Mildew injury is caused by the development of fungal on plants or organic material such as wood, paper or leather hyphae. In plants, when hyphae develop in them affects their crops. Mildew can be produced by fungi of the order or the order Erysiphales Oomycota (family Peronosporaceae).
- The vine is affected by Plasmopara viticola.
- Potatoes and tomatoes by Phytophthora infestans (Oomycetes, Peronosporales, Pythiaceae, Phytophthora, P. infestans)
- Spinach is affected by Peronospora farinosa.
- Soy is affected by Peronospora manshurica.
Phytophthora infestans causes late blight of potato. It affects not only potatoes but also tomatoes and other Solanaceae. It was the cause of the Great Irish Famine from 1845 to 1849, and the Scottish famine from 1846 to 1857.
The spores of this fungus overwinter in infected tubers, especially in those who remain in the soil after harvest, spread in warm and humid conditions. Spores develop on leaves and extend crops when temperatures are above 10 ° C and the humidity is above 75% for 2 or more days. With rain spores go down and infect young tubers, and can also be carried by wind over long distances.
In the early stages of the pest pass easily unnoticed and not all plants are affected at once. Symptoms include the appearance of dark spots on the leaves and stems of plants. Under humid conditions a white powder appears under leaves and whole plant can quickly collapse. Infected tubers develop patches of gray or black and are reddish brown beneath the skin. Rots quickly by a secondary bacterial infestation and produce very bad smell. Apparently healthy tubers will rot later, while stored for consumption or planting.