Alternaria alternata f. sp. lycopersici
Symptoms of Alternaria canker appear on stems, leaves and fruit. Brown or black necrotic lesions are usually visible on plants from which infected fruit are picked. Fruit are infected when green, but symptoms persist into the ripening period. Sunken grayish lesions are present on fruit.
Fungus overwinters in crop residue and is easily spead by wind. Wounding of young plants (by mechanical damage or pruning) provides an entry site for infection. Furrow or drip irrigation is preferred over sprinkler irrigation. Preventative fungicide sprays may be required if a “zero tolerance” for defects production system is needed.