Powdery mildew on onions: how to fight it, how to treat it

Author's rating

Author of the article

Yakov Pavlovich

Professor, Head of the Department of Vegetable Growing

Articles written

153

Powdery mildew is a fungal disease that often affects onion beds. The greatest danger is the fact that this fungal infection can progress and spread to nearby crops. Once established mycelium is almost impossible to eliminate; often the plant is completely removed from the garden. For this reason, gardeners should know what powdery mildew on onions is and how to deal with it. Premature measures to eliminate the disease will help save the crop and not endanger other crops.

Why is powdery mildew on onions dangerous?

Powdery mildew affects absolutely all onion varieties. The mycelium, having settled on the plant, gradually depletes it, taking away nutrients and juices. Over time, the leaf part dries out, becomes covered with yellow spots, a whitish coating and dies. The bulbs of such a plant do not ripen and become dry and small. With rain and wind, spores of a dangerous infection spread to other plants. Affected onions are not suitable for consumption - the collected feathers will need to be removed from the garden and burned to prevent the infection from spreading further.

Description

Photo:

The disease develops under certain conditions - low temperature (not higher than +16° C), high humidity. A dangerous infection is spread by raindrops, gusts of wind, and garden tools that contain remains of infected plants. Sudden heat can easily destroy fungal spores if the disease has just begun to develop.

The infection overwinters safely in bulbs, in the rhizomes of perennial varieties, and in plant debris. Leeks, shallots, trumpets, chives and even garlic are susceptible to the disease. Aphids, onion flies, and nematodes are frequent carriers of fungal spores and the cause of weakened onion immunity.

In addition to powdery mildew, downy mildew (downy mildew) is also found. Types of the disease differ in the location of the white coating: in true powdery mildew, infection begins on the outside of the leaf, in false mildew, on the inside.

Powdery mildew is dangerous not only because it damages the leaves, but also because it spreads to all parts of the plant very quickly and infects the ground around it. It is very difficult and time-consuming to treat infected plants; the affected leaves must be removed; it will no longer be possible to get rid of the parasitic mycelium. The bulbs of an infected plant do not ripen and become dry, small, and wrinkled.

Under what conditions does the disease develop?

Of all the fungal diseases that settle on vegetable or berry crops, powdery mildew is the most common. However, for the development of infection, certain factors are required: a decrease in temperature to 15 degrees, as well as high humidity (at least 90%). In rainy and windy weather, infection occurs extremely quickly. The fungal spores are killed immediately during hot and dry weather, but when the rains arrive, the disease will begin to spread again. As a rule, powdery mildew prefers to settle in dense plantings overgrown with weeds. In addition, the ideal place for the fungus will be shady areas in the lowlands, where there is practically no sun.

Prevention measures

In order not to suffer when treating plants with chemicals, there is no need to allow the plants to become infected. This is easy to do if you process the planting material and soil in a timely manner. The bulbs are disinfected in the spring, before planting, and the soil is cultivated in the fall.

After harvesting, the remains of plants and weeds are collected and burned, since fungal spores can attach to the leaves and overwinter. Mulching is carried out with needles and leaves of trees - this is safer than leaving parts of infected plants on the site.

The soil is dug up before frosts - the frozen top layer of soil will not preserve pests. Powdery mildew multiplies intensively in soil that is too fertilized, so you should not overdo it with complex fertilizing. A 3% solution of Bordeaux mixture will destroy the fungal spores remaining in the soil in the fall.

When growing onions, do not allow the plants to thicken, since the lack of fresh air provokes the development of infections when the conditions are suitable. Lack of sunlight and too frequent watering with cold water are factors that positively affect the possibility of onions becoming infected with powdery mildew.

Signs of infection

The gardener usually finds out that the onion is affected only after a month. By this time, the infected bulb has sprouted and the first changes can be detected on the feathers of the bulb. What are the symptoms that onions have powdery mildew:

on the leaf part you can see yellow spots, which are then covered with a grayish coating;
the surface of the leaves gradually becomes yellow;
green tissues lose elasticity, wither, sag, break, and after rain they turn purple;
progressing, grayish spots increase in diameter;
the onion looks weak, exhausted, its growth stops, and the feather part dries out completely;
the fungus, having penetrated the bulb, does not allow it to ripen and grow to normal size;
the tops become rough and therefore become covered with dust and dirt;
bow arrows dry out and break;
There are no ripe seeds in the peduncle.

See also: When to harvest onions in the Urals

Signs of infection can be most clearly seen in the morning, before the dew has evaporated. Bulbs affected by a fungal infection appear healthy in appearance, but begin to deteriorate during storage. Such material is a carrier of dangerous infection. The ashpelt retains its vital activity for four days.

Onion diseases and their treatment with folk remedies

Onion moth, secretive proboscis, and onion fly are some of the most dangerous crop pests. But there are also many diseases, and if they are not dealt with, the farmer risks losing his harvest. Diseases can be both viral and bacterial. Here are the most common ones:

Downy mildew of onion. It is often called peronosporosis. Wilting of leaves, the presence of pale spots, plaque formation, yellowing of leaves and drying out are the main symptoms of onion infection. Poor planting material and non-compliance with crop rotation rules are the most common reasons that cause downy mildew

At the first manifestations of the disease, it is important to remove the affected areas. It is recommended to plant onions in well-lit areas

Weeds should not be allowed to spread. It is recommended to choose varieties resistant to downy mildew.

Gray rot

. Damage to onion scales is another ailment. The disease usually affects the crop through the soil. The onion becomes softer, and gray rot can be seen on the surface - this means that the vegetable is affected. If the disease has affected the entire onion, it should not be eaten. Measures to combat gray mold boil down to planting healthy and clean planting material. It is equally important to protect the soil from rot and use nitrogen fertilizers for this purpose.

Cervical rot. Most often it affects onions during storage. The fungus gradually penetrates the neck of the bulb, its tissues become softer and then a dent appears. A couple of days after harvest, the rot spreads to the entire bulb. Measures to combat neck rot include good drying for a week, high-quality disinfection of the storage area for vegetables.

How to save onions from disease

As soon as the first symptoms of infection are noticed, the gardener needs to take measures to combat powdery mildew. An important task facing him is to reduce the affected area. Crops covered with a white coating are removed from the garden and burned. In the early stages of development of powdery mildew, they are treated with pesticides and products that are always at hand. Protection of the bulbs must be comprehensive - this is the only way to cope with a severe infection.

Chemical treatment

Unfortunately, treatment with chemicals does not always give a positive result - the fungus still remains inside the bulb and remains there for a long time. To completely get rid of powdery mildew, several chemical treatments are carried out.

What drugs are most often used to treat fungus:

Arceride is a brown powder that dissolves well in water. You need to mix 30 g, ten liters of water and water the plants. Irrigation is carried out at intervals of 16 days.
Polycarbacin is a contact fungicide that stops the development of the disease. For ten liters take 40 g of product.
Kurzat - contains copper oxychloride, which inhibits fungal spores and has a bactericidal effect. Apply in the early stages of the crop's growing season. Use 60 g of product per bucket of water.
Thanos - the remedy is used when the onion has 5 leaves. Contains two strong anti-fungal components.
Fitosporin is an effective and proven preparation for onions. For one treatment with phytosporin you will need one bucket of water and 20 ml of product.
Arbamide – reliably destroys fungal infections. Diluted in this way: take 30 g per bucket of water. Then all that remains is to process the beds.
Topaz is a well-known remedy for diseases that will help get rid of fungus. It is used at the first symptoms of the disease. You will need one ampoule of liquid per bucket of water.
Irrigation of beds with onions from powdery mildew is carried out up to four times per season with breaks of 14 days. It is extremely important to remember that greens treated with chemicals cannot be used for cooking. Spraying stops two weeks before harvest. Before using chemicals, you should read the instructions.

Folk remedies

Traditional methods are a safe way to protect onion plantations. To cure infected plants, use a weak solution of potassium permanganate. The scheme for this treatment is as follows: dilute 10 g of potassium permanganate in a liter of water, place the bulbs in it and wait 45 minutes. You can cure the fungus with soda ash (soda ash) - one spoon diluted in ten liters of water. A solution with wood ash also helps: mix two glasses with boiling water, infuse it, dilute it in a bucket of water and treat the beds.

See also Onions have turned black and are rotting: causes and measures to combat rot in the garden

Another effective way is to spray with a solution of copper sulfate. 10 g of the substance are dissolved in half a liter of hot water and then poured into a bucket of water. Laundry soap is also added to the water. This composition should be used up to 4 times per month. Immediately after the disease is detected, moisturizing with iodine tincture helps: 10 ml is dissolved in ten liters of water. For greater effectiveness, add 3 liters of whey - lactic acid bacteria stop the spread of the disease.

Chemical methods

A few days before planting, the bulbs should be treated with chemicals such as Benomyl or Fundazol.
The concentration of the solution should be 3%. If the first symptoms of the disease appear on plants, they should be immediately treated with fungicides. Suitable substances for this include:

Oksikhom.
Acrobat MC.
Ridomil Gold.
Cuproxat, etc.

You need to treat with different drugs, so you should purchase two or three and alternate them. Spraying onions in clear weather is carried out every two weeks, and in cloudy weather at least a week. Before use, you should carefully read the instructions for the chemicals.

Processed onions cannot be used on green feathers even after processing is completed. And from the last spraying to harvesting, at least twenty days must pass (unless a different number is indicated in the instructions for the drug).

Attention! When preventing powdery mildew, onions are sprayed with a one percent solution of Bordeaux mixture

But it is important to remember that you can harvest onions only 2 weeks after spraying with Bordeaux mixture

It is also possible to use:

"Polycarbocin";
"Arcerida";
or copper oxychloride.

To ensure that the suspensions adhere well to the plants, you can add a soap solution or skim milk. The treatment should be repeated after one and a half or two weeks.

To prevent downy mildew, before planting onions, they are treated with immunostimulating substances. The preparations Novosil and Ecosil are suitable for this purpose. Two milliliters of the substance are diluted in three liters of water.

You can also spray during onion growth:

the first time this is done at the four-leaf phase;
and the second two weeks after.

You may find our other articles on onion diseases and pests useful:

Why can a vegetable turn yellow and rot?
How to get rid of onion fly and nematode?
How to save onions from worms?

Preventive actions

Reliable protection of the garden from various diseases is regular prevention. To make it easier to care for the plant and not use chemicals in the future, it is important to take care of the following things:

adhere to the rules of crop rotation and do not plant bulbs where there were garlic, beans and shallots;
pre-disinfect the seeds before planting in a solution with potassium permanganate;
prevent neglect of plantings by promptly removing weeds;
disinfect working tools before and after manipulating vegetables;
water the plants in the morning so that they have time to dry out;
It is recommended to plant onions in places where cucumbers or cabbage used to grow;
for onion beds you should choose bright and sunny places;
deep digging in the fall will help get rid of fungal diseases and pests;
apply less nitrogen fertilizers and more mineral fertilizers with potassium and phosphorus.

In addition, as a preventive measure, vegetable beds with onions are treated with whey or a solution with wood ash. After digging, the stems and spoiled bulbs are burned so that pathogenic organisms do not accumulate there. The harvested crop is treated with fungicidal preparations and sent for storage, following the necessary rules.

What does it represent?

Peronosporosis refers to downy mildew on onions, the causative agent of which is fungi from the class of oomycetes. Fungal spores are easily recognized by the spots that form on the aboveground part of the crop. They may have a whitish, grayish or purple coating.

It manifests itself brightest and most powerfully in the mornings, when the planting beds are covered with dew. As the disease develops, the spots on the feathers grow in size, and the onion leaves themselves become fragile, easily fall off, wither and eventually die. If signs of the disease are noticed on peduncles, then this is a signal for the gardener - you can’t expect seeds from this crop.

Conditions for the development of infection are rainy and cold weather. It often happens that the seemingly established warm weather in April-May suddenly gives way to cold weather, and sometimes even frost.

With high humidity of 90%, especially in the mornings, the fungal infection flourishes, spreads by the wind and infects more and more new plantings, which happens quite quickly if they are very dense. The lack of fresh air and sunlight does its dirty work, increasing the number of infected specimens.

How to store onions with powdery mildew

To preserve onions that have been affected by fungal spores, you must follow some rules. Proper storage of the crop is accompanied by monitoring and regular checking for rot. The most productive way is to store the bulbs in braids, which are placed in a dry and warm room. The air temperature in this place should not be below 20 degrees. Well-ventilated nets are another option, but even in this case, the onions will need to be sorted out from time to time. Experienced gardeners recommend heating the crop at a temperature of 45 degrees for 12 hours before storing the bulbs. In winter, onions are stored at +1 or -2.

OnionHow to deal with onion fly

OnionsWhat is better to plant after harvesting onions