Alternaria stem canker symptoms can occur on the above ground sections of the plant. Initial symptoms on the stem is the formation of dark brown regions.
The disease can start as small brown or black black spots on stem which are irregularly shaped that can further expand to form larger lesions.
The disease can affect the base of the plants and the canker can enlarge as plants grow with a dark donation around the margin of the canker. The disease can also cause leaf symptoms.
The canker may enlarge to girdle the whole stem killing the whole plant. Brown streaks can be found in the vascular tissue above and below the canker region.
Fruit symptoms can be circular or oval lesions on green and ripe fruits. The lesions are sunken, can coalesce and have yellow/green discoloration on ripe fruits.
Conidia (spores) of Alternaria alternata f. sp lycopersici. Free water is needed for spore germination and infection process. Spores can thus be spread during heavy rain, continued dew and overhead irrigation.