Grape downy mildew is a major headache for grape growers in my country. Why do we say this? This is because grape downy mildew can harm young shoots, flower spikes, fruits, branches and other young parts, and will be affected in almost every growth period. In severe cases, it can cause grape defoliation or large-area lesions, making it impossible for the grapes to carry out photosynthesis through the leaves and the nutrients absorbed by the roots cannot be transported to the tree. Insufficient nutrition of the tree affects the differentiation of flower buds and the growth of branches and leaves, which has a considerable impact on yield. The questioner expressed the symptoms of downy mildew, so I won’t go into too much explanation here. So why do grape downy mildew outbreaks occur frequently? What factors are involved? How to prevent and treat it? Let’s introduce it below! The incidence pattern of grape downy mildew
The pathogen is grape downy mildew, which belongs to the subphylum Flagellate, class Oomycetes, order Peronomyces, and genus Plasmodium. Grape downy mildew overwinters as oospores in diseased tissues or remains in the soil with diseased leaves. In the following year, oospores germinate under suitable conditions and produce sporangia, which then produce zoospores, which are spread by wind and rain and invade through the stomata on the back of the leaves for primary infection. After an incubation period of 7-12 days, cyst stalks and sporangia are produced in the diseased area, and the spores germinate to produce zoospores for reinfection. The suitable temperature for sporangium germination is 10°C to 15°C. The suitable temperature for zoospore germination is 18℃-24℃. The low temperature, rain and dew in autumn can easily lead to the spread of diseases. The low-lying orchards, poor ventilation on the shelves, and weakened trees are conducive to the occurrence of diseases.
It can be seen from the incidence pattern that high humidity in the vineyard, low temperature frost weather, weak trees, poor ventilation, etc. accelerate the outbreak of downy mildew. This is also the main cause of downy mildew in grapes grown in the open air. factor. The principle of prevention and treatment methods is comprehensive prevention and treatment, focusing on prevention and timely treatment.
Prevention and control methods
Comprehensive control is to cultivate dominant trees, and improve the ventilation of the orchard through reasonable summer and autumn shoot pruning, vine tying, cultivating and weeding. Add compound fertilizer to meet needs before leaf growth and flowering. Apply bulking fertilizer and apply decomposed farmyard manure in trenches in autumn. When two-thirds of the leaves of the grapes have fallen, use 42 sprays of 600-800 times of Fulin to spray the grapes. After picking the fruits in autumn, use 200-300 times of Liangguoan and 600 times of Silicone to spray the entire garden once.
After harvesting the fruits, clean up the diseased branches and leaves in the vineyard in a timely manner and burn them intensively to reduce the number of disease sources. To reduce the humidity of the vineyard, timely drainage is required so that no water remains in the orchard. Where conditions permit, cover the orchard with a water-retaining film in months with heavy rainfall.
After grape fruit set, expansion period and color change period, the leaves should be supplemented with trace elements 2-3 times to promote lignification of branches and leaves.
It is necessary to strengthen the control of other diseases and insect pests of grapes and the prevention and treatment of downy mildew in the first half month of grape budding, the leaf unfolding and flowering period, the first physiological fruit drop period, and the fruit growth period, which is beneficial to preserving flowers and flowers. fruit.
Drug prevention and control: Use Mancozeb 600-700 times solution before the onset of illness, use 40% Mycobacterium 250-300 times solution when you first become sick, use Bordeaux solution Metalaxyl 10 and Mancozeb 48 Wettable powder is a special medicine for preventing and treating downy mildew. It should be used 2-3 times continuously. After the symptoms are under control, for safety reasons, spray the affected area 1-2 more times.