Grape downy mildew is a worldwide disease of grape. It takes more damage in the rainy, humid and warm areas of the grape growing season. It often causes the early fall of the grapes and causes great damage.
Symptoms of the leaves: The diseased part of the disease is angular, yellow to reddish-brown, limited to veins. Four or five days after the onset of disease, the lesions on the back of the leaves form a dense, dense, white cream-like appearance. This is a characteristic of this disease, and downy mildew has its name. Diseased leaves are the main source of infestation of fruit particles. Severely infected diseased leaves cause leaf shedding, which reduces the accumulation of sugar in the fruit and the cold resistance of overwintering buds, thereby affecting the output in the coming year.
New shoots: The upper part is hypertrophic and curved. As the spores turn white, they eventually turn brown and die.
Fruit: young fruit grains are grayed out and the surface is covered with downy mildew; the larger grains are hard-edged and remain hard, with early coloration and reddening, mildew layer is less pronounced, and softens when mature The diseased grains fell off.
?? The characteristics of the disease? The bacteria spores in the diseased tissue or with the disease in the soil in winter, can survive for 1-2 years. In the spring of the following year, germination produces spore cysts. The sporangia produce zoospores, spread to the host leaves by wind and rain, invade through the stomata, and the mycelium spreads in the cell gaps, and grows into a conical suction device to extend into the host cells to absorb nourishment, and then from the stomata. The cysts are outstretched to produce sporangia and reinfested by wind and rain. The incubation period for disease is only 4-13 days for susceptible varieties and 20 days for disease-resistant varieties.
The climatic conditions have a great influence on the incidence and epidemic. The disease mostly occurs in the autumn, is the late growth of grape disease, cool and humid climate is conducive to hair? germ germination temperature range of 13-33 °C, suitable temperature 25 °C, while there must be sufficient moisture or rain. Sporulation germination temperature range of 5- 27 °C, suitable temperature 10--15 °C, and the presence of free water. The sporangia formation temperature is 13--28°C, and most sporangia are formed at about 15°C, requiring a relative humidity of 95-100%. Zoospore production temperature range of 12--30 °C, suitable temperature 18--24 °C, there must be the presence of water droplets. The test showed that when there is rain in the sporangia, it germinates 40-50% at 21°C and germinates 95% at 10°C. The sporangium can survive for 4-6 days at high temperature and dry conditions, and can survive for 14-16 days at low temperature. Spores can invade young leaves when they are relatively wet at 70-80%, and old leaves can suffer when relative humidity is 80-100%. As a result, the epidemic of the disease is likely to be caused by the low temperature and rainfall in the fall.
Orchard low-lying, poor ventilation, high density, poor pruning is conducive to disease incidence; North and South Shelf than East West, the incidence of disease, the incidence of stand-up than a stand alone, shed plus frame than the incidence of weight, scaffolding low high Severe onset. Late application and partial application of nitrogen fertilizer stimulated over-dense autumn leaves and delayed maturity of fruit. Grapes with high calcium content are resistant to disease. ??
The prediction and forecast of grape downy mildew is based on several years of experiments and accumulated experience mainly based on the following indicators: First, the oocysts of germs can germinate when the average temperature reaches 13°C on the day when the soil moisture is high. The second is that the daily average temperature is above 13°C, and there are sporangia formation; there are more than 2-2.5 hours of water droplets on the host surface, and the bacteria can complete the infection. Third, the length of the incubation period varies depending on the temperature, and it also has a certain relationship with the disease resistance of the varieties. The incubation period of disease-resistant varieties is long. In the suitable conditions (23-24 °C, susceptible varieties) the incubation period is only 4 days short, and at 12 °C it is extended to 13 days. Fourth, at the end of the disease incubation period, there must be high humidity conditions (with rain or heavy fog) to grow sporangia for reinfection. Fifth, the main reason for the occurrence of downy mildew is how much rainfall and how long it lasts. From mid-June to mid-September each year, the sum of two consecutive days of precipitation exceeds 100 millimeters, and it is bound to become a pandemic. The specific weather forecast should refer to the local weather forecast data and the regularity of occurrence over the years.
Control method?
1 Select resistant varieties. As far as possible, the American breeds are selected because the American grapevine is more resistant to Bo than Eurasian species.
2 Prevention and control during wintering: Combine the winter pruning to thoroughly clear the garden, cut off the bo? Weak shoots, sweep the litter, and burn them together; plunge in autumn and winter, and spray 3-5 times the Baume on the plants and nearby ground. The lime sulfur mixture kills the source of sterilization and reduces the initial infection of the following year.
3 to strengthen the cultivation and management: the choice of high terrain, fertile soil, good ventilation and light, and a good irrigation and drainage system of the local park.
Rational fertilization: Apply enough base fertilizer, top dressing should apply nitrogen, phosphorus, potassium and trace elements of compound fertilizer. Timely vines, pruning branches, removing sick leaves and weeds between the rows, and strengthening drainage work.
? 4. Chemical control: should be mainly for prevention or in the early stage of its application, when it is time to spray, mainly to the back of the leaves.
In areas where the disease is heavy, spraying Bordeaux mixture 1:0.7:200 2 to 3 times before the onset of the grapevine to protect the foliage provides special effects on the control of grape downy mildew. In addition, 58% methicillin zinc WP can be 600 to 800 times; 65% Zn WP 500 fluid; 90% phosprofen (Swollenin) WP 600 times; 68.75% Yi Bao water dispersible granules 800-1200 times, 58% Lei Duomier wettable powder 500--1000 times; 69% Ankang manganese zinc wettable powder 1500 times liquid. The above-mentioned medicaments are used alternately and sprayed once every 15 to 20 days. Continuous spraying is performed 2 to 4 times depending on the condition.
The origin of Bordeaux mixture In 1883, Professor Milad, a professor at the University of Bordeaux in France, was working out a solution to the European downy mildew epidemic, and he was struggling. One day he suddenly found in the St. Julian's place in Medoch that the roadside vineyards were still full of vitality, as if they were a paradise outside the plague. Surprisingly, I was surprised to observe that I sprayed a liquid-blue-white mixture of copper sulfate and lime. In order to confirm the conjecture with experiments, he cultivated grape downy mildew to infect grape plants. The results confirmed that spraying copper persulfate-lime water was safe and unsprayed and quickly infected with frost mold. Germany began to study the proportion of formulated liquids, looking for the most powerful formula of bactericidal power. Many experiments finally succeeded. He named the drug Bordeaux mixture in honor of Bordeaux University and was first used in Bordeaux.
Bordeaux liquid is an excellent agent for the control of grape downy mildew, and germs have not been resistant to drugs for over 100 years.
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