Stemphylium solani - S. lycopersici (sny: S. floridanum), S. botryosum f.sp. lycopersici
Leaf lesions initially appear as small, brownish-black specks. These lesions develop into grayish-brown, glazed angular lesions approximately 3 mm (0.13 in.) in diameter and are often surrounded by a yellow area. Eventually they dry up and develop cracks in their centers. If numerous lesions develop yellowing of the leaf occurs, followed by leaf drop, and eventually defoliation of the plant. The fruit and stems are not affected by this fungus.
Conditions for Disease Development:
The fungus can survive in the soil and on plant debris from one year to the next. In addition, volunteer tomato plants, as well as other solanaceous crops and weeds, serve as inoculum sources. Infected transplants are also thought to be an important inoculum source. The fungus spores are spread from the surface of infected tissues by wind and splashing water. Warm, and humid or wet weather are favorable for disease development. The disease can also be a problem in arid areas when there are long dew periods, or if sprinkler irrigation is used.
The widespread use of resistant varieties has reduced the importance of this disease. Fungicides must be used for disease control when susceptible varieties are grown.