Septoria Leaf Spot -- Septoria spp.
Host: Chrysanthemum, daisy, phlox, etc.
Symptoms: Septoria leaf spot initially appears as yellow or purple spots on the leaves of plants. The spots become dark brown in color as they mature. On herbaceous plants, premature withering and death of the leaves progress from the lower to the upper parts of the plant.
Conditions Favoring Disease: This disease often occurs where overhead irrigation is used. Septoria leaf spot is favored by rainy, high-humidity and slow-drying conditions.
How Pathogen Survives/Disperses: The fungus produces tiny, black-fruiting bodies (like peppergrains), visible with a hand lens, on dead areas of the leaves. The spores are then pushed out during periods of high humidity and are spread by rain or irrigation to healthy leaves. Infections can occur whenever the leaves of the plant are wet.
Photo and write up provided by Syngenta Professional Products