Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Pea (Pisum sativum) -- Downy Mildew
 
Cause: A fungus-like microorganism, Peronospora viciae (formerly P. pisi), which overwinters on diseased plant refuse in soil. The pathogen has never been shown to be transmitted by seed internally or externally.
Symptoms: A grayish white moldy growth appears on the lower leaf surface, and a yellowish area appears on the opposite side of the leaf. Infected leaves can turn yellow and die if weather is cool and damp. Stems may be distorted and stunted. Brown blotches appear on pods, and mold may grow inside pods.

Note the gray sporulation of this fungus on the underside of the leaf.
 
Cultivar Resistance: A number of European-bred garden pea cultivars are resistant or tolerant. Semi-leafless or reduced-stipule cultivars appear extremely susceptible.
Cultural control:

  1. Plant resistant or tolerant cultivars.
  2. Rotate out of legumes for 2 or 3 years.
  3. Burn or bale infested pea straw after harvest.
Chemical control:

  1. Seed treatment can lessen or prevent seedling infection.
    1. Aliette WDG at 3 oz/100 lb seed plus a dye in Oregon (SLN OR-030001), Washington (SLN WA-020030), and Idaho (SLN ID-030001). 12-hr reentry
    2. Apron XL LS at 1.28 fl oz/100 lb seed plus a dye plus a dye. See label for reentry restrictions.
  2. Applying at planting for damping-off gives some control of early infection.
    1. Ridomil Gold SL may be banded or surface applied at 0.5 to 1 pt/A. Incorporate 2 inches deep when used. 48-hr reentry.
  3. MilStop (85% potassium bicarbonate) at 2 to 5 lb/A. 1-hr reentry.
  4. Topaz at 1 to 3 quarts/A in 100 gal water on 2- to 3-week intervals. 4-hr reentry.
  5. Wakil XL at 3.2 oz/100 lb seed, plus a dye. For pea seed exports from Washington only (SLN WA-000037). 48-hr reentry.
Content edited by: Cynthia M. Ocamb on January 1, 2010
 
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