Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Carrot (Daucus carota) -- Cercospora Leaf Blight
 
Hosts: carrot
Cause: The fungus, Cercospora carotae, that overwinters in crop refuse or on alternate hosts. Leaf spots are common in carrots grown for seed production in western Idaho and eastern Oregon.
Symptoms: Cercospora infections can occur along the leaf margin, but spots are elongated and cause the leaflet to curl. Spots not on the margin are circular. Spots are at first small chlorotic flecks that become larger and tan, brown, or black with a necrotic center surrounded by a yellowish border. Commonly, spots coalesce and, subsequently, the leaves curl. The disease may occur early in the growing season (sometimes called early blight). The spots of this diseases are easily confused with Alternaria Leaf Blight which generally is more irregularly shaped and darker in color than Cercospora Leaf Blight.

 
Cultivar Resistance: The Spartan cultivars are resistant to Cercospora.
Cultural control:
  1. Irrigate so that carrots are dry by nightfall.
  2. Rotation out of carrots for at least 1 year is important because refuse is the main way the organisms overwinter.
  3. Plow under crop debris soon after harvest.
Chemical control:
  1. Bravo Ultrex at 1.4 to 1.8 lb/A on 7- to 10-day intervals. 12-hr reentry.
  2. Cabrio EG at 8 to 12 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 with a different mode of action. Preharvest interval is 0 days. 12-hr reentry.
  3. Copper products.
    1. Bordeaux 6-6-100.
    2. Champ Formula 2 at 1.33 pt/A. 24-hr reentry.
    3. C-O-C-S WDG at 2 to 4 lb/A. 24-hr reentry.
    4. Cuprofix Ultra 40D at 1.25 lb/A on 7- to 14-day intervals. 12-hr reentry.
    5. Kocide 2000 at 1.5 lb/A or Kocide 3000 at 0.75 to 1.5 lb/A on 7- to 14-day intervals. 24-hr reentry.
    6. Nu Cop 50 WP at 2 lb/A on 7- to 14-day intervals. Do not apply within 1 day of harvest. 24-hr reentry.
  4. Dithane DF Rainshield at 2 lb/A on 7- to 10-day intervals can be used on seed crops. Washington and Oregon only (SLN WA-020028, SLN OR-020030) . 24-hr reentry.
  5. 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.
  6. Echo 720 at 1.5 to 2 pt/A on 7- to 10-day intervals . Preharvest interval is 0 days. 12-hr reentry.
  7. Gem at 4 to 6 oz/A on 14-day intervals. Do not make more than one (1) application of Gem (Group 11 fungicide) before alternating to a labeled fungicide with a different mode of action. Do not apply within 7 days of harvest. 12-hr reentry.
  8. PropiMax EC at 4 fl oz/A on 7- to 10-day intervals. Do not apply within 7 days of harvest. 12-hr reentry.
  9. Pristine at 8 to 10.5 oz/A on 7- to 14-day intervals. Do not make more than two (2) sequential applications of Pristine or other Group 11 fungicide before alternating to a labeled fungicide with a different mode of action. Preharvest interval is 0 days. 12-hr reentry.
  10. Quadris Flowable at 9 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. May be applied the day of harvest. 4-hr re-entry.
  11. Quadris Opti at 2.4 pints/A on 7- to 14-day intervals following the resistance management guidelines. Do not apply more than two (2) foliar applications of Quadris Opti or Group 11 fungicides before alternating with a fungicide that has a different mode of action. May be applied the day of harvest. 12-hr reentry.
  12. Quilt at 14 fl oz/A on 7- to 10-day intervals. Make no more than 1 application before alternating to non- Group 11 fungicides. Do not apply within 14 days of harvest. 12-hr reentry.
  13. Quilt Xcel at 14 fl oz/A on a 7- to 10-day interval. Do not apply more than one (1) application before rotating to a non-group 11 fungicide. Do not apply within 14 days of harvest. Oregon and Washington only. 12-hr reentry.
  14. Tilt at 4 fl oz/A or Tilt at 2 fl oz/A plus chlorothalonil with 0.75 lb ai/A on 7- to 14-day intervals. Preharvest interval is 14 days. 12-hr reentry.
Content edited by: Cynthai M. Ocamb on January 1, 2010
 
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