Powdery mildew (wheat) [Erysiphe graminis f.sp. tritici]
Disease survival is dependent on living host plant tissue. Ascopspores mature in the blackish fruiting bodies that are present on older leaves. Of greater importance is the route of transmission through mildew pustules located on volunteer grain, which are spread by wind and infect the new seeding ("green bridge"). The spread of conidia (infectious units) is promoted by high humidity, temperatures between 5 to 28 °C, early seeding, and a high seeding rate. In contrast, rain and leaf wetness inhibit spread of the parasite. Through haustoria, the fungus draws nutrients from the cells of the epidermis. With triticales, infection rates leading to harvest losses are rarely reached.
Winter and spring wheat, triticale.
Pattern of damage
Early infection often appears on the leaf sheaths and is easy to identify. Whitish to light gray-appearing, mildew-like pustules form on the infected plant parts (Picture 1). Older pustules turn into downy white to gray-brown growths in which dark-brown to black fruiting bodies develop to, about 0.2 mm large (Picture 2).
Good tilling of crop residue to remove the green bridge. Prevent accumulation of volunteer grain by soil management and crop rotation. Use of resistant varieties or mixtures of varieties with different resistance genes. Fertilization with silicate to strengthen the leaf epidermis. Ensure good potassium supply.