Late Blight [Phytophthora infestans]
Late blight is one of the most important diseases of the potato. With long-persisting wet summer weather, entire crops can collapse within a short period of time.
Pattern of damage
Blight is first seen on the older leaves. Brown spots with fuzzy margins develop, which gradually turn blackish. In wet weather, a fungal lawn covers the bottom of the leaf. The infection spreads quickly and causes the entire leaf to die. The stem may also become infected. Once the stem is completely infected, the part of the tomato plant above this infection dies. The fruit develops brown, hard spots that extend deeply into the flesh. The plant becomes infected by the fungus Alternaria brassicae. The leaves develop roundish spots of a gray to brownish color up to 1.5 cm in size. The leaf tissue may drop out of these spots. In some cases, the entire leaf will drop. The fungus even infects seedlings since it can survive in the seed and soil.
Combat
In terms of the selection of varieties, there are few opportunities to influence the infestation. The only effective control measure is still the use of special fungicides.