The stem nematode of onion (Ditylenchus dipsaci) belongs to the class of roundworms and causes the greatest harm in the process of vegetation, causes ditylenchus of onion and garlic.
The nematode causes primary losses of onion and garlic in the field (40-60% of the crop) and secondary losses – during storage.
Parasitize nematodes only on living tissue of plants. The nematode penetrates into the stalk and leaf pieces of garlic, including tubers and bulbs. It almost do not damage roots.
Dimensions of the body of the nematode are very small (up to 2 mm), visible only under a microscope.
The body of nematodes is spindle-shaped, the oral cavity, the oral apparatus in the form of a sharp spear, with which the nematodes pierce plant tissues and suck out the juice, is located on the head.
The economic threshold of damage is 20 individuals per 1 kg of soil.
Picture of a nematode under a microscope:
Signs of nematode damage
The nematode lays eggs in the tissues of infected plants. Larvae feed on plant juices, like and adult nematodes. Affected nematode plants of garlic first lag in growth, false stem thickens, often forming longitudinal bands; the leaves gradually turn yellow and then wither. The bulb becomes fragile, the bottom rots and disappear and the bulb is completely destroyed.
With the increase in the number of nematodes, the disease which became known as dithilenchosis is rapidly progressing. While the dead cells of the plant are colonized by other microorganisms and rot, the nematode larvae crawl to healthy parts of the same plant or migrate to the soil, infecting more and more new plants.
Ditylenchosis garlic can be easily identified by thickened with cracks stalks, deformed leaves and bulbs. Infected plants noticeably lag behind in growth. With a strong lesion, the cloves of the garlic become loose, loosely bound together.
During the storage of infected bulb of garlic at the base of dry flakes of teeth there is yellowing.
Another characteristic feature of ditylenchosis is the formation of the so-called Nematode “felt” on the surface of infected bulbs during storage. “Felt” grayish color, very similar to mold. In fact, it is nothing more than tens of thousands of individuals of nematodes that crawled to the surface of a dried bulb and are at rest, waiting for more favorable conditions for further growth and development.
Also, when storing garlic contaminated with nematode, a strong odor can be felt in the vault.
Picture shoots of garlic struck by a nematode:
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How the nematode spreads
Nematodes feed on, undergo a full cycle of development and multiply exclusively in the tissues of the host plant (onion, garlic). Therefore, the main source of infection in nature is planting material. In addition, such cultural plants as parsley, parsnip, tomatoes, potatoes, peas, oats, as well as some wild species and weeds can be places for temporary stay of nematodes.
Nematodes are spread by movement in the soil (actively) or with soil, tools and plants (passively), carried by a person from one field to another.
Life expectancy of the female is 45-75 days. Nematodes are very mobile and easily rise from a depth of up to 1.5 meters. Distance of 10 cm stem nematode onions overcomes in 3 hours.
The entire development cycle takes place in the tissues of the host plant. The total duration of the development of generation at +15 ° C is 19-23 days. During the growing season, 4-6 generations develop. They follow one another at intervals of 3-5 weeks, depending on the temperature.
Onion nematode hibernates in bulbs and dry scales or in soil. In dry, diseased bulb of garlic, nematode larvae can persist up to 4-5 years. In soil, in the absence of a host plant, up to 18 months. Getting into the wet environment, the larvae, which were at rest, are moving to active life. From the soil after sowing and planting garlic or onions they penetrate into the plant tissues through the bottom and leaves.
Reproduction of the nematode is facilitated by rainy weather and increased humidity in the vault. During storage, the nematodes crawl from diseased bulbs to healthy ones.
Video: how the nematode affects the plant
Picture of garlic bulbs which struck by nematode
How to identify the nematode in garlic without laboratory tests (video)
In the network there was a video about how to identify the nematode in garlic with the help of a blade, water, hydrogen peroxide, flashlight and mobile phone. In short, the path of action is this:
- To pick out cloves of garlic with visible defects
- Cut a piece of garlic into thin slices with a blade (or, for example, a stationery knife)
- Put them on the glass
- Treat with a solution of water and a few drops of hydrogen peroxide (this will provoke the crawling of nematodes)
- Wait 20-30 minutes
- Look through the magnification on the smartphone, highlighting the flashlight
- Grind the cloves of garlic on a blender
- Fold in a colander which is placed in a slightly larger bowl
- Pour water with hydrogen peroxide
- After 30 minutes to get a colander and using, for example, a syringe from the lower water level to draw in a sample
- Drop the sample on the glass and examine under a magnifying glass
- See the nematodes on the video (I wish everyone that in real life you would not see such a thing :))
How to identify the nematode in the soil without a laboratory
This method does not give an accurate answer to the question of the quantitative degree of infestation of the soil by the nematode, but it will help to establish the very fact of the presence of such infection. And it will be a signal that you can not plant garlic on this soil. “Most likely” is because there are a lot of nematode species and not all of them affect garlic. Well, let’s just say, if you already find some nematodes in your soil in this way, then accurately hand this soil to the laboratory for Helminthological analysis.
By the way, the method given below is a simplified method of Berman (you can Google if you need more information):
- Take a sample of the soil and sift it through a 2-3 mm sieve
- Put the soil in 4 – 6 gauze pouches, a gram of 20 in each.
- Cut a five-liter plastic bottle horizontally in half.
- Part of the bottle where there was a lid (cover removed) insert the neck down into the other part.
- To hang out our soil samples, attaching them to a jumper
- Fill the bottle with water with the addition of hydrogen peroxide
- After a day or two, carefully remove part of the bottle with soil
- Take samples of the solution from the bottom of the other part of the bottle
- Consider under magnifying glass or microscope.
On the diagram there is an example of a funnel by the method of Berman, so that it would be possible to understand how to do this with the help of a plastic bottle.
Methods for controlling nematodes in garlic
Until recently, nematicides were used to protect against phytoparasitic nematodes. The most common in Ukraine was the insecticide-nematocide Marshal (the term of its registration expired in 2013). But in the world, scientists came to the conclusion that this practice significantly exacerbates the problem of environmental protection – nematicides are very toxic, do not decompose long in soil, and their duration is limited, and the introduction is possible only with special equipment. Unregulated use of these expensive drugs can lead to a local environmental disaster. Therefore today in many countries of the world use of the majority of known nematicides is forbidden.
What can be done to prevent and control the nematode.
No type of nematode that affects garlic, does not damage lupine, facial.
The pest is not harmed by cereals (except oats), as well as clover, alfalfa.
With the nematode, you can fight with the help of rye crops. After harvesting garlic, in September they sow rye. In the spring, rye fields are dug up and the field for this year will be ready for planting vegetable crops.
The roots of marigold and marigold (of the type Tagetes erecta, Tagetes patula – see experiments) give off substances that are deadly to nematodes.
It should be noted that some weeds serve as hosts for nematodes, so after digging the antinematode precursor, it is necessary to prevent the development of weeds on the field.
Conversely, one should not plant garlic after a predecessor, which can be affected by a nematode. As precursors of garlic, it is not recommended to grow parsley, parsnip, tomatoes, cucumbers, peas, sugar beet, buckwheat, pumpkin, zucchini, pepper, potatoes that are susceptible to stem nematodes.
To remove the nematode with the help of its predecessor, you can perform the following activities
- In spring, plant mixture of plants – Raphanus 15-20 kg of seeds per hectare, Mustard white 5-10 kg of seeds per ha.
- At the moment of the onset of the flowering phase (after 35-40 days) – to carry out disking of the entire biomass.
Stalking plants of nematodes
Before sowing these crops on infected areas, it is recommended to sow huntings plants, with the help of which it is possible to reduce the number of nematodes. In garden areas, spring rape is the most commonly used as such a trapping plant. 4 weeks after sowing, the rape is pulled and burned together with the nematodes accumulated in its roots. Then the main culture is sown.
Artifical plants are also horse beans, vetch, pea, soy, beans.
Culling sick plants
One of the effective ways to prevent the spread of the disease is the timely culling of diseased plants throughout the cycle: checking seed before planting, revealing foci of ditylenchoza directly in the field, bulkheads of the harvested crop before laying it in the vault and periodically removing the diseased bulbs during storage.
Separate storage of planting garlic
Seed material of garlic should be stored in separate bins
Treatment of contaminated planting garlic before planting
To improve the a clove of garlic from the nematode, it is recommended to soak them in water at room temperature for three days or in water with a temperature of 40 ° C for two hours, or at a temperature of 45-48 ° C – 10-15 minutes.
The effectiveness of soaking in water at a temperature of 45-48 ° C will increase if before that cloves of garlic soak in water at room temperature for 2 hours.
Nematodes die and a clove of garlic do not lose their germination.
Also, soaking in water at 43-46 ° C with formalin (40% formaldehyde solution) is used. This solution can successfully kill nematodes in the seed material within two to three hours. The working solution is prepared from the calculation of 1ml formalin per 300ml water (33ml (gram) formalin per 10 liters of water). Approximately 25-30 liters of working solution per ton of planting garlic should be prepared. Garlic in the grid is lowered into the container with the working solution until the moment of complete wetting.
After the soaking is finished, the bags are pulled out onto the grilles and covered with tarpaulin, under which they are steamed for 2-3 hours. After that the bags are hung for drying or the garlic is poured evenly onto the surface. All these measures should be carried out in an open space under a canopy (in no case indoors) while using personal protective equipment.
Increase of plant immunity
The degree of development of the disease has a direct impact and the state of plants. Their immune properties can be increased by feeding them. It is proved that when nitrogen fertilizers are applied in plants, the content of ammonia toxic to the stem nematode increases.
Introduction to soil
There is also information that nematodes do not like kaolin and bentonite very much. If before the crop to make these minerals into the upper layer of the soil, the nematodes will leave therefrom.
A positive effect in the fight against the nematode is the introduction before planting garlic in the soil of carbamide at a rate of 500 kg per ha.
Using information from https://en.wikipedia.org/wiki/Ditylenchus_dipsaci
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