The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
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site maintained by the Florida
Cooperative Extension Service.
Copyright 2005, Board of Trustees, University
Bulletin 311 July, 1937
UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
WILMON NEWELL, Director
CONTROL OF ROOT-KNOT
J. R. WATSON AND C. C. GOFF
Bulletins will be sent free to Florida residents upon application to
AGRICULTURAL EXPERIMENT STATION
EXECUTIVE STAFF BOARD OF CONTROL
John J. Tigert, M.A., LL.D., President of Geo. H. Baldwin, Chairman, Jacksonville
the University Oliver J. Semmes, Pensacola
Wilmon Newell, D.Sc., Director Harry C. Duncan, Tavares
H. Harold Hume, D.Sc., Asst. Dir., Research Thomas W. Bryant, Lakeland
Harold Mowry, M.S.A., Asst. Dir., Adm. R. P. Terry, Miami
J. Francis Cooper, M.S.A., Editor J. T. Diamond, Secretary, Tallahassee
Jefferson Thomas, Assistant Editor
Clyde Beale, A.B.J., Assistant Editor
Ida Keeling Cresap, Librarian BRANCH STATIONS
Ruby Newhall, Administrative Manager
K. H. Graham, Business Manager NORTH FLORIDA STATION, QUINCY
Rachel McQuarrie, Accountant L. 0. Gratz, Ph.D., Plant Pathologist in
MAIN STATION, GAINESVILLE R. R. Kincaid, Ph.D., Asso. Plant Pathologist
J. D. Warner, M.S., Agronomist
AGRONOMY Jesse Reeves, Farm Superintendent
W. E. Stokes, M.S., Agronomist** CITRUS STATION, LAKE ALFRED
W. A. Leukel, Ph.D., Agronomist A. F. Camp, Ph.D., Horticulturist in Charge
G. Ritchey, M.S., Associate* John H. Jefferies, Superintendent
Fred H. Hull, Ph.D., Associate W. A. Kuntz, A.M., Assoc. Plant Pathologist
W. A. Carver, Ph.D., Associate Michael Peech, Ph.D., Soils Chemist
John P. Camp, M.S., Assistant B. R. Fudge, Ph.D., Associate Chemist
Roy E. Blasu, M.S., Assistant W. L. Thompson, B.S., Asst. Entomologist
ANIMAL HUSBANDRY Walter Reuther, B.S., Asst. Horticulturist
A. L. Shealy, D.V.M., Animal Husbandman** EVERGLADES STATION, BELLE GLADE
R. B. Becker, Ph.D., Dairy Husbandman
L. M. Thurston, Ph.D., Dairy Technologist J. R. Neller, Ph.D., Biochemist, Acting in
W. M. Neal, Ph.D., Asso. in An. Nutrition Charge
D. A. Sanders, D.V.M., Veterinarian R. N. Lobdell, M.S., Entomologist
M. W. Emmel, D.V.M., Veterinarian F. D. Stevens, B.S., Sugarcane Agronomist
N. R. Mehrhof, M.Agr., Poultry Husbandman Thomas Bregger, Ph.D., Sugarcane Physiologist
W. W. Henley, B.S.A., Asst. An. Husb.* G. R. Townsend, Ph.D., Assistant Plant
W. G. Kirk, Ph.D., Asst. An. Husbandman Pathologist
R. M. Crown, B.S.A., Asst. An. Husbandman R. W. Kidder, B.S., Asst. Animal Husbandman
P. T. Dix Arnold, M.S.A., Assistant Dairy Ross E. Robertson, B.S., Assistant Chemist
Husbandman B. S. Clayton, B.S.C.E., Drainage Engineer*
L. L. Rusoff, M.S., Asst. in An. Nutrition
Jeanette Shaw, M.S., Laboratory Technician SUB-TROPICAL STATION, HOMESTEAD
CHEMISTRY AND SOILS H. S. Wolfe, Ph.D., Horticulturist in Charge
W. M. Fifield, M.S., Asst. Horticulturist
R. V. Allison, Ph.D., Chemist** Geo. D. Ruehle, Ph.D., Associate Plant
R. W. Ruprecht, Ph.D., Chemist Pathologist
R. M. Barnette, Ph.D., Chemist
C. E. Bell, Ph.D., Associate W. CENTRAL FLA. STA., BROOKSVILLE
R. B. French, Ph.D., Associate W. F. Ward, M.S., Asst. An. Husbandman
H. W. Winsor, B.S.A., Assistant in Charge*
C. V. Noble, Ph.D., Agricultural Economist** FIELD STATIONS
Bruce McKinley, A.B., B.S.A., Associate Leesburg
Zach Savage, M.S.A., Associate
A. H. Spurlock, M.S.A., Assistant M. N. Walker, Ph.D., Plant Pathologist in
ECONOMICS, HOME W. B. Shippy, Ph.D., Asso. Plant Pathologist
K. W. Loucks, M.S., Asst. Plant Pathologist
Ouida Davis Abbott, Ph.D., Specialist** J. W. Wilson, Sc.D., Associate Entomologist
C. C. Goff, M.S., Assistant Entomologist
ENTOMOLOGY Plant City
J. R. Watson, A.M., Entomologist** A. N. Brooks, Ph.D., Plant Pathologist
A. N. Tissot, Ph.D., Associate
H. E. Bratley, M.S.A., Assistant Cocoa
HORTICULTURE A. S. Rhoads, Ph.D., Plant Pathologist
G. H. Blackmon, M.S.A., Horticulturist and A. H. Edn, Ph.D sings
Acting Head of Department A. H. Eddins, Ph.D., Plant Pathologist
A. L. Stahl, Ph.D., Associate Monticello
F. S. Jamison, Ph.D., Truck Horticulturist
R. J. Wilmot. M.S.A., Specialist, Fumigation Sam O. Hill, B.S., Asst. Entomologist*
R. D. Dickey, B.S.A., Assistant Horticulturist David G. Kelbertathologist
David G. Kelbert, Asst. Plant Pathologist
PLANT PATHOLOGY Sanford
W. B. Tisdale, Ph.D., Plant Pathologist** E. R. Purvis, Ph.D., Assistant Chemist,
George F. Weber, Ph.D., Plant Pathologist Celery Investigations
R. K. Vorhees, M.S., Assistant
Erdman West, M.S., Mycologist Lakeland
Lillian E. Arnold, M.S., Assistant Botanist E. S. Ellison, Ph.D., Meteorologist*
B. H. Moore, A.B., Asst. Meteorologist*
L. W. Gaddum, Ph.D., Biochemist In cooperation with U.S.D.A.
L. H. Rogers, M.A., Spectroscopic Analyst ** Head of Department.
CONTROL OF ROOT-KNOT
By J. R. WATSON AND C. C. GOFF
Conditions of Growth ..................................... 4 Control by Heat ...................................... 13
Distribution ...... .. ...... ............. ...................... 6 Steam ing .................................................. 14
Methods of Spread ..................................... 6 Lethal Temperatures for Nematodes ...... 14
Host Plants ................................... 7
Control ............................... The Hot W after Method .............................. 15
Starvation Methods ...................................... 9 Control by Chemicals ..................................... 15
On Truck Farms ........................................ 10 Root-Knot on Perennial Plants .................... 19
Drowning ...................................................... 13 Literature Cited .......................................... 21
Root-knot is probably the worst single plant pest found in
the Southern states, especially on sandy soils which have been
in cultivation for a few years. Field and garden crops from
North Carolina to Florida and California are damaged, and
the pest is occasionally found much farther north. In Florida
interest in this pest is increasing, requests from growers for
information on its control trebling in number during the last
Root-knot is a disease of plants characterized by numerous
swellings or galls on the roots. On most truck crops it is a
serious disease, stunting affected plants and as the disease
progresses causing them to turn yellow and finally droop. Seri-
ously affected plants produce little or no fruit, and this is of
inferior quality. Highly susceptible plants die from heavy
These galls on the roots should not be confused with the
nodules found on most legumes and a few other plants. The
latter are attached to the root only loosely and are easily broken
off. The root-knot gall is an integral part of the root, a swell-
ing in the root itself. It cannot be broken off without breaking
the root. Nodules are more or less uniform in shape; root-
knot galls are of many shapes and sizes, depending largely on
the age of the galls as well as the character of the host plant.
On a few fleshy rooted plants, such as pineapples, knots are
The cause of these root-knot galls is a small worm, belonging
to the group called nematodes or round worms. There is an
immense number of species of nematodes, many of which are
4 Florida Agricultural Experiment Station
parasitic, causing diseases in plants and animals. Hookworm
is an example of one which attacks man. The worms seen in
the mother of vinegar are an example of non-parasitic mem-
bers of this group. As the name indicates, they are round in
cross-section. The young of the root-knot nematode (Heterodera
marioni) are long and slender, cork-screw shaped as they work
their way through soil or swim in water. The males retain
this shape throughout life. Young females bore their way into
the roots of plants and there grow in size and change their
shape. When mature they become pear-shaped or almost round
and are about 1/12 inch long. They usually lie just beneath
the surface of the root with the sharper end towards the inside.
As a result of their growth and substances given off, the plants
form galls, somewhat as a tumor or cancer is formed in the
A large number of eggs is laid in a gelatinous mass which
remains attached to the female's body, or as Goodey (10)1 states,
"If the female lies deeply embedded within gall tissue, egg
laying may be impeded, with the result that the eggs are re-
tained within the body from which ultimately larvae escape."
He also states, "When larvae hatch from eggs laid within
galled tissues, some make their way into the surrounding soil
whilst others travel deeper into the root tissues and set up new
centers of infection, usually within the cortex." Several hun-
dred eggs are produced by a female, depending on conditions.
Godfrey and Oliveira (7) working in Hawaii found that often
600 to 800 eggs were laid by one female and in one instance
1,200 eggs were deposited. Other workers in other areas have
found smaller numbers.
CONDITIONS OF GROWTH
As in the case of all organisms, a certain range of temperature,
moisture, air, and their combinations is essential to nematode
Temperature.-In the latitude of Gainesville (Florida) growth
usually is slow between the first of November and the first of
April. During this time many host plants can be raised without
serious nematode injury which would be greatly damaged or
killed during the warmer part of the year.
1Italic figures in parentheses refer to "Literature Cited" in the back
of this bulletin.
Control of Root-Knot in Florida 5
Godfrey (4) found that damage is practically negligible at
55.4 F. and that below 60.8 F. the amount of root-knot is
substantially less than at 4 to 6 degrees higher. Townsend
(13) working at Belle Glade, Florida, states, "The mean mini-
mum temperature at which nematodes develop was found to be
58.60 F., while the range may extend as low as 53.6 F. Above
58.6 F. the rate of development is a function of soil tempera-
ture." He found that at Belle Glade the generation time varied
from 22 to 77 days.
Tyler (14) found that 88.70 F. was the highest temperature
at which the nematode completed its development and that, in
most cases, above 82.4 F. there was a marked retardation of
Although during the coolest weather in Florida nematode
development may be negligible, the temperature is not low
enough to injure the organism. There are records of its sur-
viving temperatures many degrees below 0 F.
Moisture.-Within wide limits moisture seems to play but
little part in nematode development, unless plant growth is re-
tarded. If the soil dries out, nematodes unprotected by living
roots are rather easily killed. Normally, however, only the
uppermost layer of the soil becomes dry enough to kill the
nematode. Four months' submergence is required to kill all
the eggs in the soil.
Brown (2) states, "Soil dry enough to be wind blown does
not carry nematodes. However, pieces of infested roots may
be blown on to new areas."
Sunshine.-Godfrey and Hoshino (6) found that, "The ultra-
violet of the mid-day sun on a clear day in April in Hawaii,
passing through quartz glass covers, killed the different stages
in drops of water at nonlethal temperatures in the following
periods of time: larvae in 22.5 minutes 2.5 minutes; eggs
in egg masses in 4.5 hours 0.5 hours; free eggs in 1.25 hours
0.25 hours. Killing of the nematodes from the combined
effects of sunlight, heat, and drying took place in a remark-
ably short time. Larvae were killed in 1.5 minutes 0.5 min-
utes; eggs in egg masses in 27.5 minutes 2.5 minutes; free
eggs in 17.5 minutes 2.5 minutes."
Hydrogen-ion.-Godfrey and Hagan (5) conducted tests to
determine if the hydrogen-ion concentration of the soil had
any bearing on nematode infestation. Using values between
pH 4.0 and pH 8.5 they found that there was no great difference
6 Florida Agricultural Experiment Station
in amount of infection. There seemed to be a slight reduction
at pH values of 7.6 to 8.0 as compared with lower points.
When conditions for growth, whether adverse temperature,
lack of air, or too much or too little moisture, become unfavor-
able, the eggs develop a very thick, impervious covering, or
become encysted. In this stage they may lie dormant months
or even years, to hatch into active worms when the unfavorable
condition is removed.
Development of the nematode appears to be greatly influenced
by the host plant. Godfrey and Oliveira (7) found that from
the time of inoculation the first egg was developed in cowpeas
in 19 days and in pineapple in 35 days.
Although root-knot nematodes are found in practically all
sandy soils in the Southern states which have been under cul-
tivation for any considerable time, they are more abundant,
of course, in fields where their favorite host plants have been
recently raised. Many weeds are host plants and even where
resistant crops are raised there are usually enough of these
weed hosts to carry the infestation. Nematodes are not so com-
mon or destructive in heavy soils, such as clay, but they are
abundant and destructive in muck soils which are dry enough
to grow ordinary truck crops. Newly cleared land usually is
free of nematodes, unless infested soil or plants have been
dumped on it.
Nematodes are found at practically all depths in the soil to
which the roots of their hosts will penetrate; from a few inches
to as much as four or five feet in the case of light, sandy soils.
METHODS OF SPREAD
The young worms can swim or work their way through moist
soil. Observations in fields around Gainesville indicate that
by their own activities they can spread about a foot per month
through sandy loam soils. Wind does not seem to be a factor
in their spread, as soil dry enough to blow contains no nematodes,
but water washing across infested fields onto lower land will
spread them. Dirt clinging to tools, the shoes of workers, and
the feet of animals is a common method of spreading nematodes
throughout a field. Their introduction into fresh fields is ac-
complished by this same means, but the most common method
Control of Root-Knot in Florida 7
of spread from one field to another is on the roots of plants
which are transplanted. An infested seedbed is sufficient to
spread the disease over an entire field. The very young galls
may be so small as to be scarcely noticeable, with the result
that at transplanting time the plants show little or no root-
knot, although most of them may be infested and will carry
an infestation into the fields.
Plants vary decidedly in their ability to nourish these worms
and in the effects of these worms on their growth. Some plants,
although they nourish the root-knot in growth and have num-
erous galls on their roots, are not seriously damaged. The mul-
berry tree is an example. It flourishes in spite of the infestation.
Such plants are spoken of as tolerant. Others, of which okra
is an example, are quickly killed by comparatively few galls in
their roots. Between these extremes there are plants showing
varying degrees of tolerance and susceptibility.
In other plants the worms are not able to develop, or their
development is poor. Such plants are spoken of as immune or
resistant. The resistance to nematodes, however, may be broken
down by other unfavorable conditions for growth of the host.
For instance, corn, although usually highly resistant on well
drained land, is often rather heavily infested on poorly drained
land. A plant which is weakened by a fungus disease is more
susceptible to root-knot attacks than is an otherwise healthy
plant. The reverse is true also. An infestation of root-knot
often causes a plant to be more susceptible to other diseases of
fungous or bacterial origin. Table 1 lists field and truck crops
commonly grown in Florida in the approximate order of their
susceptibility to root-knot.2 Those at the bottom of the list
are little affected and for all practical purposes can be consid-
ered as immune.
Crops which are absolutely immune to root-knot are few.
Velvet beans and the Crotalarias are examples. We have seen
but one case of an infestation on velvet beans by root-knot,
and one grove where about one-third of the cover crop of Cro-
talaria striata was infested. Generally these plants have been
absolutely immune, showing no root-knots whatever even when
2For relative susceptibility of some annual ornamentals, see Bulletin
8 Florida Agricultural Experiment Station
grown in highly infested soils. Probably in the exceptions noted
above some other factor had lowered the resistance of the plants
or increased the virulence of the nematodes.
TABLE 1.-RELATIVE SUSCEPTIBILITY OF COMMON PLANTS TO ROOT-KNOT,
IN DESCENDING ORDER.
Okra Dasheens Asparagus
Cucumbers Peppers Cabbage
Tomatoes Squash Cauliflower
Eggplant Lettuce Collards
Cantaloupes Beans Irish potatoes
Cotton Cowpeas (most Sesbania
Celery varieties) Mustard
Tobacco Rape Pecans
Peas Beets Japanese persimmon
Peaches Papayas Violets
Figs Carrots Old World grapes
Soybeans (most Pineapples Sugarcane
varieties) Sunflowers Peanuts
Watermelons Strawberries Bananas
Sweet potatoes Corn
A number of weeds are hosts of the root-knot nematode. Al-
though many usually are only lightly infested, often they are
so abundant that the number of nematodes carried over must
be very large. A few plants like Amaranthus spinosus, Eupa-
torium capillifolium, and Linaria canadensis have been found
with comparatively heavy infestations. Below are listed some
wild hosts found by the junior author.
TABLE 2.3-SOME WILD HOSTS OF ROOT-KNOT NEMATODES.
Capnoides halei-wild fumeroot
Cardamine debilis-bag cress
Cyperus (probably strigosus)
Eupatorium capillifolium-dog fennel
Eupatorium serotinum-S. upland boneset
Froelichia floridana-cotton weed
Neobeckia aquatica-lake cress
Pilea serpyllifolia-artillery plant
sIdentifications were made by E. West and L. E. Arnold of the Depart-
ment of Plant Pathology.
Control of Root-Knot in Florida 9
Portulaca pilosa-wild moss-rose
Richardia brasiliensis-Mexican or Spanish clover
Richardia scabra-Mexican or Spanish clover or Florida pussley
Samolus floribundus-water pimpernel
Saururus cernuus-lizard's tail
Sophia pinnata-tansy mustard
Tricholaena rosea-Natal grass
Urena lobata-Caesar's weed
Xanthoxalis sp. (probably corniculata)-wood-sorrels
The most practical procedure for controlling nematodes in
soil under Florida conditions will depend very much upon the
acreage and the type of farming, as well as upon the character
of the soil. In general, control is all that the average farmer
should attempt. Complete eradication from a farm or field is
so expensive and the many chances of a reinfestation are so
great that under most conditions it is hardly considered advis-
able to attempt eradication. Reduction in numbers of the worms
to a point where the desired crop can be grown profitably on the
land is enough to expect in the light of present day knowledge.
Starvation methods consist in raising on the land plants on
which the nematodes cannot live, or at least cannot flourish.
On the whole, these are the most economical methods of control,
Under general farm conditions where the farmer is raising
a variety of general farm crops and has an abundance of land,
simple rotation of crops usually is sufficient in Florida. Of the
crops commonly raised in Florida on general farms tobacco,
Irish potatoes, watermelons, cotton and soybeans, and most
varieties of cowpeas are most likely to be injured by nematodes,
and those which will most thoroughly infest the soil given
over to their culture.
As stated under life history, the worms are never found in
perfectly dry material and therefore are seldom or never intro-
duced on the seeds of plants, but bulbs or tubers may carry
them. Planting infested potatoes very readily infests the soil.
The question is often asked as to whether or not the planting
of cowpeas on the land will cause root-knot. It will not cause
root-knot if there is none in the soil when they are planted,
10 Florida Agricultural Experiment Station
but if there is even a little in the soil they will immensely in-
crease the infestation. The same is true of other susceptible
plants mentioned above. If any of these crops is found infested,
the field should not be planted to the above listed crops the
following year. The land could possibly be planted to sweet
potatoes, corn, oats, rye, peanuts, most grasses, and Iron or
Brabham cowpeas. All of these plants harbor root-knot to
some extent but their growth is not interfered with to any
material degree. In other words, they are rather tolerant and
will make a satisfactory growth, other conditions being favor-
able, even on heavily infested soil. Irish potatoes will also
grow well under nematode conditions but the nematodes will
get in the tubers, causing the surface to be rough and full of
little wart-like protuberances. Such potatoes, in addition to
being unsaleable, will not keep well.
An even better procedure is to plant the infested fields with
such crops as velvet beans, beggarweed, or one of the Crotalarias.
A heavily infested field will require the growing of such crops
for several years before the infestation will be reduced to a
point where tobacco, cotton, soybeans, etc., can be again raised
on the land. This rather long period of rotation is due to the
fact that under ordinary conditions of cultivation there are
always more or less weeds in the fields, and many of these
weeds are hosts of root-knot.
ON TRUCK FARMS
The above methods of crop rotation will also answer for
truck growers who raise some truck in connection with their
other farm crops. When the truck lands become infested the
farmers can shift crops on that acreage to corn, peanuts, etc.,
as mentioned above, but for the more intensively cultivated truck
farms this method takes too long. Often the owners of the
best trucking soils do not want to grow such comparatively low
priced crops on their land for three or four years. For them
methods which do not require such a long time have been de-
veloped at the Florida Agricultural Experiment Station.
The fact that no considerable amounts of truck crops are
grown in Florida during summer gives Florida farmers the
opportunity to reduce the number of worms in the soil to a
point where they can profitably grow susceptible truck crops
the following winter and spring season. The first of these
methods tried was summer fallowing, which consists of keep-
Control of Root-Knot in Florida 11
ing the soil entirely free of all plants during the summer. This
is accomplished by plowing the land after the truck crop is off
in the spring and harrowing it throughout the summer. This
harrowing not only serves the purpose of killing all vegetation
but also prevents a crust from forming on the soil surface. If
a crust forms under the influence of heavy rains in Florida the
soil becomes deficient in oxygen. Under these conditions many
encysted eggs do not hatch, but lie dormant until oxygen is
again allowed to enter the soil. As noted above, proper com-
binations of air, water, and heat are required for the eggs to
hatch. Nature supplies the water and heat in abundance in
the summer time but if the land is not cultivated occasionally
it becomes deficient in air. By supplying oxygen the eggs are
forced to hatch, and there being no host plants on which the
worms can live they starve to death.
There is one great objection to this method of controlling
root-knot-it depletes soil fertility. Hot summer sun and heavy
rains on the land result in not only a serious loss of nitrogen
but also of soil bacteria as well. The soil becomes dead. This
is particularly true of light, sandy soils. Heavy muck soils
will stand more of this treatment, and this method is being
used to a limited extent on this type of soil. However, in case
there is no cover crop the water table should be kept high to
prevent a rapid breaking down of the soil.
To eliminate disastrous results on soil fertility from this
summer fallow, the senior author turned to raising some crop
absolutely immune to root-knot and which therefore would not
harbor the worms (16). The first crop used for this purpose
was velvet beans, usually of the bunch type, the only cover crop
at that time known to be absolutely immune to root-knot which
would grow well and shade the ground in summer. But since
the introduction of Crotalaria into the State and the discovery
that it seems to be as immune to root-knot as velvet beans,
Crotalaria spectabilis has been largely substituted for velvet
To make this method of control an entire success in a single
summer it is essential that no other plants be allowed to grow
on the land. This will call for cultivation every two weeks or
10 days, or after every heavy rain, to keep the soil well aerated
and to eliminate weed growth. For this purpose the cover crop
should be planted in rows. The distance between rows will
depend much upon the character of the soil and the implements
12 Florida Agricultural Experiment Station
used for cultivation. Much labor in the latter part of the sea-
son will be saved if the rows are close enough together to shade
the ground, thus smothering out all weeds and making frequent
cultivation unnecessary. This distance, of course, will depend
on the soil fertility; the richer the soil the farther apart the
plants can be, as the Crotalaria will grow to large size.
When the plants are young one or two hoeings will be neces-
sary, perhaps hand weeding, to eliminate all weeds. The amount
of this labor that is necessary will depend a great deal on the
preparation of the land before the cover crop is planted. The
more thoroughly it is prepared the less trouble there will be
in eliminating weeds, grass, and other host plants.
Crotalaria is preferable to velvet beans for this cover crop
for several reasons. Its upright habit of growth makes cultiva-
tion easy. Even bunch varieties of velvet beans have a tendency
to twine more or less, which interferes with their cultivation.
In the latter part of the season they are liable to be attacked
by the velvet bean caterpillar, which may almost defoliate them.
This not only interferes with their growth but allows sun-
shine to reach the surface of the soil and stimulate weed growth.
Further, velvet beans do not grow so well as Crotalaria specta-
bilis on the lower, damper truck soils of Florida. For most
trucking soils Crotalaria spectabilis is better than Crotalaria
striata because it will grow better on lower lands and the stalks
are not so woody, therefore disintegrating more quickly in the
fall. Furthermore, the senior author has seen some cases of
root-knot on Crotalaria striata. However, on dry, sandy, poor
soils where Crotalaria spectabilis will not grow well, striata
can be used for the control of root-knot.
This cultivating and weeding of the land will, of course, cost
some money, but scarcely any more than will clearing the land
in the fall where a heavy crop of weeds and grass is allowed
to grow during the summer. The Crotalaria should be planted
as soon as the spring truck crop is off the land, and the land
can be prepared for planting. Indeed, in many cases it may
be planted between the rows before the truck crop is removed.
It is evident, of course, that the longer the cover crop remains
on the land the more thorough will be the control.
In all cases where this has been carefully done very good
control of root-knot has been secured in a single summer. So
good, indeed, that the truck crop raised on the soil the following
trucking season was not commercially injured. In some cases
Control of Root-Knot in Florida 13
we have had good results by simply sowing the Crotalaria
Broadcast over the land, allowing it to grow without cultivation
or weeding. However, this will be effective only where the
soil is in such good condition that the Crotalaria will come up
promptly and make such rapid growth as to crowd out all weeds.
Usually cultivation will be necessary. However, it may be
stopped when the Crotalaria gets high enough to shade the
ground between the rows. The dropping of the lower leaves
of the Crotalaria will mulch the soil and prevent the formation
of a crust, which would exclude from the soil sufficient air for
Root-knot nematodes cannot grow in saturated soil. This
suggests another method of controlling them. Indeed, truck lands
which usually are under water, or at least thoroughly water-
soaked, throughout most of the summer usually are compara-
tively free of root-knot. But to control root-knot by this flood-
ing method requires that the land be under water for several
months. A brief flooding even with salt water will not answer
the purpose. We have seen fields flooded with salt water for
as much as 48 hours, which, when drained and planted to truck
crops, were found to be heavily infested with nematodes.
Brown (2) summarizes his work on flooding as follows: "Four
months' submergence of soil containing the nematode killed the
larvae, but the eggs remained viable. Flooding for six months
gave approximately the same results as for four months. Nema-
todes appeared in soil flooded for a year, although apparently
in greatly reduced numbers. After soil had been submerged
for 22.5 months no nematodes were found when plants were
grown in it."
CONTROL BY HEAT
This is by all means the most thorough method of treating
the soil for nematodes. If the temperature can be raised to a
point where a potato placed in the soil is thoroughly cooked all
the nematodes will be killed. On a small scale, such as with
soil intended for potting, heating can be done in an oven. Many
tobacco growers build a very hot fire on top of the ground in-
tended for seedbeds. This is done primarily to control fungus
diseases but it will also control any nematodes that happen to
be in the soil, providing it is hot enough to penetrate to the
depth of a foot or more.
14 Florida Agricultural Experiment Station
Steaming, provided one is equipped for it, on the whole is
the most satisfactory method of treating small acreages, such
as greenhouses and permanent seedbeds. To do economical work
by this method, one must have the soil in his greenhouse or
seedbed underlaid with perforated pipe through which steam
may be forced, and, of course, a boiler for generating the steam.
This is practical only where one has a permanent seedbed which
is used year after year. The perforated pipe should be buried
to a depth of at least one foot. When ready to operate the seed-
bed should be covered with a piece of canvas, building paper,
or other similar material to hold the steam. In the coldest
part of the seedbed, that is the part farthest away from the
steam exits, a potato should be placed. When this potato is
thoroughly cooked one can rest assured that the sterilization
has been complete. The only operating expense necessary in
this treatment will be the service of one man to do the firing
and the cost of the fuel.
LETHAL TEMPERATURES FOR NEMATODES
Hoshino and Godfrey (12) carried out some experimental
work to determine accurately the time required to kill the larvae
and eggs of the root-knot nematode at different degrees of tem-
perature. It is important that the grower have this informa-
tion, especially in treating bulbs, etc., where the temperature
must be carefully kept at a certain level. These data are given
in Table 3.
Various attempts have been made in Florida to utilize port-
able equipment for steaming the soil. Uniformly this has been
found to be expensive. It is difficult to force the steam into
the soil, expensive to move the boiler, and operation is slow.
To force the steam into the soils there was used in the pine-
apple section around Fort Pierce an arrangement built some-
thing like an old-fashioned harrow, but with the teeth hollow
and connected with pipes through which steam could be forced.
Even in the very light soils of that section this was found to
be slow and expensive. Other growers have buried pipes,
through which the steam was passed in trenches. These pipes
were afterwards dug up and moved to a new section. The
expense of digging these trenches and removing the pipe was
Control of Root-Knot in Florida 15
TABLE 3.-LETHAL TEMPERATURES FOR ROOT-KNOT NEMATODES, AND TIME
REQUIRED TO KILL LARVAE AND EGGS.
Larvae _I Eggs
ature Hrs. Min. Sec. Standard Days Hrs. Min. Sec. Standard
C. F. Error Error
40 104 2 7.5 ...... 7.5 min. 4.5 ...... ..... ...... 0.5 days
41 105.8 45.0 ...... 5.0 min. ...... 33.5 ...... ...... 0.5 hours
42 107.6 22.5 ...... 2.5 min. ....... 3.25 ...... ...... 0.25 hrs.
43 109.4 7.5 ...... 0.5 min. ...... ..... 95.0 ...... 5.0 min.
44 111.2 5.0 52.5 7.5 sec. ...... ...... 47.5 ...... 2.5 min.
45 113.0 4.0 52.5 7.5 sec. ...... ...... 14.5 ...... 0.5 min.
46 114.8 3.0 52.5 7.5 sec. ...... ..... 14.5 ...... 0.5 min.
47 116.6 2.0 52.5 7.5 sec. ..-- -..... 10.5 ...... 0.5 min.
48 118.4 .. .... 57.5 2.5 sec. ...... ...... 6.5 ...... 0.5 min.
49 120.2 .. .... 57.5 2.5 sec. ...... ...... 4.25 ...... 0.5 min.
50 122.0 .... 52.5 2.5 sec. ...... ...... 3.5 ...... 0.5 min.
51 123.8 .. .... 6.5 0.5 sec. ...... ...... 1.5 ...... 0.5 min.
52 125.6 .. .... 1.5 0.5 sec. ...... ...... ..... 45.0 15.0 sec.
53 127.4 .. .... 1.0 .............. .. ..... ...... 37.5 7.5 sec.
54 129.2 .. .... ...... .............. ...... ..... ...... 5.0 2.5 sec.
55 131.0 .. .... .... ............ .. .... ...... 5.0 2.5 sec.
56 132.8 .. .... .... .......... ...... ..... ...... 4.5 0.5 sec.
57 134.6 .... ...... .................... .... 2.5 0.5 sec.
58 136.4 .. .. ...... .......... . .. .... ...... 1.0 ..............
THE HOT WATER METHOD
This method is advocated by the United States Bureau of
Plant Industry. The method is to saturate the soil with boiling
water. To make it effective large quantities of hot water must
be used and most of the objections raised against portable steam-
ing systems apply here also. The cost of heating water and
the slowness of application makes the method unsatisfactory
for large scale operations, although it will answer very well
for small seedbeds where one has a ready means of heating
the water and cheap fuel.
CONTROL BY CHEMICALS
Hydrocyanic Acid Gas (HCN).-The following method of
liberating this gas in the soil was first used by Professor Wood-
ward of the California Experiment Station. This usually is
the most satisfactory method of treating seedbeds when cost
and fertilizer effects on the soil are taken into consideration.
It is too expensive for large acreages of field crops, and is
advocated only for seedbeds and other very valuable pieces of
The method consists in saturating the soil with a solution
of sodium cyanide, which is immediately followed by a solution
16 Florida Agricultural Experiment Station
of ammonium sulfate. These two chemicals react upon each
other to give off the HCN gas, which is the killing agent. In
practice the sodium cyanide is dissolved in water. The amount
of water to be used will depend much upon its accessibility.
Where water is handy a rather dilute solution can be used;
where it has to be carried some distance a more concentrated
solution can be used. In any event, immediately after the
application of the solution the bed must be wet down about
as far as nematodes are likely to penetrate in any considerable
numbers. Very light sandy soils should be wet to a depth of
two feet; in heavier soils it is not necessary to penetrate so
Immediately after the application of sodium cyanide an am-
monium sulfate solution is added to the soil. This is poured
over the surface of the soil in the same manner as the sodium
cyanide and again wet down with enough irrigation water to
carry it to the same depth the sodium cyanide solution was
carried. The bed should be covered immediately with some
material to hold the gas-canvas, building paper, or even news-
papers will answer. The cover should be left on for about 24
hours. In order that the solutions may penetrate well the
soil should be in good condition for application, either plowed
The amount of material to use will depend upon the character
of the soil. In medium light sandy soils from 600 to 1,000
pounds of sodium cyanide per acre is necessary to give thor-
ough eradication. In very sandy soils, such as the pineapple
soils of the lower East Coast, doses as small as 300 pounds
have given thorough eradication, whereas in heavier soils
amounts up to 1,200 or 1,500 pounds per acre are required.
The amount of ammonium sulfate should be 50% greater than
that of sodium cyanide. That is to say, if 600 pounds of sodium
cyanide is used per acre 900 pounds of ammonium sulfate should
be used. The ground may be planted within a week or 10 days
after application, or as soon as it has become sufficiently dry.
One great advantage of this method, in addition to the short
time necessary between the treatment and the planting of the
seedbed, is the fact that it leaves the soil immensely rich in
nitrogen. Plants grown on treated soil make very vigorous
growth without the application of any more ammonia. Radishes
have grown as big as turnips, and other crops in proportion,
although a little phosphoric acid and potash should be added
Control of Root-Knot in Florida 17
to make a complete fertilizer. Indeed, many growers feel that
the cost of the materials, although high (the materials them-
selves cost over $100 per acre at present prices), is returned to
them in the fertilizer value and that they get the nematode
eradication for nothing.
Both the sodium cyanide and the HCN gas, of course, are
violent poisons and one working with them must be careful.
In applying the sodium cyanide the worker should always keep
his back to the wind; in other words, keep to the windward side
of the application. One should be very careful not to get the
solution of sodium cyanide on his hands, and should carefully
wash his hands before eating. With these precautions it is
safe to use these materials in the open air, as far as the operator
is concerned. It will, of course, be understood that this treat-
ment should not be used near dwellings which must be occupied
during the treatment, or for a few hours afterwards, especially
where the wind might blow the fumes toward the sleeping
quarters. Neither should it be used too near living plants
which the owner does not want killed. In practice, however,
six feet from the treated plot is sufficient for the protection
of living plants. Of course all plants on the treated plot will
be killed, with the exception of some larger weed seeds, such
as coffee beans, and unusually tough and resistant parts of
plants, such as underground stems of Bermuda grass. In addi-
tion to nematodes all insect life in the soil will be killed, includ-
ing ants, white grubs, mole-crickets, and other pests.
Sodium cyanide is not ordinarily on sale in most communities
in large quantities. Potassium cyanide can be purchased from
most drugstores but it is expensive, more so because one must
use one-third more of it than of sodium cyanide. The substitu-
tion of calcium cyanide is not advised, although this would give
off fumes in moist soils without the addition of any ammonium
sulfate. As good results have not been secured with it as with
the double treatment of sodium cyanide and ammonium sulfate.
To get the same amount of gas it is necessary to use twice as
much of it as of the sodium cyanide, and this extra cost more
than balances the smaller cost of application.
Carbon Bisulfide.-Carbon bisulfide is sometimes used in
eradicating root-knot, particularly in soil in which are growing
plants that the owner wishes to save. The method is to punch
holes about the plant to a depth of a foot or so, the depths
varying somewhat with the character of the soil. The distance
18 Florida Agricultural Experiment Station
between these holes will also vary with the character of the
soil. In light, open soils they can be farther apart than in
close, compact soils. The amount of carbon bisulfide to be put
in each hole also will vary with the character of the soil. The
margin of safety between the dosage which will kill the nema-
todes and that which will kill the roots of the plants usually is
not very great, and in practice the grower will have to experi-
ment a little until he determines the right dosage for the par-
ticular plant in question and the character of his soil. In rea-
sonably sandy soil, such as most soils around dooryards in
Florida, the holes could be about a foot apart; about a table-
spoonful of carbon bisulfide should be injected into each hole,
which should be stopped up immediately. If it is found
that this dose is killing the plant roots it should be dimin-
ished. On the other hand, if it is not effective in killing the
nematodes it will need to be increased. For safety's sake it
is best to treat the soil around one side of the plants first so
that if the roots are killed the plant will still have the roots
on the other side to maintain life. If no harm has been done
the other side of the plant can be treated.
This is not a very satisfactory method of dealing with nema-
todes. The danger of killing the plants is great and the cost
of the materials is high. It can be advised only for plants which
the owner values highly.
Sulfur.-In cooperation with a sulfur company which provided
a fellowship for this purpose, rather extensive experiments were
made in the use of sulfur for treating nematodes during the
year 1923 (17). It was found that dosages of sulfur from 250
to 500 pounds per acre had a marked effect in decreasing the
number of nematodes in the soil, but in no case was complete
control obtained even with dosages as high as a half ton per
acre. Application of sulfur to the soil increases acidity and
with doses of over 500 pounds per acre it was practically im-
possible to raise anything on the treated soils until they had
been sweetened. This method of treating soils doubtless has
some use, in the case of plants which grow well in or at least
tolerate highly acid soils.
Cyanamid.-One method of controlling nematodes in the soil,
first used by this Station (15), is treating the soil with calcium
cyanamide, generally sold under the trade name of "cyanamid".
This material is a violent poison to plants but when placed in
the soil it is quickly converted into urea and other products
Control of Root-Knot in Florida 19
-which are valuable plant foods. This material, then, has the
advantage of the double treatment of sodium cyanide and am-
monium sulfate in that it leaves the soil rich in nitrogenous
plant foods. As a general thing only the application of phos-
phoric acid and potash will be necessary after an application
-of cyanamid. However, we have never been able to secure as
thorough an eradication by the use of cyanamid as with the
-double treatment of sodium cyanide and ammonium sulfate.
This material seems to have very poor power of penetration
into the soil and must be very thoroughly mixed with the soil
if one is to get any control of nematodes. In most soils any-
where from 1,000 pounds to a ton per acre is used, depending
-much upon how thorough an eradication is desired, and the
outlay of money which seems desirable. In practice about half
,of this material is first applied to the top of the soil, which is
"then thoroughly and deeply disked. The soil is then plowed
.deeply, the remaining half of the material applied to the top
,of the plowed land and again thoroughly disked. This results
in mixing it with the soil with sufficient thoroughness. After
the application it is best, if the soil is dry, to irrigate it.
With these heavy doses of cyanamid it is usually necessary
to wait about a month before the land can be planted, although
the time will depend somewhat upon the crop to be raised.
Plants with rather large, heavy seeds, like beans, can be planted
-earlier than those with more delicate seeds, like celery; and
it is possible to transplant such sturdy plants as cabbage some-
This is one of the satisfactory ways of dealing with nematodes
-on considerable acreages where the summer starvation method
-cannot be used, and the double treatment of sodium cyanide
.and ammonium sulfate is too expensive.
ROOT-KNOT ON PERENNIAL PLANTS
The culture of perennial plants in root-knot infested regions
-is complicated by the long life of these plants, subjecting the
"plants to infestation over a long period of time, perhaps for
many years. Of fruit trees, peaches and figs are most seriously
injured by root-knot. Among ornamentals, roses on certain
rootstocks are most seriously affected; although pittosporum,
*cape jessamine, and other ornamentals are also seriously at-
tacked by root-knot.
20 Florida Agricultural Experiment Station
In planting a peach orchard it is very important that it be
placed on newly cleared land, such land usually being free of
nematodes. If there is any doubt about nematodes being on
the land intended for the peach orchard, plant it to cowpeas
or some other susceptible plant the summer before the peach
trees are to be set. For this purpose, of course, one would
want to avoid Iron and Brabham cowpeas, using a susceptible
variety. If no root-knot appears on the cowpeas the land can
be used safely for the peach orchard.
In cultivating the peach orchard be very careful not to intro-
duce root-knot. See to it that all tools which are carried into,
the orchard are free of dirt. Take the same precautions with
horses' hoofs and the shoes of the workmen. Even with the
best of precautions root-knot is liable to be introduced into the
orchard in time. To keep it down as much as possible, avoid
growing in the orchard as a cover crop plants which are sus-
ceptible, like most varieties of cowpeas. Also, to as large an
extent as possible keep down the weed growth. A good cover
crop of velvet beans, or better yet, Crotalaria spectabilis if the
soil is sufficiently moist to grow this crop, will aid much in
keeping down weed growth. Should the trees become infested
in spite of precautions, mulching them heavily will help pro-
long their life. Pile trash, leaves, etc., around them to the
depth of a foot or so if possible. Do not cultivate the ground
but mow or pull up any weeds that come up through the mulch.
A heavy mulch, cutting off the air and some light from the
ground, makes conditions less favorable for the development of
root-knot nematodes. It is, of course, essential that the trees
be carefully examined for root-knot before they are set. All
that show any signs of root-knots should be rejected.
Native plums are resistant to root-knot and peaches grafted
on plum roots get the advantage of the resistance of the root-
stock. However, peaches on plum roots are slower growing
than they are on peach roots, which makes them less satisfactory
for commercial orchards; but in the case of a few peach trees
around the dooryard, which is almost sure to be infested with
root-knot, the plum roots should be used. In the more southern
parts of the state where the growing season is longer this ob-
jection to the use of plum rootstock for peaches is not so serious
as it is farther north.
Figs are very susceptible to root-knot. They are very easily
injured to such an extent as to be unprofitable and short-lived.
Control of Root-Knot in Florida 21
In most parts of Florida with sandy soils figs are successful
only when planted near a building under which their roots can
run. This gives them some freedom from root-knot. On the
stiff clay soils of the northern part of the state root-knot is
not such a serious menace and figs are often successful when
planted out in the open.
Among the ornamentals, roses on certain rootstocks are most
susceptible to root-knot. One buying rose bushes, at least in
Florida, should insist on having them grafted on resistant stocks,
such as the Texas wax rose. Mulching the rose garden, as in
the case of peaches, will also help prolong the life of the in-
fested bush. The same is true of pittosporum, and other orna-
Pecans, pears, and other plants are also attacked by root-
knot to some extent but are not so seriously injured and can
usually be successfully raised in heavily infested soil. Even
in these cases, however, it is best to avoid using as a cover crop
plants which are particularly susceptible to root-knot.
Inquiries are often received concerning citrus trees on in-
fested land. Citrus trees seem to be entirely free from the
attack of the ordinary root-knot nematode, although there is
another nematode which sometimes attacks them and stunts
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Bul. 217. 1911.
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cicola. Phytopath. 23: 1: 41-62. 1933.
22 Florida Agricultural Experiment Station
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knot nematode in relation to root tissues of pineapple and cowpea.
Phytopath. 22: 4: 325-348. 1932.
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root-knot. Fla. Agr. Exp. Sta. Bul. 291. 1936.
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Sci. 36: 2: 83-95. 1933.
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of Heterodera radicicola in relation to time. Phytopath. 23: 3: 260-
13. TOWNSEND, G. R. Root-knot of vegetable crops (Heterodera marioni).
Fla. Agr. Exp. Sta. Ann. Rept. 1936. p. 134.
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by temperature. Hilgardia 7: 10: 391-413. 1933.
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