The incidence of early blight is mostly influenced by moisture, temperature, variety of potato, age and vigour of the plant. Optimum conditions for the development of the disease in a severe form require high temperature alternating with moist periods and a poor vigour of the plant.
Early blight was observed to be severe when the humidity was high early in the season followed by high temperature. In general, this disease is favoured by moderate temperature (17-25oC) and high humidity, around 75%. Intermittent dry and wet weather is more conducive for early blight.