I talk a lot about the root knot nematode in some of the pieces I do, and that’s because this microscopic parasite can do a lot of damage to your plants. It’s not easy to determine if you’re battling against them, and yet your plant will suffer its effects.
So let’s discuss what these itty bitty parasites are, and what they actually do. We’ll go over methods to try to eliminate them from your yard, and talk about the differences between good nematodes and bad ones.
By the time we’re done, you should know the basics of how to deal with this particular batch of parasites to the best of your ability, and how to keep them away from your prized plants!
Listen to this post on the Epic Gardening Podcast
Subscribe to the Epic Gardening Podcast on iTunes
Good Products To Fight Root Knot Nematodes:
- Growers Trust Nematode Control
- EcoClear Stop Bugging Me! Nematode Control 774521
- Monterey Nematode Control
- Down To Earth Neem Seed Meal
- Down To Earth Crab Meal
- Down To Earth Oyster Shell Flour
- Down To Earth Granular Root Zone Mycorrhizal Fungi With Beneficial Bacteria
- Nature’s Good Guys Live Beneficial Nematodes
- Root Knot Nematode Overview
- All About Root Knot Nematodes
- How To Get Rid Of Root Knot Nematodes
- Frequently Asked Questions
- Control of root-knot nematodes in organic farming systems by organic amendments and soil solarization
- Cogent Food & Agriculture
- 1. Introduction
- Controlling Root Knot Nematodes
- Root-Knot Nematodes – Vegetables
- Life Cycle/Habits
- Host Plants
- Additional Resource
- Nematode Management in Organic Agriculture1
- Nematode Damage and Detection
- Nematode Management
- Organic Amendments in Relation to Biological Control
- Management of Infected Plants
- Root Knot Nematode Disease: A Stunted Plant Growth Cause
- What is a Root Knot Nematode?
- Root Knot Nematode Symptoms
- Root Knot Nematode Control
Root Knot Nematode Overview
Wheat showing signs of root knot nematode galls. Source: CIMMYT
|Common Name(s)||root knot nematode, root-knot nematode, northern root-knot nematode, southern root-knot nematode, cotton root-knot nematode, peanut root knot nematode, British root-knot nematode, tea root-knot nematode, mature tea nematode, Indian root-knot nematode, coffee root-knot nematode, barley root-knot nematode, cereal root-knot nematode, African cotton root-knot nematode, African cotton root nematode, Thames’ root-knot nematode and other names|
|Scientific Name(s)||Meloidogyne spp. including Meloidogyne javanica, Meloidogyne arenaria, Meloidogyne incognita, Meloidogyne hapla, Meloidogyne enterolobii, Meloidogyne acronea, Meloidogyne artiellia, Meloidogyne brevicauda, Meloidogyne chitwoodi, Meloidogyne exigua, Meloidogyne fruglia, Meloidogyne gajuscus, Meloidogyne naasi, Meloidogyne partityla, Meloidogyne thamesi|
|Plants Affected||Alfalfa, African daisies, African violet, almond, apricot, avocado, azalea, banana, barley, bean, blackberry, butterfly flower, cantaloupe, carrot, capsicum, chickpea, cineraria, citrus, coffee, corn, cotton, cucumber, date palm, eggplant, grapes, hemp, hibiscus, hops, hydrangea, Jerusalem cherry, lentil, lettuce, lilac, nectarine, okra, olive, onion, papaya, pea, peach, peanut, pear, pecan, pepper, pigeonpea, pineapple, plantain, plum, potato, primula, pumpkin, raspberry, red clover, rose, soybean, squash, strawberry, sunflower, sweet potato, tea, tobacco, tomato, walnut, watermelon, many wild grasses/shrubs/trees/weeds. Thousands of species of plants may be impacted by root knot nematodes.|
|Common Remedies||Geraniol or quillaja saponaria compounds, azdirachtin, neem seed meal, crab meal, oyster shell flour, juglone (from black walnut leaves/hulls), soil solarization, addition of beneficial nematodes, planting of marigolds or sudangrass as cover crops.|
All About Root Knot Nematodes
From their name, it’s pretty easy to guess that these affect the roots of plants. But where do they come from, and what exactly are they?
What Are Nematodes?
Meloidogyne incognita on a tomato root.Source: USDA via Wikimedia Commons
A nematode is actually a form of roundworm. The category of roundworms is incredibly wide, covering at least 25,000 different species. Some of these species are beneficial to us, some are harmful.
From an agricultural perspective, there’s really two forms of nematode which are important to be aware of: predatory or parasitic.
Predatory nematodes are types which seek out and attack an assortment of other garden pests like cutworms or squash vine borers. I often refer to these as beneficial nematodes, as they help keep our gardens pest-free. These are great to have around!
Parasitic nematodes, on the other hand, are not so great. Often invisible to the naked eye, these will attack living plant matter and consume it. They can cause the plant to focus its attention on healing that damage rather than healthy growth.
Root knot nematodes, the Meloidogyne species, fall into the parasitic category. They can cause our plants to inexplicably yellow, develop stunted growth, or look weak. Their chewing on the root systems of plants can allow other plant diseases to take hold as well.
Root Knot Nematode Life Cycle
The life cycle of these particular nematodes can be quite complex, but it breaks down into a few phases. There is an embryonic stage, four juvenile stages, and an adult form.
An adult root knot nematode will create a gelatinous mass on the root system of a plant and lay its eggs into it. Up to a thousand eggs can be laid by one adult. During this embryonic stage, the nematode will go from embryo completely through the first juvenile phase.
Once the embryo has become a first-stage juvenile, it will begin to eat the egg it is encapsulated in. By the time it has consumed its egg and some of the gelatin around it to encounter soil, it has become a second stage juvenile.
This is when the root knot nematode begins to pose a danger to the plants. Second-stage juveniles will eat their way into the root. Their chewing and migration through the root causes root galls, which are bulbous masses that the plant forms while trying to heal its root system.
In time, the second stage juvenile will take up residence inside one of these galls. It will undergo its third and fourth juvenile stages inside the root knot or gall, moulting and developing until it emerges as an adult and begins the cycle anew.
Common Habitats Of Root Knot Nematodes
Root knot nematode galls on pumpkin roots. Source: agrilifetoday
Soil-dwellers, root knot nematodes can be difficult to identify. After all, you usually cannot see them with the naked eye, and they aren’t above ground. In fact, they can often do so little damage to larger plants such as trees that they are not recognized as being there at all.
However, they do in fact attack thousands of plant species ranging from food crops to trees, shrubs, and ornamental plants. There are estimated to be more than 90 different species, and while some are preferential to particular plant types, many are opportunistic.
They can be found around plant/tree roots in the soil, or inside the roots themselves. Depending on the phase of the life cycle, they may have caused the plant to create galls which they may inhabit.
What Do Root Knot Nematodes Eat?
It’s estimated that most nematode damage to food crops is done by the Meloidogyne species.
They only eat living plant material, and tend to only attack plant roots rather than to go after any above-ground plant matter. The range is very wide, comprising thousands upon thousands of plant species worldwide.
Four particular species of root knot nematode are at extremely high levels internationally and cause the majority of agricultural damage. Another seven species cause significant crop damage in their particular regions of the world, but have not reached global proportions.
The remainder of the root knot nematodes tend to feed mostly on the roots of grass, weeds, and wild plants or trees. These are still damaging to their targets, but are considered less significant as they do not directly attack human food supplies.
The following list is some (but not all) of the plants which can be impacted by root knot nematodes:
There is a bright side to all of this. A number of nematode-resistant crops are available. Check your seed packets to see if the varieties you plan on planting are nematode-resistant, as these can hold up better to the damage which the tiny parasites inflict.
How To Get Rid Of Root Knot Nematodes
Tubers with root knot nematode galls. Source: IITA
There are few organic solutions for root knot nematodes. Sure, there are nematicides available, but they’re usually only for commercial agriculture and aren’t widely available for home gardening use. So what can you do to eradicate these little parasites?
Organic Root Knot Nematode Control
There are two organic nematicide variants available: ones based on geraniol (the oil of geraniums), and ones based on quillaja saponaria, the soap bark root. Remember, though, that nematicides will kill off both beneficial and parasitic nematodes.
A geraniol compound such as Growers Trust Nematode Control or EcoClear Stop Bugging Me! Nematode Control may be useful for organic gardeners. Growers Trust features geraniol and beneficial bacteria, where EcoClear is geraniol and cinnamon oils.
Quillaja saponaria compounds such as Monterey Nematode Control use the saponins from the soap bark tree to help reduce nematode populations.
You can also use an azdirachtin product such as AzaMax, which is a pure azdirachtin extracted from neem oil. This may work as a light nematicide, but tends to be better against other pests such as spider mites, thrips, aphids, and more.
Add neem seed meal, crab meal, or oyster shell flour to your soil. All three are fertilizers, but they’re great soil builders in the war against root knot nematodes.
Neem seed meal is a gentle fertilizer which is made from the leftover material after making neem oil. It helps reduce a number of pests naturally, plus it breaks down to add low levels of nitrogen to the soil. It also can help strengthen the roots of plants to make them resistant.
Crab meal encourages beneficial soil microorganisms which reduce nematode population. It also helps plants to increase the strength of their cell walls, making them more naturally resistant to many conditions.
Oyster shell flour is in essence a form of diatomaceous earth. While it has less effect when it’s wet, it can help make the soil less hospitable to nematode populations and reduce other pests as well.
Black walnut leaves and hulls have a natural compound in them which is called juglone. This compound is an extremely effective killer of root knot nematodes, but can have an adverse effect on some plants. That’s why there’s few weeds around walnut trees!
If you want to put an organic source of juglone to work in your garden, use fresh walnut leaves or smashed hulls as a thick layer of compost on your bed, or just build a tall pile there. Regularly turn it to keep it composting. I use leaves, as they’re quick to break down.
The juglone compounds will seep into the soil when you wet down the pile, and after three to six months should have broken down enough that they will no longer be toxic to other plants. This also helps wipe out weeds or other pests that may be in your beds during composting.
Environmental Root Knot Nematode Control
Root knot nematode galls on lima beans. Source: UDel Carvel REC
Soil solarization is a common environmental method of wiping out nematodes and some species of fungi. However, soil solarization will kill all beneficial nematodes, fungi, or bacteria which are in your beds as well, so this is an option which you should not take lightly.
To solarize your soil, till the soil and flatten it out. Dampen the soil evenly, and then place a thick sheet of clear plastic overtop the soil surface, securing it tightly down so it doesn’t move. Leave the plastic on top of the soil during the hottest months of the year for at least 2-3 months.
After you’ve solarized your soil, it’s important to add back in beneficial mycorrhizal fungi, bacteria, and nematodes. These will help prevent future pest and disease outbreaks.
You can use a product such as Down To Earth Granular Root Zone Mycorrhizal Fungi With Beneficial Bacteria to replenish the fungal and bacterial growth.
For beneficial nematodes, I recommend Nature’s Good Guys Live Beneficial Nematodes, which contains three different forms to kill off a wide variety of pests. The Steinernema feltiae species is especially vital for pest control including root knot nematodes.
Marigolds release a natural compound into the soil which is toxic to root knot nematodes. If you plant marigolds as a cover crop between plantings of food crops, you may see a slow and gradual reduction in root knot nematode activity. This works cumulatively in the soil.
Growing marigolds as a cover crop means you will need to till them back into the soil at the end of their growing season. However, this adds more plant matter to the soil, which improves the soil over time. In addition, marigolds are a great companion plant for tomatoes!
Another plant which produces a similar natural compound as a cover crop is sudangrass. Related to sorghum, this grass can reach heights of up to 7 feet tall, so it will need to be mowed regularly to keep it in check.
Leave the grass clippings to break down into the soil, as it will release its nematode protection as it decays. It also adds valuable nitrogen back into the soil. If you’re growing in raised beds, you can use grass shears to keep it trimmed down, and till it under at the end of the season.
Preventing Root Knot Nematodes
Prevention is always the best cure for a pest problem, and root knot nematodes are no exception. So let’s talk about prevention.
First off, plant nematode-resistant varieties. There are a wide variety of different seed suppliers who carry nematode-resistant seed stock, usually notated as an N in the resistance charts.
If you cannot plant nematode-resistant strains, practice good crop rotation. Some species of root knot nematodes are more selective than others. Planting cover crops like marigolds or sudangrass between at-risk crops will also bring down the nematode population.
Remove the roots of old plants when clearing the bed. As root knot nematode juveniles can live in the galls they form on the roots, they will continue to multiply even as the roots are dying out. Removing the remaining root mass can extract those juveniles.
Till the soil 2-3 times in the fall. This breaks up the soil, turning the nematodes up to the surface where they will die off from exposure to the sunlight. This will impact both beneficial and parasitic nematodes, so you may need to re-add beneficial nematodes again in the spring.
Plant overwintering grass cover crops like wheatgrass, ryegrass, or rye. Sudangrass is also good and offers some nematicide properties. Keep these mowed down to a manageable level, and till them under in the spring to add more plant matter to the soil.
Regularly add more organic material to your soil. Adding more composted leaves, grass clippings, and manure to your beds will help naturally control the population of nematodes in the soil, since nematodes prefer living material to decaying plant matter.
Frequently Asked Questions
Badly-galled roots damaged by root knot nematodes.Source: UDel Carvel REC
Q: What are the symptoms of root knot nematodes in plants?
A: That’s difficult to determine, because a very healthy, vigorous plant may show no symptoms at all!
As a general rule, common symptoms of a bad root knot nematode infestation can include chlorosis (yellowing of the leaves/stems), stunted growth, wilting, and a lack of production of fruit.
However, these may be nonexistent to severe depending on the population of nematodes, the health of the plant, the natural resistance of the plant, and any number of other factors in the soil makeup. It can also be hard to separate the symptoms from other pest/disease issues.
The only real way to be sure that it is in fact root knot nematodes is to carefully remove a plant from the soil and examine its roots. If there are a lot of galls growing along the root system, it’s likely root knot nematodes at work.
While these microscopic nematode parasites can be problematic, root knot nematodes are not uncontrollable. They may be tricky, but with good garden management, you won’t have negative consequences! Have you ever battled garden nematodes? Let me know down below!
The Green Thumbs Behind This Article:
Founder Did this article help you? × How can we improve it? × Thanks for your feedback!
We’re always looking to improve our articles to help you become an even better gardener.
While you’re here, why not follow us on Facebook and YouTube? Facebook YouTube 173 Shares
Control of root-knot nematodes in organic farming systems by organic amendments and soil solarization
The efficacy of organic amendments, with or without soil solarization, for the control of the root-knot nematodes Meloidogyne incognita and M. javanica in organic farming systems was tested in pot, container and greenhouse experiments. Broiler litter, cottonseed meal, feather meal or soybean oilcake, which had been effective in reduction of galling caused by M. javanica on tomato plants in pot experiments, were applied to a field at 0.75–2.0 kg m−2. In three experiments, soil solarization alone reduced nematode populations in the soil and galling indices on tomato and pepper plants, whereas the amendments alone were not effective. Combinations of the amendments with soil solarization were more effective than the amendments or soil solarization alone in reducing nematode populations and galling indices in most cases. High soil temperatures and accumulation of ammonium/ammonia in these treatments seemed to be involved in controlling root-knot nematodes. Nematode control efficacy on the edges of solarized beds, with or without amendments, was lower than that in the middle of beds. Soil solarization in combination with organic amendments could be used for root-knot nematode control in organic farms.
Cogent Food & Agriculture
In the present study, the efficacy of fluensulfone against root-knot nematodes (Meloidogyne sp.) was evaluated in four greenhouse experiments cultivated with either cucumber or tomato. Fluensulfone was delivered through the drip irrigation system. Also, due to preliminary field observations, a series of laboratory experiments were established to evaluate the action of fluensulfone on seeds germination, root growth and plant development of three either solanaceous (tomato, pepper, and eggplant) or cucurbitaceous (cucumber, squash and melon) plants.
Specifically this study aimed to assess: (1) the efficacy of a EC formulation containing fluensulfone on second-stage juveniles (J2s) of Meloidogyne sp, on root-galling and on nematodes per gram of root on tomato and cucumber greenhouse cultivation, (2) the effect of soil-applied fluensulfone on the root and plant growth of three solanaceous and three cucurbitaceous plant species and (3) the effect of a series of different fluensulfone doses on the germination rate of three solanaceous and three cucurbitaceous plant species.
Controlling Root Knot Nematodes
The first time I ran across the root knot nematode I had no idea what it was. All I knew was that it destroyed my crop of green beans within three weeks. The root knot nematode is a small microscopic worm that lives in the soil. The female can lay up to 500 eggs on the roots of your plants. The eggs, feed on your roots and cause a large knot on the larger roots of the plant. The active worms feed on the smaller roots of the plants. This results in your plants dying rather quickly.
Once I had identified the pest that had killed all my green beans I needed to find a way to control them or eliminate them from my garden. However, this wasn’t an easy task. I refuse to use any pesticides in my garden. I know that many people here in Tahiti swear by the BIO pesticides they sell in our markets. Unfortunately, these BIO products still contain chemicals that I feel are dangerous to our health.
Digging deeper into this problem I found a working solution that worked for me. I didn’t have to use any form of pesticide to get rid of the root knot nematode in my organic garden. I abandoned the large piece of land for 3 months. Here are the steps I took to rid my garden of this pest.
- I uprooted all the infected plants. I used a large plastic ground cover to move the plants to an area that we didn’t use for planting.
- Burn the infected plants roots and all.
- Turn the topsoil in the garden or area where it is infected with the root knot nematodes.
- In the area that is infected plant marigold. You need to cover the complete area with marigold. Plant the marigold in a checkerboard pattern.
- Allow the marigold to grow in this area for 3 months. During this time keep the ground free of all weeds. Once a week use your handheld garden hoe to keep the soil turned.
- After three months turn under the marigold plants and leave them in the soil. For the next three weeks, keep turning the soil in this area and removing the weeds.
After four months I was able to plant again in this area.
- Photo Description The first time I ran across the Root Knot Nematode I had no idea what it was. All I knew is that it destroyed my crop of green beans within three weeks. The Root Knot Nematode is a small microscopic worm that lives in soil. The female can lay up to 500 eggs on the roots of your plants. The eggs, feed on your roots and cause a large knot on the larger roots of the plant. The active worms feed on the smaller roots of the plants. This results in your plants dying rather quickly.
Once I had identified the pest that had killed all my green beans I needed to find a way to control them or eliminate them from my garden. However, this wasnt an easy task. I refuse to use any pesticides in my garden. I know that many people here in Tahiti swear by the BIO pesticides they sell in our markets. Unfortunately, these BIO products still contain chemicals that I feel are dangerous to our health.
Digging deeper into this problem I found a working solution that worked for me. I didn’t have to use any form of pesticides to get rid of the Root Knot Nematode in my organic garden. I abounded the large piece of land for 3 months. Here are the steps I took to rid my garden of this pest.
1. Uprooted all the infected plants. I used a large plastic ground cover to move the plants to an area that we didn’t use for planting.
2. Burn the infected plant’s roots and all.
3. Turn the topsoil in the garden or area where it is infected with the Root Knot Nematodes.
4. In the area that is infected plant Marigold. You need to cover the complete area with Marigold. Plant the Marigold in a checkerboard pattern.
5. Allow the Marigold to grow in this area for 3 months. During this time keep the ground free of all weeds. Once a week use your handheld garden hoe to keep the soil turned.
6. After three months turn under the Marigold plant and leave them in the soil. For the next three weeks, keep turning the soil in this area and removing the weeds.
After four months I was able to plant again in this area.
- Photo Location Taken on my iPhone at my organic garden in Paea, Tahiti French Polynesia
Root-knot nematodes are tiny parasitic worms that infect plant roots. They form galls or knots on the plant roots that block the flow of nutrients and photosynthesis products. (Texas AgriLife Extension Service photo by Robert Burns)
OVERTON — Root-knot nematodes are common visitors to East Texas fields of pumpkins and many other vegetables, but their presence is anything but a holiday treat for growers, according to a Texas AgriLife Extension Service expert.
“Root-knot nematodes are the biggest problem that many of our East Texas vegetable growers have to face,” said Dr. Karl Steddom, AgriLife Extension plant pathologist.
Steddom recently completed trials comparing various fumigants and biological controls for root knot nematodes on pumpkins.
“The pleasant surprise is that one of the biological controls was one of the most effective,” Steddom said.
In his root-nematode study, Dr. Karl Steddom, Texas AgriLife Extension Service plant pathologist, tested products considered industry standard fumigants, a relatively new fumigant for which there wasn’t a lot of test data yet, and two biological controls. (Texas AgriLife Extension Service photo by Robert Burns)
And he said the results should be applicable to all the crops affected by the pest. The list is considerable. Root-knot nematodes can knock back yields and quality on pumpkins, tomatoes, sweet potatoes, beets, cucumbers, carrots, peaches, watermelons, and okra. Even ornamental plants such as roses that have been started from rootstock can be hammered by the pest.
“Some watermelon varieties are marginally affected, but they can flat-out kill some crops like okra,” Steddom said.
Root-knot nematodes are tiny parasitic worms that infect plant roots. They form galls or knots on the plant roots that block the flow of nutrients and photosynthesis products. The pest is found worldwide but thrives in the sandy soils common to East Texas, he said.
“One of the biggest problems with these is that their eggs can lay dormant in the soil for years,” he said. “They’re very difficult to get rid of, and once a grower gets nematodes in a field it can be a big issue for their production for years to come.”
The infestation may start out in a small area of a field and at first may not be at high enough levels to cause significant losses in crop yield or quality, Steddom said. But if the field is left untreated, it’s almost a sure bet that the nematode population will grow and spread throughout, he said.
Steddom began the study because there wasn’t a lot of field data on two of the label products. He could have tested the products on a number of different crops, but he chose pumpkins because they’re less labor intensive to harvest, he said.
He tested nine different combinations of products on a site at the Texas AgriLife Research and Extension Center at Overton.
He conducted the tests in a field with a field that had a sandy loam soil and a high population density of root-knot nematodes.
One of the treatments tested was Vapam and Vydate, a chemical combination considered an industry standard. Another fumigant was Paladin, a relatively new product for which there wasn’t a lot of test data, he said. The other two products were biological controls, one already on the market, another still in the experimental, testing stage.
Three of the treatments were of Actinovate, a biological fungicide that uses the bacteria, streptomyces lydicus to control nematodes. The three treatments were at 6, 12 and 18 ounces per acre.
For the test crop, he used pumpkins in raised beds, 40-inches wide and 6-inches high, under plastic mulching, a system that is comparable to what’s commonly used in commercial vegetable production.
All the treatments were applied through drip-irrigation tubing. He harvested the pumpkins on Nov. 5 and compared yields as well as the extent of root galling.
Although Steddom did not find pumpkin yield differences among the various treatments, there were differences in the amount of visible galling on roots. Microscopic counts of root-knot nematode eggs per ounce of root were collected at another laboratory.
Surprising, in terms of eggs per ounce of root, the best control was achieved by Actinovate at the lowest rate of 6 ounces per acre, he said.
For a test crop in the root-nematode control study, Dr. Karl Steddom used pumpkins in raised beds, 40 inches wide and 6 inches high, under plastic mulching, a cropping system that is comparable to what’s commonly used in commercial vegetable production. (Texas AgriLife Extension photo by Robert Burns)
The root-gall index, which is largely a visible-eye rating, was also lowest with the 6-ounce rate of Actinovate. The 18-ounce rate of NI-9 achieved similar results.
“While yield was not impacted during this study, the reduction in reproduction rates has significant implications for future crops in this field,” Steddom wrote in his official report. “Neither phytotoxicity nor differences in plant vigor were observed at any time during this study.”
The other pleasant surprise is that Actinovate is by far more user-friendly than the standard fumigants. Though the fumigants rapidly degrade and pose no risk to the end user, Steddom said, they are dangerous to those who apply them. A private pesticide license is required to purchase and use the fumigants, but the biological control is available to homeowners without a license.
Root-knot nematodes formed galls or knots on these pumpkin plant roots. (Texas AgriLife Extension Service photo by Robert Burns)
The study was funded by the U.S. Department of Agriculture’s IR-4 Project, which is also referred to as the Minor Crop Pest Management Program.
“Growers or homeowners wanting more information about root-knot nematodes and their control should contact their local county Extension agent,” Steddom said.
A county-by-county directory of AgriLife Extension agents can be found at http://county-tx.tamu.edu/ .
Root-Knot Nematodes – Vegetables
Roots with nodules or bumps
Swellings or nodules on plant roots
- Root knot nematodes are very small (0.5 to 0.75 mm), colorless roundworms.
- The most common root infecting nematodes of vegetable crops are two root knot nematode species- Meloidogyne hapla and Meloidogyne incognita.
- They dwell in the soil, enter plants roots as tiny larvae, and cause swellings (root knots) that can be easily seen (distinguishable from the nitrogen-fixing nodules found on legumes because the latter can be easily rubbed off the roots whereas root-knots are firmly attached).
- Both species thrive in a wide variety of soil types but are more commonly found on light textured soils (those with a high percentage of sand).
- The root knot nematode takes about 27 days to grow from egg to adult under normal growing season temperatures.
- The immature root knot nematode molts once in the egg, emerges as the infective larval stage and enters plant roots.
- The female nematode remains inside the root for the rest of her life, causing the swelling or “root knot” to be formed around her body, which swells into a spherical shape.
- At maturity, the female extrudes her eggs into a tan gelatinous mass that can be seen on the root knot surface.
- Each female can produce one egg mass containing from 300 to 500 eggs.
- Some nematodes also serve as vectors for plant virus diseases such as tomato ring spot and tobacco ringspot.
- Most vegetable crops may serve as host plants.
- Swelllings or nodules on plant roots can indicate root knot nematodes.
- Plants fail to establish, are stunted, wilt in hot weather and decline.
- Affected plants produce fewer and smaller fruit.
- Root crops such as carrots may be deformed (forked carrots) or have hairy roots with nodules.
- Symptoms spread through a site as the season progresses and succeeding generations of juveniles hatch out.
On left stunted and forked carrots
Sweet potato damaged by root knot nematodes
Plants fail to establish, are stunted, wilt in hot weather and decline
- Soil and tissue testing is the only accurate method to determine that nematodes are the cause of plant injury. Microscopic examination is required to identify these tiny worms.
- Prevention and biological control are the keys to success in managing this pest.
- There are no chemical treatments available to home gardeners.
- Plant only resistant varieties of susceptible plants. Resistant tomato cultivars will have an “N” after the cultivar name (usually VFN for tomato).
- Keep weeds down and rotate susceptible crops or avoid planting them for a few years.
- Pull up and remove badly infested plants.
- Some “green manure” crops (cover crops), such as mustard and rape, produce compounds that suppress root-knot nematodes.
- Enhancing the biological activity of the soil, through incorporation of compost, can also help suppress root-knot nematode populations.
- Dig up suspect plants, wash soil off the roots and carefully inspect for swellings. If root-knot is strongly suspected have your soil tested and follow recommendations.
Back to Top
Nematode Management in Organic Agriculture1
Romy Krueger and Robert McSorley2
Nematodes are usually microscopic in size and are classified as unsegmented worms, belonging to the Phylum Nematoda (Figure 1). Plant-parasitic nematodes are a concern for growers of agricultural or garden crops. These plant-parasitic nematodes will mainly feed on the roots of plants. A few kinds will feed on foliage but this not common. Many other kinds of nematodes are present in the soil as well. These include decomposers, predators, insect parasites, and animal parasites. Some nematodes are aquatic and do not affect terrestrial plants. Other nematodes act as decomposers, predators, and insect parasites. In farming systems, nematode predators and parasites of insects are beneficial, while nematode parasites of animals and plants are considered pests in agriculture. Beneficial nematodes that feed on either bacteria or fungi help in nutrient cycling by accelerating the decomposition of organic matter (Figure 2). Predatory nematodes may keep harmful nematodes at lower levels by feeding on them. Entomopathogenic nematodes (nematodes harmful to insects) may help to reduce numbers of some insect pests by infecting them with bacteria. The objectives of this publication are to provide information on plant parasitic nematodes causing damage in organic agriculture and to introduce methods for their management.
A typical plant parasitic nematode.
Different nematodes: a) Bacterivore, b) Fungivore, c) Herbivore, d) Omnivore, e) Predator
Nematode Damage and Detection
Since most plant-parasitic-nematodes feed on plant roots, symptoms are comparable to nutrient or water deficiency. These can be yield loss, stunting (Figure 3), yellowing, wilting, symptoms of nutrient deficiency, and malformations of the root (including tubers, peanuts) caused by direct feeding damage. In addition, invasion by plant-parasitic nematodes often provides an infection route for other organisms such as bacteria or fungi, since nematode activity creates an entryway into the root that would otherwise not be available. Nematode reproduction is very fast. On average, a typical life cycle may be only 30 days at summer temperatures. This means that even if nematode numbers are low at the beginning of the growing season, nematode populations can rapidly increase and can become harmful to the crop in a relatively short period of time.
Symptoms caused by plant parasitic nematodes: severe stunting in corn.
Often, the most damaging nematodes in the southeastern United States and the tropics are root-knot nematodes (Meloidogyne spp.). These nematodes are pests of nearly all major crops and are therefore widespread. Damage can be directly observed by examining the roots, because root-knot nematodes produce galls or knot-like swellings along the plant roots (Figure 4). These galls cannot not be easily removed because they are part of the plant root tissue. In contrast, nodules caused by beneficial nitrogen fixing bacteria can be easily removed. Another method to distinguish nematode galls from nodules is to slice them in half and expose to air, which will cause nitrogen-fixing nodules to appear pink or red if the bacterial colony is active, or green or brown if the colony is inactive.
Root galls caused by root-knot nematodes.
Evidence of direct feeding, apparent in the form of galls and other root malformations leads to the damage symptoms described above. The invasive stage of the root-knot nematode life cycle is the juvenile root-knot nematode, which can freely move through the soil and will enter the root of a suitable host plant. Only the female is capable of establishing a feeding site. The female will become immobile, causing the plant to form giant cells for feeding, which essentially appears as a gall on the root. The presence of root-knot nematodes can be detected by the presence of these characteristic galls.
Soil Samples. Other plant-parasitic nematodes do not cause these gall symptoms, and so soil samples should be taken to determine which nematodes are present in a field. Even when it is clear that root-knot nematodes are to blame for the damage caused, it may be beneficial to find out if other nematodes are present to determine which treatments should be employed and will work best.
For further information on taking soil samples and where to send them, please refer to the EDIS publication Nematode Assay Laboratory http://edis.ifas.ufl.edu/SR011 (Crow and Woods 2007).
In nematode management it is important to remember that nematodes can move only very short distances on their own. Therefore nematodes are mainly spread through lack of sanitation and movement of infected soil and planting material. In order to limit a build-up of nematodes, planting equipment and tools should be properly cleaned, and in extreme cases could only be used for the same field. Furthermore only soil and planting material free of nematodes should be used, because once nematodes are introduced into a field they cannot be eradicated. After harvest infected plants should be destroyed to prevent the build-up of nematodes on these crop residues and therefore in the soil. Once they become established in a site, the nematodes will persist there, and management will be required on a regular basis.
Resistant Plants and Rotation Crops. Nematode management is primarily a pre-planting activity. In order to protect the crop most activities must be started two or three months before the scheduled planting date. Several pre-plant treatments are available for the organic farmer. The choice of a suitable crop cultivar can be a critical decision. Host plant resistance achieved by traditional breeding programs can be a valuable protection against some nematodes.
Two terms that are often used when talking about host plant resistance to nematodes are “tolerance” and “resistance.” Tolerance means that the plant can withstand some damage caused by nematodes without experiencing significant yield reduction. In contrast, resistance means that nematode reproduction is very low or non-existant on the plant. Both provide protection for the crop plant, but the next crop following a tolerant plant could be damaged by the nematodes that survived on the tolerant plant. Different plant species or even cultivars of the same plant species can exhibit varying degrees of resistance or tolerance. According to the University of Missouri-Columbia extension service, the following vegetable plants are recommended as reasonably resistant to root-knot nematodes: broccoli, brussel sprouts, mustard, chives, cress, garlic, leek, groundcherry, and rutabaga (Donald 1998). In contrast, Globe artichokes, Jerusalem artichoke, asparagus, sweet corn, horseradish, some lima bean varieties, onion, and rhubarb are considered to be tolerant. However, the Alabama Cooperative Extension System provides additional information on resistant crops (Hagan et al. 1998). Cowpea (Figure 5) or black-eyed peas, which can be used as a rotation crop to reduce nematode numbers, has several cultivars that are quite different in their ability to support reproduction of the root-knot nematode Meloidogyne incognita. Planted into the sandy soils of Florida, the cultivars Tennessee Brown, Mississippi Silver, and California Blackeye #5 inhibited reproduction more effectively than the cultivar Purple Knuckle (intermediate). Population densities were high after planting the cultivars Whippoorwill, Pinkeye Purplehull, and Texas Purplehull (Gallaher and McSorley 1993). Iron Clay is another cowpea cultivar that is known to reduce population levels of M. incognita (McSorley 1999).
Cowpea with young sorghum x sudangrass in the back.
Crop rotation utilizes crops that are a poor or non-host to the nematodes found in an agricultural field. These crops can either be plants that provide a secondary cash crop grown in between cycles of the primary cash crop, or they could be cover crops that are not primary but provide benefits to the farming system such as nitrogen enrichment, nematode reduction, or possible additional income. In either case, nematode numbers are reduced simply because nematodes are deprived of a suitable host crop. This does not mean that nematode densities are reduced indefinitely, but a successful crop rotation should reduce nematode levels enough so that a following susceptible crop will produce sufficient yields and survive until the end of its regular growing season. Popular cover crops are sorghum, sorghum- sudangrass (Figure 6), different grains such as oat and rye, many grasses, marigold, cowpea (Figure 5), and some tropical legumes such as sunn hemp (Crotalaria juncea, Figure 7) and velvetbean (Mucuna spp.). These cover crops are useful to reduce root-knot nematode population densities. Table 1 lists cover crops, which demonstrated low or intermediate susceptibility to M. arenaria race 1, M. incognita race 1, and M. javanica (McSorley 1999, McSorley and Dickson 1995, McSorley et al. 1994, Krueger et al. 2007). Even though these cover crops are effective against root-knot nematodes, they might increase other harmful plant-parasitic nematodes that are also present in the soil. For example, densities of the sting nematode (Belonolaimus longicaudatus) and stubby-root nematode (Paratrichodorus minor) increased on SX-17 sorghum-sudangrass. Mississippi Silver cowpea was able to reduce P. minor and M. incognita but increased B. longicaudatus. The most effective cover crop that simultaneously reduced root-knot, stubby-root, and sting nematodes was determined to be velvetbean (McSorley and Dickson 1995). Results vary in different locations as well. In Kenya, a plant related to sunn hemp (C. ochroleuca), which successfully reduced populations of root-knot nematodes appeared to increase the occurrence of lesion nematodes (Pratylenchus zeae), whereas jack bean (Canavalia ensiformis), hyacinth bean (Lablab purpureus), and velvet bean appeared to reduce both nematodes (Arim et al. 2006). Response of nematodes is greatly influenced by the cultivar of a crop plant species. Therefore even if the same plant species is used, results may vary if the cultivar is different. Sorghum is often recommended as a cover crop to decrease population levels of root-knot nematodes, and is widely used for this purpose (Dover et al. 2004). However, use of an uncommonly used cultivar (Asgrow Chaparral) actually increased population levels of root-knot nematodes (M. incognita) in a field experiment in North Florida (McSorley and Gallaher 1992). Furthermore, reactions of plants seem also to be site dependent. Cover crops that decrease nematode populations in one field may not be effective in another, depending on local nematode species and their local populations and variants present. Since weeds can harbor nematodes, it is important to have a dense cover crop stand that blocks out weeds. For more comprehensive information, please refer to the publication of the Sustainable Agriculture Network on cover crops (Bowman et al.2007).
Mature sorghum x sudangrass.
Sunn hemp starting to show flowers.
Tillage. Tillage and the practice of fallowing fields may appear as alternatives to cover crops for nematode management. Tillage inverts and mixes soil and exposes deeper soil layers to the sun. This practice is meant to kill nematodes by desiccation, since nematodes depend on moisture for survival. This practice may kill some of the nematodes that are in the upper soil layers, however it will not reach nematodes that have retreated into moderate or deeper soil layers. Nematodes can retreat to depths greater than 12 inches (30 cm) in Florida soils, and can migrate upward once a susceptible host is planted. Once a field has been fallowed, nematodes will move into deeper soil layers to avoid drying and may enter an inactive stage that enables them to survive periods without food and in addition protects them from desiccation. McSorley and Gallaher (1993) compared the effects of tillage versus crop rotation on nematode densities in tropical corn (Zea mays) cultivar Pioneer X304C in North Florida. Tillage did not have significant effects on nematode densities, while a rotation crop of sorghum cultivar DeKalb BR64 reduced population levels of root-knot nematodes (M. incognita). These results demonstrate that tillage is not a reliable method for nematode management in Florida. Fallowing can deprive nematodes of food, if the field is kept 100% weed free, and therefore can reduce population levels. But clean fallowing is a poor practice for soil conservation and nutrient runoff. In the absence of plants that keep soil in place, wind will be able to carry some of the topsoil away. Additional soil will be lost with rainwater runoff. Rain will also carry soil nutrients into lakes and rivers, which will degrade water quality and interfere with aquatic ecosystems.
Solarization. A promising technique is the use of heat to decrease not only nematode densities, but also other harmful organisms and weed seeds. This can involve pasteurization, steaming, or solarization of the soil before planting. Of these, solarization is probably the most practical (Figure 8). It involves the covering of the soil with clear plastic. Transparent plastic sheets allow short-wave radiation from the sun to penetrate the plastic. Once the light passes through the plastic and is reflected from the soil, the wavelength becomes longer and cannot escape through the plastic. The trapped light facilitates heating of the soil to temperatures detrimental to most living organisms. There are different types of plastic sheets available, mainly differing in their thickness (insulation) and ability to let light through (transparency). Black, opaque, or translucent plastics are not suitable for solarization. Thin, transparent plastic sheets appear to achieve the best results. Katan (1981) recommended thicknesses between 25 to 30 µm. Temperatures can rise anywhere between 35°C and 60°C (95°F–140°F) during the summer months (Katan 1981, Stapleton 1991) when air temperatures are close to 32°C (89.6 F) or higher. However, cloud cover and rain limit solar radiation and may diminish the success of solarization (DeVay 1991, Katan 1980). Soil temperatures only rise to detrimental levels in the first 10 to 30 cm of soil (Katan 1987), and even in this range temperatures drop off as depth increases. The plastic has to be sealed to prevent air movement underneath the plastic, which would prevent temperatures from rising sufficiently.
The soil should remain covered for a minimum of four weeks, but increasing solarization time improves effectiveness. This helps to heat the soil at a greater depth, which means that more nematodes will be affected by it (McGovern and McSorley 1997). Furthermore it also ensures that an adequate accumulation of solarized hours is achieved, which is important in regions like Florida where the sky is often overcast during the summer months.
A combination of a suitable cover crop and solarization seems to achieve best results. Wang et al. (2006) showed that following a cowpea cover crop with solarization accomplished better results than solarization alone. In fact, the effectiveness of this combined treatment was comparable to methyl bromide fumigation, which in conventional agriculture was the most effective treatment used against soil-borne diseases and pests. The disadvantage of solarization is its negative impact on beneficial soil organisms, since they will meet the same fate as their harmful counterparts. But recovery is usually attained quickly through rapid recolonization. Furthermore, other beneficials such as Bacillus, Pseudomonas, and Trichoderma are able to survive the high temperatures generated by solarization (Katan 1987). Solarization generates considerable plastic waste, which, when farming with a sustainable approach in mind, is a drawback. However, plastic sheets could be used multiple times.
Biological Control. Biological control is the management of plant-parasitic nematodes by living organisms such as bacteria, fungi, predatory nematodes, or other invertebrates. Biological control is mainly accomplished by attempting to build-up beneficial organisms through the use of various soil amendments. The introduction of beneficial soil organisms to the soil has only been attempted successfully in a few instances. Pasteuria spp., which are bacterial parasites of various plant-parasitic nematodes occurring naturally in Florida soils, may be promising biological control agents. In a 7-year experiment with tobacco, Weibelzahl-Fulton et al. (1996) showed that M. incognita and M. javanica were suppressed exclusively by P. penetrans. Tobacco plants treated with P. penetrans had fewer galls, egg masses, and eggs than plants that either did not receive P. penetrans or lacked the biological control agent due to autoclaving the soil in which the plants were grown. Nematode-trapping fungi are also potential candidates for biological control (Wang and McSorley 2003). Their adhesive knobs, rings, or net structures trap nematodes and kill them. Other types of fungi may parasitize nematode eggs. Neither fungi nor Pasteuria spp. are available for widespread commercial use at this moment. But they can be found in a healthy soil environment, as can predators such as mites and predatory nematodes. Recent research has shown that a wide range of nematode natural enemies occur in Florida soils (McSorley et al., 2006). Most predators are generalists, meaning they feed on a variety of prey species during their lifetime. For biological control purposes, generalist predators are a disadvantage, because they will not only feed on the key pest, but on other suitable organisms as well including beneficials. Furthermore if there is not enough food available they will disperse, possibly causing the pest to rebound. On the other hand, generalist predators can keep many different kinds of pests at low population densities. Currently, no predators are commercially available for augmentive releases for nematode control in vegetable production systems.
Organic Amendments in Relation to Biological Control
Biological control is difficult in soil, because it is a complex environment. Many of the possible organisms that could provide biological control lack specificity and therefore will not focus on a particular organism and may even interfere with beneficials. Therefore biological control of nematodes is achieved mainly by conservation of existing biological control; meaning that the soil environment is modified to aid the survival and reproduction of nematode natural enemies that are already present. Primarily this is accomplished through the addition of organic amendments (Figure 9). Organic amendments can improve the soil environment to aid biological control, benefit general plant health by helping with water retention and providing additional nutrients, and affect nematodes directly and negatively through detrimental decomposition products. The impact of organic amendments on nematodes is often inconsistent and unpredictable. In most cases when organic amendments are applied, they are helpful mainly as a plant nutrient source and do not directly aid in nematode management. However, even if nematodes are unaffected by the added amendments, plant health may improve due to other favorable properties of amendments. McSorley and Gallaher (1995) observed that amendments consisting of yard waste compost (four to six-month-old wood fragments, leaves, grass clippings) used as mulch or incorporated into the soil improved yield of squash and okra even though plants experienced heavy galling. Although nematode densities in composted treatments were similar to those in non-amended soil plants benefited greatly from the improved retention of soil moisture. Kimpinski et al. (2003) showed similar results. Amendments (compost and manure) increased yield in barley and potatoes in Canada, but this was not necessarily due to reduced nematode numbers.
Organic amendments: Sunn hemp mulch applied to beans.
The addition of organic amendments may stimulate the entire soil food web, including beneficial biological control organisms. When soil is amended with nutrient-rich organic matter, microorganisms may immobilize the released nutrients (Swift et al. 1979). Free-living nematodes that feed on these bacteria and fungi may play an important role in the release of nutrients tied up in such a way (Ingham et al. 1985). Soil-inhabitating microorganisms and nematodes therefore may act together to influence the rate of decomposition and release of nitrogen from crop residues, including nitrogen-rich leguminous crops like sunn hemp. Wang et al. (2004) investigated effects of sunn hemp decomposition on the soil nematode community. Litterbags that allowed nematodes to pass in and out were filled with sunn hemp hay and buried in soil. Periodic analysis of the bags showed that sunn hemp decomposition was fairly rapid and most was completed within two weeks. Population densities of nematodes feeding on bacteria increased greatly during decomposition, and this was followed by an increase in omnivorous nematodes that fed on them. However, plant-parasitic nematodes were neither affected by the sunn hemp decomposition nor by the omnivorous nematodes. In fact, plant-parasitic nematode numbers increased over time with increasing crop biomass, which may indicate that sunn hemp residue does not have a direct detrimental effect on plant-parasitic nematodes. In another recent study, Chellemi (2006) used urban plant debris (green waste from public landfill deposited by homeowners and landscape companies) to amend pepper fields in southeast Florida. As a result, the combined density of plant-parasitic nematodes was reduced, and other disease-causing plant pathogens (Pythium spp. and Phytophthora spp.) were reduced as well. These examples illustrate the potential use of organic amendments for direct or indirect management of nematodes, but they also indicate that outcomes can be complex and unpredictable.
Management of Infected Plants
Once plants are infected with nematodes, there is little that can be done to remove or reduce nematodes. Therefore, prevention and sanitation are critical to controlling nematodes. The improvement of plant health is an important cultural technique to lessen detrimental effects on plants caused by plant-parasitic nematodes. Proper irrigation, fertilization and organic amendments as surface mulches or soil incorporated are important. Furthermore, removal of weed hosts and old crop plants immediately after harvest can reduce nematode densities for the future. Nematodes are a long-term pest, which cannot be eradicated once they become established in a site. They can only be kept at low levels with carefully selected management tactics that are often specific to the managed site.
There are a variety of additional methods that may have some effect on nematodes. These include methods such as use of rhizobacteria, chitin, sesame residues, flooding, or microwave energy. Some of these (flooding, microwaving) may be restricted to specialized situations. Performance of these methods may be inconsistent or ineffective in some situations. Amendments such as chitin or sesame residue may provide nutrients that are beneficial to overall plant health regardless of any effects on nematodes. In these cases only small test areas should be subjected to new materials to determine their effectiveness under local conditions. Many of the methods described above such as host plant resistance and rotation are more dependable under a variety of conditions.
Chellemi, D.O. 2006. Effect of urban plant debris and soil management practices on plant parasitic nematodes, Phytophthora blight and Pythium root rot of bell pepper, Crop Protection 25: 1109–1116.
Gallaher, R.N., McSorley, R. 1993. Population densities of Meloidogyne incognita and other nematodes following seven cultivars of cowpea. Nematropica 23: 21–26.
Katan, J. 1980. Solar pasteurization of soils for disease control: status and prospects. Plant Disease 64: 45–54.
Katan, J. 1981. Solar heating (solarization) of soil for control of soil borne pests. Annual. Review of Phytopathology, 19: 211–236.
McSorley, R. 1999. Host suitability of potential cover crops for root-knot nematodes. Journal of Nematology 31: 619–623.
McSorley, R., Gallaher, R.N. 1992. Comparison of nematode population densities on six summer crops at seven sites in North Florida. Journal of Nematology 24: 699–706.
McSorley, R., Gallaher, R.N. 1993. Effect of crop rotation and tillage on nematode densities in tropical corn. Journal of Nematology 25: 814–819.
McSorley, R., Dickson, D.W. 1995. Effect of tropical rotation crops on Meloidogyne incognita and other plant-parasitic nematodes. Journal of Nematology 27: 535-544.
McSorley, R., Gallaher, R.N. 1995. Cultural practices improve crop tolerance to nematodes. Nematropica, 25: 53-60.
Cover crops, which demonstrated low or intermediate susceptibility to M. arenaria race 1, M. incognita race 1, and M. javanica (McSorley 1999, McSorley and Dickson 1995, McSorley et al. 1994, Krueger et al. 2007).
Sorghum bicolor x S. sudanese
This document is ENY-058, one of a series of the Department of Entomology and Nematology, UF/IFAS Extension. Original publication date January 2008. Reviewed August 2017. Visit the EDIS website at http://edis.ifas.ufl.edu.
Romy Krueger, graduate assistant; and Robert McSorley, retired professor, Department of Entomology and Nematology; UF/IFAS Extension, Gainesville, FL 32611.
The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county’s UF/IFAS Extension office.
U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.
Root Knot Nematode Disease: A Stunted Plant Growth Cause
A root knot nematode infestation is probably one of the least talked about but very damaging pests in the gardening landscape. These microscopic worms can move into your soil and attack your plants, leaving them with stunted plant growth and eventual death.
What is a Root Knot Nematode?
A root knot nematode is a parasitic, microscopic worm that invades the soil and the roots of the plants in the soil. There are several varieties of this pest but all of the varieties have the same effect on plants.
Root Knot Nematode Symptoms
Root knot nematode can be spotted initially by stunted plant growth and a yellow color to the plant. To confirm the presence of this parasite, you can look at the roots of the affected plant. True to its name, this nematode will cause root knots or bumps to appear on
the roots of most plants. They may also cause the root system to become deformed or harry.
The root knots and deformations prevent the plant from being to take up water and nutrients from the soil through its roots. This results in the stunted plant growth.
Root Knot Nematode Control
Once root knot nematodes have invaded the soil, it can be difficult to get rid of them since they attack a wide variety of plants, including common weeds such as purslane and dandelion.
One course of action is to use non-host plants in the location that the root knot nematodes have infested. Corn, clover, wheat and rye are all resistant to this pest.
If crop rotation is not possible, the soil should be solarized followed by a year of being fallow. The solarization will eliminate the majority of the worms and the year of being fallow will ensure that the remaining pests have no where to lay their eggs.
Of course, the best control of this pest is to ensure that it never enters your garden in the first place. Only use plants that come from trusted, uninfected sources.
If you suspect that your garden has been infested with this pest, bring a soil sample to your local extension office and specifically ask them to test for the pest. Root knot nematode is a quickly growing menace that is not always on the radar of local offices and is not routinely tested for unless requested.