roots or infected plant debris, affects nearly all cultivated plants and weeds in the crucifer family. Several strains of the microorganism, however, are specific to certain groupings of crops. High humidity, fog, drizzle, and heavy dew favor disease development and spread. Optimum conditions for disease development are night temperatures of 46 to 61oF for 4 or more successive nights, and day temperature approximately 75oF or lower. The systemic phase of the disease is the most destructive because it renders the heads useless for the freezing trade. All commercial-processing cultivars are very susceptible.
Symptoms: The first observable symptom is small, light green-yellow lesions on the upper leaf surface, later showing on the under-surface. The spot turns yellow as it enlarges. In high humidity, a grayish white funguslike growth is on the leaf's underside.

Spots can be seen on the outsides of stalks. Streaks of brown to purple tissue, often in a net-necrosis pattern, are on the insides of stalks. These streaks may extend up to the small florets of the curd, stunting the curd. Streaking is difficult to detect without breaking the stalk for examination.

Heavily infected leaf.

 
Cultivar Resistance: These disease-resistant, fresh-market cultivars have performed well in the Willamette Valley: 'Futura', 'Citation', 'Premium Crop', 'Green Comet', 'Green Valiant', and 'Crusade'.
Cultural control:

  1. Eradicate cruciferous weeds (wild mustards, etc.) that may harbor the fungus.
  2. Manage irrigation to reduce periods of high humidity.
  3. Spring-planted, summer-harvested crops have fewer problems than fall-harvested.
Chemical control:

  1. Actigard at 0.5 to 1 oz/A on 7-day intervals for up to four (4) applications. Begin applications 7 to 10 days after thinning, before disease is present. If disease is present in the area, tank mix the first application with another fungicide registered for downy mildew. Preharvest interval is 7 days. 12-hr reentry.
  2. Agri-Fos at 1.25 to 2.5 quarts/A on 1- to 3-week intervals. Do not use with acidifying compatibility agents. 4-hour reentry.
  3. Aliette WDG at 2 to 5 lb/A on 7- to 21-day intervals. Do not apply within 3 days of harvest. 12-hr reentry.
  4. Alude at 1.25 to 2.5 quart/A on 7- to 21-day intervals. 4-hr reentry.
  5. Bravo Ultrex at 1.4 lb/A. Do not apply within 7 days of harvest. 12-hr reentry.
  6. Cabrio EG at 12 to 16 oz/A on 7- to 14-day intervals. Do not make more than one application of Cabrio EG or other Group 11 fungicide before alternating to a labeled fungicide with a different mode of action. Preharvest interval is 0 day. 12-hr reentry.
  7. Champ Formula 2 at 0.33 to 0.66 pt/A. Older leaves may redden at the higher rate. 24-hr reentry.
  8. C-O-C-S WDG at 3 to 4 lb/A. 24-hr reentry.
  9. Cuprofix Ultra 40D at 0.75 to 1.25 lb/A on 7- to 10-day intervals. 12-hr reentry.
  10. Dithane DF Rainshield at 2 lb/A for seed production only. Washington (SLN WA-020028) and Oregon (SLN OR-020030) only.
  11. Dithane F45 Rainshield at 1.5 quarts/A on 7- to 10-day intervals can be used on seed crops only. Oregon only (SLN OR-090016). No portion of treated seed crop may be used or distributed for food or feed for 1 year (365 days) after the last application. 24-hr reentry.
  12. Echo 720 at 1.5 pt/A on 7- to 10-day intervals when disease threatens. Preharvest interval is 7 days. 12-hr reentry.
  13. Forum at 6 fl oz/A on 7-day intervals. Must be applied as a tank-mix with another fungicide that has a different mode of action (non-group 15). Do not make more than two (2) sequential applications before alternating to a labeled fungicide with a different mode of action. Do not apply within 7 days of harvest. 12-hour reentry.
  14. Kocide 2000 at 0.75 to 1.5 lb/A or Kocide 3000 at 0.5 to 0.75 lb/A on 7- to 10-day intervals. 24-hr reentry.
  15. Legion 80 WDG at 2 to 5 lb/A on 7- to 21-day intervals. Do not apply within 3 days of harvest. 12-hr reentry.
  16. MilStop (85% potassium bicarbonate) at 2 to 5 lb/A. 1-hr reentry.
  17. Nu Cop 50 WP at 0.5 to 1 lb/A on 7-day intervals. Do not apply within 1 day of harvest. 24-hr reentry.
  18. Presidio at 3 to 4 fl oz/A on 10-day intervals as a tank-mix . Preharvest interval is 2 days. 12-hr reentry.
  19. Quadris Flowable at 6.2 to 15.5 fl oz/A on 7- to 14-day intervals. Do not apply more than one (1) foliar application of Quadris or other Group 11 fungicide before alternating to a labeled fungicide with a different mode of action. Preharvest interval is 0 day. 4-hr reentry.
  20. Revus at 8 fl oz/A on 7- to 10-day intervals. Do not make more than two (2) foliar applications of Revus before alternating to a labeled fungicide with a different mode of action (non-group 40). Preharvest inter-val is 1 day. 4-hr reentry.
  21. Ridomil Gold Bravo SC at 1.5 pints/A or Ridomil Gold SL at 0.125 to 0.25 pint/A tank-mixed with other fungicides registered for control of downy mildew. Do not apply within 7 days of harvest. Warning Resistance to Ridomil has been confirmed in the Pacific Northwest. To minimize further development of resistance, do not make foliar applications if Ridomil was used at planting, do not use as a curative spray once disease has developed, and use only as a preventive spray and only in combination with another registered fungicide. 48-hr reentry.
  22. Topaz at 1 to 3 quarts/A in 100 gal water at 2- to 3-week intervals. 4-hr reentry.
Biological control:
  1. Sonata at 2 to 4 qt/A on 7- to 14-day intervals. Can be applied up to and on the day of harvest. 4-hr reentry.
Content edited by: Cynthia M. Ocamb on January 1, 2010
 
Top

In print since 1954 and on the web since 1996. Questions or comments, please contact us.