Alternaria alternata f. sp. lycopersici
Symptoms of Alternaria canker appear on stems, leaves and fruit. Large dark brown cankers form on stems; cankers may dry and split. These cankers will girdle the stem as they enlarge, killing the entire plant.
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.