Powdery mildew is a common disease in strawberry growing areas. Damage leaves, petioles, flowers and young fruit. In the Guangzhou area, it occurred severely in 1993, causing great losses. Symptoms of diseased leaves develop red to mauve, no obvious lesions on the edge of the leaves, and later the multiple lesions heal into large spots with a layer of white powder on them, often with more white powder on the back of leaves. Severe red necrosis occurs when the petiole is severely affected. After the victim died, it turned brown and died. The early fruits suffer, the diseased part becomes brown, hardened, and matures in advance, but it has no economic value. The surface of the diseased part of the above-mentioned victim organs is covered with a white powdery object, which is a conidium of pathogenic bacteria. The pathogen of pathogenic strawberry powdery mildew is Oidium sp., which belongs to the semi-known fungi. The mycelium appears superficially, producing a finger sucker deep into the epidermal cells of the host to absorb nutrients. Conidiophore erect, clustered. Conidia are elliptical, single-celled, colorless, and clustered on conidiophores that can easily fall off (Figure 2). No sexual generation was found in Guangzhou. Occurrence of the disease Strawberry powdery mildew is a kind of living parasitizing fungus (special parasitism) in which the mycelium is overwintering in the infested tissue. If the diseased tissue dies, the mycelium on the surface will soon die. Spore life is not long. When the environmental conditions in the spring of the following year are appropriate, new conidia are produced in the wintering mycelium, and the initial infection and reinfestation of the strawberry are carried out through the air flow propagation to make the disease worse. Powdery mildew is a drought-resistant fungus. Although it is beneficial to diseases in wet weather, conidia can germinate and infect in dry weather, but rain is not beneficial to it. Therefore, strawberry powdery mildew is cultivated in open field or in facilities. The environment can happen. Where plants are planted too densely and applied with too much nitrogen, the disease is more serious. Control methods 1. Strengthen cultivation and management to pay attention to the drainage of the field, when the plants are dense, the plants should be separated in time, and diseased leaves and old leaves are often removed. 2. The medicines are used to prevent and control spraying at the beginning of the disease. The effective medicines are: (1) 40% extermination agent 500 times; (2) 15% triadimefon WP 3000~4000 times; (3) 50% extinguishment Special wettable powder 600~800 times.
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