Occurrence and Control of Grape Downy Mildew in Southern China
Downy mildew is one of the five major diseases in the southern grape growing areas. Especially in recent years, the promotion of greenhouse cultivation in southern China and the cultivation of shelter from rain are the diseases of grape downy mildew and easy impregnation after the exposing period. Infringement of grape lightness weakens the tree vigor. Affecting the quality of fruits, early defoliation, affecting flower bud differentiation, directly leading to lower output in the coming year, is a major disease that the majority of farmers can not ignore.
1 The diseased leaves of the victimized lesions started as translucent, oily lesions, ranging from pale yellow to red-brown. On the 4th to 5th day after the onset of disease, a dense white cream was formed on the opposite side of the diseased spot; afterwards, the leaf was dehydrated and scorch, followed by falling, the upper tip was hypertrophic and curved after bending, and the white was finally browned to death; the young fruit was affected by discoloration and graying. The surface was covered with mildew.
2 Occurrence of the pathogens of Downy mildew belongs to the genus Algae, the flagellin subphylum, the downy mildew, the downy mildew, and the uniaxial downy mildew. It is an obligate parasite that breeds between parasitized grape tissue cells. The pathogenic bacteria are mainly borne by oospore in diseased tissues (mainly diseased leaves) and can live for 1-2 years. In the spring of the following year, the oospores germinate one after another within 1-2 months, resulting in zoosporangium and then swimming. The spores are transmitted to the near-ground leaves by the storm splash. The germ tubes produced by zoospore germination can be immersed in the host from the stomata and lenticels, and then the hyphae develop between cells and grow into a conical suction device to reach the host cells. The nutrient is sucked up, and then the cyst stem is rapidly protruded from the stomata. The sporangium on which it grows is easily detached from the stem, spreads with the airflow and rain, and invades the leaves and other young tissues again. Diseased leaves and other diseased tissues are combined with ovipositors and sperms to form oospore for winter.
The climatic conditions have a great influence on the disease epidemic. Frozen and humid climates are favorable for disease. The germ oospore germination temperature range is 13-25-33Â°C, and there must be sufficient water at the same time. The germination temperature of the sporangium is 5-10-15-27Â°C, and there must be free water. The temperature range for mycelium growth is 7-29Â°C, and the climatic conditions for sporangia formation are 95-100% relative humidity. The humidity of pathogenic bacteria infestation is required to be 70-80% relative humidity. Under suitable temperature and humidity, the incubation period is 4-7 days, but it varies depending on the variety resistance. Disease resistant varieties can grow for 20 days.
3. Incidence conditions 3.1 The climate downy mildew is a kind of cold, high-humidity disease. It has little wind in spring and autumn, and it is cloudy with rainy weather. It is favorable for downy mildew, and rainfall is the main cause of disease epidemics.
3.2 Management of water retention in orchards, over dense plants, low shelving, overcrowding of branches and leaves, poor ventilation and light transmission, and heavy losses in vineyards.
3.3 Varieties Varieties of different resistance to downy mildew, European and American species are generally stronger than Eurasian species, studies have shown that the type of diseased leaves have dense and large stomata, and the resistant type leaves are sparse and sparse, with white deposits around the stomata. .
4 Prevention and control are mainly prevention-based, and integrated prevention and control is performed through combination of cultivation management and pharmaceuticals.
4.1 Clean up the garden in winter to kill the overwintering germs. Clean the fallen leaves, prune the diseased branches, and burn them in a concentrated manner. The whole garden is deeply turned and the pathogens in the topsoil are buried in the soil. In conjunction with the winter pruning, the entire garden is sprayed with an eradicator (Baume 3-5 degrees lime sulfur plus 0.5% sodium pentachlorophenol). . During the pompon period, the entire park sprayed Baume 3-5 degree lime sulfur again, which can effectively reduce the initial impregnation.
4.2 Adjust the orchard's microclimate to increase ventilation and light transmission to reduce humidity. Specific measures such as appropriate relaxation of plant spacing, parallel to the wind direction, the scaffolding should not be too low, to avoid partial nitrogen fertilizer, increase phosphorus and potassium fertilizers and lime, enhance plant resistance to disease, leaves not too dense, the lower wire of the grape support up, and Appropriate irrigation and drainage.
4.3 Chemical control In the south of the Shelter Shelter vineyards, a 1:0.7:200-type Bordeaux mixture was sprayed on the day before the film was uncovered, and once every 10 days for three consecutive times, good protection effects could be achieved. In the early stages of the disease, 20% metalaxyl or 40% methotrexate 400-600 times, or 40% bisphosphonate 200-300 times, or 50% wettable methophos 400-500 times can be used.
4.4 Educate or plant more disease-resistant varieties in disease-endemic areas.