THE IMPORTANCE OF NEMATODE ANALYSIS
Nematodes are microscopic organisms which are found everywhere in the soil. They are known by such commons names as eelworms, nemas, round worms, threadworms, and worms. Many varieties live freely in the soil and feed on bacteria, fungi, and algae. There are varieties, however, which are parasites and feed virtually on all animals and plant life. They can cause severe damage to crops. All crops are subject to nematode damage. Laboratory analysis is the only sure way to determine the presence of parasitic nematodes.
Nematode populations are subject to seasonal fluctuations. The largest populations generally occur when root growth is most rapid in you particular area for the crop you are growing. Damage in crops is usually very patchy in the areas that it occurs. Populations and nematode activity will decrease as root growth declines and soil temperatures cool below 60°F or rise above 85°F. The optimum soil temperature range for sampling is between 60-80°F. Moisture content of the soil also effect nematode populations and activity. Optimum moisture content should be 40%-80% of field capacity.
GENERAL INFORMATION ON NEMATODES
There are two general types of nematodes. They include ectoparasitic and endoparasitic nematodes. Ectoparasitic nematodes spend their entire life cycle outside of the host. They feed by inserting a stylet or spear into the plant usually at the root system. Some examples of ectoparastic nematodes include: lance, sting, spiral, stunt, stubby root, dagger, and ring. Endoparasitic nematodes spend part of all of their life cycle within the plant. These include: cyst, root knot, lesion, and stem and bulb nematodes. Soil samples take at the root level will usually reflect populations of even endoparasitic nematodes through larval populations, which have not yet entered the plant root system.
SYMPTOMS OF NEMATODE DAMAGE
Symptoms of nematode damage vary greatly with the type of nematode, the age of the plant, and the plant part that is affected. Some classic symptoms associated with nematode damage include:
It is important to note that knots on roots are not always associated with nematode damage. Nitrogen fixing nodules appear much like root knot nematodes on the root. Some plants naturally produce them. It is also important to note that knots need not be present to have a nematode problem. If one or more of the above symptoms are present, testing for nematode damage is indicated.
HOW TO SAMPLE
Proper sampling techniques are important to ensure the best possible data. The following are guidelines to use when taking soil samples for laboratory analysis.
When sampling for a specific type of crop certain guidelines should be followed:
1) TURF AND ORNAMENTALS
Samples
should be taken at a depth of 3”-6” or at the root level. Areas
around the periphery of the damage should be sampled as nematodes move
to thriving areas as the kill one area out. Make a composite sample of
10-20 locations per area sampled. This will provide a more uniform sample,
as nematodes are not distributed evenly throughout the soil.
2) VEGETRABLE AND FIELD CROPS
Sample
should be taken at a depth of 3”-6” or at the root level. Samples
should be taken at pre-plant to ensure vigorous growth of the plant. Young
established plants would be more severely affected by lower nematode populations.
Take about 10-20 plugs per sample to ensure a more uniform sample. Even
if crop rotation is used it is important to identify nematodes that may
affect a new crop.
3) TREES, WOODY ORNAMENTALS, AND VINES
Take sample
far enough from the trunk to include feeder roots along with the soil sample.
Several cores should be taken per area and mixed thoroughly to ensure a more
uniform sample.
NEMATODE SUSCEPTABILITY CHART
CROP AND COMMON DAMAGING NEMATODES
|
|
| Alfalfa | root knot, stem, lesion, cyst, pin, stubby-root |
| Beans | root knot, sting, pin, cyst, stubby-root, stunt |
| Banana | root knot, burrowing, lesion, lance |
| Citrus | citrus, burrowing, lesion |
| Corn | sting, lesion, stubby-root, lance, cyst |
| Cotton | root knot, sting, lance |
| Grapes | root knot, dagger, sting |
| Oats | cyst, anguina, lance |
| Ornamentals | root knot, lesion, spiral reniform |
| Potato | root knot, golden nematode |
| Soybeans | cyst, sting, root knot, stunt |
| Tomato | root knot, dagger, sting |
| Turf | root knot, cyst, lance, sting, spiral, ring, bentgrass, nematode, stunt, sheath |
| Wheat | cyst, anguian, sheath, root knot, pin, stubby-root, stung |
**Please note that these are a few nematodes commonly found to cause damage to these crops. Other nematodes not listed may also be damaging to these crops in above threshold populations.
INTERPRETATION OF DATA
Interpretation of nematode counts is crop dependent. It is therefore very important that crop information be included when the sample is submitted for testing. If this information is not included, you will receive a more general interpretation of the results as to whether treatment is needed or not. It is important to remember that different plants are more susceptible to different types of nematodes.
The data will normally be reported to you on the basis of nematodes per 100cc. of soil. When requested they may also be reported per pint of soil. Root samples are analyzed on a per gram of root basis. The will vary with sample and will be clearly noted as to the per gram weight volume on the report form. Cyst nematodes may be reported as either larva per 100cc. or as eggs per gram of soil.
The report to you will include the following:
Please note that A&L Labs will not make recommendations for the use of a particular nematicide. Further interpretation of the data can be acquired from you state or county extension agency or agricultural services. They will be able to advise as to recommended levels and treatment for you particular crop and area of the county.
CONTROL
If the nematode data you receive suggests that control of a problem is warranted, there are two methods which can be considered to achieve this goal. They are cultural and chemical control methods. A combination of the two can also be used to help eliminate future problems.
A. CULTURAL CONTROL
Cultural controls of nematode problems include: crop rotation, flooding,
weed control, use of resistant varieties, and use of natural enemies. Weed
control is a very important yet easy way to help reduce nematode populations
as nematodes are obligate parasites and will die if there is nothing for
them to feed on.
B. CHEMICAL CONTROL
Chemical control consists for two broad methods. They include fumigants and
non-fumigants. Fumigants are injected into the soil and must be applied
several weeks before a crop is planted. They cannot be used on an already
established crop. Non-fumigants can be used on an already existing crop
and are usually applied as a contact nematicide by mixing them with water.
Nematicides are highly toxic to humans. They are specifically labeled for
use as to the crop type and application rates that they may be applied at.
This varies state to state in many cases. If you decide to use a nematicide
to treat an existing problem, you should contact your extension service,
chemical dealer, or consult you states nematicide applications handbook.