Root knot nematodes tomato

What To Do For Tomatoes Affected By Nematodes

Your garden is your sanctuary, but it’s also home to some pretty intimidating creatures. Root knot nematodes can be overwhelming to a tomato plant if you’re unprepared, so read on and learn everything you need to know to help prevent these pests from becoming serious problems.

It takes a lot of work to go from seedling to slicing tomato, but the job gets even tougher when you’ve got tomatoes affected by nematodes. Tomato root knot nematode is one of the most common tomato problems in the garden, but you can still get great yields if you catch it early and implement a tomato nematode prevention program for future plantings.

Nematodes in Tomatoes

Everybody knows about plant diseases and the bugs that can become serious pests, but fewer gardeners are familiar with plant parasitic nematodes in tomatoes. Unlike other diseases and pests, root knot nematodes survive by feeding directly off of the nutrients pumped through tomato roots. They form galls that can reach up to an inch wide where they hide and reproduce, causing a number of symptoms that point to problems in infected plants’ transport systems.

Yellowing plants, stunted growth and general decline are early symptoms, but

unless your bed is heavily infected with nematodes, a large tomato planting will only show these symptoms in a relative few plants. They typically appear in soils where tomatoes and other root knot nematode host plants have been grown in the last three to five years, and populations increase the longer an area is used.

Tomato Nematode Prevention

If you suspect your tomato plants have nematodes, start by digging up a particularly weak plant. Roots that have a lot of unusual knobby growths are infected with these parasites. You can choose to pull those plants right away or attempt to limp them through the rest of the season. With great care and supplemental water and fertilizer, you can still harvest plenty of tomatoes from a lightly infested plant, and even a serious infestation may yield some fruit if the nematodes attacked late in the plant’s life cycle.

Once your harvest is complete, you’ll have to decide what to do about the infected bed. Crop rotation is a popular cure for many plant diseases, but because root knot nematode is so flexible, you may not find a vegetable you’d like to grow that isn’t troubled by it. Many gardeners choose to rotate with French marigolds planted no more than 7 inches apart across the bed. If you decide to go this way, keep in mind that nematodes will still try to feed on grass and weeds, so it’s important to keep everything but the marigolds out of the bed. You can turn the marigolds under after two months and replant with tomatoes if you’d like.

Other options include adding valuable organic matter that helps support your tomatoes, using soil solarization to kill the nematodes with heat or fallowing the garden and rototilling it every two weeks to prevent weed establishment.

After a bout with nematodes, you should choose nematode resistant tomatoes to improve your chances of a heavy harvest. Popular varieties that are able to better withstand attacks from these garden pests include:

Carnival
Celebrity
Early Girl
Lemon Boy
President
Quick Pick

You’ll be able to easily identify any of the many tomato strains with this resistance by the letter “N” after their name, such as “Better Boy VFN.”

Nematodes

Recognising you have a problem with nematodes is not always as they work undercover, or more specifically, underground. What happens is young nematodes burrow into the roots and their feeding stimulates the production of tumour like growths and these inhibit the plant’s ability to take up water and nutrients.

So the result is a weak plant, reduced growth and productivity and plants become susceptible to secondary fungal infections and to sudden wilting.

If your garden is infected with nematodes, you probably won’t even notice their presence during the cool seasons and that’s because their populations peak during summer and by that stage, when you do notice plants wilting, it’s too late to do anything about that particular crop. The difficulty is knowing if they’ve got them at all. And the only way to do that is to dig the plants up, rinse off the soil off the soil like I’ve done with this kohlrabi and check. And I can see that this has got nematode infection. It’s not bad. That’s why the plant has grown really well. But in severe cases, these roots, these fibrous roots wouldn’t be able to be seen at all. It would be just tumour-like growth and perhaps the plant would completely rot and die.

So which plants are most affected by the Root Knot Nematode? Well, the Solanaceae or potato family and that includes some of our favourite food plants. Things like eggplant, capsicum, chilli and tomatoes, and that’s in fact where I first discovered what nematodes were doing in my garden.

They were growing beautifully one week, and the next week, they were going yellow and wilted, even though the soil was moist. Now there are some other things, some surprises that occurred. Like this Ceylon Spinach, totally unrelated to the potato family and yet that got nematodes as well. Now, there’s one group of plants that we can be comfortable about growing in nematode infected soil and that’s the peas and beans. The legumes.

Like this Snake Bean. These do produce nodules on their roots and you mustn’t confuse them with nematodes. This is natural. This is what they do. They put nitrogen into the soil and if you look closely, you can see they’re clean and rounded. They’re not tumour shaped as the nematodes cause on other plant roots, so you can grow these in nematode infected soil. And that brings me back to the bed.

Everything I’m growing in here, apart from the Ceylon Spinach, is not going to be affected by Root Knot Nematodes. I’m resting my bed to reduce their population.

Often you can eat crops that that have been affected by nematodes, but if you do have that situation, get rid of the roots. Don’t put them in the compost heap, drop them into a plastic bag and put them into the garbage.

No the secret to living with nematodes, which I practice here involves a couple of strategies. Firstly, organic rich soil. By putting in compost, manures and mulches, you can encourage beneficial nematodes to attack the pest species. And practice crop rotation. Don’t make life easy for nematodes by planting the same crops in the same soil, year in, year out. Vary your crops and make it difficult for nematodes to really enjoy living in your garden.

There is one other, newly confirmed technique for controlling nematodes and that involves this – sowing mustard seed as a green manure. Once you’ve cleared the crops, you just broadcast mustard seed over the surface, rake it in, water it, grow it until it’s 45 centimetres high and then you dig it in and something very special happens. If the soil is moist, the mustard will decompose and it releases a chemical known as ‘Isothiocyanates.’ We all know what it tastes like. If you’ve eaten mustard or horseradish, it’s the same thing that gives them their hot flavour and it’s that chemical that fumigates the soil controlling nematodes. And we’ve got the CSIRO to thank for that 21st Century solution to nematodes.

While no infected garden will ever be entirely free of these pests, don’t worry. With some careful observation and some simple organic gardening techniques, you can look forward to abundant harvests for years to come.

STEPHEN RYAN: I’m with Jerry on that one. Looking after your soil is definitely the key to a great garden.

Still up in Queensland, Colin’s found a wonderfully peaceful spot that’s an oasis for native plant lovers.

Managing Nematodes in Gardens

Revised by Robert Heinz
MU Extension Plant Nematology Lab
Melissa Goellner Mitchum
Division of Plant Sciences and Bond Life Sciences Center

Note
SCN Diagnostics will analyze your soil for nematodes.

Most plants, whether naturally occurring or cultivated, have nematodes associated with them. Some nematodes are endoparasitic, spending their lives within plants (Figure 1). Others are ectoparasitic, and only their stylets — hollow, protrusible spears used to puncture plants — enter the plant to extract plant nutrients (Figure 2).

Figure 1
Juvenile of root-knot nematode (endoparasite) penetrating a tomato root. Magnified 1,800 times.

USDA-ARS micrograph

Figure 2
Dagger nematode (ectoparasite) feeding from cortex cells deep inside the root of a plant.

U. Zunke, Institut fur Angewandte Botanik photo

Nematodes have a wide host range and are seldom considered a pest of just one plant species. Nematode injury may include malformed flowers, leaves, stems and roots. Some endoparasitic nematodes cause tissue abnormalities known as galls or “root knots,” which block the flow of nutrients through the plant (Figures 3 and 4).

Figure 3
Root-knot nematode on melons. Note malformed fruit. Fruit typically ripens slowly or unevenly.

Pat Donald photo

Figure 4
Root-knot galls on cantaloupe roots.

Nematode feeding sites can provide entrance for other disease organisms and increase plant damage. Nematodes are a greater problem where conditions favor nematode growth, such as long growing seasons, sandy soil and plants under stress.

Soil usually contains many free-living, or non-plant-parasitic, as well as plant-parasitic nematodes. Often, several genera of plant parasites are present in the same soil, though only one or two may cause major plant damage. When plant damage is observed, a trained person is needed to identify the nematodes present and determine if these species are capable of causing plant damage.

Root-knot nematodes are the most damaging plant-parasitic nematodes in the home garden, though other nematodes can also cause problems. Nematodes can severely restrict all the vital functions of plant roots, including the absorption and transfer of water and nutrients.

Nematode spread

Most plant parasitic nematodes, especially root-knot, get into the garden by either infested soil or infested transplants. Infested soil is easily moved from one garden to another on equipment — not only tractors and implements but also hand tools such as shovels, hoes and rakes. Shoes or boots can carry soil that contains nematodes. Wheelbarrow and vehicle tires can also move nematodes, especially when muddy. Thousands of root-knot juveniles can be present in a tablespoon of soil. Before moving equipment and tools from a known root-knot infested garden to a noninfested one, power-wash off all traces of soil or disinfect by washing with a 10 percent bleach solution.

Harmful nematodes such as root-knot can get into a garden through the generosity of neighbors or family members who share their favorite vegetable or flower transplants. Careful inspection of the roots of transplants for root-knot galls is helpful, but often on young roots they may be too small to be seen. Usually, transplants purchased from a reputable dealer will be free of root-knot nematodes.

Another source of nematode-infested soil is improperly or partially decomposed compost. Roots infested with root-knot galls should be destroyed and not composted. The compost pile needs to be properly managed to ensure that harmful nematodes do not survive. Heat generated from decomposition and winter temperatures can kill root-knot nematode, but not always. Care should be taken when adding compost back into the garden to ensure that nematodes and other soil-borne pathogens are not reintroduced and spread throughout the garden. For more information on composting, see MU Extension publication G6956, Making and Using Compost.

Plant symptoms

Plants affected by plant-parasitic nematodes show foliar symptoms similar to those caused by inadequate moisture, poor nutrition or root rot. Affected plants may be stunted and have pale or yellow-green foliage. They may wilt readily under warm, breezy conditions even when soil moisture is adequate. Plant symptoms may range from the undetectable to plant death, depending on the susceptibility of the plant, environmental conditions and the number and species of nematodes attacking the plant. Established plants usually can withstand nematode feeding on the roots, but young plants are particularly vulnerable.

Nodules on the roots of beans and peas can be mistaken for early symptoms of root-knot nematode. Nodules are beneficial structures caused by certain bacteria that supply soil nitrogen to peas and beans. Nodules are attached to the side of roots rather than swollen parts of the roots or nematode cysts.

Management

If nematodes are causing damage, use one or more of the following management measures:

  • Freezing
  • Relocate the garden
  • Rotate crops
  • Grow nematode-resistant varieties
  • Grow early cool-season crops that are least affected
  • Destroy roots at harvest
  • Add organic matter
  • Solarize soil and leave fallow

Freezing

Freezing winter temperatures in many areas of Missouri limit root-knot nematode survival. Soil freezing can be enhanced by keeping a root-knot infested garden clean of grass or other insulating debris. Winter tilling can also help facilitate the penetration of cold temperatures by turning over and loosening the soil.

Relocating

Where space permits, choosing another garden site is a worthwhile consideration. However, moving the garden to a new site does not ensure complete escape from plant-parasitic nematodes. They may be present in many areas because they can survive and sometimes thrive on the roots of certain farm crops, weeds and woody plants. If the new site has a population of root-knot nematodes, continuous gardening with susceptible crops can soon increase nematode numbers to damaging levels. This may necessitate another move or other measures. Do not continue to grow nematode-susceptible plants in an area with a history of nematode problems. Check seed catalogs for resistant varieties, and adopt other management techniques to prevent nematode damage.

Crop rotation

Most vegetables can be attacked by root-knot nematode. Some plants are more susceptible than others, and some actually grow well when root-knot nematodes are present. See Table 1.

Plants related to each other usually are susceptible to the same diseases and should not be planted close to each other or follow each other in a rotation. Root crops should not be planted in the same area of the garden in succeeding years because most are susceptible to the same diseases.

Table 1
Common vegetable crop susceptibility to root-knot nematode.

Very susceptible Somewhat susceptible1 Fairly resistant Resistant2
Tomatoes Swiss chard Broccoli Globe artichoke
Okra Peas Brussels sprouts Jerusalem artichoke
Beans Parsnips Mustard Asparagus
Squash Irish potatoes Chives Horseradish
Peppers New Zealand spinach Cress Some lima bean varieties
Carrots Fall-grown turnips Garlic Onion
Cucumbers Fall-grown spinach Leek Rhubarb
Muskmelons Groundcherry
Eggplant Rutabaga
Watermelons

1 Nematode damage has been observed in these plants but does not occur as often and is not as severe as with the very susceptible plants.

2These plants grow well when root-knot nematodes are present.

Resistant varieties

Fortunately, many nematode-resistant tomato varieties are now available. Tomato varieties that have nematode resistance will have an N designation on the seed packet. Varieties resistant to the wilt-causing fungus Fusarium will have an F designation, and those resistant to the wilt-causing fungus Verticillium will have a V designation. Multiple pathogen resistance is designated as VF or VFN.

Plant-parasitic nematodes often interact with other soil pathogens, causing more plant damage than either pathogen would cause alone. The interaction may render plant resistance ineffective.

The use of nematode-resistant varieties is a good management choice because it involves minimal effort and expense. However, resistant varieties are not available for all vegetable crops, and in some cases, resistance is incomplete. Incomplete resistance means that the nematode levels will build up if host plants are grown, but the number of nematodes will increase more slowly than if a susceptible plant is grown.

Early-season cropping

Lettuce, onions, radishes, leafy greens, green peas, early beans, and cabbage (and related plants) can be planted early and escape serious nematode damage. These spring-planted crops grow when temperatures are too cool for root-knot nematode reproduction and activity. The plants are harvested before nematode damage becomes serious. However, late-summer plantings of some of these crops for fall production can be severely damaged by nematodes. Nematode damage permanently retards growth and development of these plants.

Root destruction

Destroy roots as soon as the plants are no longer wanted or productive in the garden. Nematodes continue to feed and reproduce on root fragments in the soil and build up for the next crop, causing damage in susceptible crops. The effects of root-knot nematode damage are most evident in full-season root crops (Figures 5, 6 and 7).

Figure 5
Root-knot galls on a tomato root system. Infected root system (left) compared to a healthy root system (right).

Simeon Wright photo

Figure 6
Root-knot galls on carrot roots.

C. Overstreet, Louisiana State University photo

Figure 7
Sweet potatoes infected with root-knot nematodes. Note the characteristic cracking.

Society of Nematologists photo

Organic matter

High soil organic matter helps retain moisture and adds to the available plant nutrients. Increased water and nutrients help plants fight nematode attack. Organic matter in the form of peat, manure or compost will increase the decay of organic matter, releasing nutrients through microbial action. The increased level of microbes in the soil favors the build-up of organisms that feed on all soil microbes, including nematodes. When adding compost, ensure that it does not include partially decomposed roots containing plant-parasitic nematodes or other soil-borne pathogens.

Organic matter can also be introduced into the soil through planting a green manure crop such as the legumes clover or vetch, or nonlegumes, such as rye. When used as green manure crops, these crops are planted in the fall or early spring and tilled into the soil before planting. Some evidence indicates the incorporation of this green manure crop produces compounds that are toxic to nematodes.

Soil solarization and fallow

Soil-borne pathogens such as root-knot nematodes can be killed in the upper layers of the soil by soil solarization. This process traps the heat from the sun shining through clear plastic and kills the plant pathogens. Soil solarization needs to be done during the summer when air temperatures and solar radiation are high and in an area where no plants are growing. Moist soil improves efficiency of the kill. Cover the area with thin polyethylene film, and leave the film in place for at least three months. For the solarization to be effective, soil temperatures should be maintained between 98 and 126 degrees F for several months.

Keeping part of the garden fallow can also reduce the numbers of root-knot nematodes because they will not have a host on which to feed. The fallow section must be kept free of weeds to be effective. Covering the fallow section with black plastic may be helpful.

Soil analysis

The most accurate way of diagnosing a nematode problem is a laboratory soil analysis. A good sample taken between late May and early September is essential for accurately assessing the presence of nematodes, the species involved and their relative abundance.

A good sample consists of several subsamples taken from different areas of the garden surrounding the roots of symptomatic plants. Garden soil containing roots should be randomly sampled if the area has a history of nematode infestation. Each subsample should represent the upper 7 to 8 inches of soil and an area of about 100 square feet. A hand trowel is an adequate sampling tool if the soil is soft or has been tilled recently. To collect a subsample, make a trowel-size hole 7 to 8 inches deep, and then remove a slice of soil from the side of the hole. This slice of soil is a subsample.

Collect the subsamples in a container, and mix thoroughly. From this mixture, remove about 1 pint as the sample. Promptly seal the sample in a plastic bag and submit for analysis. If shipment is delayed, keep the sample out of the sun and reasonably cool.

Root Knot Nematode (source: wikipedia.org)

Nematodes are the most numerous multi-cellular animals on earth, with more than 80,000 species described, including about 2,500 being plant parasitic. Nematodes are elongated, non-segmented microscopic eel-like roundworms that can be beneficial or non-beneficial. They live in soil and plant root tissues. Most are considered beneficial to the soil, as they contribute to the decomposition of organic matter. Only a small percentage of nematode species are parasitic and harmful to crops, causing damage to plants by feeding on roots. Some nematodes attack soil-living insect pests and can be used as biocontrol organisms. Other insect parasitic nematodes can be applied topically to caterpillars in the same way a pesticide might be applied. But the nematodes we discuss here are classed as plant parasitic. Insect parasitic nematodes are discussed briefly on the Biological Control page of this website.

There are several nematode species that can cause problems in tree fruit orchards. Parasitic nematodes that can damage tree fruit roots are the Root Lesion, Root Knot, and Dagger nematodes in apple trees, and the Root Lesion nematode in Cherry and Pear trees. Young apple trees infected with nematodes may exhibit poor growth, and gradual decline in yields. These can be symptoms of other disorders though, making it a challenge to diagnose without sampling and looking at the roots. Nematode problems tend to be worse in poor, sandy soils where trees may be suffering water or nutrient stress. Although apple replant disease is primarily caused by fungal pathogens in the soil, nematodes can also be involved. Additional information on nematodes and replant disease can be found here, at the PNW Plant Disease Management Handbook online.

Root knot nematode egg mass. (credit: Andrew Nyczepir, Bugwood.org)

Specific Nematodes and their Damage

  • Root Lesion nematodes (Pratylenchus penetrans and P. vulnes, primarily), sometimes associated with apple replant disease, penetrate roots with their piercing-sucking mouth parts (a stylet), causing damage by feeding on and migrating through the cortical tissue. Because of this they are classed as migratory endoparasites. They feed and tunnel inside the roots, and move back into the soil to find more roots to feed on. They live and reproduce in the roots, causing affected tissues to be more easily accessible to soil fungi. Severely infected roots may lack feeder roots. Apple trees, especially younger trees infected with P. pentrans have poor growth, and a gradual decline in yield. The actual feeding damage may not be obvious. A review of root lesion nematodes can be found here, (R. W. Smiley, PNW 617, March, 2010).
  • Root Knot nematodes (Meloidogyne spp.), are sedentary endoparasites, meaning they tunnel into roots to find feeding sites. Once the feeding sites are established, they don’t leave the root. However, they may stick out from the roots as they grow. Their feeding leads to impaired root functions like nutrient and water uptake, as they live inside the roots. They can cause distinctive swellings called galls on the roots of affected plants. A review of root knot nematodes can be found here, (Major emerging problems with minor meloidogyne species, A. A. Elling, Phytopathology, 103(11):1092-1102, November, 2013).
  • Dagger nematodes (Xiphinema americanum) are migratory ectoparasites, that attack roots from the outside, feeding on epidermal cells with their long stylets. They are commonly vectors of viruses, for example the tomato ringspot virus, which causes apple union necrosis and decline (especially for Red Delicious on M106 rootstocks), and the Cherry rasp leaf virus (CRLV). Additional information about dagger nematodes and CRLV can be found here, (First report of Xiphinema rivesi, (Nematoda, Longidoridae) in Washington State, 98(7), July, 2014).

General Symptoms

Recognizing nematode damage and symptoms can be problematic. Depending on the species and density of the nematode population, the tree’s susceptibility, and the environmental conditions, you may not detect damage symptoms. If otherwise healthy, many trees can tolerate moderate levels of parasitization without sustaining a significant loss in production. However, when nematodes are a problem you will see circular groupings of trees with poor growth in an orchard that otherwise looks healthy. These are due to pockets of higher population densities. Untreated, these patches may spread. Notable aboveground symptoms of nematode damage are lack of vigor, twig dieback, and decline in growth and yield. Infestation to older trees may include chlorosis, orange bark, higher susceptibility to fruit skin disorders and reduced fruit size. Belowground symptoms include poor growth of feeder roots and main roots and soil adhering to roots. Root knot nematode infestations cause a characteristic swelling of the roots, called galls. The only way to confirm that observed symptoms are caused by nematodes is through close examination of the soil and/or root tissues.

Sampling

To make management decisions, it is important to know the nematode species present and their population densities. If a previous orchard or crop had problems caused by the same species of nematode that are listed as pests of fruit trees, population levels may be high enough to cause damage to young trees. If nematode species have not previously been identified, soil samples should be taken and sent to a diagnostic laboratory for identification. It is best to sample in late summer or early fall when populations are likely at the highest density and more easily detected. Soil and root samples are taken at the tree dripline, at a depth of between 6 inches to 36 inches depending on the point that feeder roots are present. The general procedure is to place a handful of soil in one container and a handful of feeder roots in another. It is important to sample the fine feeder roots because nematodes prefer to feed on them rather than the larger roots. Take 10 to 20 subsamples from a given area, mix soil thoroughly, and combine into one sample. When sampling single trees, take two to five subsamples, depending on the size of the tree. Damage may result at 20 to 50 nematodes per 100 g soil; however, that range of numbers is only a suggested damage level. The numbers are based on replicated studies, but local soil types, climate, moisture, and other factors vary widely, and so our numbers may not be representative. For a list of laboratories performing nematode identification and testing services visit this . You should contact the testing laboratory prior to sampling to get handling and submission instructions, and test pricing.

Control Stategies

Applying soil fumigants and sealing tarps (source: J. Weiland, 2012. from: PNW Plant Disease Handbook)

Nematodes are usually introduced to new areas with infested soil or plants, and can be carried from one field to another with orchard machinery. Removing old roots before replanting and choosing resistant rootstocks and certified clean plants are good preventive measures to control nematodes. Fumigants are not effective if plant residue containing nematodes (e.g. Root Knot) remains in the ground. Trees can be monitored for symptoms of decline throughout the growing season, and if nematode infestation is suspected, it is important to know the species present, and their population densities, for management decisions. Soil and root samples can be collected in areas of concern after harvest (i.e., in the fall when populations are the highest) to determine types and numbers of nematodes. (See the above section on sampling and testing.)

Growers use pre-plant fumigants, post-plant nematicide applications, short-term biological controls (e.g. marigolds), green manure cover crops, or biofumigants. Bio-nematicides, like Brassica and mustards can be used by organic and conventional growers. Bio-nematicides have the ability to decrease plant parasitic nematodes without affecting beneficial microorganisms and nematodes, by releasing chemical compounds that may be toxic to nematodes and other pathogens (reference). Additional information about soil fumigation can be found here.

Fumigation

Orchards have typically been pre-plant fumigated with methyl bromide or other treatments to kill soil organisms before replanting. Fumigants are broad-spectrum biocides that can have negative impacts on soil health by killing beneficial organisms. Fumigants only last for so long, then the nematode populations may return. (reference) Methyl Bromide is now being phased out under an international ban, so alternative fumigants and treatments are needed. (reference) Research at the USDA Agricultural Research Station in collaboration with Washington State University has focused on alternatives to methyl bromide fumigation. Some of these alternative methods are outlined below.

Cultural and alternative control methods

Crops in the Brassiceae family have shown promise as cover crop “biofumigation” (source: Univ. of Arkansas)

There are a variety of methods that have been employed to control nematodes:

  • Fallowing is a practice where a field is planted with non-susceptible or resistant plants for a period of 3 to 5 years. For this to work, old roots should be removed prior to planting.
  • Soil supplements such as mustard green manures can be used to help suppress nematodes and soil borne diseases, and to build soil quality. (For more in-depth information visit here and here.)
  • Resistant nematode-free certified rootstocks or seedlings should be used. (Clean Plant Network)
  • Cover cropping If the root lesion nematode P. vulnes is present, maintain a poor host cover crop for that species, such as tall fescu, red fescue, or a perennial ryegrass as an orchard ground cover. However, these are hosts for P. penetrans and should not be used if this species is present. Mustards are hosts of root knot nematodes and should be avoided if that nematode is suspected to be present. Certain cover crops (e.g. wheat and Sudan grass) that induce microbial shifts in the soil or act as antibiotics to suppress pathogens, have also been effective treatments for nematodes and soil borne diseases while helping soil quality (reference). And certain mulches have been found to reduce lesion nematode populations.
  • Soil solarization is a method used as an alternative to fumigation. Moisten soil and cover with clear plastic. Leave in place for 4-6 weeks during the hottest part of summer. Root knot nematodes including eggs will die when soil temp reaches 125°F for 30 minutes. This works for about a year because only the top foot of soil is heated.

Resources

Select Chapters from the Pacific Northwest Plant Disease Handbook:

  • Nematodes. R. Ingham and H. J. Jensen, Oregon State University, PNW Plant Disease Management Handbook, webpage.
  • Apple – Dagger Nematode, PNW Plant Disease Management Handbook, webpage.
  • Apple – Root-lesion Nematode, PNW Plant Disease Management Handbook, webpage.
  • Cherry – Dagger Nematode, PNW Plant Disease Management Handbook, webpage.
  • Cherry – Ring Nematode, PNW Plant Disease Management Handbook, webpage.
  • Cherry – Root-lesion Nematode, PNW Plant Disease Management Handbook, webpage.
  • Cherry – Rasp Leaf, PNW Plant Disease Management Handbook, webpage.
  • Fumigating Soils for Nematode Control, PNW Plant Disease Management Handbook, webpage.
  • Orchard Soil Fumigation. T. J. Smith, WSU Extension, Chelan, Douglas and Okanogan Counties, PNW Plant Disease Management Handbook, webpage.

Alternative Control

General Nematode Topics

  • Major emerging problems with minor Meloidogyne species (Root knot nematodes), A. Elling (WSU Dept. Plant Pathology), Phytopathology, V103, 2013.
  • Introduction to the Integrative Management of Plant-parasitic Nematodes, A. Peetz (USDA ARS, Corvalis, WA), Presentation, 2014.
  • Pathogen & Nematode Management, WSU-CSANR website.

166 Wilson Road,
Middle Swan

All about Nematodes

Nematodes are microscopic worm like creatures that live in soil. In fact, they are the most numerous multi-celled creature on earth, found on every continent. The mere mention of them strikes fear into the heart of most gardeners in Perth – however the reality is that many nematodes are actually beneficial and in fact an essential part of healthy soil biology.
Many nematodes feed on bacteria, fungi, algae, small invertebrates and other nematodes. However there are a few varieties which feed on plant roots. They lay their eggs in the roots, and as they hatch and numbers grow, they deprive the plant of moisture and nutrients and the plant shows signs of yellowing, stunted growth, and may die.
Root knot nematodes thrive in sandy soils, and prefer warm conditions. Areas with long, dry summers and short winters suit them well. So does this sound familiar??
Identification
If you are concerned you MAY have root knot nematodes, the only way to be sure is unfortunately to rip out a plant and have a look! There will be warty lumps along the root surface.
Be aware that nitrogen fixing species (peas, beans, legumes) have nitrogen fixing nodules on their roots, which can sometimes be wrongly suspected of being nematodes.
The good thing is there ARE things that can be done.
If you have root knot nematodes in your garden, it is usually a symptom of the soil’s condition, and shows an imbalance in soil biology. Nematodes usually live in the top 30cms of soil, and eggs can survive for a few months in fallow ground. However if you plant in a crop which the nematode’s don’t feed on, and leave it for some months, the nematodes will starve.
The first thing to do is to incorporate more organic material into the soil. Lots of it. Animal manures are beneficial, especially chicken manure, because the nitrogen content stimulates conditions that are not ideal for the nematodes. There is also some evidence that raising pH (which fresh manure will do) will also help with nematode control.
Adding organic material also helps alter the balance of soil biology, and will encourage other nematode species to build up numbers that will then prey on the root knot nematode. Remember the organic gardener’s mantra; feed the soil! Unfortunately this is never a ‘once off’, but your garden will benefit hugely from regular (at least yearly) generous top ups.
Photo to the right is root knot nematode damage.
Crop Rotation
Certain types of plants are particularly susceptible to root knot nematodes. Tomatoes are one. Many types of vegetables are susceptible (carrots, peas, beans, capsicum), as are grape vines, roses, and some stonefruit. The practise of crop rotation is beneficial. Brassicas (cauliflower, broccoli, kale, cabbage, mustard, kohl rabi, turnips, brussel sprouts, bok choi, radish, rocket, mizuna, collards) actually emit a substance into the soil that kills root knot nematodes, so if you have an infestation, plant out members of this family thickly.
Green Manure Crop

Green manure seeds contain members of the brassica family and have the added benefit of adding a large amount of organic matter once it has been slashed and returned to the soil. We sell green manure seed packs @ GLSC.

Marigolds

African and French marigolds both exude a substance into the soil which will kill root knot nematodes. However they must be planted thickly (one or two flowers dotted around your vegie garden simply won’t be enough) and left in the ground for at least three months to be effective.
Molasses
Using approx. 2 tablespoons of molasses per litre of water (dissolve when the water is warm), apply this to the nematode infected soil with a watering can. (Note: I have read varying quantities recommended – even up to 1:4 molasses to water ratio!) Molasses is available in many forms. Look for the least refined and most organic possible. We do sell it in small tubs, or you could try health food stores or stock feed suppliers, but you may need to buy larger amounts.
Molasses works by increasing the food source for bacteria in the soil. It changes the balance of bacteria/fungi/nematodes in the soil biology, and this may not necessarily be a good thing. Earthworms can be adversely affected also. Use this treatment sparingly and as a last resort.
(Note: Molasses is advocated by some as a regular soil additive. For plants that prefer a bacterial dominant soil biology (eg. Turf/grasses) this may be the case. It would be beneficial when planting a new lawn, or when trying to revitalise a struggling one for instance. However we wouldn’t recommend it for shrubs and trees as woodier plants benefit from a more fungal dominant soil biology.)

Photo to the right is nitrogen fixing nodules. (Not nematode damage.)

Solarisation
Leaving bare soil covered with plastic weighted down at the edges will work to ‘cook’ the soil and kill nematodes. Of course, it will also affect beneficial soil biology the same way. For bad infestations, turn through the soil every few weeks to ensure the maximum exposure to sun & heat throughout the top 30cm layer. Areas left like this for a few months, particularly over summer, will have less problems in future seasons. Just remember to re-inoculate the soil with lots of healthy biology – use lots of compost to dig through before re-planting.
What to do with infected plant material
Firstly, ensure all roots are dug up and not left in the soil. Very hot composting methods will destroy root knot nematode eggs, but if you are uncertain that your composting methods will do the job, then cut off the roots and dispose of by burning. The tops of infected plants are fine for composting.

Nematodes don’t move a huge distance on their own – it is thought only a metre or so. Practising good hygiene (being careful not to distribute infected soil or root material on garden tools or by careless digging) and selective planting, crop rotation and soil improvement methods, you should be able to control their numbers so they do not have such a devastating effect on your crops.

Root-knot nematode

Crop rotation

Root-knot problems increase and control becomes more difficult when tomatoes or other susceptible crops are grown without rotation.

However, crop rotation will not eliminate infestations because root-knot nematodes can remain in the soil as eggs for at least a year between host crops and most species can feed on a wide range of weeds. Nonetheless, rotation can significantly reduce losses when a field is planted again to a susceptible crop.

Winter cereals are useful because they are generally poor hosts and little nematode reproduction occurs during the cold winter months. It is more difficult to find summer crops with good resistance to root-knot nematode, though sorghum x Sudan grass hybrids (particularly cv. Jumbo) are useful against most populations of the nematode.

Fallow and cultivation

Repeated cultivation kills nematodes in the upper soil layers by exposing them to mechanical abrasion, and the heating and drying action of the sun. If the field is maintained weed free, nematodes also die of starvation. In warm, moist soils in Queensland, a 4-6 month fallow may reduce root-knot nematode populations by more that 95 per cent. Longer fallow periods are not normally economically feasible and they increase the risk of soil erosion.

Sanitation

As nematode populations have the capacity to increase rapidly, plough out plants as soon as the crop is harvested to prevent further multiplication. At this time, most of the nematode population is in the roots rather than the soil. Therefore, if these roots are removed from the field and destroyed (e.g. by burning), the nematode population immediately and substantially reduces.

Resistant varieties

Tomato varieties with nematode resistance are available but not always commercially acceptable because of poor agronomic characteristics. Experimental breeding lines with nematode resistance are being tested and may be more suitable. These varieties provide adequate but not absolute protection against common populations of M. incognita and M. javanica. M. hapla and some races of M. incognita are sometimes capable of attacking resistant varieties.

Nematicide treatments

Seedbeds – In crops established from seedlings, transplants must be free of root-knot nematodes. Before planting, fumigate all seedbeds with a registered chemical according to label directions.

Potting mixes – If peat, sand and other components are obtained from sources free of root-knot nematode and are not contaminated before use, the treatment of potting mixes for nematode control is unnecessary. Treatments for damping-off fungi (e.g. aerated steam at 60°C for 30 minutes) will also kill nematodes.

Field – If the management practices above are adopted, nematicides should only be needed in the field as a last resort (e.g. in sandy soils where tomatoes are particularly prone to nematode damage). Even in situations where root-knot nematode problems are usually severe, the use of good management practices reduces the nematode population pressure and gives nematicides a greater chance of providing effective control.

The following information is a suggested decision-making timetable that will assist your management of nematodes in tomatoes.

If you are growing a crop susceptible to root-knot, check a sample of roots and determine the level of galling approximately 12 months before planting tomatoes. Eight months before planting, destroy nematode-infested root systems and plough out the crop immediately after harvest. Maintain a weed-free fallow until a cover crop is planted. Plant a cover crop that is not susceptible to root-knot nematodes, such as winter cereals or forage sorghum. Two months before planting, collect soil samples and either do a bioassay or test the soil for nematodes. If the results of nematode analyses or bioassays, or the previous occurrence of nematode problems, suggest that nematodes are likely to cause damage, either plant a nematode-resistant variety or apply a preplant nematicide.

Chemical registrations and permits

Check the Australian Pesticides and Veterinary Medicines Authority’s chemical database and permit database for chemicals registered or approved under permit to treat this pest on the target crop in your state or location. Always read the label and observe withholding periods.

Root Knot Nematode

Note Number: AG0574
Published: April 1999
Updated: January 2010

Common name

Root knot nematode or eelworm.

Scientific name

Meloidogyne species, including M. arenaria, M. hapla, M. incognita, M. javanica.

Introduction

Potatoes are very susceptible to root knot nematodes which have a broad host range and are the most economically damaging of all the nematode species to agricultural crops world wide. Root knot nematodes prefer warm temperatures and are likely to become established in potato crops grown in relatively warm areas in the north and north west of Victoria.

Generally, they are not a major problem in traditional cool climate potato production districts but have become established in some localised areas. The greatest losses occur where potatoes are grown intensively or rotated with other susceptible crops.

Symptoms

Infested potato plants may show varying degrees of stunting, yellowing of leaves and a tendency to wilt under moisture stress. Roots have swellings or galls, and beads or knots (hence the common name). Affected tubers have blisters or swellings. Symptoms are most severe when crops are grown on sandy soils and warm climates above 25C.

Root knot nematode reduces the quality, size and number of tubers. Infested potatoes can become more susceptible to bacterial wilt, Pseudomonas solanacearum, and symptoms are more severe when plants are also infected with fungal pathogens such as Verticillium and Rhizoctonia.

Description

Nematodes or eelworms are small (less than 1 mm in length) soil-borne pests which attack plant roots. They are the most common multicellular organisms in soil.

Biology

Juvenile nematodes hatch from egg masses (eggs surrounded by a gelatinous layer) deposited by females. Juveniles move through the soil to the plant roots where they use a needle-like stylet to puncture roots (just behind the root tip) and suck out the cell contents. After entering the plant, the juvenile nematodes undergo a series of moults. On becoming adults, the males leave the roots while the females stay in the roots and continue to feed.

Invasion and feeding by the female nematode stimulates the host cells to enlarge and multiply into giant cells, causing the galls on the roots. Once a female nematode establishes a feeding site, her body enlarges and protrudes through the root. After mating with a male she lays eggs in a sticky substance on the outside of her body. Some species of root knot nematode can produce eggs without males. In temperate climates, generation time is four to six weeks and there are usually three or four generations per year.

Survival

Nematodes survive in the soil as egg masses. The gelatinous layer around the egg masses provides protection against desiccation and chemicals. Each female produces 500 -1000 eggs. Eggs hatch under favourable conditions and juvenile nematodes infest roots of potatoes and other host plants.

Root knot nematodes also survive in the absence of potatoes by infesting alternative hosts, including many weed species.

Few species, except M. hapla, can survive extreme cold.

Dispersal

Root knot nematode may be spread by planting infested tubers. Potato tubers may be infested but not show symptoms. Symptoms may develop when tubers are stored, particularly when exported to warmer climates where nematode numbers can rapidly increase.

Egg masses may be transported into clean paddocks via soil adhering to farm machinery.

Host range

Potato (Solanum species) and over 2000 other plant species, including many species of vegetables and weeds.

Control

There are no potato cultivars that are resistant to root knot nematode. Chemical control is difficult and may not be economical for most Victorian potato growers.

Use the following methods to control root knot nematode:

  • Monitor crops for symptoms of root knot nematode infestations.
  • Practise good farm hygiene.
  • Avoid planting susceptible crops in paddocks contaminated with root knot nematodes.
  • Rotate crops with resistant, immune or non-host crops such as grasses (sudan grass) or cereals (barley, rye, wheat) in combination with a weed-free fallow to reduce nematode numbers. Many pasture legumes, such as white clover, and the common weed fat hen or Chenopodium sp, are very susceptible to root knot nematode.

Correct diagnosis is essential for effective pest and disease control.
For further information, phone Crop Health Services on (03) 9210-9356 or fax (03) 9800 3521.
For further information on registered chemicals, phone DPI Chemical Information Service.

Acknowledgment

This Agnote was developed by Jillian Hinch, La Trobe University, Bundoora in April 1999.

It was reviewed by Kathy Pullman and Gordon Berg, Plant Standards, DPI in April 2006 and January 2010.

ISSN 1329-8062

Published and Authorised by:
Department of Environment and Primary Industries
1 Spring Street
Melbourne, Victoria

This publication is copyright. No part may be reproduced by any process except in accordance with the provisions of the Copyright Act 1968.

The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication

Common Name

AUTHOR Grahame Jackson
Information from CABI (2014) Meloidogyne incognita Crop Protection Compendium (http://www.cabi.org.cpc/); and information (and Photo 3) from Diseases of vegetable crops in Australia (2010). Editors, Denis Persley, Tony Cooke, Susan House. CSIRO Publishing. Photos 1&2 Gerlach WWP (1988) Plant diseases of Western Samoa. Samoan German Crop Protection Project, Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) Gmbh, Germany.

Photo 2 John Bridge, Tropical Plant Nematology Advisor, CABI Bioscience, Egham, UK. Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.

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