Onions: Methods for combating diseases and pests and measures for their prevention

The list of possible diseases and pests of onions is quite impressive. Exposure to them largely depends on the variety of the crop and compliance with the rules for its cultivation. Diseases and pests must be dealt with in a timely manner, starting with preventive measures.

Diseases of onions

Onion diseases can be triggered by bacteria, viruses, fungi. In each case, there are certain features.


This disease is fungal. It is also called black moldy rot or black mold. The causative agent is a fungus of the genus Aspergillus.


During cultivation, the disease is rarely detected. The only sign is the discoloration of the neck of the bulbs – this is the way the pathogen enters the fruit.

The main symptoms of aspergillosis are detected during storage of the crop:

  • watery bulbs;
  • black powdery mass of spores under the husk, between juicy scales;
  • possible complete drying of the bulbs.

Aspergillosis often affects immature and poorly dried bulbs. The high temperature in the storage room and insufficient ventilation in it can also provoke the disease.

Affected specimens must be disposed of, they cannot be saved.

Preventive measures are as follows:

  • burning plant residues;
  • observance of the terms of harvesting – it must fully ripen;
  • complete drying of the crop;
  • compliance with storage conditions: ventilation in the room, the correct temperature and humidity levels.


This bacterial disease can be caused by Bacteriaceae, Pseudomonadaceae, Myconacteriaceae. The affected plant completely or partially dries out, may die.


Bacteria are found in the particles of infected plants. They can be carried by pests and animals, wind, water for irrigation, precipitation. The pathogen also persists in the soil. It can get into healthy plants through damaged roots, greens, even the slightest wound is enough.

Signs of onion bacteriosis are as follows:

  • softening of the affected bulbs;
  • unpleasant odor;
  • small flies;
  • in the section, the affected tissues are visible – they are between healthy scales, have a brown color.

More often, bacteriosis affects onions during harvesting and storage. The reason may be damage to the fruit or insufficient drying.

Bulbs affected by bacteriosis must be thrown away, they are not suitable for food. To reduce losses, fruits should be regularly inspected and spoiled specimens should be discarded.

Prevention of bacteriosis consists in the following measures:

  • burning plant residues;
  • soil disinfection;
  • moderate watering of the crop, its termination before harvesting;
  • careful harvesting – fruit damage should be minimized;
  • complete drying of the harvested crop.


This fungal disease is caused by the bacterium Urocystis cepulae Frost. Chlamydospores are found in the soil, can get on the seeds with dust. Spores germinate at a temperature of 13-22 degrees, and infection of the culture can occur at 10-25 degrees.


Shoots are usually affected when planting seeds. The disease is expressed by the following symptoms:

  • the appearance on the feathers of narrow longitudinal stripes with a gray color and swollen epidermis;
  • drying of stripes with a rupture of the epidermis and the protrusion of black powdery masses;
  • the disease can also affect an adult culture, affecting the outer fleshy scales.

Affected seedlings die, resulting in crop loss. If the bulbs still form, but are infected, then black spores are contained inside. The peel of the fruit cracks over time, the spores enter the soil, remaining in it for up to 5-6 years.

Smut prevention involves the use of disease-resistant varieties. Crop rotation should also be observed – onions should be returned to their original place at least 3 years later. Planting a crop with seeds in an infected area is not worth it for 6 years.

yellow dwarfism

The disease is viral. It is also called viral streak. The disease is caused by the Onion yellow dwarf virus. The virus is found in the bulbs, spread by aphids, with an incubation period of up to 2 weeks.

yellow dwarfism

The disease is expressed by the following symptoms:

  • yellow stripes on feathers;
  • leaf deformation;
  • twisting and lodging of feathers, their flattening is possible;
  • strong inhibition of growth and development of culture.

Affected plants must be removed and burned in a timely manner.

Prevention of the disease consists in the following measures:

  • aphid control – insecticides such as Aktara should be used;
  • the use of varieties resistant to this disease;
  • planting a crop with seeds, including for seedlings or sets – the virus is not contained in such planting material.

Downy Mildew

This disease is also called peronosporosis. The causative agent is the pseudofungi Oomycetes belonging to the Peronosporon family. They persist for a long time in fallen leaves, bulbs.

Downy Mildew

The symptoms of the disease are as follows:

  • Blurry shapeless or angular spots, a slightly pronounced border is possible. Such formations are pale yellow, yellow-brown, red-brown, purple. They are slightly convex, gradually turn brown and dry. The spots grow and can merge into one large spot that occupies the entire leaf.
  • Affected feathers are twisted and dry, may crack deeply.
  • Spots develop on one side, and a mild white powdery coating appears on the back. It may also have a gray or gray-purple color.
  • Peronosporosis usually starts from the top of the crop, which is in contrast to black spot, which proceeds with similar symptoms.

Downy mildew is more common in spring. Gradually, it affects all parts of the plant. The development of the disease is facilitated by high humidity and temperature differences – low at night and rather high during the day.

Features of treatment depend on the goals of growing onions. If it is grown on a turnip, then you should get rid of the affected plants, and spray the rest. The drug Oxyhom is effective. It is necessary to dissolve 20 g of the product in a 10-liter container with water, spraying is carried out 2 times a month.

When growing a crop on a feather, spraying with chemicals is unacceptable, so the following measures must be taken:

  • stop feeding with organic matter;
  • temporarily limit watering;
  • apply potassium-phosphorus fertilizers;
  • when harvesting, warm it up for 12 hours at 40 degrees;
  • treat the crop storage room with bleach – 0,4 kg per 10 liters of water, the treatment is carried out in 2 months.

Prevention of downy mildew consists in observing the rules of crop rotation and careful rejection of planting material. When planting onion sets, it should be warmed up at 2 degrees for 40 hours 12 weeks before sowing.


The disease is viral, its causative agent is Allium virus I Smith. The carrier is the four-legged garlic mite.


The symptoms of the disease are as follows:

  • small elongated specks or wide stripes of light green or cream color;
  • leaf stunting, feather lodging;
  • bending arrows, the appearance of longitudinal mosaic stripes;
  • damage to inflorescences: friability, sterility or a small number of seeds.

Affected specimens must be disposed of. The remaining methods of struggle are reduced to the prevention of the disease:

  • insecticide treatment to control the vector;
  • burning plant residues;
  • moderate watering and fertilizing;
  • compliance with crop rotation.


This disease is also called capitate rot or green mold. It is caused by fungi of the genus Penicillium.


The symptoms of the disease are as follows:

  • the appearance of brown watery spots on the bottom or outer scales;
  • gradual softening of the affected tissues;
  • the appearance of plaque on the affected tissues, first whitish, then green moldy;
  • rash of a huge amount of spores when the scales break;
  • to the touch, the affected bulbs seem empty.

Massive green mold appears when onions have been in storage for several months. The process is accelerated at high temperature and humidity in the room. Freezing of the crop and mechanical damage to the fruit also contributes to the development of the disease.

Affected specimens must be disposed of. Preventive measures are as follows:

  • thorough drying of the harvested crop before storage;
  • compliance with storage conditions – at positive temperatures, air humidity should be 60-80%;
  • soil disinfection;
  • burning plant residues.

Gray mold

The causative agent of this disease is Botrytis cinerea. The spores and sclerotia of this mold may contain soil and plant debris.

Gray mold

When growing a crop, the pathogen affects the scales of the neck of the bulbs, so the disease is sometimes called neck rot. Infection is promoted by constant humidity, rainy weather, pests.

The defeat of gray rot often occurs during harvesting, and manifests itself during storage. The development of the disease is provoked by high temperature and humidity in the room.

Signs of sulfur rot are as follows:

  • damage to the fruit begins at the base of the neck, gray rot is visible on the surface;
  • if you press next to the neck, then this area will be washed;
  • damage to the fruit is clearly visible in the section: softness, turbidity, usually gray in color, the pulp looks like after cooking.

If the disease manifests itself during storage of the crop, then the next year it is necessary to take the following measures:

  • disinfect the soil;
  • burn all plant residues, if this measure was not taken in the fall;
  • when growing a crop, treat it with fungicides such as Quadris, Switch, Bravo;
  • artificially accelerate the ripening of the crop – limit nitrogen fertilizers by increasing potassium-phosphorus top dressing;
  • after harvesting, burn all plant residues.

It is recommended to choose varieties resistant to this disease. When planting with seeds, pre-treat them.

Onions affected by gray rot should not be eaten. Damaged specimens identified during storage must be thrown away.


This fungal disease is caused by Stemphylium allii Oud. More often it is observed in plants that are already affected by downy mildew.


The symptoms of the disease are as follows:

  • distinct brown-violet spots;
  • abundant plaque on spots, first pinkish-violet, then brown;
  • breakage of leaves and arrows in the affected areas;
  • the formation of feeble seeds, the process may even stop;
  • leaf death.

Dry and warm weather favors the development of stemfiliasis. Methods of control and prevention of the disease are similar to the situation with downy mildew.


The disease is caused by fungi of the genus Fusarium. In another way, the disease is called root rot or bottom rot.


The signs of damage are as follows:

  • fruit lag in growth;
  • the appearance of a pinkish coating;
  • poor development of the root system, brown color of the roots;
  • yellowing of feathers, their gradual death – the process starts from the tips, but such a sign is not mandatory.

Affected plants must be immediately removed and burned, otherwise the disease will pass to healthy specimens.

Be sure to treat the crop with a suitable fungicide. It can be Fundazol or Quadris.

Prevention of Fusarium involves the following measures:

  • preparation of planting material – treatment with fungicides;
  • burning plant residues;
  • soil disinfection – a solution of potassium permanganate, copper sulfate;
  • the introduction of potassium-phosphorus fertilizers – increase the resistance of the crop to the disease;
  • compliance with crop rotation rules – onions do not need to be returned to their original place for at least 3 years.

Pests of onions

In addition to possible onion diseases, you should also be aware of pests that are dangerous to it. Some of them also affect other cultures.

Onion bun

The pest is also called the small narcissus fly. It affects only those plants that have mechanical damage or are affected by other pests. Adults reach an average of 7 mm in length and are bronze or metallic green in color.

Onion bun

The signs of culture damage are as follows:

  • growth retardation;
  • yellowing and wilting of the tops of feathers;
  • softening of the bulbs, rotting, the appearance of an unpleasant odor.

Damage to the culture is caused by insect larvae. They appear in June. The bulbs are the wintering grounds for the pest.

Previously, onion hoverfly was fought with chemicals, but other methods are now recommended:

  • timely removal of affected plants;
  • watering with a solution of sodium chloride – 0,2 kg per 10 liters of water, water when the feather grows up to 5 cm, then after 3 weeks.

Prevention is the observance of crop rotation and deep digging of the soil in the fall.

Lukovaâ flies

This is one of the main problems of onions and other bulbous plants. The onion fly is similar to the common one, but ashy in color. Insect activity begins in mid-May. It lays eggs in plant scales and soil. The hatched larvae penetrate the plant, which serves as food for them.

Lukovaâ flies

The signs of a pest are as follows:

  • wilting and drying of feathers;
  • slowdown in plant growth or its complete cessation;
  • the appearance of an unpleasant specific odor;
  • bulb rot;
  • white worms under the upper scales of the fruit.

There are many ways to get rid of onion flies:

  • Chemicals. They resort to Aktara (Thiamethoxam), Imidacloprid, Diazinon, Dimethoate, Ripcord. You need to act according to the instructions, the right amount of the drug is dissolved in water and the culture is sprayed.
  • Tobacco dust. It can be used to dust the culture, mixing with ash and black pepper or naphthalene in equal parts. Another option is spraying. It is necessary to dissolve 10 g of the product in 250 liters of water, leave for 2 days and treat the plants – 1 liter of solution per 1 sq. m.
  • Ammonia. This method is good in the early stages, when the pest has been noticed, but the larvae have just begun to lay. It is necessary to dissolve 3 tbsp. l. funds in 10 liters of water and spray them on the culture in the afternoon.
  • Kerosene. The tool is detrimental to the larvae of the onion fly. Enough 50 g of kerosene per bucket of water, you need to spray the soil near the bulbs.
  • Laundry soap. It is necessary to dissolve half a bar in a bucket of water. The resulting solution should treat not only the soil, but also the greens.

It is easier not to fight the larvae of the onion fly, but to prevent the appearance of the pest. Preventive measures are as follows:

  • compliance with crop rotation rules – do not plant onions after other plants of this family, do not return it to its original planting site for at least 3 years;
  • digging the site in the fall for a full spade bayonet;
  • alternating beds of onions and carrots – both cultures have their own kind of fly that cannot tolerate the smell of such a neighborhood;
  • processing of planting material – 2 minutes of soaking in a solution of potassium permanganate is enough;
  • regular loosening of the soil – flies do not like loose soil, so they do not lay eggs there;
  • preventive treatments of plantings with wood ash, tobacco dust, laundry soap.

Onion Mite

It is difficult to notice such a pest with the naked eye because of the whitish color and small size – about 1 mm. An insect appears at high temperature and sufficient humidity.

Onion Mite

Culture damage can be identified by the following signs:

  • deformation of feathers, the appearance of a white coating;
  • dehydration of the bulb and its wrinkling;
  • the appearance of yellow spots on the bulbs;
  • friability of fruits, the appearance of larvae on them, resembling dust;
  • mold may appear on the affected areas.

Onion mite can harm not only culture, but also humans. It can be an allergic reaction, asthmatic complications, digestive disorders.

You can fight the pest in the following ways:

  • treat with chemicals – you need to resort to acaricides and insectoacaricides;
  • regularly dispose of affected plants.

You can disinfect the affected bulbs by heat treatment – lower them for 5 minutes in water heated to 45-50 degrees.

Getting rid of onion mites is not easy, so it is important to follow preventive measures:

  • processing of planting material – heating at 35-40 degrees during the week;
  • culling of the crop – all specimens with the slightest signs of damage are not suitable for storage;
  • treatment with nettle infusion – brew the leaves in boiling water in a ratio of 1: 5, leave for 5 days, then dilute in 10 parts of water and spill the culture under the root;
  • disinfection of the premises for storing crops, organization of ventilation in it;
  • pruning greenery before storing.


The insect is also called onion. In addition to onions, it is dangerous for garlic, cucumbers, melons, and flowers. The length of an adult is about 0,8 cm, the wings are fringed, the body is narrow and elongated, the color is light yellow or dark brown. The larvae have no wings, the color is whitish or greenish-yellow.


Harm is brought mainly by larvae and females of tobacco thrips. Their food is the cell sap of plants.

The signs of damage are as follows:

  • angular spots, first light, then brown;
  • black dots of excrement at the bottom of the spots;
  • curvature of the affected feather, yellowing of the tips;
  • culture slowdown.

When affected by tobacco thrips, the crop suffers, so it is necessary to deal with this pest:

  • insecticides for treatment: Aktara, Actellic, Fitoverm, Fufanon;
  • sticky traps – apply special glue for insects on strips of yellow or blue cardboard and spread them between rows;
  • spraying with infusion of tobacco leaves – grind dry raw materials, add a little water, leave for 3 hours, after filtering for another 36 hours, dilute for spraying in two parts of water;
  • celandine – dip 100 g of dry grass or 400 g of fresh stems and flowers into a liter of water, leave for 3 days, use for spraying;
  • sulfur for fumigating rooms where onions will be stored – per 1 cu. m need 60 g of the substance.

Prevention of the appearance of tobacco thrips involves the following measures:

  • compliance with crop rotation rules;
  • burning plant residues – the pest hibernates in them;
  • digging the site in the fall – it is better to dig on a full bayonet, the pest for wintering is deepened by about 7 cm;
  • removal of weeds – insect nutrition in spring;
  • warming up the planting material – two days at a temperature of 40 degrees.

You can find out about another means of onion pest control in the following video:

Proper cultivation of onions and timely prevention of crop damage by diseases and pests avoids many problems. They cannot be ignored, since the qualitative and quantitative characteristics of the crop will suffer, the duration of its storage will decrease, and losses over this period will increase significantly.

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Anna Evans


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