Leaf spot (Alternaria spp.)
The pathogen attacks all parts of the plant at all stages. Small, dark brown water soaked, round to irregular lesions, with concentric rings, 1-8 mm in diameter appear on the leaves and under excessive atmospheric and soil humidity the spot increases in size and number. The lesions may also appear on the midrib and veins of the leaves. Milder attacks cause only defoliation, in severe cases the plant may die. The pathogen is seed-borne. Temperature of 20-300C and humid conditions favour the disease.
- Use certified disease-free seeds.
- Use resistant varieties where available. Varieties totally covered with hair seem to be resistant.
- Destruction of crop residues and weeds.
- Early planting i.e. immediately after onset of rains.
- Follow intercropping system of sesamum + sunflower.
- Copper based fungicides could be used as a preventive measure when conditions are conducive to disease development.