Fight against powdery mildew

Powdery mildew is a disease caused by fungi belonging to different genera and attacking a very large number of plants. It causes the appearance of a white, grayish felt in circular spots on the leaves, stems and, more rarely, fruits and flowers. It gradually spreads over both sides of the leaves and can cause deformations on young shoots and the development of brownish spots. The disease weakens the plant and reduces harvests. Under what conditions does powdery mildew develop? Powdery mildew generally appears in spring and summer. The filaments of the fungus settle on the surface of the plant tissues and develop suckers to feed. They produce microscopic infectious spores that are transmitted through the air and contaminate other plants. Their dissemination is favored by temperatures between 10 and 30 °C: 25-28 °C are optimal temperatures. Sheltered, confined situations and moderate humidity are also conducive to the development of the fungus. Some produce spores that contain a high water content allowing them to infect plants even in dry conditions. The spores persist over winter on plant tissues or on fallen plant debris and spread their spores the following spring. Which plants are mainly affected by powdery mildew? It mainly affects apple trees, blackcurrant bushes, gooseberries, currant bushes, many brassicas, and cucurbits (zucchini, squash, cucumber, etc.), peas, asters, delphiniums, roses, but also azaleas, begonias, oaks, etc. The species of fungi causing powdery mildew have a relatively narrow host range (number of species on which the fungus develops). The species bringing the disease to peas is different from that affecting apples. However, spontaneous plants (weeds, etc.) can also be affected and be vectors of the disease! How to fight against powdery mildew? Choose resistant species! Prevent powdery mildew attacks by choosing resistant varieties, there are more and more of them. Space out plants. Sow or plant at sufficient distances to promote good air circulation and regularly ventilate shelters. Destroy infected leaves quickly and gradually to avoid contamination. Inspect the garden in autumn and burn any affected parts. In this way, you will limit the quantity of infectious spores spread by the fungi contaminating the plants the following spring. The most widely used anti-powdery mildew product remains sulfur. Be careful, some vegetable species such as melons are sensitive to it. In this case, favor products based on seaweed powders. Horsetail decoctions will also be effective.