No gardener wants clear, creepy worms writhing around in their garden soil like they’re straight out of Lovecraft horror stories! However, should you immediately dig them out or give these little worms the benefit of the doubt?
The clear worms in the soil are nematodes. The free-living nematodes that eat other organisms in the soil are beneficial whereas plant-parasitic nematodes (PPNs) are harmful as they feed the roots of plants, causing serious damage to the plant and even death.
Nematodes are a fascinating and diverse array of creatures abundant in any plot of land. Not all nematodes are the same and you’ll have to know which ones are good and bad for your garden’s health.
Nematodes are members of the Nematoda phylum (roundworms) and have existed for more than 400 million years. These small, worm-like organisms live off bacteria, fungi, other nematodes (free-living), or animal and plant hosts (parasitic).
Nematodes can either be microscopic (~50 µm) or large enough to be visible to the human eye (~3 mm or longer), with the parasitic variety capable of growing to be several meters long. In fact, the largest recorded nematode was the Placentonema gigantisma found in the placenta of a sperm whale. It measured 8 meters (26 feet) long and had 32 ovaries.
These organisms are some of the most successful organisms on the planet, surviving a wide range of habitats and conditions. Nematodes are more popularly viewed as the parasitic worms which can be the cause of serious diseases in the human body. However, these clear, transparent worms have a more benevolent role in the soil wherein they regulate and fertilize the soil.
Plant-parasitic nematodes (PPNs) are harmful to plants because they can trigger plant diseases such as root-knot and cysts. However, free-living nematodes are beneficial because they act as control agents in regulating the nutrient levels and the population of other organisms in the soil.
Plant-parasitic nematodes often infect crops such as rice, maize, potato, soybean, tomato, wheat, soybean, and sugar beet. Sources vary on the loss attributable to plant-parasitic nematodes from 15-20% loss to crops per annum worldwide which amount to $78-150 billion. Though numbers vary, we can conclude that they are a serious threat to agriculture.
Free-living nematodes prey on other microscopic organisms or organisms of similar size. They also prey on other nematodes such as plant-parasitic nematodes which help protect plants. By perpetuating the circle of life, these free-living nematodes maintain soil health and fertility.
For gardening and agriculture, terrestrial nematodes are divided as 1) plant-parasitic (harmful) or free-living (beneficial); which includes 2) bacterivores, 3) fungivores, 4) predators, 5) and omnivores.
The shape and structures of their mouths are clear markers on which group they belong to.
Take note that you will need a microscope to properly examine these organisms. As a matter of warning, it’s always best to have a professional step in to do the analysis in case of doubt.
The most commonly discussed and analyzed nematode group are the harmful plant-parasitic nematodes (also known as PPNs) due to their negative effects in agriculture. They attack plant cells, especially the root system. This leads to health deterioration to plant failure if left unattended.
Plant-parasitic/feeder nematodes (PPNs) are undesirable because their presence can cause disease and death in plants such as root-knots and cysts. These nematodes often gather around the root system of the plants, feeding off the root surface or feeding within the root itself.
Plant-parasitic nematodes are considered so harmful that they have been the subject of European Legislation since 1969. Notably, the government of Scotland has taken proactive steps to protect their potato crops by strictly monitoring and testing agricultural soil for the presence of plant-parasitic nematodes.
A few examples of Plant-Parasitic Nematodes are:
1) Soybean Cyst Nematode (Heterodera glycines)
2) Root Lesion Nematodes (Pratylenchus spp.)
3) Cyst Nematodes (Heterodera and Globodera spp.)
Beneficial nematode groups cycle nutrients, control organism population in the soil, disperse microbes, and serve as a food source for higher level predators. These nematodes would consume harmful lower level organisms or organisms of similar size such as fungi, other nematodes, and insects.
All in all, free-living nematodes contribute greatly to soil fertility and plant health by being a part of the ecosystem as predator and prey.
A few example of Free-Living Nematodes are:
1) Sydney Brenner’s Model Nematode (Caenorhabditis elegans)
2) Aphelenchus avenae
Bacterivorous nematodes feed off bacteria in the soil through stoma in the shape of a hollow tube. They are the main grazers of soil bacteria, regulating the bacterial population in soil.
They also play a role in decomposing organic matter. At lower nematode densities, the presence of these bacterial-feeder nematodes control disease and cycle nutrients. Bacteria is a rich source of nitrogen which is eventually released into the soil as ammonium (NH4+).
A few example of Bacterivorous Nematodes are:
1) Sydney Brenner’s Model Nematode (Caenorhabditis elegans)
3) Chiloplacus symmetricus
Fungivorous nematodes live off fungi by puncturing the fungi’s cell wall and draining out its internals. They function similar to bacterivorous nematodes but prey on fungi.
Similar with bacterivorous nematodes, fungal-feeders also play a role in decomposing organic matter. Not only do fungal-feeders consume disease-causing fungi but they also help mineralize and release nutrients for plants. Similar to bacteria, fungi are a rich source of nitrogen which is eventually released as ammonium (NH4+) when consumed by the nematode.
A few example of Fungivorous Nematodes are:
1) Aphelenchus avenae
3) Scottnema lindsayae
Predatory nematodes feed off different types of organisms, consuming nematodes, protozoa, and other insects. They consume either by eating their prey whole or by attaching themselves to larger organisms, whittling away at their prey’s defenses until they can drain its internals.
A few example of Predatory Nematodes are:
1) Heterorhabditis bacteriophora
3) Phasmarhabditis hermaphrodita
Predatory nematodes consume plant-parasitic nematodes which makes them quite beneficial in protecting plant growth and development by regulating the population of harmful nematodes or other animals of similar size such as insects.
Omnivorous nematodes consume different organisms or have different prey depending on what stage of life they are at. Unlike most nematodes which have specific feeding diets, omnivorous nematodes seem to be outliers by comparison.
Omnivorous nematodes play a vital role in the soil food chain for microbes. Like with other nematodes, they serve as predator and prey for other organic life in the soil.
A few example of Omnivorous Nematodes are:
1) Actinolaimus tripapillatus
Terrestrial nematodes which can be seen by the naked eye, save for a few exceptions, do not cause any harm. Most plant-parasitic nematodes are microscopic in size. Terrestrial nematodes are a completely normal and vital part of the soil’s ecosystem.
Terrestrial nematodes live in the thin film of moisture between soil particles. In fact, a spadeful of soil can host up to hundreds of thousands of nematodes but you can’t even see it! A single teaspoon can already hold several hundred nematodes!
Rather than a visual inspection of the soil, a more accurate indicator of the presence of harmful nematodes would be the symptoms plants show when they are being attacked by plant-parasitic nematodes.
The plant-parasitic nematode symptoms are connected to the root where nematodes attack. This causes inhibited root functions which show up as discoloration of the leaves, stunted growth, sparse foliage, wilting, and death. Since these symptoms are so similar to other plant diseases, it is always recommended to have experts conduct a thorough soil analysis.
Plants extracted from the soil afflicted with plant-parasitic nematodes will show symptoms of a plant-parasitic nematode infestation. For example, potato cyst nematodes will produce spherical cysts on the roots which look like pinheads.
More notorious symptoms such as knots and cysts are much more noticeable. These are serious symptoms caused by Meloidogyne spp. and Heterodera glycines, respectively. Their effects appear as bulbous growths on the root systems of susceptible plants, leading to plant deterioration and failure.
Unfortunately, plant-parasitic nematodes are almost impossible to remove from the soil once introduced due to their resilience. Integrated land management is a possible solution which combines 1) crop rotation, 2) chemical nematicides, 3) biological control, and 4) nematode-resistant crops.
These methods must be used in tandem with one another to effectively reduce the population of plant-parasitic nematodes, allowing other more beneficial organisms to take over.
Crop rotation is a tried and tested method in improving soil fertility and health. Crop rotation merely involves alternating or cycling different crops per growing season.
This works because nematodes are prey-specific. Of course, this technique is not applicable if you do not want to change the plants in your garden or field.
They have a diet and they stick to it. The loss of the prey plant and the introduction of a new plant group will leave these nematodes without a source of food. In effect, the nematode population will die off due to starvation or predation from other microorganisms.
Chemical nematicides are readily available nowadays and have proven effective in reducing the plant-parasitic nematode population. Despite being frowned upon by growers, the use of chemical nematicides is justified in case of nematicide attacks found in preceding and subsequent crops planted in the same plot of land.
The use of chemical nematicides is highly regulated because of their varying environmental effects. Chemical nematicides cannot be used frequently hence it is highly recommended that the manufacturer’s label is followed!
Always be up to date with your country’s list of prohibited and allowed chemical nematicides.
Biological control involves the use of other predatory organisms to prey on plant-parasitic nematodes, reducing their population in the soil. Predators of plant-parasitic nematodes include other predacious nematodes, fungi, protozoa, collembola, and mites, among others.
More beneficial nematodes can be manually introduced into the soil. Beneficial nematodes can be commercially bought which improves soil quality and fertility.
Recent studies have been considered using nematode-trapping fungi, Duddingtonia flagrans, which produce adhesive hyphae which act like web traps. They will act as natural predators against nematodes
Studies on finding PPN-eating organisms are still ongoing. The hope is that these can be utilized to provide a clean, organic solution against plant-parasitic nematodes.
Nematode-resistant crops reduce plant-parasitic nematodes by being unsuitable hosts for the parasite, leaving plant-parasitic nematodes with no available food sources for sustenance. In tandem with crop rotation, nematode-resistant crops can be used to make the soil more hospitable next growing season for more susceptible plants.
Certain plants have greater resistances over nematodes relative to other plants. However, these are highly dependent on the species or variety in relation to the growing conditions. For more information, an informative key made from botanical data from Queensland, Australia is available online.
Soil solarization can reduce nematode population in the top 30 cm (12 inches) of the soil. However, this is only a temporary solution made to benefit shallow-rooted crops and young plants. Soil solarization does not provide a long-term solution to fruits bearing trees or plants which have deeper root systems.
Due to its short-term effects, soil solarization is not part of integrated land management. It is better used for potted plants where the amount of soil is more manageable, allowing gardeners to reuse and recycle soil.
Soil solarization is done by taking moist soil and placing it under a clear, plastic tarp. It should be left in an open area in direct sunlight for 4-6 weeks, preferably during the hottest period of summer.
The natural world has innumerable creatures which look identical but are actually different organisms which lead to misidentification. Other organisms which look like clear worms in soil include 1) pot worms and 2) fungus gnat larvae.
Pot worms are worms comparatively larger than most terrestrial nematodes. They are white, clear, and shiny, ranging from ~5-15 mm (~0.19-0.59 inches). Often found in compost pits, pot worms can also find their way in garden soil when there is decaying organic matter that they can feed on.
Pot worms should be left alone since they only consume decaying organic matter. They aid in decomposition which also produces and cycles nutrients in the soil. They play an important role in the ecosystem which warrants their peaceful existence in your garden.
Pot worms differ from nematodes through size alone. They can be observed with the naked eye alone as opposed to the microscopic size of nematodes.
Fungus gnats larvae are the offspring of fungus gnats flies (Mycetophilidae and Sciaridae family) which hatch from yellow-white eggs. They have white bodies and black heads with a length of ~6.35 mm (~0.25 inch). They are pests that live and grow in soil, feeding on plants until reaching full maturity.
Fungus gnats larvae are a serious concern for any gardener and should be removed immediately. Getting rid of fungus gnats can be done by applying neem oil, soil covers, castile soap, cinnamon, traps, and biological control.
YourIndoorHerbs has you covered for a more in-depth discussion in getting rid of fungus gnats.
There is a wide selection of plants that repel pests such as insects, nematodes, and other organisms. Plants like thyme, oregano, and basil, among others, make for popular companion plants.
These plants, often herbaceous, have evolved to reduce pests from attacking them via essential oils which some pests find repulsive. By placing these plants near susceptible plants, the instances of pest-induced diseases are reduced.
Oregano is a favorite here in YourIndoorHerbs due to its culinary uses and health benefits. We’ve compared it with other herbs like thyme and basil. Any of these plants will do wonders in protecting any garden from pests!
- Nematodes are clear worms which can be microscopic or large enough to be seen by the human eye. They are a hardy and resilient species which have adapted to a wide range of conditions.
- Plant-parasitic nematodes are a serious concern since they can cause diseases to the plants by attacking their roots. Free-living nematodes serve as an important piece of the soil’s ecosystem, cycling nutrients, and consuming other harmful nematodes.
- Integrated land management is the best way to reduce plant-parasitic nematode population in the soil. It’s a holistic approach which combines crop rotation, chemical nematicides, biological control, and nematode-resistant plants.
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