Control methods of downy mildew of Welsh Onion

Scallion downy mildew is a very common disease of scallion, easy to occur under cool and humid conditions, mainly damaging leaves and pedicels, short diseased plants, deformed or distorted leaves, a large number of white mold on the surface when humidity is high, so that the normal growth of scallion is seriously affected, thus affecting the quality and planting efficiency of scallion, let's take a look at the prevention and control methods of scallion downy mildew!

hazard symptom

The whole plant infected Chinese onion overwintering stopped growing, plant height decreased, leaves thickened, yellow and curved. Spring and autumn rain can form a white mold layer, yellow change withered. Yellow and white long oval large spots appeared on the leaves and pedicels of scallion infected again, with white mold layer on the surface, which turned green or dark purple later, and the diseased plants were pale yellow and withered seriously. After miscellaneous bacteria are born on the diseased spot, sometimes a black velvety mold layer is formed.

occurrence regularity

Diseases often occur in high temperature and rainy years in winter or high temperature and rainy years from March to April. Diseases occur once in spring and autumn when the average temperature is 15℃, especially in April and May when there is much rainfall. Diseases are more common in plots with poor ventilation such as continuous cropping, poor drainage, low-lying land and shady land. Thick sowing, excessive fertilization seedbed, from the next humidity, conducive to disease occurrence.

control methods

1. Select plots with high terrain and easy drainage for planting, and rotate with crops other than onions for 2~3 years.

2. Choose disease-resistant varieties. Generally red skin, yellow skin varieties are more resistant, such as Yefu No. 1.

3. Dressing seeds with 0.3% of 35% redomil or soaking seeds in warm water at 50℃ for 25 minutes.

4. Clean up the residues of diseased plants when harvesting, take them out of the field and bury them deeply or burn them.

5. At the early stage of disease, spray 90% aluminum triethyl phosphonate WP 400~500 times solution, or 75% chlorothalonil WP 600 times solution, 50% metalaxyl copper WP 800~1000 times solution, 64% disinfectant alum WP 600 times solution.