Nematodes or Eelworms (25 X actual size)
GARDENERS FACTSHEET NO. 11
June 1979
CONTROLLING NEMATODES
IN THE VEGETABLE GARDEN
Dr. John M. Gerber
Vegetable Specialist
Nematodes or eelworms are inconspicuous agricultural pests
that may seriously injure plants or at the very least reduce yields.
Often the poor yields will be passed off as “another bad year for
my garden”. However, the damage may well have been caused by
nematodes.
Nematodes are very small worm-like animals, generally
ranging from 1/64 to 1/16 inches long. The plant parasitic
nematodes are divided into two groups according to the method
in which they feed on plants. The ectoparasites live outside the
plant roots and pierce plant tissues with a stylet or spear which
then sucks out plant juices. The endoparasites actually enter the
plant roots to live and feed inside.
Actual damage may go unnoticed if other growing conditions are
optimum. During a good growing season you may simply
experience a 15-30% reduction in yield. When growing conditions
are marginal such as during dry weather or following an invasion
by insect pests, the added stress of nematodes may seriously
injure the plants.
SYMPTOMS PRODUCED BY NEMATODES
The symptoms that are likely to be found on underground
parts of the plant include:
1. Root knots or galls. Galls are abnormal enlargements of
the roots caused by feeding of nematodes.
2. Root lesions. These are sunken, rough, discolored areas
of the roots caused by feeding of nematodes.
3. Excessive branching. Often roots may branch excessively
producing a “hairy” appearance.
4. Injured root tips. Root tips may stop growing and die due
to feeding by nematodes.
Feeding by nematodes will limit root growth and result in
weak plants. Above-ground symptoms include slow growth,
wilting, and a generally unhealthy appearance.
COMMON NEMATODES
The root-knot nematode is probably the most common,
producing large conspicuous galls on tomatoes, cucumbers and
Products and suppliers mentioned by name in this publication are used as examples and in no way imply endorsement or recommendation of these products or
suppliers.
Issued in furtherance of Cooperative Extension work, acts of Congress of May 8 and June 30, 1914 (as amended), in cooperation with the U.S. Department of
Agriculture, D.S. Padda, Director, College of the Virgin Islands Cooperative Extension Service. The College of the Virgin Islands Cooperative Extension
Service is an Equal Opportunity/Affirmative Action organization, providing educational services in the field of agriculture, home economics, rural
development, 4-H youth development and related subjects to all persons regardless of race, color, religion, sex or national origin.
melons. Other vegetables that may be damaged include beans,
carrots, okra, lettuce and sweet potatoes. The root-knot nematode
lives and feeds inside the root, producing galls (endoparasite). It
can seriously reduce root growth, resulting in stunted, weak
plants.
Stubby root nematodes feed on the root tips without
entering the root (ectoparasites). As new roots appear, these too
are attacked, resulting in a small, compact root system composed
of many stubby branch roots. The most susceptible crops include
tomatoes, sweet corn, beans, cabbage and onions.
Many nematodes are found in the Virgin Islands that attack
vegetable plants. It is often difficult to determine which nematode
is doing the damage because the above-ground symptoms are
similar. Since the control measures for all nematodes are the same,
identification of the exact organism is not usually necessary.
CONTROL
Methods of preventing nematode damage include crop
rotation, additions of organic matter, use of resistant varieties,
soil fumigation and use of granular nematocides. While crop
rotation is known to reduce nematode populations in vegetable
fields, it is difficult to rotate in the home garden. Also, since the
common .root-knot nematode is known to attack over 2,000
species, rotation is difficult, if not impossible.
It has been demonstrated that additions of large quantities
of organic matter to soils encourages several nematode parasitic
fungi. These fungi attack many species of nematodes and may
reduce the nematode population considerably. Additions of
organic matter (compost, manure, peat moss, etc.) will also
promote healthier plants which will be better prepared to sustain
some nematode damage.
There are varieties of common vegetables that have some
resistance to nematodes. When you choose varieties, look for the
letter “N” with the variety name, indicating resistance to
nematodes. Three tomato varieties that did well in trials
conducted at the College of the Virgin Islands Agricultural
Experiment Station were Better Boy VFN, N-5 and N-69. Better
Boy VFN is available from several stateside seed companies. N-S
and N-69 can be purchased from:
University of Hawaii
Department of Horticulture
Seed Specialist
Plant Science Building
3190 Maile Way
Honolulu, Hawaii 96822
Although crop rotation, addition of manure and-the use of
resistant varieties will reduce nematode damage, the only sure
methods of nematode prevention are the use of soil fumigation
and granular nematocides. Soil fumigation is an
expensive, time consuming and somewhat dangerous procedure
for the home gardener. However, it is by far the
most effective means of eradicating nematodes for several years.
Granular nematocides are easier to use, but must be applied
annually to be most effective.
Soil fumigation requires the soil to be covered with a plastic
tarpaulin and the fumigation gas to be released under the plastic.
Specific directions depend on the type of fumigant employed. To
be effective the soil should not be hard packed but loose and
crumbly.
Soil fumigants are available from the following distributors:
Ochoa Fertilizer Company, Inc..
G.P.O. Box 3128
San Juan, Puerto Rico 00936
H. V. Grosch Co.
P.O. Box 45
402 Comercio Street
San Juan, Puerto Rico 00902
Agro Servicios, Inc.
G.P.O. Box 393
San Juan, Puerto Rico 00936
Complete instructions should be supplied by the dis-
tributor. Great care must be exercised when using fumigating
gasses. They are highly toxic and can be fatal if inhaled. A gas
mask is recommended for safety.
Granular nematocides can be broadcast over the garden
and worked under the soil with a roto-tiller. These are safer to
use than fumigants, however they are also toxic and
must be handled with care. Actual rates and handling procedure
information is available on the product label. Common
nematocides for vegetables are Furadan, Mocap and Dasanit.
These are available only to gardeners who have taken a pesticide
training course and have received a Pesticide Applicators
Certificate. Check with your Cooperative Extension Service for
such training.
These nematocides must be used according to label
directions. Do not use any product which is not registered for
use on your specific vegetable.