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The most common onion disease is peronosporosis. For onion crops, this disease occurs not only during the growing season, but also during storage.
- Description of the disease
- Peronosporosis infection
- Treatment methods
- Prevention methods
Description of the disease
Peronosporosis or downy mildew is a fungal disease that can affect onions in all phases of development. In most cases, the disease appears within the first three years of life. Downy mildew is especially dangerous for the testes, as the seeds may not yield a harvest. Peronospora conidia persist and overwinter in the mycelium, and oospores in bulbs or rhizomes. Downy mildew can affect most perennial onions.
When choosing varieties, preference should be given to varieties with flat leaves - allspice and slug onion. In case of peronosporosis, onion feathers develop poorly. Their color becomes pale green, then changes the shade to yellow. The plant bends.
These signs appear from the moment of disembarkation after 3 weeks. You may notice a lag in development. The signs of peronosporosis stand out noticeably against the background of healthy plants. At high humidity, the aerial part is covered with a purple bloom. If you do not take any measures to eliminate the fungal disease, then the feathers will be covered with rusty spots and rot.
The most favorable conditions for the development of downy mildew are high humidity and air temperature over 15 degrees. The development of a fungal disease occurs in rainy or cool weather. If the beds are heavily shaded and fresh air does not come in, this can also lead to the development of downy mildew. Conidia are formed and mature only at temperatures from 3 to 27 degrees and humidity above 90%.
The sensitivity of the spores to the sun is high, so infection occurs only in the morning. In dry weather, there may be no fungal plaque, since the pathogen dies in the sun. Infection occurs through a diseased plant. The disease spreads to other bulbs through spores. They can be carried over long distances by wind or raindrops.
At the first signs of peronosporosis, you should stop feeding the plant with nitrogen and organic fertilizers. It is recommended to use phosphate-potassium fertilizers instead. It is also necessary to reduce watering. During the growing season, if downy mildew is found, the plant should be sprayed with a fungicidal agent.
Video for the prevention of peronosporosis:
For this purpose, you can use Bordeaux liquid (1%), a suspension of Polycarbacin or Arbamide. The last two chemicals are diluted in 10 liters of water, adding 30-40 g of one of the preparations. If necessary, the treatment is repeated after 1-2 weeks. The use of Bordeaux liquid should be done 2 weeks before harvest.
It should be remembered that after processing with chemicals, onion feathers should not be eaten. This rule does not apply to the onion. In the fight against powdery mildew, you can prepare fermented grass from weeds. Take half a bucket of weeds, chop finely and cover with hot water.
Leave to infuse for several days, then strain and spray the plant in the evening. Many gardeners from peronosporosis use fermented milk products diluted in water.
You can take spoiled milk, kefir, whey. Dilute any of these products in cold water in a ratio of 1:10, stir and spray the plants. You can get rid of peronosporosis using wood ash, which is used for pollination of the beds. You will need 50 g of ash per square meter. By combining several methods, further spread of the infection can be avoided.
In order to prevent downy mildew, in order to prevent infection with a fungal disease, the following recommendations must be followed:
- Remove plant residues
- Observe the crop rotation
- Disinfect seeds before planting
The cleaning of lodged feathers should be done in dry weather. They need to be cut and burned. Choose varieties that are not prone to fungal diseases. Planting onions is recommended in sunny and well-ventilated areas. The soils are preferably sandy loam or loamy. Planting onions in the same place should be done after 3-4 years.
In this way, re-infection can be avoided during further planting. A huge plus will be the cultivation of pumpkin, cabbage or cucumber onions on site. Perennial onion varieties should be planted in isolation from other varieties. After harvesting and drying the bulbs, you need to provide the necessary storage conditions. By following these rules, the spread of the infection can be avoided, even if the infection has already occurred.