Pacific Pests, Pathogens, Weeds & Pesticides - Online edition

Pacific Pests, Pathogens, Weeds & Pesticides

Lettuce downy mildew (209)

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Photo 1. Brown patches on lettuce caused by downy mildew, Bremia lactucae.

Photo 2. Downy mildew, Bremia lactucae, on lettuce showing sporulating areas between the main veins.

Photo 3. Magnified part of Photo 2, showing the spores of downy mildew, Bremia lactucae, on lettuce.

Summary

  • Worldwide distribution. Temperate and sub-tropical countries. On lettuce and relatives in daisy family, and weeds. An important disease.
  • Round to angular spots, light green to yellow, merging and turning brown, sometime soft and slimy. Spores on the underside.
  • Spread is by spores in wind over long distances.
  • Cultural control: in nursery – avoid overcrowding; in field - avoid overlapping crops; 2-3-year rotation; spacing; drip irrigation; weed; collect trash and burn after harvest.
  • Chemical control: copper, mancozeb, or chlorothalonil (protectants); or metalaxyl (systemic) with mancozeb (or alternating with mancozeb).

Common Name

Lettuce downy mildew

Scientific Name

Bremia lactucae; there are several strains of the oomycete.

AUTHOR Grahame Jackson
Information (and Photo 1) from Diseases of vegetable crops in Australia (2010). Editors, Denis Persley, et al. CSIRO Publishing; and from CABI (2014) Bremia lactucae (downy mildew of lettuce). Crop Protection Compendium. (https://www.cabi.org/cpc/datasheet/9937/); and from Scheufele S (undated) Lettuce, Septoria blight. The Center for Agriculture, Food, and the Environment. University of Massachusetts Amherst. (https://ag.umass.edu/vegetable/fact-sheets/lettuce-septoria-blight). Photos 2&3 Kohler F, et al. (1997) Diseases of cultivated crops in Pacific Island countries. South Pacific Commission. Pirie Printers Pty Limited, Canberra, Australia.

Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.

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