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Onion peronosporosis is a fungal disease that often affects the plant at any stage of its maturation. The onion can become infected with the fungus every year, since the spores overwinter either in the soil or on the bulb, without causing it to rot. This disease is widespread, and for many farmers it becomes a big problem, so you need to know what to do if the onion is infected with downy mildew.
Description of the disease
Downy mildew (downy mildew in onions) has this name because of the gray-purple bloom on the "feathers" of the plant.
Peronosporosis on onions, a photo of which makes it possible to see possible manifestations of the fungus, does not appear before planting. This makes the selection of unsuitable planting material unrealistic. The disease develops rapidly, and the stronger the lesion, the more additional symptoms can be noticed.
There are the following signs and stages of the development of the disease:
- The earliest manifestations of false dew can be seen in the second half of April - early May, when small yellow spots appear on the leaves and peduncles. And after a while, gray-purple spores of the fungus appear on the infected plants.
- Powdery bloom is best seen in the morning when the beds are covered with dew.
- With the development of the disease, the spots on the leaves increase. Onion feathers become brittle. Over time, they sink to the ground and wither. The plant looks sick.
- Due to the penetration of the infection deep into the bulb, the culture cannot develop normally. If the stalks are infected, the seeds often do not ripen.
Fungal disease can destroy up to 50% of the onion crop, so you need to know not only how peronosporosis manifests itself, but also the basic conditions under which the disease occurs.
The main conditions for the development of false dew are a sharp change in temperature and high humidity in the morning, that is, dew retention. During dry summers, fungus is less common. Peronosporosis on onions develops if the temperature drops to +16 ° C, and the humidity rises to 90-100%.
Such weather conditions are observed at night, in spring and early summer. At this time, spores awaken, and when the sun rises and the air temperature becomes higher (but the dew has not evaporated yet), they begin to develop intensively.
The incubation period of peronosporosis lasts from 3 to 15 days, and during the season the fungi develop up to 6 generations.
Favorable conditions for the onion to get sick with peronospora is a lack of fresh air and sunlight. Therefore, it is necessary to choose the right place for the beds and not plant the plant too tightly.
For planting onions, agronomists recommend choosing those parts of the garden where sunlight enters freely. It is better to place the beds away from moisture and shade, since constant dampness and lack of sunlight are excellent conditions for the spread of the fungus. Spores are carried by air currents and water droplets during rain or heavy watering.
The fungus often remains in the soil along with leftover onions from last year's contaminated crop. In order to prevent a new infection, it is recommended to change the place for planting the vegetable.
If signs of fungus are found on the plant, it is necessary to abandon organic fertilizers and switch to phosphorus-potassium fertilizers. Since the downy mildew of onions develops well in high humidity, then, upon finding symptoms, it is recommended to reduce watering.
In the fight against the disease, chemical and folk remedies are used to treat the affected areas. During the growing season, onions can be sprayed with fungicides, but after processing, green feathers should not be eaten.
The bulbs can be eaten by first reading the instructions for use of the chemical, as the vegetable will be unsuitable for food for some time. In the future, to consolidate the result, gardeners recommend spraying with soapy water.
Pesticide treatment is quite effective, but there are other, safer options for dealing with downy mildew. Various home methods and methods are used effectively and without harm to human health, and the fight against infection is being carried out with folk remedies.
One of the most effective solutions is whey. It contains bacteria that are harmless to the plant, but harmful to the fungus. The serum is diluted 1:10 with water. Then the diseased onion is sprayed with the resulting solution.
It is much easier to prevent disease than to save a contaminated crop. Therefore, experienced gardeners are advised to regularly prevent the disease using the following measures:
- Carefully remove crop residues from the topsoil.
- For the winter, it is imperative to dig up the soil where the infected vegetable grew.
- For planting, do not use the same plot of the garden.
- Sow only healthy seeds.
- Before planting the onions, warm the planting material at a temperature of +40 ° C for at least 8 hours.
- Inspect plants periodically for signs of disease.
- Carry out appropriate maintenance in the open field: weed the weed, water in the morning.
Tips from a seasoned gardener
Experienced gardeners have been faced with such a problem for many years, therefore, advice and rules have been formed, observing which you can effectively deal with peronosporosis and prevent its occurrence:
- After the crop has been harvested, the bulbs must be thoroughly dried until dry scales form.
- Having seen the first signs of onion downy mildew, it is recommended to remove the infected specimens and treat the rest of the plants with wood ash at the rate of 50 g per 1 m².
- Plant onions only on the sunny side of the garden and do not place them too densely.
A good method of preventing and treating many plant diseases, including downy mildew, is feeding from herbal infusion.
To prepare the product, you will need chopped grass. Weeds will do too. The herb is poured with boiling water and insisted for 4 days. During this time, the greens should ferment. Then the infusion is filtered and the onion is sprayed with it.