How to prevent and control downy mildew in Welsh onions? These methods you need to master

Downy mildew in Welsh onions is a very common disease of Welsh onions, prone to occur under cool and humid conditions. It mainly damages leaves and flower stalks. Diseased 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 of Welsh onions and planting returns. Let's take a look below 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 become curved. 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 that later turns green or dark purple. In severe cases, diseased plants wither and turn pale yellow. After saprophytic fungi grow on the lesions, sometimes a black velvety mold layer also forms.

Occurrence patterns

The disease often occurs in years with high temperature and frequent rain in winter or with high temperature and frequent rain from March to April. When the average temperature is 15°C, the disease occurs once each in spring and autumn. It is especially prone to occur when there is a lot of rainfall from April to May. There are more diseases in plots with continuous cropping, poor drainage, low-lying land, shaded land, and other locations with poor ventilation. In seedbeds with thick sowing and excessive fertilization, the humidity below is high, which favors the occurrence of the disease.

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 relatively resistant to disease, such as Yefu No. 1, etc.

3. Dress seeds with 35% Ridomil at 0.3% of the seed weight, or soak seeds in warm water at 50°C 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% methylamyl copper wettable powder at 800-1000 times dilution, or 64% oxadixyl mancozeb wettable powder at 600 times dilution.