Potato downy mildew is a fungus that primarily infects potato both in spring and autumn, and if not treated, it can destroy large-scale production. The first signs of potato mildew infection are yellow spots of irregular shape on the potato leaves. Subsequently, the spots become brown and the leaf is dried in the area of the spot. With increased moisture a white fluff develops on the bottom side of the leaf. When potatoes are infected external dark spots appear, while later inside the potato, under the infected surface area, the potatoes darken and rot.
The rate of growth of potato mildew depends on environmental conditions. Specifically, with a relative humidity of 90-100% and a temperature of 17-20°C the fungus grows rapidly. When the temperature is more than 25°C the spread slows down, while when it is more than 30°C the growth pauses. Pausing does not mean stopping the disease; when the conditions become proper for growth again, the fungus will grow once more.
To control downy mildew, the cultivation of tomato near potato crops must be avoided and the residues of previous crops must be destroyed. Care must also be taken to ensure that seed potatoes are carefully selected so as not to become infected; for this reason it is recommended to use certified potato seeds. If conditions are proper for fungus growth, preventive sprays with multi-action contact fungicides are recommended every 8-12 days. When symptoms occur, spraying is necessary with a combination of systemic fungicides and multifunctional contact fungicides.