![Root-knot nematode](https://webarchive.library.unt.edu/eot2008/20090117014353im_/http://attra.org/images/nematode/root_knot_nematode.jpg)
Root-knot nematode—Meloidogyne brevicauda Loos ©Jonathan
D. Eisenback, Virginia Polytechnic Institute and State University
|
Abstract
This publication provides general information on the tiny worm-like
organisms called nematodes. A more detailed description of the genera
of nematodes that attack plants is provided as well as various methods
to diagnose, discourage and manage plant parasitic nematodes in
a least toxic, sustainable manner.
Table of Contents
Introduction
Nematodes are tiny, worm-like, multicellular animals adapted to
living in water. The number of nematode species is estimated at
half a million, many of which are "free-living" types
found in the oceans, in freshwater habitats, and in soils. Plant-parasitic
species form a smaller group. Nematodes are common in soils all
over the world (Dropkin, 1980; Yepsen,
1984) As a commentator in the early twentieth century wrote:
If all the matter in the universe except
the nematodes were swept away, our world would still be dimly
recognizable, and if, as disembodied spirits, we could investigate
it, we should find its mountains, hills, vales, rivers, lakes
and oceans represented by a thin film of nematodes. (Sasser,
1990) |
An important part of the soil fauna, nematodes live in the maze
of interconnected channels—called pores—that are formed
by soil processes. They move in the films of water that cling to
soil particles. Many genera and species have particular soil and
climatic requirements. For example, certain species do best in sandy
soils, while others favor clay soils. Nematode populations are generally
denser and more prevalent in the world's warmer regions, where longer
growing seasons extend feeding periods and increase reproductive
rates. (Dropkin, 1980) In the southern United
States, as many as ten generations are produced in one season. (Yepsen,
1984)
![Lance nematode](https://webarchive.library.unt.edu/eot2008/20090117014353im_/http://attra.org/images/nematode/lance_nematode.jpg)
Face view of lance nematode, Hoplolaimus sp. ©Jonathan
Eisenback, www.mactode.com |
Light, sandy soils generally harbor larger populations of plant-parasitic
nematodes than clay soils. This is attributable to the more efficient
aeration of sandy soil, the presence of fewer organisms that compete
with and prey on nematodes, and the ease with which nematodes can
move through the root zone. Also, plants growing in readily drained
soils are more likely to suffer from intermittent drought, and are
thus more vulnerable to damage by parasitic nematodes. Desert valleys
and tropical sandy soils are particularly challenged by nematode
overpopulation. (Dropkin, 1980)
Plant-parasitic nematodes—the majority of which are root
feeders, completing their lifecycles in the root zone—are
found in association with most plants. Some are endoparasitic, living
and feeding within the tissue of roots, tubers, buds, seeds, etc.
(Sasser, 1990) Others are ectoparasitic, feeding
externally through plant walls. A single endoparasitic nematode
can kill a plant or reduce its productivity, while several hundred
ectoparasitic nematodes might feed on a plant without seriously
affecting production. (Ingham, 1996) A few
species are highly host-specific, such as Heterodera glycines
on soybeans and Globodera rostochiensis on potatoes. (Sasser,
1990) But in general, nematodes have a wide host range.
Endoparasitic root feeders include such economically important
pests as the root-knot nematodes (Meloidogyne species),
the cyst nematodes (Heterodera species), and the root-lesion
nematodes (Pratylenchus species). (Sasser,
1990) Important ectoparasitic root feeders include: root (Paratrichodorus
and Trichodorus), dagger (Xiphinema), needle (Longidorus,
Paralongidorus), ring (Criconemella, Macroposthhonia),
stunt (Tylenchorhynchus and Merlinius), pin (Paratylenchus),
and spiral (Helicotylenchus, Rotylenchus, and Scutellonema)
nematodes. Direct feeding by nematodes can drastically decrease a
plant's uptake of nutrients and water.
Nematodes have the greatest impact on crop productivity when they
attack the roots of seedlings immediately after seed germination.
(Ploeg, 2001) Nematode feeding also creates
open wounds that provide entry to a wide variety of plant-pathogenic
fungi and bacteria. These microbial infections are often more economically
damaging than the direct effects of nematode feeding.
Major Plant-parasitic
Nematode Genera in the U.S. & Associated Damage to Plants
- Root-knot nematodes (Meloidogyne
species) form galls on injured plant tissue. The galls
block water and nutrient flow to the plant, stunting growth,
impairing fruit production, and causing foliage to yellow
and wilt. Roots become rough and pimpled and susceptible
to cracking.
- Cyst nematodes (Heterodera species)
give plants an unthrifty or malnourished appearance, and
cause them to produce smaller-than-normal tops. Foliage
is liable to wilt and curl, while roots become thick and
tough and take on a red or brown coloring.
- Sting nematodes (Belonolaimus species)
are found mainly in the South, especially in sandy soils
with meager organic-matter content. Areas of stunted plants
are an early indicator. As these areas grow larger and finally
meet, the plants that were first affected will start to
die at the margins of older leaves.
- Root-lesion or meadow nematodes (Pratylenchus
species) cause internal browning in potato tubers and
in the roots of corn, lettuce, peas, carrots, tomatoes,
and brassicas. (Yepsen, 1984)
|
![Mononchoid nematode](https://webarchive.library.unt.edu/eot2008/20090117014353im_/http://attra.org/images/nematode/monochoid_nematode.jpg)
Mononchoid nematode feeding on another nematode. ©Jonathan
Eisenback, www.mactode.com |
Nematode control is essentially prevention, because once
a plant is parasitized it is impossible to kill the nematode without
also destroying the host. The most sustainable approach to nematode
control will integrate several tools and strategies, including cover
crops, crop rotation, soil solarization, least-toxic pesticides,
and plant varieties resistant to nematode damage. These methods
work best in the context of a healthy soil environment with sufficient
organic matter to support diverse populations of microorganisms.
A balanced soil ecosystem will support a wide variety of biological
control organisms that will help keep nematode pest populations
in check.
Back to top
Symptoms and Sampling
Usually, sampling is done because the grower observes a section
of field with unhealthy plants, or notices an unexplained yield
reduction. Because nematodes damage roots, any condition that stresses
the plant—such as drought (or even hot spells), flooding,
nutrient deficiencies, or soil compaction—will tend to amplify
the damage symptoms noted above. Failure to respond normally to
fertilizers and slower-than-normal recovery from wilting are signs
of nematode infestation. In the undisturbed soil of groves, turf,
and pastures, visible symptoms of nematode injury normally appear
as round, oval, or irregular areas that gradually increase in size
year by year. In cultivated land, nematode-injured spots are often
elongated in the direction of cultivation, because nematodes are
moved by machinery. (Dunn, 1995)
It is important to note that species of nematode are present in
all soils; their mere presence does not necessarily mean that they
are damaging plants. Harmless or even beneficial species are found
in proximity to plants, right along with the parasitic species.
Beneficial nematodes feed on such pests as Japanese beetle grubs
and plant-parasitic nematodes, and release nutrients into the soil
by eating bacteria and fungi. (Ingham, 1996;
Horst, 1990) An experienced nematologist can
identify species, and determine which, if any, are responsible for
the observed damage.
Nematode sampling techniques vary depending on the crop, the root
depth, the type of nematode causing damage, and the time of the
season. The procedure presented here is a generic sampling technique
for annual crops. Soil samples taken in the late summer are best
when testing for the presence of nematodes. Root-zone soil samples
are best taken immediately after harvest, or just prior to harvest
if the crop showed signs of damage. First, fields should be divided
into 20-acre blocks that have similar damage, soil texture, or cropping
history. From each block take several sub-samples, mixing them well
to create a single one-quart sample for each block. Soil samples
should be kept cool, but not frozen.
Samples for established perennial crops are best taken from the
feeder root zone, which is usually located around the canopy drip
line. (Dropkin, 1980) Your county or state
Cooperative Extension Service can provide names of commercial labs
that have nematode-identification services.
Back to top
Preventing Further Spread of
Nematodes
Preventing nematodes from entering uninfested areas is important;
under their own steam they can spread across a field at a rate of
three feet per year. The following measures will help prevent human-assisted
spread of nematodes to uninfested fields:
- Use certified planting material
- Use soilless growing media in greenhouses
- Clean soil from equipment before moving between fields (washing
equipment—including tires—with water is most effective)
- Keep excess irrigation water in a holding pond so that any nematodes
present can settle out, pump water from near the surface of the
pond; plan irrigation to minimize excess water
- Prevent or reduce animal movement from infested to uninfested
fields
- Compost manure to kill any nematodes that might be present,
before applying it to fields (Kodira and Westerdahl,
1995)
- Eliminate important weed hosts such as crabgrass, ragweed, and
cocklebur
(Yepsen, 1984)
Back to top
Managing Soil Biology
The basis of sustainable nematode control is the maintenance of
a healthy soil food-web. This begins with routine application of
organic matter. There is substantial evidence that the addition
of organic matter in the form of compost or manure will decrease
nematode pest populations and associated damage to crops. (Walker,
2004; Oka and Yermiyahu, 2002; Akhtar
and Alam, 1993; Stirling, 1991) This could
be a result of improved soil structure and fertility, alteration
of the level of plant resistance, release of nemato-toxins, or increased
populations of fungal and bacterial parasites and other nematode-antagonistic
agents.
(Akhtar and Malik, 2000) Reduced
nematode damage from increased organic matter in soil is likely
a combination of these interaction. Higher organic matter content
increases soil's water-holding capacity, and supports thriving communities
of the decomposers and predators that make up the soil's "digestive
system."
Nematodes are important participants in this underground energy-transfer
system. They consume living plant material, fungi, bacteria, mites,
insects, and each other, and are themselves consumed in turn. Some
fungi, for example, capture nematodes with traps, sticky knobs,
and other specialized structures. (Dropkin, 1980)
Nematodes and protozoa regulate mineralization processes.
Evidence suggests that between 30 and 50 percent of the nitrogen
present in crop plants was made available by the activity of bacteria-consuming
nematodes. (Ingham, 1996) Research in Denmark
has indicated that nematodes convert about as much energy as earthworms
in certain forest soils. (Dropkin, 1980) Don't
forget, the vast majority of nematodes found in the soil are not
plant parasites.
The food-web's stability is challenged by the yearly turning of
the soil, which reduces the numbers of organisms that displace or
prey on plant-parasitic nematodes, while bringing more nematodes
to the surface from deeper soil. If the same host crop is planted
year after year, plant-parasitic nematodes may increase to damaging
levels. Root-feeding nematodes are very opportunistic, and are among
the first organisms to invade after a disturbance.
(Dropkin,
1980; Ingham, 1996)
Keeping these facts in mind, it is important to actively manage
soil biology using minimum-tillage practices, compost, animal manures,
green manures, cover crops, and crop rotations. These practices
help promote the growth of beneficial organisms while suppressing
plant parasites. Certain organisms that are associated with well-managed
crop soils—e.g., Rhizobacteria and mycorrhizae—may induce
systemic host resistance to nematodes and to some foliar diseases.
(Barker and Koenning, 1998) For further information
see the ATTRA publications Sustainable
Management of Soil-borne Plant Diseases and Conservation
Tillage.
Soil amendments
for nematode control
Some sources of organic matter
known to be nematode-suppressive include oilcakes, sawdust,
sugarcane bagasse, bone meal, horn meal, compost, and certain
green manures. |
Most nematode species can be significantly reduced by tilling in
chitinous materials such as crushed shells of crustaceans (shrimp,
crab, etc.). This is effective because several species of fungi
that "feed" on chitin also attack chitin-containing nematode
eggs and nematodes. Increasing the amount of chitin in the soil
will also increase the population of these fungi. A shrimp-shell-based
fertilizer called Eco Poly 21™ Micro shrimp fertilizer is
available from Peaceful Valley Farm Supply. At 2002 catalog prices,
it would cost between $87 and $216 to treat an acre with this product
(the suggested application rate is 20 to 50 lbs. per acre). Clandosan™,
a nematicide made of crab shells and agricultural-grade urea, can
be used as a pre-plant treatment (it should not be used on plants
because the amount of urea in it can "burn" or kill them).
(Fiola and Lalancettle, 2000)
Back to top
Crop Rotations and Cover Crops
Crop rotation to a non-host crop is often adequate by itself to
prevent nematode populations from reaching economically damaging
levels. However, it is necessary to positively identify the species
of nematode in order to know what plants are its host(s) and non-hosts.
A general rule of thumb is to rotate to crops that are not related
to each other. For example, pumpkin and cucumbers are closely related
and rotating between them would probably not be effective to keep
nematode populations down. A pumpkin/bell pepper rotation might
be more effective. Even better is a rotation from a broadleaf to
a grass. Asparagus, corn, onions, garlic, small grains, Cahaba white
vetch, and Nova vetch are good rotation crops for reducing root-knot
nematode populations. Crotalaria, velvet bean, and grasses like
rye are usually resistant to root-knot nematodes. (Wang,
et al., 2004; Yepsen, 1984; Peet,
1996) Rotations like these will not only help prevent nematode
populations from reaching economic levels, they will also help control
plant diseases and insect pests.
Allelochemicals are plant-produced compounds (other than food compounds)
that affect the behavior of other organisms in the plant's environment.
For example, sudangrass (and sorghum) contain a chemical, dhurrin,
that degrades into hydrogen cyanide, which is a powerful nematicide.
(Luna, 1993; Forge, et al, 1995;
Wider and Abawi, 2000) Some cover crops have
exhibited nematode-suppressive characteristics equivalent to aldicarb,
a synthetic chemical pesticide. (Grossman, 1990)
Farmers in Alabama have added sesame into rotation with cotton,
peanuts, and soybeans. Nematode levels are reduced and yields significantly
increased among those crops in fields previously planted in sesame.
Sesame yields averaged 1500 lbs per acre, well above the world average
of 500 to 600 lbs per acre. (Anon, 1997a)
Research shows that sesame may be an effective rotation crop to
control peanut root knot nematode (Meloidogyne arenaria)
and southern root knot nematode (Meloidogyne incognita).
Sesame rotation is not effective, however, for the Javanese root
knot nematode (Meloidogyne javanica).
(Starr
and Black, 1995) Commercial nematode control products derived
from sesame include Dragonfire™ (oil), Ontrol™ (seed
meal)—both manufactured by Poulenger USA—and Nemastop™
(ground up sesame plant) from Natural Organic Products.
In South Texas, soybean varieties were shown as possible alternatives
to grain sorghum in cotton cropping sequences. Eighteen soybean
varieties of maturity group 5, 6, 7, and 8 were tested in Rotylenchulus
reniformis-infested soil, either nonfumigated or fumigated
with 1,3- dichloropropene. Reproductive rates of R. reniformis
were compared in the first year. Both experiments were planted with
cotton in the second year to measure the rotational effects of soybean
on cotton yield compared with grain sorghum and fallow. The high-yielding
soybean cultivars with potential to suppress reniform nematode were
“HY574,” “Padre,” “DP7375RR,”
and “NK83-30.” (Westphal and Scott,
2005)
A 2000-2002 Maryland study evaluated crop rotations and other cultural
practices to manage southern root-knot nematodes and lesion nematodes.
Researchers grew nematode-susceptible potatoes and cucumbers, and
compared the effect of several summer rotations on nematode problems.
A summer rotation of sorghum sudangrass (Sorghum bicolor x Sorghum
arundinaceum var. sudanense) reduced the root knot nematode
population as effectively as the control treatment (soyabean cultivar
with no known root-knot resistance and one nematicide application).
Poultry litter/tillage (Year 1) and fallow (Year 2) were equally
effective in managing the lesion nematode population. To maintain
the effect, the rotations had to be included annually. Either summer
or early-autumn sampling dates were more effective than midspring
to identify threshold levels of the pests. (Kratochvil
et al., 2004)
Nematodes
and pH
Cyst nematodes do not hatch well in very acid soils (pH 4)
or alkaline soils (pH 8). They do best in soil with a near-neutral
pH of 6. This can be used to some advantage. For example,
potatoes may be safest from nematode damage in an acid soil,
while cabbage and beets can be planted in alkaline soil. But
most plants do best at the pH that favors nematodes. (Yepsen,
1984) |
![Mustard](https://webarchive.library.unt.edu/eot2008/20090117014353im_/http://attra.org/images/nematode/mustard.jpg)
Mustard. Photo courtesy of USDA
ARS. |
Researchers have observed that brassicas (e.g., rapeseed, mustard)
have a nematode-supressive effect that benefits the following crop
in a rotation. This “mustard effect” is attributed to
glucosinolate compounds contained in brassica residues. Toxicity
is attributed to enzymatically induced breakdown products of glucosinolates,
a large class of compounds known as isothiocyanates and nitriles
that suppress nematodes by interfering with their reproductive cycle.
These glucosinolate breakdown products are similar to the chemical
fumigant VAPAM® (metam sodium), which degrades in soil to methyl
isothiocyanate. Glucosinolate compounds are also responsible for
the pungent flavors and odors of mustards and horseradish.
(Brown
and Morra, 1997) Jack Brown, PhD, a plant breeder specializing
in brassicas at the University of Idaho, has released two biofumigant
varieties, “Humus” rapeseed and “IdaGold”
mustard, each containing elevated levels of glucosinolates. Cover crop seed for mustards, rapeseed, and oilseed radish are available from a variety of sources. Several Extension Service bulletins describe the use of brassica cover crops in greater detail.
Allelopathic
cover crops
Some plants produce allelochemicals that function as nematode-antagonistic
compounds, such as polythienyls, glucosinolates, cyanogenic
glycosides, alkaloids, lipids, terpenoids, steroids, triterpenoids,
and phenolics, among compounds from these plants—e.g.,
castor bean, chrysanthemum, partridge pea, velvetbean, sesame,
jackbean, crotalaria, sorghum-sudan, indigo, tephrosia—are
exuded during the growing season or released during green
manure decomposition. Sunn hemp, a tropical legume, and sorghum-sudan,
a prolific grass plant grown for its biomass, are popular
nematode-suppressive cover crops that produce the allelochemicals
known as monocrotaline and dhurrin, respectively. (Chitwood,
2002; Grossman, 1988; Hackney
and Dickerson, 1975; Quarles, 1993;
Wang et al., 2002; Williams
and Williams, 1990a, 1990b, 1993) |
Here are some examples of how brassica crops are being used to
manage nematodes:
-
Oil radish as a green manure has dramatically reduced stubby
root nematode (Trichodorus) and root lesion nematode
(Pratylenchus) in Idaho potato fields.
(Anon,
2001)
-
Oil radish is used as a "trap crop" for the sugarbeet
cyst nematode, its roots exude chemicals that stimulate hatching
of nematode eggs. The larvae that emerge are unable to develop
into reproductive females—reducing the population densities
for the following crop. (Hafez, 1998)
-
Rape or mustard plantings in rotation with strawberries have
checked the increase of some nematodes. (Brown
and Morra, 1997)
-
Rapeseed and sudangrass green manures grown prior to potatoes
at Prosser, Washington, provided between 72 and 86 percent control
of the root-knot nematode in that crop. (Stark,
1995) In the same study, on-farm research in western Idaho
showed that rapeseed green manures decreased soil populations
of rootlesion nematodes to a greater extent than did sudangrass
green manures. Fall sudangrass should be plowed down after it
is stressed (i.e., the first frost, stopping irrigation). Winter
rapeseed and canola should be incorporated in very early spring.
(Cardwell and Ingham, 1996)
Rotation
The best rotation to control the Columbia root-knot nematode
in potatoes involves planting a summer non-host crop, followed
by a winter cover crop (rapeseed) incorporated as a green
manure. Non-host crops include supersweet corn (Crisp and
Sweet 710/711), pepper, lima bean, turnip, cowpea, muskmelon,
watermelon, squash, rapeseed, canola, mustard, and sudangrass
(Trudan 8, Sordan 79). (Ingham, 1990)
For root lesion nematode control on potatoes, researchers
found that forage pearl millet (Canadian Hybrid 101) and marigold
(Crakerjack) as rotation crops with potatoes resulted in fewer
root lesion nematodes and increased potato yields than rotation
with rye. (Ball-Coelho et al., 2003) |
Marigold (Tagetes species) is one of the most highly studied
crops for its ability to suppress nematodes with antagonistic phytochemical
exudates, namely the polythienyls. Research also demonstrates that
rhizobacteria living in association with marigold roots are suppressive
to root lesion and other nematodes. These multiple effect nematode-control properties can benefit other crops when marigolds are grown
in rotation.
(Sturz and Kimpinski, 2004) African
marigold (Tagetes erecta) and French marigold (Tagetes
patula) are popular ornamentals in the horticultural trade
with several nematode-suppressive varieties each. (Dover
et al., 2003) Muster John Henry or little marigold (Tagetes
minuta) is sold as the “Nematicidal” marigold,
but it controls a relatively limited range of nematode species and
readers should note that it is classified as a noxious weed in California.
Tomatoes planted two weeks after African marigolds (Tagetes
erecta) were disked into the soil showed a 99 percent reduction
in root-lesion nematode damage compared to a tomato-tomato or fallow-tomato
rotation. (Grossman, 1999) The French marigold
cultivar “Single Gold” provided 99 percent control of
nematodes in Dutch tests. (Ogden, 1997) Burpee
Seed Co. has carried a French marigold variety known as “Nema-gone.”
The most effective marigold cultivars are those that germinate quickly,
grow vigorously, and have deep root penetration. Cover crops exhibit
tremendous variability in their susceptibility to or suppression
of the four major types of plant-parasitic nematodes. For example,
cover crops that suppress root-knot nematodes may be susceptible
to sting nematodes. It is important to identify the nematode species
in the field—and know what their plant hosts and antagonists
are—before planning a cover-cropping strategy.
Allies from
the Prairie
In Ontario, certain prairie species have been found to provide
excellent nematode control when used as a cover crop, including
blackeyed susan, gaillardia, and switchgrass, according to
Marvin Pritts, PhD, of Cornell University. (Anon,
1996) Another North American native known as "Indian
Blanket” or “Blanket Flower” (Gaillardia
pulchella) was effective in controlling southern root knot
nematode (Meloidogyne incognita) on sweet potato. Tissue extracts
of Indian Blanket were lethal to various plant-parasitic nematodes
but were innocuous to free-living nematodes. Root exudates
of Indian Blanket were lethal to mobile juvenals of M. incognita and were inhibitory to the hatch of eggs at concentrations
of 250 parts per million or higher. Indian Blanket could be
used to manage southern root knot nematode as a rotation crop,
a co-planted crop, or a soil amendment to control root-knot
nematode. (Tsay et al., 2004) |
Fields left fallow but kept weed-free for one to two years usually
have an 80 to 90 percent per-year reduction in root-knot populations.
(Sasser, 1990) This host-free period can be
achieved in one season, rather than two years, by disking every
ten days all summer. While such disking offers the added advantage
to reduce perennial weeds, it is expensive in terms of fuel costs,
possible erosion, and loss of organic matter through oxidation.
(Ingham, 1996)
Back to top
Botanical Nematicides
Certain plants are able to kill or repel pests, disrupt their lifecycle,
or discourage them from feeding. Some of these—marigolds,
sesame, castorbean, and various brassicas—have been discussed
previously as nematode-suppressive cover crops. In this section
we will look at plants whose extracts or essential oils can be applied
as nematicides.
Botanical Nematicides |
Producers or Distributors |
Beneficial Nematodes
Steinernema species |
|
Biocontrol Bacteria
Deny, Blue Circle (Burkholderia cepacia)
Activate (Bacillus chitinosporus) |
|
Biocontrol Fungi
DiTera (Myrothecium verrucaria)
MeloCon, BioAct (Paecilomyces lilacinus) |
|
Chitin
ClandoSan
Shrimp Shell meal |
|
Botanical Nematacide
Nemastop (Organic extracts w/Fatty acids)
Dragonfire (sesame oil)
Ontrol (sesame meal)
Nemagard (ground up sesame plant)
Neem cake
Armorex (sesame oil, garlic, rosemary
eugenol, white pepper) |
|
Adapted from Quarles,
William. 2005. Directory of least toxic pest control products.
The IPM Practitioner, Vol. 26, No. 11/12. p. 17. |
Nitron Industries Inc.
P.O. Box 1447
Fayetteville, AR 72702
800-835-0123
Johnny’s Seed
184 Foss Hill Rd.
Albion, ME 04910
207-437-4301
BioLogic
P.O. Box 177
Willow Hill, PA 17271
717-349-2789
Hydro-Gardens, Inc.
P.O. Box 25845
Colorado Springs, CO 80936
800-634-6362
Stine Microbial Products
2225 Laredo Trail
Adel, IA 50003
515-677-2605
Rincon Vitova Inc.
P.O. Box 1555
Ventura, CA 93002
800-248-2847
Valent USA
P.O. Box 8025
Walnut Creek, CA 94596
800-624-6094
Peaceful Valley Farm Supply
P.O. Box 2209
Grass Valley, CA 95945
888-784-1722
Prophyta
Inselstrasse 12
D 23999 Malchow
Poel, Germany
Igene (PMG) Biotechology
9110 Red Branch Rd.
Columbia, MD 21045
410-997-2599
ARBICO
P.O. Box 8910
Tucson AZ 85738
800-827-2847
Monsoon Neem Products
P.O. Box 4558
Petaluma, CA 94955
707-778-6137
Soils Technology Corp
2103 185th St.
Fairfield, IA 52556
800-221-7645
Poulenger USA
3705 Century Blvd. #3
Lakeland, FL 33811
866-709-8102
Natural Organic Products
7105 Rossiter St.
Mt. Dora, FL 32757
325-383-8252
For hundreds of years, Indian farmers have used the neem tree
(Azadirachta indica) for its pesticidal, antifungal, and
antifeedant properties. In research trials, potting soil amended
with plant parts from the neem tree and Chinaberry tree (Melia
azadirach) inhibited root-knot nematode development on tomatoes.
(Siddiqui and Alam, 2001) However, no neem
products are currently registered in the U.S. for use against nematodes.
Margosan-O™, Azatin™, Superneem 4.5™, Neemix™,
and Triact™ are neem products registered as insecticides,
fungicides, and miticides. Neem cake, made from crushed neem seeds,
provides nitrogen in a slow-release form in addition to protecting
plants against parasitic nematodes. It is sold as a fertilizer in
the U.S. through many farm and garden supply stores. Neem cake can
be mixed with fertilizers such as composted manures, seaweed, and
kelp. Recommended rates are 180 to 360 lbs. per acre or 2 lbs. per
100 to 160 sq. ft. (Anon, 1998) Neem cake
is toxic to plant-parasitic nematodes and is not as detrimental to
beneficial free-living soil organisms.
(Riga and
Lazarovits, 2001) In greenhouse trials, 1 percent neem cake
(mass/mass soil) caused a 67 to 90 percent reduction in the number
of lesion (Pratylenchus penetrans) and root-knot (Meloidogyne
hapla) nematodes in tomato roots grown in three different soils.
In the field, 1 percent neem cake (mass/mass soil) reduced the number
of lesion nematodes by 23 percent in corn roots and 70 percent in
soil around roots. (Abbasi et al., 2005)
Essential oils from various plants have shown promise as potential
sources for new nematicides. Most of these plants are aromatic and
culinary herbs that contain the nematicidal compounds carvacrol
and thymol. At very low concentrations (1000 micrograms per liter,
or .001 gm per liter, or .0038 gm per gal, or 0.38 gm per 100 gal)
several oils immobilized juvenile root-knot nematodes and some also
reduced hatching of eggs. The essential oils from the following
plants ranked the highest for nematicidal activity: caraway, fennel,
applemint, spearmint, Syrian oregano, and oregano. (Oka
et al., 2000) The toxicity of the essential oil from wormwood
or Sweet Annie (Artemisia annua) leaves was evaluated in
vitro against second-stage juveniles (J2) of the root knot nematode
(Meloidogyne incognita) and pre-adults of the reniform
nematode (Rotylenchulus reniformis). Complete mortality
(100 percent) of both nematodes was found in 500 and 250 parts per
million concentrations of the essential oil and gradually decreased
with lower concentrations. (Shakil et al., 2004)
Back to top
Biocontrols
Several microbial pathogens have been developed into commercial
formulations against nematodes. These include the bacteria Pasteuria
penetrans (formerly known as Bacillus penetrans), Bacillus
thuringiensis (available in insecticidal formulations) and
Burkholderia cepacia. Nematicidal fungi include Trichoderma
harzianum, Hirsutella rhossiliensis, Hirsutella
minnesotensis, Verticillium chlamydosporum, Arthrobotrys
dactyloides, and Paceilomyces lilacinus. Another fungus,
Myrothecium verrucaria, found to be highly effective in
the control of nematodes (Anon, 1997b),
is available in a commercial formulation, DiTera™, from Abbott
Laboratories. Circle One, Inc. offers a combination of several mycorrhizal
fungal spores in a nematode-control product called Prosper-Nema™.
Stein Microbial products offers the bacterium Burkholderia cepacia
in a product called Deny™ and Blue Circle™. Rincon-Vitova
offers a product called Activate™ whose active ingredient
is the bacterium Bacillus chitinosporus. (Quarles,
2005)
The insect-attacking nematode Steinernema riobravis can
provide root-knot nematode control comparable to that achieved with
chemical nematicides. (Grossman, 1997) Although
the exact mechanisms of control are not known, researchers hypothesize
that an allelochemical is involved (perhaps manufactured by symbiotic
bacteria that live within S. riobravis) that repels plantparasitic
nematodes. Recent research measured the effect of beneficial nematodes
on root-knot nematodes (Meloidogyne species) infecting
tomatoes and peanuts. In the laboratory, peanut seedlings treated
with the beneficial nematodes Steinernema feltiae and Steinernema
riobrave showed resistance to pest nematodes. In the greenhouse,
scientists tested application levels and timing on peanut and tomato
plants. On peanuts, pre- and post-infestation applications of S. feltiae suppressed M. hapla penetration but not
egg production. Only pre-infestation applications of S. riobrave
suppressed M. hapla. The tomatoes were infested with Meloidogyne
incognita eggs and treated with Steinernema glaseri
or Heterorhabditis megidis applied at the same times as
the tomato treatments. The low rate of S. glaseri suppressed M. incognita penetration into tomato roots and the high
rate of S. glaseri reduced egg production. (Pérez
and Lewis, 2004) Those interested in using this biocontrol will
need to experiment with application rates and techniques to develop
methods best suited to their operations. Additional information
on insect parasitic nematodes can be found on an Ohio State University Web site.
A soil-dwelling predatory mite, Hypoaspis miles, preys
primarily on fungus-gnat larvae but will also attack spring tails,
thrips, and nematodes. (Anon, No date) These
mites are available commercially for the control of fungus gnats
in greenhouse production of tomatoes, peppers, cucumbers, flowers,
and foliage plants. The mites are applied to the planting media.
It is clear that a wide range of organisms feed on, kill, or repel
nematodes. These organisms are most effective, and are found most
commonly, in healthy, well-managed soils.
Back to top
Plant Resistance
Generally speaking, a resistant cultivar is more effective against
sedentary endoparasitic species such as root-knot and cyst nematodes
than against “grazing” ectoparasitic species. Root-knot
and cyst nematodes spend most of their lifecycle within the root,
relying on specialized cells for feeding. Upon entering the roots
of resistant cultivars, these nematodes become trapped as the feeding
cells necessary for their survival fail to develop.
Many crop cultivars—tomatoes and soybeans in particular—have been specifically bred for nematode resistance. The “N”
designation on tomato seed packages (usually as part of “VFN”)
refers to nematode resistance. A few cultivars of potatoes are resistant
to the golden nematode, which is a pest only in a small area of
the northeastern U.S. Although most cultivars of potatoes are susceptible
to infection by nematodes, some varieties tolerate infection better
than others. For example, population densities of root-lesion nematodes
(Pratylenchus penetrans) that would affect yield in “Superior”
are tolerated with little effect by “Russet Burbank.”
(MacGuidwin, 1993)
Richard L. Fery, PhD, a geneticist at the USDA’s Agricultural
Re search Service in Charleston, South Carolina, developed two nematode-resistant
varieties of bell pepper, “Charleston Belle” and “Carolina
Wonder,” available from commercial seed companies. (Sanchez,
1997) Charleston Belle and its susceptible parent, “Keystone
Resistant Giant,” were compared as spring crops to manage
the southern root-knot nematode (Meloidogyne incognita)
in autumn-cropped cucumber and squash. Cucumber grown in plots following
Charleston Belle had lower root gall severity indices than in crops
following Keystone Resistant Giant. Cucumber yields were 87 percent
heavier and numbers of fruit 85 percent higher in plots previously
planted to Charleston Belle than to Keystone Resistant Giant. Squash
grown in plots following Charleston Belle had lower root gall severity
indices than those following Keystone Resistant Giant. Squash yields
were 55 percent heavier and numbers of fruit 50 percent higher in
plots previously planted to Charleston Belle than to Keystone Resistant
Giant.
These results demonstrate that root-knot nematode-resistant bell
pepper cultivars such as Charleston Belle are useful tools to manage
M. incognita in double-cropping systems with cucurbit crops.
(Thies et al., 2004) Nematode-tolerant or resistant
cultivars of snap beans (“Harvester” and “Alabama
#1”), lima beans (“Nemagreen”), and sweet potatoes
(“Carolina Bunch,” “Excel,” “Jewel,”
“Regal,” “Nugget,” and “Carver”)
also exist and may be used in a similar strategy to reduce nematode
levels for crops that follow.
The choice of nematode-resistant rootstock for perennial fruit
production is important to ensure protection of trees and vines
against these unseen pests. Consult with a local farm advisor to
confirm that the rootstock you choose is appropriate for the area.
Table 1. Nematode-resistant
rootstock for perennial fruit. |
Fruit |
Rootstock |
Apple |
|
Pears |
|
Asian Pear |
|
Citrus |
|
Grapes |
|
Peach & Nectarines |
Nemaguard, Nemared, Citation, Hansen 536
( Anon, 2004) |
Plums |
|
Apricots & Almonds |
Nemaguard, Nemared, Myrobalan, Marianna
2624 ( Anon, 2004) |
Cherries |
|
Breeding for nematode resistance in most crops is complicated by
the ability of the nematode species (primarily cyst nematodes and
root-knot nematodes) to develop races or biotypes that overcome
the genetic resistance factors in the crop. In order to maintain
resistant crop cultivars on farms, researchers suggest that susceptible
and resistant cultivars be planted in rotation. When a nematode-resistant
cultivar is planted, nematode populations generally decrease, but
over the course of the growing season the few nematodes in a particular
population capable of overcoming this resistance begin to increase.
If in the following season the farmer plants a susceptible cultivar,
the overall nematode numbers will still be low enough to avoid significant
yield reduction, but more importantly, the selective pressure favoring
the increase of the “counter-resistant” bio types is
removed. As long as the farmer continues to alternate susceptible
and resistant cultivars (and, better yet, incorporate non-host crops
into the rotation), the nematodes can be kept at non-damaging levels.
Transgenic crop resistance to nematodes and other pests is being
developed for numerous crops by various companies worldwide. The
use of genetically modified organisms is not accepted in organic
production systems. For more information on this subject see the
ATTRA publication Genetic
Engineering of Crop Plants.
Back to top
Red Plastic Mulch
Springtime field tests at the Agricultural Research Service in
Florence, South Carolina, indicate that red plastic mulch suppresses
root-knot nematode damage in tomatoes. According to Michael Kasperbauer,
one of the researchers, “The red mulch reflects wavelengths
of light that cause the plant to keep more growth above ground,
which results in greater yield. Meanwhile, the plant is putting
less energy into its root system—the very food the nematodes
feed on. So reflection from the red mulch, in effect, tugs food
away from the nematodes that are trying to draw nutrients from the
roots.” The research team planted tomatoes in sterilized soil,
mulched them with red or black plastic, and inoculated the roots
with nematodes. Plants inoculated with 200,000 nematode eggs and
mulched with black plastic produced 8 pounds of tomatoes, while
those mulched with red plastic produced 17 pounds. The red mulch
is available commercially from Ken-Bar, Inc., of Reading, Massachusetts.
Back to top
Solarization
Soil solarization, a method of pasteurization, can effectively
suppress most species of nematode. However, it is consistently effective
only where summers are predictably sunny and warm. The basic technique
entails laying clear plastic over tilled, moistened soil for approximately
six to eight weeks. Solar heat is trapped by the plastic, raising
the soil temperature. The incorporation of poultry litter prior
to solarization, or use of a second layer of clear plastic, can
reduce effective solarization time to 30 days. (Brown
et al., 1989; Stevens et al., 1990) Brassica
residues are also known to increase the solarization effect, in
a process known as biofumigation. The plastic holds in the gaseous
breakdown products of the brassica crop (or food processing wastes),
thereby increasing the fumigation-like effect. (Gamliel
and Stapleton, 1993) Large-scale field experiments using cabbage
residues with solarization obtained results comparable to solarization
combined with methyl bromide. (Chellami et al.,
1997)
Solarization is well documented as an appropriate technology for
control of soilborne pathogens and nematodes, but the economics
of purchasing and applying plastic restrict its use to high-value
crops. Further information on solarization is available from ATTRA
on request.
Soil Steaming
Steaming the soil suppresses nematodes in a manner similar
to solarization. There are prototype steam machines capable
of performing field applications, but steaming is probably
economical only for greenhouse operations or small plantings
of high-value crops. (Grossman and Liebman,
1995) For more information on steaming, contact ATTRA. |
Back to top
Flooding
In certain parts of the country (e.g., Tule Lake in California)
where water is usually available and water pumping equipment and
dikes already exist, and for certain large-scale monocultures (e.g.,
potatoes), flooding is sometimes used as a management tool to control
nematodes. But for most farms, it is probably not an option. Flooding
the soil for seven to nine months kills nematodes by reducing the
amount of oxygen available for respiration and increasing concentrations
of naturally occurring substances—such as organic acids, methane,
and hydrogen sulfide—that are toxic to nematodes. (MacGuidwin,
1993) However, it may take two years to kill all the nematode
egg masses. (Yepsen, 1984) Flooding works best
if both soil and air temperatures remain warm. An alternative to
continuous flooding is several cycles of flooding (minimum two weeks)
alternating with drying and disking. (MacGuidwin,
1993) But note that insufficient or poorly managed flooding
can make matters worse, as water is also an excellent means of nematode
dispersal.
Back to top
Summary
Each combination of nematode and host is different. As the nematode
population density reaches a certain level, the host crop yield
suffers. Some hosts support faster population increases than others.
Environmental conditions can also affect the relative dangers posed
by nematode populations. (Dropkin, 1980) As
we begin to develop a better understanding of the complex ecologies
of soils and agricultural ecosystems, more strategies for cultural
and biological control of nematodes will be developed. The trick
will be fine-tuning these general strategies to the unique ecology,
equipment, and financial situation of each farm.
Back to top
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Back to top
Further Resources
Agbenin, N. O., A. M. Emechebe, P. S. Marley. 2004. Evaluation
of neem seed powder for Fusarium wilt and Meloidogyne control on
tomato. Archives of Phytopathology and Plant Protection, Vol. 37,
No. 4. pp. 319-326
Budh Ram, and B. L. Baheti. 2003. Management of reniform nematode,
Rotylenchulus reniformis on cowpea through seed treatment with botanicals.
Current Nematology, Vol. 14, No1/2. pp. 27-30.
Hagan, A. K, W. S. Gazaway, E. J. Sikora. 1994. Nematode suppressive
crops. Circular ANR-856, Alabama A&M and Auburn Universities.
Accessed April 2005. http://www.aces.edu/pubs/docs/A/ANR-0856/
Kiewnick, S, and R. A Sikora. 2004. Optimizing the efficacy of
Paecilomyces lilacinus (strain 251) for the control of root-knot
nematodes. Communications in Agricultural and Applied Biological
Sciences, 2004, Vol. 69, No. 3, pp. 373-380.
Koenning, S. R., Edmisten, K. L., Barker, K. R., Bowman, D. T.,
and Morrison, D. E. 2003. Effects of rate and time of application
of poultry litter on Hoplolaimus columbus on cotton. Plant Dis.
87:1244-1249.
Morris, J. B. and J. T. Walker. 2002. Non-traditional legumes as
potential soil amendments for nematode control. Journal of Nematology,
2002, Vol. 34, No. 4. pp. 358-361.
Tiyagi, S. A. and Ajaz Shamim. 2004. Biological control of plant
parasitic nematodes associated with chickpea using oil cakes and
Paecilomyces lilacinus. Indian Journal of Nematology, Vol. 34, No1,
pp. 44-48.
Back to top
Web Resources
Nematode
Management in Commercial Vegetable Production (PDF / 3.42MB)
University of Florida
The Phase out of Methyl
Bromide
US Environmental Protection Agency
The
Sting Nematode (PDF / 266KB)
Kansas State University
Nematodes:
Management Guidelines for Kansas Crops
Kansas State University
Root
and Soil Analyses for Nematodes in Corn
University of Nebraska-Lincoln
How
to Take a Soil Sample for Corn Nematode Assay
University of Nebraska-Lincoln
Cotton
Disease and Nematode Management
University of Missouri
Detecting
and Avoiding Nematode Problems (PDF / 1.44MB)
Michigan State University
Nematode
Management, Chapter 8 (PDF / 148KB)
Vegetable Crop Pest Management, Bulletin E-2160
Michigan State University
Scouting
for Corn Nematodes (PDF / 347KB)
Iowa State University
The Soy
bean Cyst Nematode Management Guide
North Central Soybean Research Program
Marigolds
as Cover Crops
Department of Entomology & Nematology, University of Florida
Nematode
Suppressive Cover Crops (PDF / 48.3KB)
Alabama Cooperative Extension
Nemaplex: The
Nematode-Plant Expert Information System
A Virtual Encyclopedia on Soil and Plant Nematodes
Department of Nematology, University of California
- Biological Control of Nematodes
- Cultural Manipulations for Nematode Management
- Host Plant Resistance (HPR) Against Nematodes
- Chemical Ecology of Nematodes
Plant Nematode
Problems and their Control in the Near East Region
FAO Plant Production and Protection Paper 144
Soil
Organic Matter, Green Manures and Cover Crops for Nematode Management
(PDF / 46.7KB)
University of Florida
Management of Nematodes
with Cowpea Cover Crop
University of Florida
Natural
Enemies of Nematodes
The Biological Control of Nematodes - Nemabc
The
Ectoparsitic Nematodes of Illinois
University of Illinois at Urbana-Champaign
Lesion
Nematodes
University of Illinois at Urbana-Champaign
The
Soybean Cyst Nematode Problem
University of Illinois at Urbana-Champaign
Insect Parasitic
Nematodes
Ohio State University
Cover
Crops: Marigold
Ontario Ministry of Agriculture, Food and Rural Affairs
Oilseed
Radish: A New Cover Crop for Michigan (PDF / 348 KB)
Michigan State University
Knowledge
Expectations for Pest Control Advisors: Nematodes
Department of Nematology, University of California
Take
Cover from The Elements: Brassica Cover Crops
American Vegetable Grower, March 2004
Glucosinolate-Containing
Seed Meal as a Soil Amendment to Control Plant Pests, 2000-2002
(PDF / 892KB)
University of Idaho for National Renewable Energy Laboratory
Oregon
Cover Crops: Rapeseed
Oregon State University
Oregon
Cover Crops: Sudangrass and Sorghum-Sudangrass Hybrids
Oregon State University
Columbia
Root-Knot Nematode Control in Potato Using Crop Rotations and Cover
Crops
Oregon State University
Mechanisms
of a Sunn Hemp Cover Crop in Suppressing Nematodes
University of Florida, Department of Entomology and Nematology
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Peaceful Valley
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P.O. Box 2209
Grass Valley, CA 95945
888-784-1722
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Warminster, PA 18077
800-888-1447
Circle One International,
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18744 Titus Rd.
Hudson, FL 34667
877-359-6753
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2611 West Lucas St.
Florence, SC 29501-1242
803-669-5203
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Ken-Bar, Inc.
25 Walkers Brook Dr.
P.O. Box 504
Reading, MA 01867-0704
617-944-0003
800-336-8882
Nematodes: Alternative Controls
By Martin Guerena
NCAT Agriculture Specialist
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