Carrot (Daucus carota)-Cercospora Leaf Blight

Cause The fungus, Cercospora carotae, overwinters in infected crop debris 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.

Cultural control

  • Irrigate so that carrots are dry by nightfall.
  • Rotation out of carrots for at least one year is important because infected crop debris is the main way the organisms overwinter.
  • Plow under crop debris soon after harvest.
  • The Spartan varieties are resistant to Cercospora.

Chemical control If the disease is common, spraying may be necessary. Formulas for timing sprays have been developed for this disease. Seed-to-seed crops-apply once in fall and once or twice in spring. Steckling production-apply once in fall and once to twice after transplanting in spring.

  • Cevya (Group 3) at 3 to 5 fl oz/A on minimum interval of 7 days. Preharvest interval is 7 days. 12-hr reentry.
  • Chlorothalonil (Group M5) formulations are labeled.
    • Bonide Fung-onil is available for home gardens. H
    • Bravo Ultrex at 1.4 to 1.8 lb/A on 7- to 10-day intervals. Preharvest interval is 0 days. 12-hr reentry.
    • Echo 720 at 1.5 to 2 pints/A on 7- to 10-day intervals. Preharvest interval is 0 days. 12-hr reentry.
  • Copper products (Group M1) offer limited control and are not recommended as stand-alone materials.
    • Badge SC at 1 to 4 pints/A on 7- to 14-day intervals. Preharvest interval is 0 days. 48-hr reentry.
    • Bordeaux 6-6-100.
    • Champ Formula 2 at 1.33 pints/A. 48-hr reentry.
    • Champ WG at 2 lb/A on 7- to 14-day intervals. 48-hr reentry. O
    • C-O-C-S WDG at 1 to 1.9 lb/A. 48-hr reentry.
    • Cueva at 0.5 to 2 gal/100 gal water on 7- to 10-day intervals. May be applied on the day of harvest. 4-hr reentry. O
    • Cuprofix Ultra 40 Disperss at 1.25 lb/A on 7- to 14-day intervals. 48-hr reentry.
    • Kocide 2000 at 1.5 lb/A or Kocide 3000 at 0.75 to 1.5 lb/A on 7- to 14-day intervals. 48-hr reentry. O
    • Nu-Cop 50 DF at 2 lb/A on 7- to 14-day intervals. 48-hr reentry. O
    • Previsto at 1 to 2 quarts/A on 7- to 14-day intervals. 48-hr reentry. O
  • Demethylation-inhibiting (DMI) fungicides (Group 3) are labeled for use.
    • PropiMax EC at 4 fl oz/A on 7- to 10-day intervals. Do not apply within 14 days of harvest. 12-hr reentry.
    • Tilt at 4 fl oz/A or Tilt at 2 fl oz/A plus chlorothalonil at 0.75 lb ai/A on 7- to 14-day intervals. Preharvest interval is 14 days. 12-hr reentry.
    • Topaz at 4 fl oz/A on 7- to 10-day intervals. Preharvest interval is 14 days. 12-hr reentry.
  • Fontelis (Group 7) 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.
  • Inspire Super (Group 3 + 9) at 16 to 20 fl oz/A on 7- to 10-day intervals. Make no more than two (2) sequential applications. Preharvest interval is 7 days. 12-hr reentry.
  • Mancozeb formulations (Group M3) are labeled.
    • Dithane DF Rainshield at 2 lb/A on 7- to 10-day intervals can be used on seed crops only. Washington and Oregon only (SLN WA-020028, SLN OR-020030). 24-hr reentry.
    • Dithane F45 Rainshield at 1.5 quart/A on 7- to 10-day intervals can be used on seed crops only. Washington and Oregon only (SLN WA-090020, SLN OR-090016). 24-hr reentry.
    • Roper DF Rainshield at 2 lb/A on 7- to 10-day intervals can be used on seed crops only in Oregon (SLN OR-130003) and Washington (SLN WA-130003) only. 24-hr reentry.
  • Merivon Xemium (Group 7 + 11) at 5.5 fl oz/A on 7- to 14-day intervals. Do not make more than two (2) applications be-fore alternating to a fungicide in different FRAC groups (non-Group 7 and non-Group 11). Preharvest interval is 7 days. 12-hr reentry.
  • Miravis Prime (Group 7 + 12) at 6.8 fl oz/A on 7-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 7 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
  • Strobilurin fungicides (Group 11) are labeled for use. Do not make more than one (1) application of a Group 11 fungicide before alternating to a labeled fungicide with a different mode of action.
    • Cabrio EG at 8 to 12 oz/A on 7- to 14-day intervals. Preharvest interval is 0 days. 12-hr reentry.
    • Pristine at 8 to 10.5 oz/A on 7- to 14-day intervals. Preharvest interval is 0 days. 12-hr reentry.
    • Quadris Flowable at 9 to 15.5 fl oz/A or Quadris Opti at 2.4 pints/A on 7- to 14-day intervals. May be applied the day of harvest. 4-hr reentry for Quadris Flowable, 12-hr reentry for Quadris Opti.
    • Quilt or Quilt Xcel at 14 fl oz/A on a 7- to 10-day interval. Do not apply within 14 days of harvest. 12-hr reentry.
  • Trilogy at 0.5% to 1%. Not labeled for use in Oregon. Do not use above 90°F or when plants are under heat or moisture stress. Do not use when foliage is wet as good coverage is essential. Poor control as a stand-alone product. 4-hr reentry. O

Reference Gugino, B.K., Carroll, J.E., Widmer, T.L., Chen, P., and Abawi, G.S. 2007. An IPM program for managing fungal leaf blight diseases of carrot in New York. Plant Disease 91:59-65.