Early Blight of Potato

  • Symptoms

  • Trigger

  • Biological Control

  • Chemical Control

  • Preventive Measures

Early Blight of Potato

Alternaria solani


In a Nutshell

  • Dark spots with light halos on leaves.
  • Brown stains and rotten spots on potatoes.




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.

Biological Control

Clean and disinfect your tools thoroughly. Spray algal limestone or rock flour on infected plants.

Chemical Control

Always consider an integrated approach with preventive measures together with biological treatments if available. Use products containing mancozeb and chlorothalonil to control early blight.

Preventive Measures

Use healthy seeds or transplants.,Use tolerant varieties.,Plant in well-drained and well-ventilated sites.,Apply plant fortifiers for general strengthening of the crops.,Crop rotation with non-hosts plants.,Control susceptible weeds in and around fields.,Do not over-fertilize with potassium.,Maintain adequate levels of both nitrogen and phosphorus.,Store tubers at cool temperatures and in well aerated sites.,Remove infected plants completely.,Be careful to leave no residues behind after harvest.