Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Carrot (Daucus carota) -- Powdery Mildew
 
Cause: Erysiphe heraclei, a fungus. It can be found on fall-planted carrots and overwinters on the carrot seed crop. Another host plant is wild carrot. Some cultivars, like 'Nantes' and 'Imperator', appear more susceptible to the disease. Severe infection results in low yields and poor seed quality.
Symptoms: The disease affects foliage, stems, and umbels. Patches of white feltlike fungus appear on lower leaves first, then spread to the terminal growth. The fungus often covers entire leaves with its masses of white mycelium and powdery spores. Infected foliage becomes brittle and may eventually turn brown, shrivel, and die. Diseased pedicels may turn brown, resulting in the florets' premature death.
Cultural control: Isolate new carrot fields from established infected fields.
Chemical control:
  1. 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 fun-gicide before alternating with a different mode of action. Preharvest interval is 0 days. 12-hr reentry.
  2. 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 alternat-ing to a labeled fungicide with a different mode of action. Do not apply within 7 days of harvest. 12-hr reentry.
  3. Kaligreen at 2.5 to 3 lb/A on 7- to 10-day intervals. Might be used to supplement a normal program when powdery mildew is first observed. May be applied up to the day before harvest. 4-hr reentry.
  4. Kumulus DF at 3 to 10 lb/A. 24-hr reentry.
  5. Laredo EC at 8 to 12 fl oz/A in a minimum of 20 gal water by ground or 10 gal water by air on 14- to 21-day intervals. For car-rots grown for seed only in Oregon only (SLN OR-060020). 24-hr reentry.
  6. Microthiol Disperss at 3 to 10 lb/A. Do not apply if temperature will exceed 90°F within 3 days after application. Do not allow spray drift to sensitive plants (spinach, etc.). Do not use within 2 weeks of an oil treatment. 24-hr reentry.
  7. PropiMax EC at 4 fl oz/A on 7- to 10-day intervals. Do not apply within 7 days of harvest. 24-hr reentry.
  8. 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.
  9. 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 with a different mode of action. May be applied the day of harvest. 4-hr reentry.
  10. Quilt at 14 fl oz/A on 7- to 10-day intervals. Make no more than one (1) application before alternating to non-Group 11 fungicides. Do not apply within 14 days of harvest. 12 hr-reentry.
  11. 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.
  12. Rally 40WSP at 5 to 7.5 oz/A on 14- to 21-day intervals for seed crop only. For Oregon only. (SLN OR-080037). Carrot seed may not be distributed for human consumption or animal feed. 24-hr reentry.
  13. Switch 62.5WG at 11 to 14 oz/A on 7- to 10-day intervals. No more than two (2) sequential applications alternating with another fungicide with a different mode of action for 2 applications. Do not allow cattle or other livestock to feed upon leaves of vegetables. Preharvest interval is 7 days. 12-hr reentry.
  14. Thiolux Jet at 3 to 10 pounds/A. 24-hr reentry.
  15. Tilt at 2 fl oz/A in a tank mix with 0.75 lb a.i. of chlorothalonil on 7- to 10-day intervals. Preharvest interval is 14 days. 12-hr reentry. .
Biological control:
  1. Sonata at 2 to 4 qt/A on 7- to 14-day intervals for disease suppression. Can be applied up to and on the day of harvest. 4-hr reentry.
References:
  1. Dillard, HR., and Cobb, AC. 1992. Powdery mildew of carrot in New York. Plant Disease 76:972.
  2. Glawe, DA., Pelter, GQ. and du Toit, LJ. 2005. First report of powdery mildew of carrot and parsley caused by Erysiphe heraclei in Washington State. Online. Plant Health Progress doi:10.1094/PHP-2005-0114-01-HN.
Content edited by: Cynthia M. Ocamb on January 1, 2010
 
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