What is onion nematode?
The nematode causes damage not only to onion beds. This pest is dangerous for parsley, tomatoes, and radishes. How to recognize it?
Description and characteristics
The onion-garlic nematode is a white thread-like worm. The length of the pest is 1-1.5 mm, and the thickness is 0.05 mm.
In the front part of the body there is a sharp, needle-shaped organ with which the nematode sucks out the cell juices of plants. The back of the body is pointed. Females are larger than males.
The larvae differ from mature individuals by having an inferior reproductive system and miniature size - only 0.3 mm in length. The eggs of the parasite are absolutely tiny -70×30 microns.
Attention. On dry onion scales, the parasite remains viable for more than two years, and in dried, infected garlic - up to five years.
The worm overwinters in onion heads and cloves of garlic, as well as in soil and seed material. Distributed everywhere. In Russia it is found mainly in heavy soils.
Peculiarities
What type of worm is a nematode? The pest is a large family of parasitic roundworms. There have recently been discussions about the species identity of the worm. Previously, onion stem nematode and potato nematode were classified as the same species. However, then scientists found that the food items of these parasites are different, which causes some physiological differences.
Soil-dwelling nematodes patiently wait for a host plant to appear. They can survive without a food source for up to 18 months. In search of food, the worms rise from a depth of 1.5 m. Adults infect stems, leaves and bulbs.
Important. A massive invasion leads to the destruction of that part of the plant in which the parasites have settled. They then leave the dead tissue and move to the next plant.
The pest is amazingly resilient. Nematode eggs and larvae can withstand temperatures down to -80°C for 20 minutes. Therefore, frosty winters have little effect on the number of pests living in the soil.
When the humidity drops, the worms enter suspended animation, in which they can remain for up to 20 years.
Breeding period
The onion nematode reproduces inside leaves and bulbs by laying eggs. The eggs hatch into larvae that go through four stages of development.
The life cycle of the parasite takes about 45 days. Thus, during one gardening season, three or four generations have time to grow.
Thousands of individuals live on one plant at the same time. Sexually mature individuals mate directly in the plant host. Each female lays up to 400 eggs (8-10 eggs per day).
The optimal temperature for parasite reproduction is +13…+18°C. But even in the range from +1°C to +35°C, the reproduction of worms does not stop.
The larvae emerge from the eggs after a few days. Young individuals begin to actively feed, devouring plant tissue. Grown larvae are able to move to neighboring plants.
Eating habits
The nematode pierces the plant tissue with its stylet - a pointed organ at the front of the body - and sucks out the cell juices. Parasite enzymes released during feeding inhibit the development of greens and onions.
After some time, the plant most densely populated by parasites dies. And nematodes, sensitive to the quality of nutrition, leave dead tissue and move to neighboring plants.
Description of the pest
A round, small worm with a thread-like white body, no more than 1.5 mm long - this is the onion nematode (what other worms can threaten onions?). The pest settles in onion crops and feeds on plant juices. As a result, the growth of the onion is inhibited, its rhizome dries out, the trunk is deformed, and the vegetable gradually dies.
A needle-like organ called a stylet is located at the front of the worm, which it uses to suck out plant sap.
The feeding principle of the parasite is very similar to the same actions of the spider: it pierces the plant with a stylet, introduces digestive enzymes into it and sucks out the juice. Enzymes disrupt the vital activity of stems and rhizomes, after some time the affected parts of the plant die, and the nematodes move to the neighboring bulb.
Pest larvae are even smaller in size, but otherwise similar to adults. Insects lay eggs in the bulbs and leaves of plants. Each bulb can harbor several thousand parasites.
Sometimes soil becomes a temporary place of residence for worms. The larvae go through four stages of development, and at each of them they molt.
The life cycle of the onion nematode is a little more than a month, which means that several generations of insects appear in one season.
In addition to onions, nematodes damage and destroy other agricultural and even some ornamental crops, such as:
- potato;
- tomatoes;
- oats;
- parsnip;
- tulips and others.
Symptoms of onion nematode infection
Infection is indicated by symptoms such as underdevelopment and deformation of leaves, their yellowing and drying, loosening of the bulb, and its cracking. The bottom becomes rotten, falls off, and the bulb is completely destroyed.
In an onion that has been subjected to early infection by a nematode, the first leaf that appears is curved and swollen; later, as it grows, the curvature of the leaves and thickenings, located mainly in their lower parts, become more and more noticeable.
If the seedlings were infected at a later stage of development, the diseased plants may be almost indistinguishable from healthy ones, but white spots often appear on the bulbs.
Cutting these bulbs open reveals granular, loose, fleshy scales that are unevenly thickened. In the initial stage of the lesion they are white, and later acquire a gray or brown color. Cavities form between the inner scales, the bulb becomes soft to the touch, and its bottom and sides may crack.
If onion nematode colonizes garlic, its stem thickens and cracks. The leaves curl, bend in waves, dry out and turn yellow. The bulb loosens and becomes damp to the touch, its bottom may become rotten and fall off.
Signs of crop damage
Infestation of a plant by a parasite can be noticed at any stage of plant development. Nematode damage to onions can be seen by the following external signs:
- The surface of the bulb is loose, the structure is rotten.
- The stem and leaves are underdeveloped and have stopped growing.
- The leaves dry out and do not recover after watering. The color of the greenery changes.
- There are cracks throughout the entire area of the husk; it quickly falls off at any touch.
- The bottom becomes soft and may fall off.
At the early stage of infection, the first leaf becomes bent and swells slightly. Over time, the bulb grows, and these changes become more noticeable and pronounced.
Infections that occur later are more difficult to detect. In this case, whitish spots appear on the bulbs, and the peel scales become fleshy and thickened.
The active life of the parasite changes the color of onion tissue from white to gray or dark brown. Cavities appear between the scales, and the root crop becomes loose and soft. The foliage turns yellow and curls.
What is the danger of onion and stem nematodes?
The onion nematode invasion threatens to significantly reduce the quantity and quality of the crop.
The parasite carries many diseases, which in turn slow down the growth of plants or lead to their death. Worms damage the root system, compromising its integrity. This is how pathogenic microorganisms - viruses and bacteria - penetrate inside the plants.
In addition, plants infected with a nematode have reduced resistance to other parasites, such as hoverflies, mites, and onion flies.
Diseases of onion and garlic caused by nematodes reach their greatest development by the time of harvest. Onion heads infected with worms begin to rot after storage. If there is high humidity in the room, worms are able to move from infected heads to healthy neighboring ones.
Methods of pest control
Pest control is carried out in several ways:
- compliance with the rules of crop rotation - crops affected by the nematode are returned to their original place no earlier than after 4-5 years;
- selection of healthy material for sowing - the seedlings are carefully inspected before planting, removing specimens with signs of onion nematode infection;
- maintaining optimal storage conditions - low temperature (0...+2˚С) and low humidity (50-60%) in the storage reduce the activity of the pest.
In addition, among the methods of combating nematodes, folk remedies and chemicals are distinguished.
Traditional methods
The use of traditional methods in the fight against onion nematode is ineffective. These means can destroy only a small part of the adult population.
Summer residents practice the following methods:
- Treatment of planting material with hot water. The sets and seeds are soaked for an hour in hot water at a temperature of 45˚C. Then they are dried and planted in the soil.
- Disinfection of seed material in an infusion of wood ash for two hours. After soaking, the seeds or sets are thoroughly dried.
- Warming up the seeds at a temperature of 42-45˚C the day before planting.
- Processing the seed in a solution of potassium permanganate, formaldehyde or 1% saline solution - leave for 30 minutes.
Chemicals
Chemical preparations show maximum effectiveness.
One of the popular chemicals is called “Percalcite”. This is an oxygen-containing preparation that destroys nematode cysts with eggs and larvae in the soil.
Use the product in dry weather. The drug is scattered over the sown area 5-10 days before sowing. For one square meter use 200-300 g of the substance. Then the preparation is sealed with a shovel or rake to a depth of 10-15 cm.
Another effective remedy is carbamide (urea). It is applied 30 days before sowing at the rate of 100 g per square meter. m.
How to properly store onions
Before storing the crop in the vegetable storage facility, fumigation is carried out - cleaning and disinfection of the premises. To do this, you can invite sanitary workers or carry out the procedure yourself using sulfur dioxide: 50 g of sulfur per 1 square meter. m area within 24 hours.
Bulbs must be carefully inspected before storage. It is important that the humidity in the storage does not exceed 65-70% and the air temperature is maintained within +2-3°C.
Onion nematode is a dangerous pest. Only by observing crop rotation and disinfecting planting material will it be possible to preserve the harvest and protect it from parasites.
Preventive measures
One of the most reliable ways to protect crops from infection is prevention. Regular use of preventive measures reduces the risk of onion nematode invasion to a minimum.
The following methods are used as prevention:
- regularly changing the place where the crop is planted - alternating plants, among other things, improves soil fertility;
- treatment of seed material before planting with high temperature or chemicals;
- destruction of plant residues after harvesting - special attention is paid to the destruction of infected plants and weeds;
- regular application of inorganic fertilizers.
How to deal with nematodes?
As you can see, the onion nematode can cause a lot of trouble. Control measures consist of complex procedures. After all, this worm can remain in the soil for a long time in a state of suspended animation, without showing any activity. But often crops are infected in the spring, when there are favorable conditions for development. Often at this time there is a sufficient population of the parasite on the site. So, it is possible to predict the appearance of nematodes:
- using chemicals;
- annually changing ornamental or vegetable crops for cultivation on a certain plot of land;
- observing the rules for storing crops;
- processing seed material, carefully selecting seeds.
If the seed is already affected by nematodes, experts advise using chemicals that affect the parasite at any stage of development.
