The fungus spreads by the wind.

White plaque reduces the harvest of tomatoes, tomato seedlings dry out ahead of time and loses leaves. In some seasons, Septoriosis can cause a yield to reduce 40-50%. Septoriosis first affects the lower leaves, gradually choosing to the middle and upper tier. If you look at seedlings in the photo, it is noticeable that the lesion of the fungus is manifested by small brown, later dirty white spots with a dark brown border. On the leaves of seedlings, you can find black dots called the picnides of the mushroom. On stable varieties, the spots on the leaves appear very small (up to 1-2 mm in size), picnides are practically not formed. The fungus spreads by the wind.