Powdery mildew
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Powdery mildew is a fungal disease that affects a wide range of plants. It is one of the easier diseases to spot, as its symptoms are quite distinctive. Infected plants will display white powder-like spots on the leaves and stems. The lower leaves are the most affected, but the mildew can appear on any part of the plant that shows above the ground. As the disease progresses, the spots get larger and thicker as massive numbers of spores form, and the mildew spreads up and down the length of the plant.
Powdery mildew in wheat
Erysiphe graminis, the fungus that causes powdery mildew, can persist between seasons in wheat stubble that is left in the field, or in wheat that is left to overwinter. It thrives in cool humid conditions. Controlling the disease involves eliminating those conditions as much as possible. Wheat plants should not be overcrowded in the field. This allows better air circulation among the lower parts of the plants, which lowers the humidity levels. Nitrogen fertilizers encourage lots of leafy growth, and in farming systems that use them they should be used sparingly to control powdery mildew. Rotating the field with non-host plants is another way to keep mildew infection to a minimum. Reducing splash from contaminated soil also helps control spores. Chemical control is possible with anti-fungals such as Triadimefan and Propiconazole. Some farmers are experimenting with spraying plants with waste milk, with varying degrees of success.