Septoria leaf spot is one of the most destructive diseases on tomato and is caused by Septoria lycopersici. It is most destructive during moderate temperatures and high rainfall. The disease destroys so much of the leaves that the plants fail to mature their fruits properly.
Symptoms of Septoria leaf spot
The disease occurs at any stage during the growth season but is most evident after the plants set their fruit. Septoria leaf spot infects the older leaves neat the ground with water soaked spots which often are scattered thickly over the leaf. These spots become roughly circular and have grey centres surrounded by darker margins. Later the centres show tiny dark specks in which the spores of the fungus are produced.