Beneficial nematodes for vegetable gardens

Earthworms and Nematodes: The Ecological and Functional Interactions

2.3. Interaction between earthworms and nematodes and their effects on plants

Few studies have investigated the effects of earthworm and nematode interactions on plant growth .

Dionísio et al. evaluated the effect of the inoculation of earthworms P. corethrurus and Amynthas spp. in tomato plants infested with the plant-parasitic species Meloidogyne paranaensis in a greenhouse. Six adult worms of Amynthas spp. or P. corethrurus, isolated or in the same proportion (3, 3), were inoculated in pots containing soil sterilized in a steam oven. After 1 week, tomato seedlings (Rutgers” cultivar) were transplanted into the pots, and 5 mL of a suspension of M. paranaensis containing 5000 eggs and/or juveniles was inoculated per pot. The authors observed a reduction in the number of galls plant per plant after 65 days in the treatments in which the earthworms were inoculated, with reduction varying from 39.2 to 55.2% for Amynthas spp. and P. corethrurus, respectively (Figure 6). Nonetheless, the combination of the two species resulted in the reduction of 50.0% incidence of galls.

Figure 6.

Galls per tomato plant (Solanum lycopersicum ”Rutger”) inoculated with earthworms (Amynthas spp. and P. corethrurus) and plant parasite nematodes. Letters indicate statistical differences (p < 0.05) by Tukey’s test (Modified from ).

The authors indicated that the action of the earthworms occurred probably after the inoculation of the nematodes, because tomato is highly susceptible to attack by nematodes, especially at the seedling stage . Thus, two explanations were presented. First, the earthworms Amynthas spp. and P. corethrurus are epigeic and endogeic, respectively, and ingested a greater (P. corethrurus) or smaller (Amynthas spp.) soil quantity. Further, they might also have ingested eggs/juveniles of M. paranaensis, which might have been destroyed or inactivated in the passage through the digestive system, thereby reducing the possibility of gall formation in plants. Second, the eggshell of M. paranaensis might have been destroyed by the enzymes in the digestive tract of earthworms, mainly chitinase , releasing the larvae inside. Thus, the released larvae remained in the infested state in the tissues, coelom, and hemocele without essential development and, normally, without growth, what is called as paratenosis . Therefore, future experiments are needed to perform parasitological tests of the earthworm tissues to better interpret the results.

Contrary results are cited by Lafont et al. evaluating the effects of P. corethrurus and Radopholus similis (cave nematodes) on banana plants (Musa acuminata, subgroup Cavendish, ”Grande-Naine”). The study was conducted in a greenhouse by using pots containing soil, which was previously frozen (−20°C) for 2 days to eliminate the native microfauna. The total biomass of inoculated P. corethrurus was 5.0 (g pot−1); 4 weeks later, the plants were inoculated with a R. similis suspension containing 450 eggs. The results showed the absence of the control of nematodes in the soil; however, the plants developed better in the presence of earthworms (Figure 7) and also showed a reduction in the severity of necrosis in the root system. Similar results have also been reported by Loranger-Merciris by using P. corethrurus in banana plants infected with R. similis, Helicotylenchus multicinctus, and Pratylenchus coffeae.

Figure 7.

Shoot dry and root fresh biomass of banana plants under different treatments at the end of the experiment: N- E- Absence of fauna; N- E+ P. corethrurus earthworms alone; N+ E- R. similis nematodes alone; N+ E+ earthworms plus nematodes. Bars indicate standard errors, n = 12. For each treatment, the means with the same letter are not significantly different based on Bonferroni test at p < 0.05 (Source: Adapted from ).

The reduction of nematode damage in plants in the presence of earthworms was also observed by Demetrio et al. , who evaluated the potential of the earthworm Amynthas spp. in reducing the infection of Meloidogyne javanica (worldwide parasite of tomato crop) as well as the effects of the inoculation of these organisms on some soil biological attributes. Under similar conditions as those used in , different densities of Amynthas spp. were inoculated (0, 2, 4, 6, and 8 animals per pot) in the presence of tomato plants, which received a suspension containing 3000 eggs and/or juveniles of M. javanica. At the end of the experiment, the increase in carbon content of the microbial biomass and positive correlation of this attribute with the dry mass of the plants was verified. The results of this experiment showed that the earthworms were not able to reduce the infection of the plant-parasitic species in the tomato roots; however, in the presence of these invertebrates, the damage caused was reduced. Further, a positive correlation was noted between the number of inoculated earthworms and the dry mass of tomato (Figure 8a).

Figure 8.

The better development of plants even with the formation of galls in the presence of earthworms can be attributed to several factors: physical changes of the soil by the action of these invertebrates, since galleries formed are normally used by plants as a preferred route for root growth, in addition to facilitate the infiltration of water and oxygen throughout the soil profile . Second, chemical changes, which might increase the availability of P and N mainly, because of the acceleration of nutrient cycling, as well as the continuous deposition of NH4+ by earthworms, both by the production of casts and organo-mineral excrements. These processes could stimulate communities of nitrifying bacteria and growth-regulating-hormone producers, as well as the deposition of mucus-rich nitrogen compounds on the walls of the galleries .

The physico-chemical variations promoted by the earthworms alter the biological component of the soil, thereby mainly stimulating the microorganisms (Figure 8b) that can be reflected in the colonization of the roots by arbuscular mycorrhizal fungi . This contributes to the greater absorption of nutrients, mainly phosphorus; the development of plant growth-promoting rhizobacteria such as Pseudomonas spp. fluorescents , which produce siderophores, that is, increase the availability of Fe2+ to plants; or to the production of antibiotics that inhibit the effects caused by clinical and subclinical pathogens . These physicochemical and biological factors can favor the development of plants and compensate for the damage caused by plant-parasitic species in the roots.

The results of these studies showed that earthworms have a remarkable potential to be used as an alternative in the biological control of plant-parasitic species in several crops; however, further studies are needed to elucidate the mechanisms involved in this process as well as to reveal the interactions with other plants.

What Are Beneficial Nematodes and How Do They Work?
Beneficial Nematodes are microscopic, non-segmented roundworms that occur naturally in soil throughout the world. Inside the nematode’s gut is the real weapon — beneficial bacteria that when released inside an insect kill it within 24 to 48 hours. The nematodes enter the larvae via the mouth, anus, respiratory openings, or directly through the body wall of the pest. Next, nematodes eject their bacteria inside the pest’s body. These bacteria multiply and cause blood poisoning of the pest, leading to death. They also convert host tissue into nutrition for the nematodes to feed on and multiply. As the food resources within the dead pest become scarce, nematodes exit the pest and immediately start searching for a new host. Haz clic aquí para preguntas frequentas en Español.

How Do I Choose the Right Nematodes?
Use our complete Beneficial Nematode Selection Chart to select the proper species by pest. If you are unsure about which nematode to use or your target pest is not listed, please call us and one of our sales representatives can guide you to the correct species.

What’s the Application Rate?

  • 5 million treats 1,600 sq. ft.
  • 10 million treats 3,600 sq. ft.
  • 50 million treats 1 acre.
  • 250 million treats 5 acres.
  • 500 million treats 10 acres.

It is best to make at least two applications, separated by 7-10 days in order to stagger the life cycles of the nematodes and to assure complete coverage. In cases of severe infestations, applications should be made every 7-10 days or until infestation subsides.

When Should They Be Applied?
Nematodes should be applied in morning or evening when soil temperatures are 42°F – 95°F. Beneficial nematodes remain effective up to 95°F, but no longer parasitize prey above that. Please Note: one hard freeze will not harm beneficial nematode populations; however, prolonged freezing temperatures will.

Apply early in the morning or predusk when temperatures are cooler and the sun is not as bright (UV rays harm nematodes). Timing of applications during the year can be pest-specific to what is being controlled and their life cycle. Remember, beneficial nematodes control soil-dwelling life stages.

A second application of beneficial nematodes is recommended for best results. This follow-up can be done around 1-2 weeks after the initial application; or, it may be better applied during fall months in the case of pests with overwintering, soil-dwelling life stages. In the presence of high pest populations, applications should be made every 7-10 days or until infestation subsides.

How Long Can Nematodes Be Kept Before Use?
Beneficial Nematodes should be used as soon as possible. If you need to store them, it is best to store them in a refrigerator for no longer than 2 weeks.

How Are Nematodes Applied?
The solution can be applied using a watering can, Hose End Sprayer, backpack or Pump Sprayer or through irrigation or misting systems. Mix nematodes into water and gently agitate. Apply when the sun is low on the horizon as the nematodes are photophobic and do not like direct light. See our video on how to apply nematodes here.

To determine the mix rate of nematodes to water:
The mix rate of nematodes with water is highly variable due to water pressure, differences in application equipment, how fast or slow you walk while applying, how long your stride is – all of these factors play into the ‘how to’ of applying beneficial nematodes. The bottom line is that you need to do a small experiment first and it will be simple after that!

Here’s the Test Run:

  • Place a small amount of food coloring in the hose end sprayer container that you will be using to make the application. Make it a bright color so you can see it as it dilutes in your experiment.
  • Mix this with a specific amount of water of YOUR choosing
  • Go out to the area you need to spray. Then walk and spray until the food coloring is gone. Eyeball what percentage of your area was covered – was it 10%, 25%, 50%?
  • Once you figure out how far that initial mix went you can easily do the math to determine how much of the nematode package to use with each re-load.
  • If you have nematodes left over after the first round, just re-do the process and increase the mix rate of nematodes to water.

For best results use a Hose End Sprayer that allows you to set the mix rate. Do not use a hose end sprayer that does not have the ability to spray in controlled doses.

Should The Soil Be Moist After The Nematode Application?
The soil should be moist at time of application and lightly watered immediately after application. After application, regular watering of the treated area will provide sufficient moisture. Generally speaking, water every 3-4 days if rainfall does not occur.

How Long Does It Take To See Results?
Noticeable changes in pest populations are not evident until around two weeks after application. Beneficial nematodes need time to fully parasitize and kill their host, then move onto the next host. Nematodes kill the pests from the inside out. You will not see dead insect bodies as you would with a chemical knockdown. Adult pest populations should gradually decrease as the nematodes continue to kill infected life stages.

How Often Should Nematodes Be Applied?
Nematodes are recommended for use whenever larvae or grubs are present. Generally, this is during the spring and fall months. Because larvae feed on plant roots, beneath the soil surface, severe damage can be done before realizing there is a problem. Look for signs of an adult insect, such as leaf-notching. If adult insects are present, their eggs will be hatching soon. Keep in mind, one application may not eradicate a population of insects that has become established over a period of years.

Will Nematodes Live Through The Winter?
In general, harsh winter weather in most parts of the country almost guarantees a significant decline in the population of the nematodes. In most cases, nematodes (just like insects) will become dormant during cold weather. Any survivors would be few in number to provide adequate insect control. If your insect pest returns the following year, another application may be necessary.

When Nematodes Are Applied To One Area Will They Move To Other Areas?
Nematodes, due to their microscopic nature have limited range of movement. Generally NemAttack™, our formulations of Steinernema will stay where you put them, but NemaSeek™ (Heterorhabditis) will continue moving through the soil until they find a pest to infect.

How are Beneficial Nematodes Shipped?
REFRIGERATE UPON ARRIVAL. Remove nematode tray(s) and sleeves from insulated shipping container or packaging and place in refrigerator until ready to use. The Beneficial Nematodes are shipped in an easily dissolved formulation that you mix with water.

Will the beneficial nematodes harm my dog?
Beneficial nematodes can be used around and will not harm mammals, aquatic life, birds, reptiles or amphibians.

Additional Nematode Information

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ARBICO Organics Guarantees Live Beneficial Nematodes Upon Arrival of Product. Call us at 1-800-827-2847 with questions. We look forward to speaking with you!

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Monday – April 06, 2009

From: Plano, TX
Region: Southwest
Topic: General Botany
Title: Will molasses harm beneficial organisms in my garden?
Answered by: Nina Hawkins

QUESTION:

If I use molasses in the garden, I am hoping this will NOT kill the beneficial nematodes and my earth worms, or other good bugs such as lady bugs? Thanks.

ANSWER:

Boy, your seemingly simple question sure turned out to be a doozy to research! I am not a soil biologist, so please bear in mind that this is not the answer of an expert, but rather that of a gardener searching for reliable information – just like you! The short answer is no, using molasses as a soil amendment or foliar spray in your garden should not harm any beneficial organisms living in your garden. Molasses (both liquid and granular) is a widely accepted organic soil amendment that is used to promote biological activity in the soil by providing a readily available source of food (carbohydrates) to microbes already living in the soil. One of your local organic gardening experts, Howard Garrett, also recommends spraying a molasses mixture onto garden plants before releasing beneficial insects (lady bugs, green lacewings and trichogramma wasps) to encourage them to stay in your garden and claims that molasses used in the garden repels fire ants. Maryanne Caruthers-Akin, another organic gardening expert out of Portland, OR, uses molasses in her garden beds to attract earthworms – so no harm there. The Hawaii Agriculture Resource Center says that molasses soil amendments affect the “soil microbial ecology, usually resulting in lowered populations of plant parasitic nematodes as well as having other favorable effects on plant growth. The specific mechanisms are not well understood and vary with the crop, soil conditions, and nematode species present.” (Links are listed below.) I have been completely unable to find any information claiming that the use of molasses will harm beneficial nematodes and it is uncertain just how molasses works to discourage “bad” nematodes. Perhaps healthier plants are simply a less appealing target. Whether molasses will improve your soil or not depends on how healthy and biologically active it already is, but, as long as you use it according to the instructions provided on the product, it certainly won’t harm the other organisms that call your garden home. As a side note I’d like to mention that, barring past use of chemicals that may have decreased the natural amount of biological activity in your soil, plants that are native to your area usually do not require any soil amendments to grow and thrive and are actually adapted to living in soils that are less biologically active.

Dear Dirt Doctor by Howard Garrett

Earthworms – Surprising Partners in the Creation of Healthy Soils – Tilth

Molasses Soil Amendment for Crop Improvement and Nematode Management – S. Schenk

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While most of the thousands of nematode species on Earth are not harmful, some cause diseases in humans and other animals or attack and feed on living plants. Luckily, there are ways to deter these pesky pests from disrupting your garden soil.

The few parasitic species of these translucent, unsegmented worms measure about 1/50 inch long and cause root knots or galls, injured root tips, excessive root branching, leaf galls, lesions or dying tissue, and twisted, distorted leaves. Plants most commonly attacked at the roots include cherry tomatoes, potatoes, peppers, lettuce, corn, and carrots. Plants that sustain leaf and stem system injury include chrysanthemums, onions, rye, and alfalfa.

What Are Nematodes?

Often referred to as roundworms, nematodes are not closely related to true worms. They are multicellular insects with smooth, unsegmented bodies. The nematode species that feed on plants are so tiny that you need a microscope to see them. The adults often look long and slender, although some species appear pear-shaped. These plant parasites are not the same roundworms as the filarial nematodes that infect the human body, spread diseases, and wreak havoc on the immune system.

Some nematodes feed on the outer surfaces of a plant while others burrow into the tissue. Soil-dwelling nematodes are the most common culprits, but some species can damage plant roots, stems, foliage, and flowers.

No matter where they feed, these tiny worms can seriously damage to crops with their sharply pointed mouths by puncturing cell walls. The real damage occurs when a nematode injects saliva into a cell from its mouth and then sucks out the cell contents. The plant responds to the parasitic worms with swelling, distorted growth, and dead areas. Nematodes can also carry viruses and bacterial diseases inject them into plants. The feeding wounds they make also provide an easy entrance point for bacteria and fungi.

Beneficial nematodes that enrich the soil may feed on the decaying material, insects, or other nematodes.

What Nematodes Look Like

Unlike most other disease-causing organisms, plant-parasitic nematodes seldom produce any characteristic symptoms. Most of the symptoms that do appear are vague and often resemble those caused by other factors — such as viruses, nutrient deficiencies, or air pollution. Nematodes feeding aboveground may cause twisted and distorted leaves, stems, and flowers.

Root nodules invaded by nematodes. Getty Images

If nematodes are feeding on the roots, a plant may look yellowed, wilted, or stunted and infected food crops will usually yield poorly. If you suspect worm injury to roots, carefully lift one of the infected plants and wash off the roots for easier inspection. If nematodes are causing damage, you may see small galls or lesions, injured root tips, root rot, or excessive root branching.

How They Spread

Whether they feed above or below ground, most nematodes spend at least part of their life cycle in the soil. While they can’t move very far under their own power, they can swim freely in water and they move more quickly in moist soil — so it’s a good idea to keep your soil well-drained. They also spread by anything that can carry particles of infested soil, including tools, boots, animals, and infected plants.

What About Beneficial Nematodes?

Beneficial nematodes can range from 1/25 inch to several inches long and have slender, translucent, unsegmented bodies. Their roles in the garden vary. Some are soil dwellers that break down organic matter, especially in compost piles. You can easily spot these 1/4-inch-long decomposers.

These types actually combat a variety of pest species, including weevils, clearwing borers, cutworms, sod webworms, chinch bugs, and white grubs. Nematodes attack and kill these insects by either injecting deadly bacteria or entering the host, parasitizing, and then feeding on it.

Whenpurchasing and applying them to your garden, it is very important to select the right species because different kinds of nematodes are effective against different pests. In addition, nematodes require moist, humid conditions and fairly warm soil to do their job well. Water all application sites before and after spreading nematodes and follow application instructions carefully.

Nematodes

Types of nematodes

There are numerous soil-inhabiting nematode species, but not all are harmful to plants. This information sheet deals only with plant-parasitic nematodes. Within this group, some nematodes spend their life within the plant roots. These are endoparasitic. Others are ectoparasitic, and only their stylets (hollow spears used to puncture roots) enter the plant to extract nutrients from the roots or root cells. Plant-parasitic nematodes have many hosts and are seldom plant-specific.

Root knot nematodes

Root knot nematodes (Meloidogyne) are the most damaging species in the home garden. These nematodes have a very wide host range, affecting more than 2000 plant species worldwide. Root knot nematodes enter the roots as larvae, causing the plant roots to form galls or knots, and there may be excessive root branching. Underground organs such as potato tubers or carrot taproots may be damaged and become unmarketable. The nematode larvae mature in the roots, where they mate. The female adults enlarge, remain in the roots, and lay eggs into an egg sac that exudes into the soil. The eggs hatch and the young larvae go on to infect more roots.

Plants are damaged because the galls or root knots block the transport of water and nutrients through the plant. Nematode feeding sites in the roots can also provide entrance for other disease-causing organisms, like fungi or bacteria, leading to increased plant damage. Nematodes are a greater problem where conditions favour them, such as a long growing season, sandy soil and if plants are under water or nutrient stresses.

Root lesion nematodes

Although they are present in home gardens, where they can affect fruit trees, roses and turf, root lesion nematodes (Pratylenchus) are more damaging to broad-acre crops like cereals. Root lesion nematodes use the stylet to puncture roots and enter the cells. They move through the root, piercing cells, extracting cell contents, and leaving behind a trail of both cell-killing metabolites and eggs. Root cell death results in browning and lesioning of the roots. These lesions can rapidly coalesce, resulting in browning of whole roots. Individual lesions may fully encircle a root. These nematodes also damage feeder roots and root hairs, further reducing a plant’s effective extraction of water and nutrients from the soil. The overall effect is a weak, shallow root system with many dead or dying areas. When the soil dries out, root lesion nematodes become inactive and survive in a dry form in the soil or in root tissue of old crops. As the soil moistens, the nematodes become active again and reinfect the fresh roots of the new crop.

Cause

Many nematodes occur naturally, at low levels, in most soils. Most plant-parasitic nematodes enter the garden through infested soil or infested transplants. Once nematodes are present, they are almost impossible to eliminate, but their damage to plants can be reduced. Inspect the roots of transplants before placing them into your garden, whether they originate from a reputable dealer or a neighbour. This will help to keep your garden clean. Successive growth of plants that host the nematodes will lead to an increase in their population.

Parasitological review
The relations between nematodes and plants

Interest in the nematodes which parasitize plants is increasing rapidly. The work of the past has established the importance of nematodes in crop production, although the full extent of the damage they do has not yet been measured. Taxonomic studies have been prominent in the past and continue to be of fundamental importance since the nematode faunas of the soils of the world are still incompletely known. Many species are proven pathogens of plants, and many more remain to be tested. Nematodes are known to damage plants directly; they may also act as members of a group of organisms associated with disease. Nematodes live in all parts of plants, sometimes with marked effects on plant tissues, such as the stimulation of giant cell formation and of gall production. They may also retard normal cell differentiation or cause necrosis. The details of the histopathology of infections are known for a few species of plants and nematodes. That genetic differences exist in the response of plants to nematodes is amply proven. The physiological nature of such differences, however, is not known. Resistant and tolerant varieties of crop plants are already available for a limited number of plant-nematode associations; the number of such varieties will increase rapidly in the immediate future. Much work has been done to find practical systems of killing nematodes in soil under field conditions. Soil fumigation is assuming greater importance each year in farming practises both here and abroad. As research in this area continues, the cost of the chemicals will decrease and better methods of application will be devised. The chief current problem is to find active nematocides that are not phytotoxic.

It should be obvious from this review of the relations between nematodes and plants that there is great need for basic work in every branch of the subject in order to provide the foundation from which to offer solutions to the practical problems of nematode diseases in agriculture.

Nematodes As Pest Control: Learn About Beneficial Entomopathogenic Nematodes

Entomopathogenic nematodes are rapidly gaining in popularity as a proven method of eradication of insect pests. But what are beneficial nematodes? Keep reading for more information on using nematodes as pest control.

What are Beneficial Nematodes?

Members of the Steinernematidae and Heterorhabditidae families, beneficial nematodes for gardening purposes, are colorless roundworms which are non-segmented, elongated in shape and usually microscopic and commonly found living within the soil.

Entomopathogenic nematodes, or beneficial nematodes, can be used to control soil borne insect pests but are useless for control of pests found in the leaf canopy. Beneficial nematodes for gardening insect control may be used to squash pests such as:

  • Caterpillars
  • Cutworms
  • Crown borers
  • Grubs
  • Corn rootworms
  • Crane flies
  • Thrips
  • Fungus gnats
  • Beetles

There are also bad nematodes and the difference between good nematodes and bad ones is simply which host they attack; bad nematodes, also called non-beneficial, root-knot or “plant parasitic” nematodes, cause damage to crops or other plants.

How do Beneficial Nematodes Work?

Beneficial nematodes as pest control will attack soil borne insect pests with no harmful effects on earthworms, plants, animals or humans, making it an environmentally friendly solution. They are morphologically, ecologically and genetically more diverse than any other animal group

with the exception of arthropods.

With over 30 species of entomopahogenic nematodes, each with a unique host, finding a suitable nematode to aid in pest control is not only a “green” solution of integrated pest management but a simple one as well.

Beneficial nematodes have a lifecycle consisting of egg, four larval stages and an adult stage. It is during the third larval stage that the nematodes seek a host, usually insect larvae, and enter it through the host mouth, anus or spiracles. The nematode carries bacteria called Xenorhabdus sp., which is subsequently introduced into the host whereupon death of the host occurs within 24 to 48 hours.

The Steinernematids develop into adults and then mate within the host’s body, while the Heterorhabditids produce hermaphroditic females. Both nematode species ingest the host’s tissue until they mature to the third juvenile phase and then they leave the remains of the host body.

Nematodes as Pest Control

Using beneficial nematodes for gardening pest control has become an increasingly popular method for six reasons:

  • As previously mentioned, they have an incredibly wide range of hosts and can, therefore, be utilized to control numerous insect pests.
  • Entomopathogenic nematodes kill the host quickly, within 48 hours.
  • Nematodes may be grown on artificial media, making a readily available and inexpensive product.
  • When nematodes are stored at proper temperatures (60-80 F./15-27 C.), they will remain viable for three months and if refrigerated at 37-50 F. (16-27 C.), may last six months.
  • They are tolerant of most insecticides, herbicides and fertilizers, and the juveniles can survive for a time without any nourishment while searching for an appropriate host. In a nutshell, they are resilient and durable.
  • There is no insect immunity to the Xenorhabdus bacteria, although beneficial insects often escape being parasitized because they are more active and apt to move away from the nematode. The nematodes cannot develop in vertebrates, which make them extremely safe and environmentally friendly.

How to Apply Entomopathogenic Nematodes

Beneficial nematodes for gardening can be found in sprays or soil drenches. It is crucial to apply them at the perfect environmental conditions needed for their survival: warm and moist.

Irrigate the application site both before and after introducing the nematodes and only use them when soil temperatures are between 55-90 F. (13-32 C.) in filtered sun.

Use the nematode product within the year and do not store in areas of high heat. Remember, these are living creatures.

Beneficial Nematodes

When it comes to nematodes, it’s the destructive ones that get all the press. And they deserve it–plant parasitic nematodes cause an estimated $78 billion in damage to crops worldwide.

It’s only been recently that beneficial nematodes have stolen the spotlight. After decades of trying, researchers now know how to efficiently mass-produce these insect-parasitic nematodes for use in the farming industry, and that’s good news for gardeners. These tiny critters help control many common garden pests, including armyworms, rootworms, fleas, fungus gnats, stem borers, root weevils, cutworms, and billbugs. In field research, they’ve been shown to be just as effective as traditional insecticides on these pests.

Today, there are dozens of American companies selling beneficial nematodes to farmers and home gardeners. The worms can be used as a pest control for lawns and golf courses, gardens and greenhouses.

Nematodes for Gardeners

For gardeners, beneficial nematodes are attractive as biological pesticides because of their effectiveness and environmental safety. They contain no toxins and are harmless to humans and all other warm-blooded animals. They won’t harm fish or plants and are ideal for insect-infested areas around drinking wells or other environmentally sensitive locations that preclude the use of chemical pesticides. As a testament to their safety, the U.S. Environmental Protection Agency waived registration requirements for beneficial nematodes.

“We see a lot of gardeners using beneficial nematodes on white grubs,” says Jim Cate, president of Integrated Biocontrol Systems in Lawrenceburg, Indiana. “They’re good on a number of beetles that live in the soil. For example, carrot weevil, asparagus weevil, black vine weevil.”

However, effective use of beneficial nematodes requires knowledge of the nematodes and the insect you want to control. Simply applying them like a traditional pesticide won’t work.

What is a Nematode?

In an average backyard, there are billions of naturally occurring nematodes (also known as roundworms) in the soil. They are 0.6 to 2 millimeters long and often hardly visible. Some feed on plants, some feed on animals, some feed on decaying organic material or bacteria, and some (the beneficial nematodes) feed on insects.

Beneficial nematodes belong to one of two genera: Steinernema and Heterorhabditis. Four species of Steinernema and one species of Heterorhabditis are commercially available in the United States. Steinernema is the most widely studied beneficial nematode because it is easy to produce. Heterorhabditis is more difficult to produce but can be more effective against certain insects, such as the white grubs of Japanese beetle.

“There are hundreds of nematode species parasitic on insects, but only a few that show commercial potential. Currently, only five species are produced commerically in the U.S.,” says Harry Kaya, professor of nematology at the University of California-Davis. “We expect to see more beneficial nematodes available in the future because some nematodes are more effective on certain insect pests.”

How Nematodes Work

The life cycle of beneficial nematodes consists of six distinct stages: an egg stage, four juvenile stages, and the adult stage. The adult spends its life inside the host insect. The third juvenile stage, called a dauer, enters the bodies of insects (usually the soil-dwelling larval form). Some nematodes seek out their hosts, while others wait for the insect to come to them. Host-seeking dauers travel through the soil on the thin film of water that coats soil particles. They search for insect larvae using built-in homing mechanisms that respond to changes in carbon dioxide levels and temperature. They can also follow trails of insect excrement. Other species have a “sit-and-wait” strategy, like a praying mantis. When the mobile insect tunnels by them, they attack.

After a single dauer nematode finds and enters an insect (its skin or natural openings), the nematode releases a toxic bacteria that kills its host, usually within a day or two. In less than two weeks, the nematodes pass through several generations of adults, which literally fill the insect cadaver. (Steinernema reproduction requires at least two dauer nematodes to enter an insect, but a single Heterorhabditis can generate offspring on its own.) Nematode adults feed until they exhaust their food supply (the insect carcass), and as that time nears, the life cycle is halted.

As if they know time is running out, the entire host population of nematodes–as many as 200,000–become dauer nematodes, each with the ability to kill another insect. Eventually, they leave the insect carcass and begin to search for another host. Since it is nonfeeding, the dauer nematode can last for weeks in the soil.

How to Use Nematodes

For the home gardener, localized spraying is probably the quickest and easiest way to get beneficial nematodes into the soil. Although there’s no need to worry about wearing rubber gloves or protecting your clothes, take reasonable precaution against splashing them on you. Beneficial nematodes, unlike many of their cousins, are harmless to mammals.

Producers ship beneficial nematodes (dauers) in the form of gels, dry granules, clay, and water-filled sponges. All of these dissolve in water and release the millions of nematodes. A typical spraying will introduce hundreds of millions of nematodes–each ready to start seaching for an insect–into your garden.

Nematodes should be sprayed on infested areas at a time when the targeted pest is in the soil. Timing is important, or else you’ll have to repeat the application.

Northern gardeners should apply nematodes in the spring and fall, when the soil contains insect larvae. “Most of the beneficial nematodes are adaptive to cold weather,” says Cate, at Integrated Biocontrol Systems. “In fact, the very best time to control white grubs is in the fall.”

If you’re in a warmer climate, beneficial nematodes are most effective in the summer. In any case, if you’re unsure of when to apply beneficial nematodes, call your Extension service. Find out when and for how long the soil-dwelling stage of the target insect will be present and plan your nematode application for that time.

Moisture

Beneficial nematodes move in water-filled spaces between particles of soil. If the soil is too dry or too tight, they are not able to move and search out host insects. Commercial suppliers recommend watering the insect-infested area before applying nematodes. An additional sprinkling after releasing the nematodes will help rinse them off plants and grass into the soil.

Ultraviolet Light

Exposure to ultraviolet light or extreme temperatures can kill nematodes. During the warmer summer months, apply nematodes in the early evening, when the intensity of light is reduced and soil temperature is lower. Remember, watering your lawn before application will lower the soil temperature. Nematodes are either killed or less effective when soil temperatures are below 60oF or higher than 93° F.

For the typical garden, nematodes will take about two to three weeks to show results. You should see fewer of the targeted adult insects in your yard or garden. If you applied the nematodes in the fall, you should see results the following spring.

How can you make sure the nematodes have worked? If you want hard evidence, you’ll have to do some digging.

“Look for insect activity,” says Kaya. “If you dig up the soil you can usually find a dead insect. If the nematodes killed the insect, it should be brown or reddish orange, depending on what type of nematode was used. Secondly, it shouldn’t have a putrid smell.” Insects killed by Steinernema turn cream to dark brown, while Heterorhabditis turns insects orange-red. (They may even glow in the dark!) For most gardeners, nematodes must be reapplied each year.

Though be nematodes will overwinter in the soil, there will not be enough of them to effectively control pests for more than one season. Effective use of nematodes depends on a high enough number of the organisms to overwhelm your garden pests. Surprisingly, nematodes will work even when combined with some powerful pesticides. Farmers use nematodes in combination with diazinon, but home gardeners should check the package instructions before combining the two. On the other hand, the pesticide carbaryl will kill beneficial nematodes.

Because of its high nitrogen content, fertilizer can reduce nematode effectiveness. Manufacturers recommend that fertilizers not be used two weeks prior to and after nematode application. Again, check the package instructions.

Choosing a Supplier

How will you know if the nematodes have arrived at your home alive and well? Unless you test the product on water-covered grubs in a bucket, you won’t. If you want viable nematodes delivered to your door, you should pick a reputable supplier. Choose a company that sells several different nematode species. Ask how long they’ve been selling them and which target pests each of the nematode species controls. You should get a pretty good sense of the supplier’s expertise. After you get the nematodes, it’s up to you.

Beneficial nematodes attack many soil-dwelling insects, but not all of them. Control of some insects is questionable. For example, researchers say the beneficial nematodes commercially available may or may not be effective in controlling Japanese beetles (white grubs), however nematode suppliers claim a combination of Heterorhabditis and Steinernema will do the trick. Also, nematodes shipped in clay or granule form may not be certified organic. Ask your supplier if they ship nematodes on live hosts. An application of 100 million nematodes will typically cover 2,000 square feet and cost between $15 and $22. If you’ve got a severe insect problem, however, you may want to double the recommended density to increase their effectiveness.

Dan Hickey is a former editor at National Gardening.

Photography by Keith Weller/USDA-ARS

Choosing a Supplier

How will you know if the nematodes have arrived at your home alive and well? Unless you test the product on water-covered grubs in a bucket, you won’t. If you want viable nematodes delivered to your door, you should pick a reputable supplier. Choose a company that sells several different nematode species. Ask how long they’ve been selling them and which target pests each of the nematode species controls. You should get a pretty good sense of the supplier’s expertise. After you get the nematodes, it’s up to you.

Beneficial nematodes attack many soil-dwelling insects, but not all of them. Control of some insects is questionable. For example, researchers say the beneficial nematodes commercially available may or may not be effective in controlling Japanese beetles (white grubs), however nematode suppliers claim a combination of Heterorhabditis and Steinernema will do the trick. Also, nematodes shipped in clay or granule form may not be certified organic. Ask your supplier if they ship nematodes on live hosts. An application of 100 million nematodes will typically cover 2,000 square feet and cost between $15 and $22. If you’ve got a severe insect problem, however, you may want to double the recommended density to increase their effectiveness.

Dan Hickey is a former editor at the National Gardening Association.

Photography by Keith Weller/USDA-ARS

“Brood” nematodes are mixed with the appropriate nutrients to encourage them to multiply. After an incubation period, they are “fed”, where they rapidly multiply squillionfold, enter an all-important “infective juvenile” stage and are subsequently “harvested”. Samples are laboratory-tested before batches are prepared for sale, packed in cartons and put in cold storage before dispatch.

The production process requires intricate planning to meet supply and demand, which is determined by seasons and soil temperature. My tour may read like a horror story, but I was fascinated.

Biological warfare for beginners

Use water-in nematodes outdoors against:

  • Slugs, ant nests (dependent on soil temperature).
  • Leatherjackets, chafer grubs (in April and October, to coincide with vulnerable parts of their life cycles).
  • Carrot fly, cabbage root fly, cutworms, onion fly, sciarid fly, caterpillars, gooseberry sawfly, thrips and codling moth (all can be attacked with a single product).

Use water-in nematodes indoors and out against:

  • Vine weevils, sciarid fly (both dependent on soil temperature).

Use predators indoors against:

  • Whitefly (Encarsia wasp), red spider (Phytoseiulus mite), mealy bug (Cryptolaemus larvae).

Buy and apply

  • Packs are usually sold via mail order (see nemasysinfo.com for stockists).and delivered at the optimum time for application (taking into account north/south soil temperature difference).
  • Follow instructions about storage and application methods to the letter.
  • Use a soil thermometer, not guesswork. Once you get the hang of this, it is less fiddly than it sounds.
  • Nematodes will only snap into action when added to water and applied to already moist soil. Apply in the evening since soil rarely dries out overnight.
  • Results may not be obvious instantly, and you will see no corpses.
  • See the RHS website for further information about biological pest control.
  • Visit greengardener.co.uk for other non-chemical pest controls such as barriers and natural sprays.

A Guide on How Beneficial Nematodes Kill Soil-Dwelling Insect Pests

There are many types of nematodes, but this post is referring to the three species of beneficial nematodes BioLogic produces (Steinernema feltiae, Steinernema carpocapsae and Heterorhabditis bacteriophora). These beneficial nematodes feed on soil-dwelling soft bodied pest insects only, and pose no threat to humans, pets, plants or other beneficials like earthworms, honey bees or praying mantises. These microscopic roundworms are naturally occurring, but are generally found in populations too low to be effective as pest control. So, by augmenting the natural beneficial nematode population with our products you are able to control a wide variety of common insect pests. This posts intends to explain how beneficial nematodes work to kill soil-dwelling pest insects.

So, how do nematodes work?

There are a few different ways nematodes seek out their prey (e.g. ambush predators or cruising predators), but in general the nematodes will seek out or wait for a pest insect in the soil. Nematodes can move quite a bit vertically, but tend to move less so horizontally in the soil which is why it’s important to apply them properly so they can reach the target insect(s). Once they find their prey, the nematodes will enter through an opening like the mouth or anus of the insect. Once inside, the nematodes release an insect-pathogenic (or “insect-killing”) bacteria that these beneficial nematodes carry naturally. The bacteria and the beneficial nematodes have a symbiotic relationship; the bacteria need the nematodes to transport them into the insect, and the nematodes need the bacteria in order to break down their food (a beneficial nematode probiotic if you will!) The bacteria then multiplies, usually killing the insect within a day or two. This bacteria is not harmful to humans or other vertebrates. The nematodes actually finish maturing to adults and reproduce inside the insect, before new juvenile nematodes emerge from the pest insect ready to hunt down new prey a week or two later. Since the nematodes reproduce so well inside insects, they are a great longer term natural pest control. Depending on conditions you typically only need to apply once/year (or sometimes less!) as long as you apply in high enough concentrations.

Pretty cool, huh? We think so!

Nematodes 101

Nematodes are microscopic, worm-like organisms that live in the soil. There are well over 15,000 known species, making them the most numerous multicellular animals on earth! A single handful of garden soil can contain thousands.

Bad Nematodes

Most nematodes are harmless, but a handful of troublesome species attack the outside surfaces of plants, burrowing into the plant tissue and causing root, stem, folar and even flower damage. Other nematodes live inside the plants for part of their lives, causing damage from the inside out. Plants injured by nematodes are also more susceptible to bacterial and fungal damage as well. Unfortunately, it’s not always easy to distinguish nematode damage from other issues like poor fertility or disease. A soil test may be required to positively diagnose nematodes as the problem.

Good Nematodes

Not all nematodes are bad! In fact, there are numerous nematodes that occur naturally in the soil that break down organic matter (like in your compost pile!). Increasingly, nematodes are also introduced into gardens and on farms as an organic, biological control method to help control pests such as grubs, fleas, cutworms, and root maggots.

Once released, nematodes get right to work. Depending on the type of nematode released, they either “cruise” around the soil to find the larvae of pests or wait for a host insect to pass by and then “ambush” them. The nematodes release toxic bacteria that kills the pest larvae within 24-48 hours. The bacteria then serves a food source for the nematodes to reproduce. Once the food source dwindles, the nematodes start the search for a new host, helping to eliminate pests from your garden.

If a particular pest is causing problems in your garden, consider applying beneficial nematodes. You can purchase nematodes online (see below), and they are easily applied by mixing them with water and spraying with a hose or watering can. However, because nematodes are living organisms, it’s important to take care when selecting, handling and applying them. They require adequate moisture, moderate temperature, and can’t be exposed to direct sunlight. And as with any pest control, it’s important to purchase and apply the right type. Explore the resources below to learn more about nematodes.

Resources:

Beneficial Nematodes, UVM Extension
IPM Laboratories, Inc.
The Bug Lady
Nematode 101: The good, the bad, the indifferent, Mid-Atlantic Grower 2002

Gardening Tips Soil Life damage garden microorganisms pests soil health

How it Works!

Biological Insect Pest Control:
Finally, there is a safe way to control insect pests – safe for the gardener, the consumer as well as for plants and animals. This is in contrast to chemical controls, which affect all adversely, including the soil microflora (beneficial fungi and bacterium).

How does it work?
Most insect pest damage is caused by the larval stage of the insect. Prior to pupation, the larvae feed voraciously in order to store the energy required to pupate and form the adult. Once adults are visible, much of the damage has been done and the life cycle is reaching its conclusion. By this time, the next generation is ‘in production’.


Nematode is a microscopic worm, and is a natural enemy of insect larvae. CSIRO scientists have found that nematodes are able to invade and kill a large number of insects which, left unchecked, are capable of causing large-scale crop damage. Although most nematodes are harmless, some are dangerous, including roundworms that affect livestock.
Usually found in soil, the nematode detects insect movement and then follows a trail of carbon dioxide to find the insect. Entomopathogenic Nematodes (ENs) enter through the insects natural body openings; mouth, anus or respiratory inlets (spiracles) and then penetrate the blood cavity from the gut or breathing tubes.


Once in the insects blood, the EN infective juvenile releases a bacterium, found only in ENs, which multiplies and kills the insect; usually in about a day. The bacteria then convert the insect into suitable food for the nematodes and produce a range of antibiotics and anti-feedants that preserve the dead insect while the nematodes feed and breed within it.
After about 10 days, a medium sized insect cadaver may produce up to 100,000 or more infective juvenile ENs that are released into the soil and seek out new insect pest hosts.

Commercial Use
CSIRO Entomology research in Australia and overseas has shown ENs to be effective against a range of insect pests. These include:
Scarab beetles on amenity turf, ornamentals and blue berries;
Cutworms, webworms, billbugs and mole crickets on amenity turf; termites in houses and trees;
Fungus gnatson plant nurseries, hydroponics and mushroom houses;
Peach borer moth in apples in China;
Weevils on ornamentals, strawberries, cranberries, citrus and bananas;
Carpenter worm in shade trees in China and fig trees in the United States.

Perhaps the most spectacular use of this technique occurred in Australia almost 30 years ago. CSIRO successfully introduced a nematode that sterilises the Sirex wasp, the main pest of Australia’s one million hectares of pine forest. The total cost was approximately $1.5 million, and it has been estimated that the economic saving to the dollars over a single growing cycle.


CSIRO Entomology has continued to lead the world in the on-going development of the technology and was the first organization ever to use ENs commercially – against black vine weevil in ornamental plants from 1981 and against borer moth in black currants in 1983. Since then, various ENs have been introduced around the world to control a variety of pests, though control is usually in niche markets.

Production and Use

To use ENs in insect control, researchers select the best nematode species, the best strain of that species, produce it in vast quantities and apply it evenly so larger numbers of ENs can reach their insect pest. It takes around 2 billion nematodes to treat one hectare.

CSIRO has developed a patented process of mass producing required quantities of various nematode species.
ENs are living organisms which require both oxygen and water in order to survive. Although it would be possible to supply nematodes held in a water suspension, this has proved impracticable because the water would need to be constantly aerated and even then, the shelf life would be restricted to just a few days.
CSIRO Entomology has also patented better ways of formulating ENs, and this has resulted in a formulation that can be readily mixed in spray tanks and delivered without clogging spray nozzles. Further developments of this new technology are leading towards a ‘nematode mix’ which will survive comfortably for longer periods than currently available.


Even now, a longer shelf life has been achieved by manipulating the organism’s physiology and causing them to enter into a period of hibernation. In this state, the nematodes have only around 1% of the normal oxygen requirement, and it is important that no fungal contamination develops. It is also critical to ensure that a precise water content is maintained.
Ecogrow now supplies a range of nematode formulations aimed at specific insect pest types. These are packaged so as to ensure the continued viability of the nematodes for the duration of the stated shelf life. The shelf life, depending on the nematode type, can be as long as six months from date of formulation, however this is achieved only in highly controlled environments. To activate the mix prior to applying it, only water need be added.

Application
The application of nematodes is similar to, but slightly more complex than applying standard insecticides. Because they are living organisms, they can be adversely affected by ultra-violet light and will only survive in moist environments. The also require a water film to move through on their way to their insect hosts. The mix will also sediment in spray tanks if these are not agitated regularly.

Key application requirements are:
Apply in the evening
Water thoroughly both prior to and after application – 500 – 1,000 litres per Hectare
Maintain moist soil conditions until pests are controlled
Apply the mix evenly to ensure consistent coverage
ENs cannot infect at temperatures below around 15C and become stressed at temperatures of above 30C
Avoid chemical contamination of spray tanks
Avoid drying winds

Domestic Use
EoGrow has signed an exclusive agreement to develop and market the CSIRO Entomology technology, and is funding further research and development. This process will lead to the development of an ever-increasing range of host-specific treatments. Many such treatments are well advanced and are undergoing extensive field testing prior to release.
EcoGrow is now able to make available products suitable for use in domestic environments that do not require expensive equipment. Indeed, no special equipment is required!
The two initial products being offered are TURFNEM1 (for the control of beetles in lawns such as scarabs and billbugs) and GNATNEM (for the control of the fungus gnat which is a pest affecting seedlings, cuttings and ornamental crops in horticulture).
Each product is available in two sizes; 15 million and 50 million nematodes respectively. In terms of coverage, a 50 million container of TURFNEM1 is sufficient for 250 m2 for control of black beetle.

How Ecogrow ENS Work

Further Information
If you would like further information, please contact;
EcoGrow Environment
Telephone: +61 2 6284 3844
Email: [email protected]

Entomopathogenic nematodes

Entomopathogenic or beneficial nematodes have been used quite successfully for insect management. In Pacific Northwest nursery production they are used primary for suppression of root weevil, thrips, and fungus gnat larvae.

For root weevil suppression, insect parasitic nematodes are used for the soil-dwelling stage of the weevils. Drenches weevils species such as black vine weevil, strawberry root weevil, and rough strawberry root weevil are timed for the late spring-early summer prior to emegence of adult weevils or applied in the late summer-early fall to manage the young weevils the emerge from summer-laid eggs. These drenches should be applied when soil temperatures are sufficiently warm (at least 55-60 degrees F) for survival and activity of the nematodes.

Nematodes may be applied in various ways including with a bucket or watering can, or through overhead and drip irrigation lines (remove screens). Nematodes generally work best in container substrates but field releases may help to suppress nematodes. Pulling back mulch or plant debris can increase the efficacy of the drenches when applied in the field. WSU entomologist Lynell Tanigoshi (now retired) saw the infection rate for larval and pupal stages of root weevils, 12 days after receiving insect parasitic nematode drenches, increase from 13.2% to 58.4% when debris was removed compared to no removal prior to the applications in strawberries.

Want more information on entomopathogenic nematodes? There are several useful sites with information about using nematodes for insect management.

An updated resource Pacific Northwest Extension Publication, PNW 544, Using Entomopathogenic Nematodes for Crop Insect Pest Control is nice place to start learning about use of nematodes for pest control. The authors are Carol Miles, Caitlin Blethen, Randy Gaugler, David Shapiro-Ilan, Todd Murray. Revised May 2012. <21 September 2017>

Dreves, A. and J. Lee. 2015. Entomopathogenic Nematodes. PNW Insect Management Handbook. March 2015. <21 September 2017>

Barbercheck. M. 2015. Insect Parasitic Nematodes for the Management of Soil-Dwelling Insects. Penn State College of Agricultural Sciences. March 2015. <21 September 2017>

We held a very hands-on workshop in Oregon that has practical information particulary concerning application techniques
Proceedings of the Beneficial Nematode Workshop, Sept. 7, 2000. NWREC, Aurora, OR <21 September 2017>

Wainwright, S. 2017. Where to buy “THE GOOD BUGS”: Supplier beneficial insects, mites and nematodes for commercial growers. Buglady Consulting. <21 September 2017>

Just for fun, check out the following creative website about nematodes
Imaginemas <21 September 2017>

Original version: <26 July 2012)

Last update <9 September 2017>

Author: R.L. Rosetta, Extension Nursery Integrated Pest Management, Department of Horticulture, Oregon State University/NWREC.

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