A review of early blight on potatoes

CHIPS 38 Geographic distribution Early blight is widespread in most areas where potatoes or tomatoes are grown, but is especially prevalent in the tropics and temperate zones. The disease is a potential threat where potatoes are grown under irrigation or during times of heavy dew. Early blight is prevalent in all provinces in South Africa and is a limiting factor in production in late summer. Early blight is one of three diseases taken into account when selecting new potato varieties in South Africa, the other two being late blight and common scab. Early blight tuber rot may occur if tubers wounded during harvest are inoculated by A. solani spores found on or near the soil surface. Tuber rot is, however, not common and has limited distribution. Economic importance The primary damage of early blight is due to premature defoliation of the plant. Photosynthesis rates increase and respiration rates decrease in apparently healthy tissues. Physiological changes are difficult to measure and evaluation of crop loss is based on the level of disease. Early literature (1945) cites yield losses of 5 50%. There is often a discrepancy between damage to foliage and yield loss, which is due to the increase in disease spread at the end of the season, when most of the yield has been produced. When tomato fruit or potato tubers become infected, the quantity and quality of marketable produce is decreased and the number of secondary pathogens increases. Control of early blight has been shown to increase yield.