Pea (Pisum sativum)-Downy Mildew

Cause A fungus-like microorganism, Peronospora viciae (formerly P. pisi), which overwinters on diseased plant refuse in soil. The fungus 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.

Cultural control

  • Plant resistant or tolerant cultivars. A number of European-bred garden pea cultivars are resistant or tolerant. Semi-leafless or reduced-stipule cultivars appear extremely susceptible.
  • Rotate out of legumes for 2 or 3 years.
  • Burn or bale infested pea straw after harvest.

Chemical control

  • Seed treatment can lessen or prevent seedling infection. Research out of WSU has shown a benefit from combining seed treatments.
    • 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
    • Allegiance-FL at 1.5 fl oz/100 lb seed plus a dye. See label for reentry restrictions.
    • Apron XL at 0.16 to 0.64 fl oz/100 lb seed plus a dye. See label for reentry restrictions.
    • Curzate 60DF at 0.56 fl oz/100 lb seed plus a dye in Washington (SLN WA-000035A) only, for export only. 12-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
  • MilStop (85% potassium bicarbonate) at 2 to 5 lb/A or 1 Tbsp/gal water. 1-hr reentry. H O
  • Phosphonates formulations (Group 33) are effective but good coverage is important. Ideally, apply prior to disease development.
    • Fosphite at 1 to 3 quarts/A on 2- to 3-week intervals. 4-hr reentry.
    • Fungi-Phite at 1 to 3 quarts/A on 1- to 2-week intervals. 4-hr reentry.
    • Phiticide at 2 to 4 pts/A on 2- to 3-week intervals. 4-hr reentry.
  • Ridomil Gold SL may be banded or surface applied at 0.5 to 1 pint/A. Incorporate 2-inches deep when used. Apply Ridomil Gold SL at 0.125 to 0.2 pint/A in a tank-mix on a 14-day schedule. Preharvest interval is 3 days. Studies by WSU report the persistence of fungicide-resistant pathogen populations. 48-hr reentry.
  • Trilogy at 0.5% to 1%. 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
  • 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.

Reference Inglis, D., Gundersen, B., and Derie, M. 2001. Evaluation of seed fungicides for controlling metalaxyl-resistant downy mildew on green pea, 2000. F&N Tests 56:ST17.