Brown Spot: Alternaria longipes, Alternaria tenuis, Alternaria alternata

Symptom

• Brown spot in contrast to frog-eye spot is not normally observed in the nursery but is very much prevalent in the field.
• In India a decade back it was considered to be of minor importance but gradually it is gaining importance specially in tobacco grown in monsoon season.

• Initially it appears on lower and older leaves as small brown, circular lesions, which spread, to upper leaves, petioles, stalks and capsules even.
• In warm weather (300C) under high humidity, the leaf spots enlarge, 1-3 cm in diameter, centres are necroses and turn brown with characteristic marking giving target board appearance with a definite outline.
• In severe infection spots enlarge, coalesce and damage large areas making leaf dark-brown, ragged and worthless.

Management

• Removal and destruction of diseased plant debris can check the primary infection promptly.
• Continuous growing of tobacco after tobacco must be avoided in the heavily infected fields.
• Weekly, spraying of fungicides such as Maneb - 0.2%.