Early Blight of Potato:

Occurrence & importance:

  • Occurs in humid and warm areas of world
  • Cause losses up to 5-78%
  • $45 million is spent on fungicides to control early blight of potato.

Etiology:

Causal organism: Alternaria solani
Order: Moniliales
Family: Dematiaceae

Symptoms:

  • On leaves dark brown spots appear surrounded by yellow halo.
  • Concentric rings (like target board) develop. These spots resemble with bull’s eye.
  • In drought spots turn hard, in humid rotting patches appear
  • Stem show brown to black lesions
  • In severe attack leaves shriveled, dehisce*(split apart) & fall off.
  • On infected tubers sunken*(deepen from normal surface) and irregular lesion appear.

Disease cycle: soil, warm humid, PLB (cool, moist)

  • Fungi remain viable in dry infected leaves or debris for a year or more
  • Contaminated tubers also primary source of inoculum
  • Secondary infection occurs through wind, water & insects that aid fungal spores to move from infected to healthy plants.

Epidemiology:

  • 13.6-23.6°C,
  • Dew, Infrequent rain & more than 80 % RH favors the fungal growth.

Management:

  • Cultural practices:  a) crop rotation (b) Sanitation (c) burning of residues
  • Spray Zineb, Dithane M-45 0.2%, Blitox-50 0.25% at 10-21 days interval.
  • Resistant genotypes i.e. Desiree

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