Powdery mildew on onions

Mildew of onionPowdery mildew or peronosporium is one of the most dangerous diseases of onions. The disease intensively develops with high humidity and low temperature of the order of 13-16 degrees. If the disease has only begun to appear and after the humid weather the heat is established, the conidia of the fungus may die in the sun.

Infection can be carried by rain drops, wind or with the remains of infected plants when carrying out plant care. Fungus can overwinter in affected bulbs, in the root of perennial varieties of onions or in infected plant remains. The disease can occur on all varieties of onions: shallots, batoon, shnitt, leeks and even garlic.

Symptoms of powdery mildew in onions

The disease can occur on the onion-batten in early spring with the growth of leaves if it is promoted by weather conditions. At the first stage, there are no differences between diseased and healthy plants, but after two to three weeks on the leaves and peduncles light yellow spots are formed, which are covered with a grayish coating. Sick plants begin to lag behind in growth, their leaves first turn yellow, then dry out. The disease also infects the bulb, and although the signs of the disease on the bulb are not visible, such fruits do not grow to the right size, are poorly stored.

Prevention of powdery mildew on onions

Посевы лука следует размещать на хорошо прогреваемых солнцем и проветриваемых участках. Почва тоже должна способствовать быстрому испарению лишней влаги (лёгкий супесок или суглинок).

As for the crop rotation, the onions are returned to their former place after 4-5 years. The culture is best sown after the pumpkin crops under which were introduced complex fertilizers. A good measure to prevent the development of peronosporiosis is the use of a healthy planting stock or varieties resistant to the disease. This disease does not tolerate high temperatures, so after harvesting onion sowing should be warmed at a temperature of 35-40 degrees for 8-10 hours.

When growing onions, fertilizing with nitrogen fertilizers should be carried out only during the first stages of vegetation, in the future, high nitrogen content in the plant lowers its immunity. Thickening of plantings and excessive watering cause a high degree of soil moistening, which serves as a good environment for the development of powdery mildew. When detecting affected plants, they should be immediately removed from the site so that they do not harm other crops.

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