Stem and bulb nematode management in garlic

Ministry of Agriculture, Food and Rural Affairs

Stem and bulb nematode management in garlic

The stem and bulb nematode is a pest that can cause significant damage to garlic crops. The cool, wet weather experienced this spring has resulted in the spread of this pest within fields where infested garlic cloves were planted last fall.

The stem and bulb nematodes can survive in garlic cloves used for seed as well as in the soil. In fact they are often introduced into a field of garlic by planting infested cloves that otherwise look healthy. One stage (4th juvenile) of the nematode is particularly adapted to resist desiccation and freezing and can persist for many years under dry or cold conditions. A single female can lay up to 500 eggs within her life span and several generations can be produced within one growing season. It only takes 19 days for these nematodes to develop into mature adults when temperatures average around 15°C. They can live for 45 to 75 days depending upon the environmental conditions. The short period of time between emergence from the egg and maturity together with the frequency of reproduction often results in an explosion of this pest population under cool, wet conditions.

Stem and bulb nematodes feed on cells near the basal root plate of the garlic plant. As they feed they inject enzymes into the cells which break down cell walls resulting in a rotting around the root plated. During wet weather some nematodes may leave the infested garlic and swim to neighbouring healthy garlic plants. They enter neighbouring plants by getting in between the scales of the garlic bulb near the soil line. Under wet conditions, the nematodes can swim a short distance up leaves of small emerging plants in the spring and then move down between the leaves in films of water left from rain or dew. Later in the season, the nematodes can infect garlic plants through scales of the bulbs. If infection is closer to harvest, the nematodes may not cause noticeable damage to the mature bulbs. Growers may unknowingly select these infested bulb and cloves to be used as seed in the fall.

Managing stem and bulb nematode is not easy once it is introduced and becomes established in a field. Planting clean, nematode-free seed into non-infested soil is the best option to avoid this pest. Unfortunately the nematode has a very extensive host range with over 450 species of plants that can be infected. However, there are several races of this nematode, each with a specific limited host range. Although the entire host range for the Ontario race of stem and bulb nematode is not known, studies at the University of Manitoba indicate that the Ontario race can also infect and multiply in yellow pea, as well as pinto, kidney and navy bean. Once introduced, a four year crop rotation with non-susceptible crops such as a cereal crop, fumigating soil or planting a nematode suppressing cover crop such as oriental mustard before planting garlic can help suppress this nematode in soil.

Planting clean, nematode-free seed is the most important practice in managing this pest. If clean, nematode-free seed is not available, growers can try dipping infested cloves in a hot water bath at 49°C for 20 minutes; however, this is a very tricky technique and must be performed carefully to prevent damage to cloves. If the temperature drops below 49°C, the effectiveness of the hot water to kill nematodes in the cloves is significantly reduced. If the temperature of the hot water bath increases above 50°C, the garlic may be damaged resulting in poor emergence. Other management options are currently being investigated by the Ontario Ministry of Agriculture Food and Rural Affairs, the University of Guelph and Agriculture and Agri-Food Canada.

Figure 1. The basal plate of garlic bulbs (the region of the bulb where the roots attach) severely infested with the stem and bulb nematode appear rotted and can be easily separated from the bulbs.

Stem and bulb nematode

Quick facts

How to identify stem and bulb nematode

The University of Minnesota Plant Disease Diagnostic Clinic can test seed, plants and field soil for the presence of Ditylenchus dipsaci, the stem and bulb nematode. Contact the clinic for more information about how to send a sample.


  • Leaves turn yellow, wilt and collapse.
  • Plants may be stunted or die back prematurely.
  • Infected plants are often clustered together, resulting in one or more distinct patches of discolored plants.
  • Garlic bulbs turn brown, shrivel and become light weight.
  • Wrapper layers often crack and become detached from the basal plate of the bulb.
  • Onion leaves have swollen, distorted, blister like areas.
  • Onion bulbs are brown and soft on some layers when cut open.
  • Secondary organisms may cause extensive rot within the bulbs.
  • Bulb damage can progress in storage.

Plants affected by stem and bulb nematode

The stem and bulb nematode, Ditylenchus dipsaci, can infect over 450 genera of plants. Most races of the nematode primarily infect a limited number of plants. The race of stem and bulb nematode that infects garlic also infects onion, chive, leek, celery, parsley, salsify, shasta pea, hairy nightshade and miner’s lettuce.

How do stem and bulb nematodes survive and spread?

Although not widely distributed throughout Minnesota, stem and bulb nematodes can be introduced to a field on infected seed, plant debris, soil or water.

The nematodes live and feed within plant leaves, stems and bulbs. Nematodes enter plants by:

  • Penetrating young plant tissue below ground.
  • Climbing through films of water on the plant stem and entering through stomates, which are the natural openings within leaves.
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Multiple generations of nematodes live within a plant. They migrate to soil only when the plant becomes so degraded that it’s no longer suitable for nematode feeding and reproduction.

Life cycle

Stem and bulb nematode populations can increase dramatically over a growing season.

  • Female nematodes lay 8-10 eggs a day for 25-50 days (a total of 200-500 eggs per female).
  • Eggs hatch into a juvenile nematode which looks similar to the adult nematode.
  • The nematode goes through four molts before becoming a reproductive adult.
  • A nematode can go from egg to maturity in about 20 days at 60 F.
  • Mature nematodes live for 43-73 days.

Stem and bulb nematodes can survive on weeds or volunteer crop plants during crop rotation. They can also survive multiple years in a desiccated (dried out) state in plant debris, seed and soil. These desiccated nematodes rehydrate and infect a new crop in the presence of moisture.

How to manage stem and bulb nematode

Plant only clean, nematode free seed.

Do not move soil or plants from infested fields

If stem and bulb nematode is identified in a field, use strict sanitation procedures to prevent further spread of the pathogen.

  • Clean all tools and equipment on site after working in an infested field.
  • Do not use garlic from an infested field for seed. Even healthy looking bulbs may be infested with a small number of nematodes.
  • Infested seed can be sold for food if damage doesn’t make the product unmarketable.
  • Nematodes survive in infested bulbs and wrappers. Don’t bury culls in the field. Don’t move culls or crop debris to a new area.

Practice crop rotation

Rotate out of garlic for four years. Carrots, potatoes, spinach, corn and wheat are good choices for rotation crops because they are poor hosts for stem and bulb nematode. Control weeds and volunteers during rotations.

Use green manure

Mustard, rapeseed, oilseed, radish and sorghum-sudangrass can be used as a green manure. When tilled into the soil, these crops release compounds toxic to nematodes. Use of green manure has been shown to reduce nematode populations in other crops.

Don’t use hot water treatment for garlic

Hot water treatments were recommended in the past to kill nematodes in infested garlic seed. Unfortunately, this treatment only reduces the number of nematodes in seed and doesn’t completely eliminate them. Increasing the temperature or duration of the treatment damages the garlic seed. This treatment is no longer recommended.

Pests of garlic are nematodes. How to identify it and how to fight.

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.

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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:

Option 1

  1. To pick out cloves of garlic with visible defects
  2. Cut a piece of garlic into thin slices with a blade (or, for example, a stationery knife)
  3. Put them on the glass
  4. Treat with a solution of water and a few drops of hydrogen peroxide (this will provoke the crawling of nematodes)
  5. Wait 20-30 minutes
  6. Look through the magnification on the smartphone, highlighting the flashlight

Option 2

  1. Grind the cloves of garlic on a blender
  2. Fold in a colander which is placed in a slightly larger bowl
  3. Pour water with hydrogen peroxide
  4. After 30 minutes to get a colander and using, for example, a syringe from the lower water level to draw in a sample
  5. Drop the sample on the glass and examine under a magnifying glass
  6. 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):

  1. Take a sample of the soil and sift it through a 2-3 mm sieve
  2. Put the soil in 4 – 6 gauze pouches, a gram of 20 in each.
  3. Cut a five-liter plastic bottle horizontally in half.
  4. Part of the bottle where there was a lid (cover removed) insert the neck down into the other part.
  5. To hang out our soil samples, attaching them to a jumper
  6. Fill the bottle with water with the addition of hydrogen peroxide
  7. After a day or two, carefully remove part of the bottle with soil
  8. Take samples of the solution from the bottom of the other part of the bottle
  9. 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.

Antinematode precursors

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

  1. In spring, plant mixture of plants – Raphanus 15-20 kg of seeds per hectare, Mustard white 5-10 kg of seeds per ha.
  2. 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.

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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.

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Ministry of Agriculture, Food and Rural Affairs

Managing stem and bulb nematode in garlic starts in the fall

Soon it will be time to plant garlic for next year’s crop. Growers are advised to be careful not to plant cloves infested with the stem and bulb nematode. Several fields of garlic in Ontario have been completely destroyed by stem and bulb nematodes in recent years. This microscopic worm-like pest has been spreading from field to field unknowingly in contaminated garlic cloves sold and used for seed. Although growers attempt to discard bulbs severely infested with stem and bulb nematodes (Figure 1), those that appear healthy and without symptoms growing adjacent to or near severely infested plants become infested in the field.

Figure 1 . Garlic bulbs severely infested with stem and bulb nematodes.

If the cloves of theses bulbs are used for seed this fall, the plants that grow from cloves of the healthy looking but contaminated bulbs will develop symptoms the following season. Furthermore the nematodes from this infested seed will eventually infect healthy plants growing nearby and the pest will spread.

Obvious symptoms of stem and bulb nematode damage often do not appear until late June or early July. Severely infected plants appear stunted, turn yellow, dry prematurely and are easily pulled from soil leaving the rotted region of the bulb where the roots attach, called the basal plate, in the soil (Figure 2). Infested garlic bulbs tend to be soft, shriveled, discoloured and lighter in weight. Often bacteria, fungi, maggots and mites will invade severely infested bulbs causing them to become mushy with soft rot and decay.

Figure 2. Garlic plants infected with stem and bulb nematode appear stunted, turn yellow, dry prematurely and are easily pulled from soil.

For a successful garlic crop next year, growers are strongly advised to plant garlic cloves that are free from disease and stem and bulb nematodes this fall. If symptoms appeared in the garlic crop this past season that is also being kept for seed to plant this fall, it may be wise to discard the seed no matter how good it looks and start over. Obtain seed from a reputable source that does not have stem and bulb nematode. If that is not possible, another option is to purchase clean seed from the clean seed program developed at the University of Guelph New Liskeard Research Station and now sold through August’s Harvest.

Growers could attempt to soak their seed in hot water to kill the nematodes that are deep in the cloves as follows:

  1. Pre-soak cloves in water (4-5 parts water: 1 part garlic cloves) held at 38°C (100°F) for 30-40 minutes
  2. Soak cloves in the hot water bath held at 49°C (120°F) for 20 minutes (Start timing when the temperature reaches 49°C (120°F) and stir the hot water constantly to avoid hot spots)
  3. Immediately immerse the hot water treated cloves in a cool water bath held at 19-22°C (64-72°F) for 10-20 minutes (Do not use ice water!)
  4. Allow the hot water treated seed to dry for a day or so in a well-ventilated area.
  5. Plant hot water treated cloves within a week of treating (do not store treated cloves, as this may increase the occurrence of fungal diseases)

Use extreme caution when performing the hot water treatment. It is advised that good quality and accurate thermometers be used to monitor the temperature of the hot water bath. If the water gets up to 52°C or higher, the cloves will cook and not germinate. If the water does not get hot enough, the nematodes will not be killed and infestation will occur the following spring.

Growers should plant their clean garlic or hot water treated seed in a field that had not grown garlic for at least 3-4 years, since the nematodes will survive in soil from many years. In a recent study conducted at the University of Manitoba, the stem and bulb nematode strain that has infested Ontario garlic was also found to infect and reproduce on yellow peas, beans and chickpeas. Based on this information, garlic should not be planted in fields that had peas or beans in the rotation.

What is a nematode?

Nematodes are microscopic eel-like organisms that live in soil and water. Most soil dwelling nematodes are beneficial organisms that play a role in the break down and release of nutrients from organic matter. Some beneficial nematodes prey on other nematodes as well as soil-borne insect, fungal and bacteria pests. Unfortunately there are several species of nematodes that feed on or in roots, stems or bulbs resulting in significant yield reduction in both field and horticulture crops grown in Ontario. Examples of these include stem and bulb nematode, root knot nematode and root lesion nematode to name a few.

Figure 3. The stem and bulb nematode Ditylenchus dipsaci.

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