Epidemiology of grey mildew and Alternaria blight of cotton

Grey (Areolate) mildew (Ramularia areola) and Alternaria blight (Alternaria macrospora) are two important fungal foliar diseases affecting cotton in India. Both the diseases are polycyclic in nature. The primary inoculum for grey mildew is through conidia or ascospores from infected debris and/or perennial cottons and the secondary spread is through primarily infected leaves. Whereas for Alternaria blight the spread is initially from seed-borne inoculum (in Gossypium herbaceum and Gossypium arboreum cottons) and/or crop debris and the secondary spread is from sporulating lesions on older leaves. Both R. areola and A. macrospora require a temperature regime of 20–30?°C with prolonged high humidity (>80%) and frequent rains for infection and disease development. However, it has been observed that cool weather coupled with prolonged dewy periods in the absence of rains has also been found conducive for the development of both the diseases. So, suitable epidemiological tools and models are required to predict the disease development, spread and to design suitable management practices.