Early Blight of Potato
On the leaves, grey to brown spots appear and grow in a concentric manner around a clear center - the characteristic “bullseye” formation. These lesions are surrounded by a bright yellow halo. As the disease progresses, entire leaves may turn chlorotic and shed, leading to significant defoliation. Sunken, irregular lesions appear on the surface of potato tubers. Beneath the lesion, the tuber tissue is leathery or corky with a brown discoloration.
Alternaria solani overwinters primarily on infected crop debris in soil or alternative hosts. The fungus needs high temperatures (20 - 25°C) in combination withhigh humidity (90%) to grow. It penetrates the leaf epidermis directly or enters through leaf pores. Plants suffering from a lack of nitrogen are prone to Early Blight. Tubers harvested green or in wet conditions are susceptible to wounding and infection. Storage at cool temperatures, high relative humidity and with plenty of aeration promotes wound healing.
Clean and disinfect your tools thoroughly. Spray algal limestone or rock flour on infected plants.
Always consider an integrated approach with preventive measures together with biological treatments if available. Use products containing mancozeb and chlorothalonil to control early blight.