Radish (Raphanus sativus)-White Rust

Latest revision: 
March 2023

Cause Albugo candida, a fungus-like microorganism, can cause disease on radish, rapeseed, and wild mustards. Crucifers in general are potential hosts, as well as spinach and horseradish. In the Pacific Northwest, white rust can be severe on radish seed crops. All round, red varieties and some selections of 'Daikon' appear susceptible. The pathogen overwinters as oospores in stagheads (galls formed on infected seed heads) or plant debris as well as mycelium in infected hosts. Pieces of staghorns are often found as seed contaminants and can be the primary source of infection in a field. The oospores can germinate and infect young plants, leading to pustules on leaves. Sporangia are produced in pustules, can be moved by wind, rain, or insects, and can germinate, giving rise to zoospores. Zoospores are motile; they swim for a short distance and then invade the plant by germinating through the stomata. Sporangia require some drying in order to germinate but disease development is favored by moist conditions and temperatures between 50°F and 77°F. Dew, fog, or periods of extended rainfall and cool temperatures are ideal for zoospore activity. White rust is often associated with downy mildew.

Symptoms First symptoms may appear as small, light green spots, which later turn white and finally result in blister-like raised white pustules usually on the lower leaf surface. Pustules can develop on the upper or lower leaf surfaces or on stems and consist of masses of sporangia. Systemic infections can occur, causing the aboveground portion of young seedlings to be distorted and appear abnormally shaped. Infections of the flower parts may cause a bizarre outgrowth on the seed stalk. Seed pedicels may terminate and form staghorns without seeds developing. Seed yield and quality are severely reduced.

Cultural control

  • Plant only seed grown in white rust-free plantings.
  • Avoid sprinkler irrigation.
  • Practice a 3-year rotation between susceptible crops.
  • Select fields away from established radish fields.
  • Control wild mustards around the field.
  • Plant resistant varieties.
  • Plow under infected plants or volunteers and incorporate plant debris into soil soon after harvest.

Chemical control Seed treatment minimizes spread through contaminated seed.

  • Captan 4F at 2.2 fl oz/100 lb seed plus a dye.
  • 42-S Thiram at 8 fl oz/100 lb seed plus a dye. See label for reentry restrictions.

Use systemic fungicides at planting. To minimize development of resistant fungi, do not make foliar applications for other diseases if Ridomil is used at planting. Do not use in the greenhouse. Ridomil is not registered in British Columbia.

  • Ridomil Gold Copper. See label for rates. Do not apply within 7 days of harvest. 48-hr reentry.

Spray applications after planting, especially if dews or rainy weather are forecast.

  • Badge SC (Group M1) at 1 to 2.25 pints/A on 10-day intervals. Preharvest interval is 0 days. 48-hr reentry.
  • Phosphorous acid-based products (Group P7) are labeled for use.
    • Fosphite at 1 to 3 quarts/A at 2- to 3-week intervals. 4-hr reentry.
    • Fungi-Phite at 1 to 3 quarts/A at 1- to 3-week intervals. 4-hr reentry.
  • 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 16 oz/A. Preharvest interval is 0 days. 12-hr reentry
    • Quadris Flowable at 6 to 15.5 fl oz/A. May be applied day of harvest. 4-hr reentry.

Reference Johnson, D.A. 1990. White Rust of Seed Radish. WSU Extension Service EB1570.