Symptom

Alterneria leaf spot with concentric rings. 

• All the aerial parts of the plant, i.e., stem, leaves, inflorescence and capsules are liable to be attacked.
• These may appear on any portion of the leaf and are irregular, scattered, and have concentric rings.
• These are brown and later become covered with bluish-green or sooty growth.
• When the attack is severe the spots coalesce and form big patches resulting in premature defoliation of the plant which gradually wilts away.
• In one case the capsules, when half mature, wilt suddenly, turn brown and due to collapse of the pedicel the capsules fall or hand down.
• They are smaller in size and have under-developed and wrinkled seeds with little oil content.

Management

• Seed treatment may be useful in combating the initial phase of the disease.
• Use of healthy seed and treat the seed with Captan or Thiram @ 4g/kg seed or spray Mancozeb at 2.5g/lit concentration at an interval of 15days commencing from 90days of crop growth.