How to treat grape downy mildew effectively? Detailed control methods
Grape downy mildew is a worldwide grape disease and one of the main diseases of grapes. It occurs in all grape-producing regions of China, especially commonly in rainy and humid areas. When the disease is severe, leaves scorch and fall early, new shoots grow poorly, yield decreases, quality deteriorates, and plant cold resistance is poor. Now let us look together at the best way to treat grape downy mildew!
Conditions for onset
Grape downy mildew mostly occurs in autumn, and a cool, humid climate favors its onset. The germination temperature range of the pathogen's oospores is 13-33°C, with an optimum temperature of 25°C, and sufficient moisture or rain dew is also required. The germination temperature range of sporangia is 5-27°C, with an optimum temperature of 10-15°C, and free water must be present. The formation temperature of sporangia is 13-28°C, with the most sporangia formed at around 15°C, requiring a relative humidity of 95-100%. The production temperature range of zoospores is 12-30°C, with an optimum temperature of 18-24°C, and water droplets must be present. Therefore, low temperatures and abundant rain in autumn easily lead to the prevalence of this disease.
Damage symptoms
1. Leaf damage: Initially small, pale yellow, water-soaked spots with indistinct edges appear, which gradually expand into brown irregular or angular lesions, and several lesions connect to form irregular large patches. When the disease is severe, diseased leaves wither and fall early.
2. Damage to young shoots: Water-soaked spots form, then become brown, slightly sunken lesions. When the disease is severe, new shoots become distorted, growth stops, and they may even die. Tendrils, rachises, and petioles can sometimes also be damaged, with symptoms similar to those on young shoots.
3. Damage to young fruit: The diseased part fades in color, hardens and sinks, and white downy mildew grows on it, making it very easy to shrivel and drop. When berries are half-grown and damaged, the diseased part is brown to dark, and soft rot causes early dropping. After the fruit colors, it is no longer infected.
Agricultural control
1. Remove sources of inoculum: Thoroughly clean the orchard in autumn, prune diseased shoots, collect diseased leaves, and bury them deeply or burn them in a centralized manner.
2. Strengthen orchard management: Carry out summer pruning in time, tie up branches and vines, and improve ventilation and light conditions on the trellis.
3. Pay attention to weeding and drainage to reduce ground humidity.
4. Appropriately increase the application of phosphorus and potassium fertilizers, and apply lime to acidic soil to improve the plant's disease resistance.
3. Choose anti-drip anti-fog film as the external covering material for the facility to reduce air humidity and prevent fog formation.
4. During the day, room temperature should be raised quickly to above 30°C, and night temperature should be maintained at 10-15°C, with air humidity no higher than 85%.
5. Build rain-shelter facilities in the vineyard to prevent rain splashing and cut off the spread of the grape downy mildew pathogen.
Chemical control
1. Treatment measures: Spray 300 times "Liangguoan" plus 600 times "Wofengsu" mixed with 1000 times "garlic oil" and "silicone" 2 times, with an interval of about 10 days each time.
2. Prevention plan
① Half a month before bud break, use 60-100 times "Liangguoan" solution plus for whole-orchard spraying to kill pathogens and nourish the tree.
② During leaf expansion and flowering, use 300 times "Liangguoan" solution, 600 times "Wofengsu", and "silicone", spraying 2 times at an interval of 10 days.
③ During the first physiological fruit drop period, use 300-500 times "Liangguoan" plus 600 times plus "silicone" for spraying.
④ During the fruit growth period, use 300-500 times "Liangguoan" and 600 times for regular spraying, basically with an interval of 10-15 days each time.
⑤ After autumn harvest, use 200-300 times "Liangguoan" with 600 times and "silicone" for 1 spraying.
⑥ After 2/3 of the leaves have fallen, use 60-100 times "Liangguoan" solution for whole-orchard spraying to kill pathogens and nourish the tree.