How to treat grape downy mildew effectively? The latest control methods are here
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 drop early, new shoots grow poorly, yield decreases, quality deteriorates, and the plants have poor cold resistance. Now let us take a look at how to treat grape downy mildew effectively!
Conditions for onset
Grape downy mildew mostly occurs in autumn, and a cool, humid climate favors the disease. The temperature range for germination of the pathogen's oospores is 13-33°C, with an optimum temperature of 25°C, and sufficient water or dew is also required. The temperature range for sporangium germination is 5-27°C, with an optimum temperature of 10-15°C, and free water must be present. The temperature range for sporangium formation is 13-28°C; sporangia form most abundantly at around 15°C, requiring a relative humidity of 95-100%. The temperature range for zoospore production 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 an epidemic of this disease.
Damage symptoms
1. Leaf damage: Small, pale yellow, water-soaked spots with indistinct edges first appear, then gradually expand into brown irregular or angular lesions; when several lesions connect, they form large irregular patches. When the disease is severe, diseased leaves dry up and drop early.
2. Damage to young shoots: Water-soaked spots form, then turn brown and slightly sunken. When the disease is severe, new shoots become twisted, growth stops, and they may even die. Tendrils, rachises, and petioles can sometimes also be affected, with symptoms similar to those on young shoots.
3. Damage to young fruit: The diseased part loses color, hardens and sinks, and white downy mildew grows on it; the fruit easily shrivels and drops. When berries are half-grown and affected, the diseased part is brown to dark, and the fruit soft-rots and drops early. After the fruit colors, it is no longer infected.
Agricultural control
1. Remove sources of inoculum: Thoroughly clean the orchard in autumn, prune out 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 a timely manner, tie up branches and vines, and improve ventilation and light penetration in the trellis canopy.
3. Pay attention to weed control 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 plants' disease resistance.
3. Use anti-drip, fog-reducing film as the outer covering material for protected facilities to reduce air humidity and prevent fog from forming.
4. During the day, the room temperature should be raised quickly to above 30°C, and the 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 rainwater from splashing and cut off the spread of the grape downy mildew pathogen.
Chemical control
1. Treatment measures: Spray “Liangguoan” at 300 times plus “Wofengsu” at 600 times mixed with “garlic oil” at 1000 times and “organosilicon” 2 times, with an interval of about 10 days each time.
2. Preventive plan
① Half a month before bud break, use “Liangguoan” at 60-100 times solution and spray the whole orchard to kill pathogens and nourish the trees.
② During leaf expansion and flowering, use “Liangguoan” at 300 times solution, “Wofengsu” at 600 times, and “organosilicon”, spraying 2 times at 10-day intervals.
③ During the first physiological fruit drop period, use “Liangguoan” at 300-500 plus 600 times plus “organosilicon” for spraying.
④ During the fruit growth period, use “Liangguoan” at 300-500 times and 600 times for regular spraying, basically at intervals of 10-15 days each time.
⑤ After fruit harvest in autumn, use “Liangguoan” at 200-300 times with 600 times and “organosilicon” for 1 spraying.
⑥ After 2/3 of the leaves have fallen, use “Liangguoan” at 60-100 times solution to spray the whole orchard, killing pathogens and nourishing the trees.