The earliest signs are oblong pale spots with grey centers found on leaves. Individual spots are small, 1-2 mm in diameter. The spots coalesce and become usually about 4-5 cm in length and 2-3 cm in width. In advanced stages of infestation, the black dots become concentric rings. The grey centers become thin and eventually tear. In severe cases of attacks, hundreds of spots appear on both sides of the leaves. Severely affected leaves wilt and dry up.
The disease is caused by the fungus on the scale of rhizomes which is the primary source of infection during sowing. The secondary spread is caused by wind, water and other physiological and biological agents. The pathogen can survive on infected debris for a year.
Apply bioagents such as T. harzianum, T. Viride which have shown evidence for reduction in disease incidence. Also, plant extracts of P. longifolia is effective for the disease control.
Always consider an integrated approach with preventive measures together with biological treatments if available. Treat seed material with mancozeb @3 g/l of water or carbendazim @1 g/l of water for 30 minutes and dry in the shade before planing. Apply mancozeb @2.5 g/l of water or carbendazim @1 g/l of water at 2-3 sprays fortnightly.