Late Blight of Potato:

History and Importance:

  1. Most destructive*(economic and social impact) disease of potato
  2. In 1845 destroyed large area in Europe (Ireland). Great Irish Famine
  3. Large No. of people died, remaining migrated

Etiology:

Causal organism: Phytophthora infestans
Order: Peronosporales

Family: Pythiaceae

Symptoms:

  • On leaves and stem dark brown or black dead lesion*(injury/wound) appear
  • Blighted areas appear as faded green patches
  • In moist conditions decay giving offensive smell
  • Dead areas started from tip or margins
  • In severe attack tubers skin give black discoloration
  • White sporulation appears on lower surface of leaves.
  • Infected tuber tissues are copper brown, reddish or purplish in color.

Disease cycle:

  • Pathogen survive from season to season in infected tubers in field or through contaminated seeds
  • Secondary spread is through wind, water & leaf eating insects.
  • Potato tubers can become infected in the field when sporangia are washed from lesions on the foliage and enter into the soil.
  • Infections generally begin in tuber cracks, eyes or lenticels.

Epidemiology:

  • 12-13°C temp.
  • more than 90 % RH

Management:

  • Seed tubers selected from healthy field
  • Sanitation: weeding for low humidity
  • Tuber treatment with mercuric chloride (1:1000)
  • High ridging as 15 cm*(because low lying areas conserve more moisture that favors pathogen growth).
  • Irrigation time should be adjusted in such a way that don’t extend the night dew duration.
  • Store in potato tubers in dry & well aerated place.
  • Spray with systemic fungicides (dimethomorph, Cymoxanil, fluopicolide).
  • Hilling: Covering of newly emerged plant at the base*(helps in early weed control and avoid from direct water contact).

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