How to prevent and control downy mildew in Welsh onions? The latest control methods are here
Downy mildew in Welsh onions is a very common disease of Welsh onions. It occurs easily under cool and humid conditions, mainly affecting leaves and flower stalks. Infected plants become stunted, and leaves become deformed or twisted. When humidity is high, a large amount of white mold grows on the surface, seriously affecting the normal growth of Welsh onions, thereby affecting the quality and cultivation benefits of Welsh onions. Now let us take a look at the control methods for downy mildew in Welsh onions!
Damage symptoms
Overwintering Welsh onions infected throughout the whole plant stop growing, plant height decreases, and leaves thicken, turn yellow, and curl. During continuous rainy periods in spring and autumn, a white mold layer can form, and the plants turn yellow and wither. In Welsh onions that are infected again, large yellow-white elongated oval lesions appear on the leaves and flower stalks, with a white mold layer on the surface, which later turns green or dark purple. In severe cases, the infected plants wither and turn light yellow. After miscellaneous fungi grow on the lesions, a black velvety mold layer sometimes also forms.
Occurrence pattern
In winter with high temperature and frequent rain, or in years with high temperature and frequent rain from March to April, the disease often occurs. When the average temperature is 15°C, the disease occurs once each in spring and autumn, and it is especially likely to occur when there is a lot of rainfall from April to May. Continuous cropping, poor drainage, low-lying land, shady land, and other plots with poor ventilation have more disease. Seedbeds with thick sowing and excessive fertilization have high humidity underneath, which is favorable for disease occurrence.
Control methods
1. Choose plots with high terrain and easy drainage for planting, and carry out a 2-3 year rotation with crops other than onions.
2. Select disease-resistant varieties. Generally, red-skinned and yellow-skinned varieties are more disease-resistant, such as Yefu No. 1, etc.
3. Treat seeds with 35% Ridomil at 0.3% of seed weight, or soak seeds in 50°C warm water for 25 minutes.
4. At harvest, clean up diseased plant residues and carry them out of the field for deep burial or burning.
5. In the early stage of disease occurrence, spray 90% fosetyl-aluminum wettable powder at 400-500 times dilution, or 75% chlorothalonil wettable powder at 600 times dilution, 50% metalaxyl-copper wettable powder at 800-1000 times dilution, or 64% oxadixyl-mancozeb wettable powder at 600 times dilution.