Bulletin 136 April 1917
UNIVERSITY OF FLORIDA
Agricultural Experiment Station
CONTROL OF ROOTKNOT
and other means
J. R. WATSON
Fig. 67.-Root-knot on watermelon. (Original.)
The Station Bulletins will be sent free upon application to the Experiment
BOARD OF CONTROL
P. K. YONGE, Chairman, Pensacola, Fla.
T. B. KING, Arcadia, Fla.
E. L. WARTMANN, Citra, Fla.
W. D. FINLAYSON, Old Town, Fla.
F. E. JENNINGS, Jacksonville, Fla.
J. G. KELLUM, Secretary, Tallahassee, Fla.
1. Old, cultivated land is commonly so heavily infested
with the root-knot nematode as to make the growing of sus-
ceptible crops either impossible or unprofitable.
2. Cyanamid thoroly mixed with soil which is promptly
and thoroly irrigated will so greatly reduce the number of
nematodes present as to make the growing of susceptible crops
3. The amount required will vary from 1000 to 5000
pounds per acre, according to the depth and nature of the in-
4. An interval of from one to several weeks must intervene
between treatment and planting of the land.
5. The cost of the material is such that its use is advocated
only on seed beds and truck lands under intensive cultivation.
6. Cyanamid is, among commercial fertilizers, a cheap
source of ammonia and much, sometimes all, of the first cost
is offset by its value as a fertilizer.
CONTROL OF ROOT-KNOT BY CALCIUM CYANAMIDE
AND OTHER MEANS
BY J. R. WATSON
In November, 1914, the attention of the writer was called
to the poisonous properties of the commercial compound called
cyanamid." It occurred to him that the substance might have
some value if used against pests inhabiting the soil; against
nematodes in particular. Some preliminary tests on radishes
in infested soil were so encouraging that during the spring of
1915 more extensive tests were undertaken, and in July of that
year the matter was taken up as a regular project for investi-
gation. Varying results were secured by a variation of the
quantities of cyanamid applied, the manner of application, and
the soil used. It is not the purpose of this bulletin to go into
the details of these experiments or to tabulate the results. The
aim is to state only the essential results of experiments and to
give those details which are essential to the trucker or gardener
applying the material.
WHAT IS ROOT-KNOT?
Root-knot is a disease of certain plants, characterized by
irregular swellings of the roots. These should not be confused
with the nodules of the nitrogen-fixing bacteria which are
found on most legumes and a few other plants. Such nodules
are usually small, roundish, and all on any given plant are of
about uniform size and appearance, also, they are attached
loosely to the root. The galls of the root-knot nematodes vary
much in size and shape, and are swellings in the root itself
instead of being attached to it. (Fig. 67.) Above the ground
the symptoms of the presence of root-knot are, progressively, a
checking of plant growth, failure to produce normal fruits, a
yellow, sickly appearance and a premature death.
These swellings are caused by minute worms which belong
to the group commonly known as eel-worms or round worms,
and technically called nematodes. They are related to hook
worms, vinegar eels and intestinal worms. The males are
long and slender but the adult females are pear-shaped. Both
are minute, and barely visible to the unaided eye.
After fertilization, the females produce young which are
slender like the mature males. These force their way thru the
148 Bulletin 136, Control of Root-Knot
soil until they find the roots of some attractive food plant.
They bore into the roots to feed on the tissue, and probably
give off a poison which stimulates the plant to produce the
swelling or gall.
The worms travel slowly thru the soil, a foot or two a
month being about the maximum rate. But they may be car-
ried by rain water much more rapidly. They are not commonly
found on newly cleared land, but old, long-cultivated fields in
the sandy soils of Florida usually have a more or less heavy
Cyanamid" is the trade name for a mixture consisting
chiefly of the chemical compound calcium cyanamide (about
45%) ; and hydrated lime (27%), carbon (13%), calcium carbon-
ate (4%), and calcium sulphide (2%). It is a black powder, the
color being due to the carbon. It is a concentrated nitrogenous
fertilizer which analyzes from 15 to 24 percent ammonia. At
present prices, it is the cheapest source of ammonia available
among commercial fertilizers. It contains no potash or acid
phosphate, and therefore is not a complete fertilizer.
The valuable ingredient of cyanamid" is the calcium
cyanamide (CaCN). It is this component that kills the nema-
todes and adds the plant food to the soil. When moderate
doses are mixed with soil, calcium cyanamide quickly disin-
tegrates, probably changing first to urea, then to ammonia,
and then to nitrates. In large doses, however, some of it may
go into a polymeric form called dicyanamide." This disin-
tegrates more slowly and has a very harmful effect on any
crop that is planted too soon after the application of the
cyanamid. This effect is much more pronounced when the soil
is dry. Too large an amount of cyanamid will have the same
effect even if no dicyanamide is formed.
EFFECT OF CYANAMID ON NEMATODES IN RADISH BED
As previously stated, in the first experiments radishes were
used. On November 30, 1914, six small plots, each containing
three, square yards, were treated with cyanamid in quantities
varying from 3 tons to 200 pounds per acre. The cyanamid
was applied as a top dressing, and hoed in. Four similar plots
were used as checks. All plots were on land known to be
heavily infested with nematodes. On December 4, radishes
were planted in all plots but a very poor stand was obtained
and the plots were replanted on December 13. On March 18
Florida Agricultural Experiment Station 149
and April 20 the radishes were gathered. The results of the
test are tabulated below.
Production of Radishes on Plots Treated With Cyanamid, and Effect on
Plot Number 1 2 3 4 5 6 7 8 9 10
acre................ 6000 0 3000 0 1600 800 400 0 200 0
infested ........ 0 33 0 25 24 5 50 8 33
in grams ...... 240 260 475 335I 780 i1015 525 I 230 670 535
This experiment seemed to indicate that: (1) Cyanamid
used at the rate of 1600 pounds or more per acre markedly
reduced the number of nematodes present; and (2) if used too
strong or applied too near the time of planting, it inhibits
growth or entirely kills the young seedlings.
Thinking that the material would penetrate the soil better
if applied in solution, the cyanamid was dissolved in water and
the soil thoroly drenched. Contrary to expectations, this method
did not yield as satisfactory results as that first tried.
EXPERIMENTS WITH COWPEAS
In March, 1915, experiments with cowpeas were undertaken
on plots containing a hundredth of an acre each. The increased
size of the plots was intended to reduce the possibility of un-
reliable results being secured by the migration of worms into
the plots from the sides. To prevent the nematodes being
washed over the plots from the surrounding land, the plots were
ridged so that they were slightly higher in the middle. The
cyanamid was applied as a top dressing and worked into the
soil with a disk harrow. The dose varied from 300 pounds to
a ton per acre.
Cowpeas were planted three weeks after the application of
the cyanamid. They did well until dry weather set in when
all of those plots that had received 600 pounds or more per acre
showed signs of scorching. On those plots that had received
1500 pounds or more per acre the cowpeas were not as good
as on the check plots that had received no cyanamid. On those
150 Bulletin 136, Control of Root-Knot
plots that received 1500 pounds or more per acre, there were,
at first, few knots on roots that did not extend to a depth below
six inches, while on the check plots the roots were knotted to
the very crown. Three months later the nematodes had worked
upward so that on the treated plots also knots began to be
formed nearer the surface. Evidently the material had not
reached a sufficient depth. However, the plots that had received
300 pounds or more per acre showed fewer knots than the
EXPERIMENTS IN A GREENHOUSE
A bench in the Station greenhouse was filled to a depth of
five inches with infested soil and then divided into seven com-
partments of approximately a square yard each. It was pos-
sible here to control conditions better than in the field and espe-
cially to eliminate the migration of nematodes into the treated
TREATING THE PLOTS
Section 1 was treated with cyanamid at the rate of 4 tons
per acre. It was mixed with the dry soil and then wet down.
At that time, March 29, 1915, the importance of a thoro mix-
ing of the material with the soil was not properly appreciated
and the mixing was not as thoro as it should have been.
Section 2 was treated at the rate of 21/2 tons per acre. The
cyanamid was dissolved in water and applied to the soil which
was then thoroly stirred.
Section 3 was treated with the same dose in water as sec-
tion 2, but the soil was not stirred. The water was depended
upon to distribute the cyanamid thruout the bed.
Section 4 was not treated with cyanamid but was left as a
check. It was thoroly wet down.
Section 5 was treated with cyanamid at the rate of 2 tons
per acre, applied as in section 2.
Section 6 was treated at the rate of 1440 pounds per acre.
stirred in dry and then wet down.
Section 7 received the same dose as section 6 but it was
added in solution.
EFFECT OF THE TREATMENT
On April 8 these plots were planted to tomatoes, cabbages,
peppers, and lettuce. On the three plots that had received the
heaviest doses, very few seedlings appeared. On the three
receiving the weaker doses they appeared but soon died. Sec-
tion 6 was almost sterile on May 21, only a few weeds from
Florida Agricultural Experiment Station 151
large seeds showing. On the check, section 4, there was a
vigorous germination of both weed and tomato seeds; the tomato
plants were heavily infested with nematodes and soon died.
Owing to unsatisfactory temperature conditions, the bench
was abandoned during the summer, not even being watered
except by rain which leaked thru the roof.
REPLANTING THE BENCH
On September 11, the bench was again planted to lettuce,
cabbage, celery, carrots, cucumbers and tomatoes. And again,
some of the plants in sections 1, 2 and 3, died. Evidently the
plots being dry during the summer had prevented the deconm-
position of the cyanamid. A few cabbages in one plot only,
section 1, lived. Replantings in that section showed scorching
of the tomatoes as late as January, 1916. These recovered,
however, and made good growth. Up to the present time all
plants grown in this section have been free from nematodes,
except those grown in the small portion where the September
planting of cabbages was not killed. Apparently, by the in-
sufficient mixing, this portion had failed to receive its share of
Section 2 has remained free from nematodes. Evidently a
dose of 21/2 tons per acre on shallow soil will kill all nematodes.
Of the seeds replanted in November, celery was not scorched
at all, cabbage showed some scorching, lettuce considerable, and
cucumbers and tomatoes scorched quite badly.
On section 3 the effects were about the same with a regard
to scorching, but there were a few nematodes on the plants.
These results coincide with those of other experiments, which
indicates that one does not get as good results when the cyan-
amid is added in water. The top layer of the soil seems to
absorb the material.
Section 5 showed one corner next to the check to be heavily
infested, the remainder free. This uneven distribution led to
the suspicion that the partition between plots had worked loose;
a suspicion which was verified upon examination. The nema-
todes were exterminated in this section by a dose of 2 tons
In section 6, by May, 1916, a few knots became noticeable
on tomatoes. Up to that time none had been noticed. Probably
1440 pounds per acre is a little too small a dose for thoro
eradication, altho it greatly reduced the number of nematodes.
152 Bulletin 136, Control of Root-Knot
Section 7 with the same dose as section 6, but added in
solution, had some root-knot, but markedly less than the check.
In section 4, check, all plants were so heavily infested with
nematodes that they made very little growth.
EXPERIMENTS WITH WINTER TRUCK
In November, 1915, another series of thirteen plots, each
containing a hundredth of an acre, was treated with cyanamid.
The dose ranged from 420 to 3600 pounds per acre. To two
of these plots the material was added in solution, and two were
left untreated for checks. On the other nine plots, about half
of each dose was broadcasted over the surface of the ground
and the plot was then plowed deeply. The remainder of the
dose was then applied as a top dressing to the plowed land
and thoroly disked in. The soil was rather dry at the time of
application and it was not irrigated.
Few nematodes were found on the plots that had received
1500 pounds or more per acre. But by June, 1916, a few of
the truck plants on each of the plots, even on the one that had
received 3600 pounds per acre, showed knots.
EFFECT IN PLOTS NOT IRRIGATED
Other plots were started on July 1, 1916, using doses vary-
ing from 1/2 to 3 tons per acre. This was applied as in the last
experiment. No rain fell for a week after the application.
Later examination showed that in none of the plots were the
nematodes entirely exterminated, but there were very few in
the plot that had received 3 tons of cyanamid per acre and they
were in two spots only. Perhaps those spots had not received
their proper proportion of the material. On this plot all crops
planted three weeks after treatment ultimately showed serious
scorching altho heavy rain had fallen before planting. Cowpeas,
corn, okra, and beans were planted. English peas planted on
October 21, nearly four months after the treatment, showed
some scorching on plots that had received 2 tons or more per
These experiments indicate that the application of the mate-
rial to dry soil is not very satisfactory. The nematodes are not
entirely eradicated with doses as heavy as 3 tons per acre, and
the scorching effect on the plants is serious and long continued.
EXPERIMENTS ON SEED BEDS AT SANFORD
Some cooperative experiments were started with Mr. C. M.
Berry, Agricultural Demonstration Agent for Seminole County.
Florida Agricultural Experiment Station 153
This is an especially favorable locality for applying the cyan-
amid treatment. The permanent water table is little if any
more than two feet below the surface so that nematodes cannot
go very deep into the ground, and the system of subirrigation,
with which the truck farms are provided, enables the grower to
thoroly saturate the soil at any time he may wish.
The material was used at the rate of a ton per acre. Half
of it was plowed under and the other half was then spread
over the plowed land and thoroly disked in. The material was
applied with a fertilizer spreader, thus insuring a very uniform
distribution. The land was thoroly irrigated immediately after
the disking was completed. Celery and lettuce were planted on
these plots about a month later.
GOOD RESULTS SECURED
The experiments were highly successful. On two of the
treated seed beds the nematodes were entirely exterminated.
During the previous year these beds had been so severely in-
fested that the owners had decided to abandon them. A care-
ful search made at the time the celery and lettuce were being
transplanted, failed to reveal any knots and the plants all
looked healthy. Untreated seed beds only a few rods away
were seriously infested with nematodes.
On a third treated seed bed, there were a few infested spots.
These could be detected readily by the stunted yellow plants
they bore. All were on higher parts of the bed, suggesting
that perhaps these parts were not wet thoroly after the appli-
cation of the cyanamid.
A fourth seed bed was treated but not according to direc-
tions. Instead of plowing half of the cyanamid under it was
all put on after the ground was plowed and then disked in.
The results corresponded to those previously mentioned when
cowpeas were used. The roots near the surface were free from
knots but some that extended to a depth of five inches or more
showed some knots.
The results of these representative experiments, in connec-
tion with others which gave similar results, the details of which
are not given here, justify the following conclusion. Cyanamid
applied at rates of from one to three tons per acre, according
to the nature and the depth to which the soil is infested, and
thoroly mixed with the soil, reduces the number of nematodes
present to an extent sufficient to make it possible to grow with
154 Bulletin 136, Control of Root-Knot
profit susceptible plants on land which, before treatment, would
not produce them profitably. The reduction, in some cases,
amounted to apparent extermination.
The thoroness of the control will depend upon several fac-
tors. The dose is one of the most important. This will depend
much upon the depth of the soil or the depth to which the
nematodes are found. The character of the soil is, apparently,
also important. In one case, a dose of 1/ ton per acre on the
very light, sandy, pineapple soils (old established dunes) about
Fort Pierce, seem to have produced as good results as 2 or 3
tons on the Station farm at Gainesville.
MANNER OF APPLICATION
The manner of application is a very important factor.
Cyanamid even when in solution does not penetrate the soil to
any considerable depth. It is quickly absorbed by certain con-
stituents of the soil called colloids. The scarcity of these com-
pounds in the sandy soils of the Fort Pierce section probably
accounts for the comparative effectiveness of the small dose
mentioned above. It is probably this absorption by the colloids
which is responsible for the poor results obtained when the
material was applied in solution. The top layer of the soil
absorbs the material and the nematodes in the deeper layers
escape. The same results followed when all of the dose was
applied as a top dressing to the plowed land and then disked in.
It is therefore necessary to mix the material with the soil as
thoroly as practicable. Under farm conditions it would seem
that this is best accomplished by spreading somewhat more
than half of the amount on the surface, plowing it under as
deeply as possible, and then adding the remainder and disking
it in thoroly. This method was found most successful on the
A more uniform distribution can be obtained with a fertil-
izer spreader and as a uniform distribution is very important,
the use of one is strongly recommended. In some cases when
the land was not plowed as deeply as desired, the practice of
following the plow with a bucket of cyanamid and sprinkling
the material in the bottom of the furrow was resorted to. On
a small garden plot it is practical to have the cyanamid hoed
or spaded in, thus securing a more even distribution.
It is best to choose a dry period for the application of
cyanamid as the material will mix better with dry earth. In
Florida Agricultural Experiment Station 155
wet ground lumps tend to form as the material absorbs water
readily. If stored for some months, particularly during the
rainy season, cyanamid absorbs water from the air and forms
hard lumps. These must be broken before the material can be
used. All cyanamid used should be sufficiently fine to pass thru
an 18-mesh wire mosquito-screen. Chunks of the material
added to the soil not only are useless for killing nematodes, but
they remain in the soil for a long time before they entirely dis-
integrate, and have a very harmful effect on subsequent plant
growth. When fresh, the material is a very fine powder which
IRRIGATE THE FIELD
When cyanamid has been thoroly mixed with the soil, the
field should be at once irrigated. Enough water should be used
to wet the soil thoroly to the depth ordinarily reached by nema-
todes, which is 15 or 18 inches in the usual loose sandy soils of
our State, or to ground water. Altho the greater number of
worms is in the first 8 or 9 inches of soil, it is necessary to kill
the few below that depth, otherwise they will in a few weeks'
time restock the upper layers of soil.
This thoro irrigation is very important for at least two
reasons. It completes the distribution of the cyanamid begun
by the plow and disk harrow so that more of the nematodes
are reached and killed, and it hastens the decomposition of the
cyanamid, shortening the time that must elapse before the crop
can safely be planted. Altho a heavy rain immediately after
application is equivalent to an irrigation, the use of the cyan-
amid method of dealing with nematodes is not advised except on
land that can be irrigated. One cannot safely depend upon the
weather, and the material is too costly to lose.
VERMICIDAL EFFECT NOT DUE TO NITROGEN OR LIME
Early in the work the question arose: Can the killing of
the nematodes be due to the nitrates or to the lime in the
cyanamid rather than to the calcium cyanamide? To throw
light on this question, four 1/100 acre plots were laid off. One
was treated with cyanamid at the rate of a ton per acre. An-
other was treated with hydrated lime. The amount used was
equal to that contained in 20 pounds of cyanamid, 141/2 pounds.
A third plot was treated with nitrate of soda.' The amount
used, 27 pounds, corresponds with the amount of nitrogen,
figured as ammonia, contained in 20 pounds of cyanamid. A
fourth plot was left untreated as a check.
156 Bulletin 136, Control of Root-Knot
The plot treated with cyanamid showed markedly fewer
nematodes than the check altho they were not all killed. The
plots treated with lime and nitrate of soda showed no decrease.
It is interesting to note that the plants on the nitrate of soda
plot showed even more severe scorching than did those on the
cyanamid plot. However, the effect passed off more quickly,
the later plantings showing more scorching on the cyanamid
plot. The nitrate of soda becomes available more quickly and
also leaches out more quickly than does the cyanamid.
TIME BETWEEN TREATMENT AND PLANTING
The length of time which must elapse between the applica-
tion of the cyanamid and the planting of the crop will, of
course, be directly proportional to the dose. The manner of
application also influences the length of time required. Thoro
mixing with the soil to as great a depth as is practicable also
shortens the time. Lumps of cyanamid may injure plants in
their immediate vicinity for months. As previously stated, a
thoro irrigation immediately after application is a very import-
ant factor in lessening the time the land must remain idle.
The soil should not be allowed to become dry for weeks after
the material is applied. Scorching is always more severe when
the soil becomes dry.
The length of time the land must lie idle will also vary
markedly with the crop to be used. Some plants are much more
sensitive to the compound than are others. Radishes are the
most tolerant of any plant tried and tomatoes are the least.
It is important, in order to get the maximum returns from the
fertilizer value of the cyanamid, to plant as soon as possible
after treatment. From the results obtained from preliminary
experiments the following periods of rest would seem to be
fairly safe when the dose is not more than one ton per acre,
and is thoroly mixed with the soil which is at once thoroly
irrigated and kept moist after the seeds are planted.
Radishes may be planted within a week or ten days. Celery,
lettuce, rape, parsnips, cabbage, cauliflower, collards, water-
melons, corn, peppers, and beans in about three weeks. For
cowpeas, cucumbers, cantaloupes, okra, and Irish potatoes one
should wait about a month. For English peas six weeks should
elapse, and for tomatoes at least two months.
In the case of tomatoes one could treat the land several
months in advance of planting time, perhaps in the fall for
Florida Agricultural Experiment Station 157
land intended for the spring crop, and in the meantime grow
on the land some short season crop, such as radishes, lettuce,
Often the scorching does not appear immediately upon
plants grown or set out too soon on treated land. They may
prosper for a week or two and have an unusually deep green
color and show scorching only after the elapse of a week or
more. If the dose is much too strong for the time intervening,
the plants will show scorching at once or fail to come up at all.
This is especially true of those growing from small seeds.
At present, cyanamid retails for about $75.00 a ton. To this
must be added the cost of application. This should, however,
be but little higher than that for any other fertilizer. In esti-
mating the cost one must take into consideration the value of
the material as a fertilizer.
As previously stated, cyanamid is a very rich nitrogenous
fertilizer, analyzing as high as 24% ammonia. At the present
prices it is, among commercial fertilizers, the cheapest source
of nitrogen. It is more slowly available than nitrate of soda,
but is more lasting in its effects. Only in exceptional cases,
such as when growing unusually valuable truck crops, should
it be necessary to add any additional ammonia to soils treated
for nematodes, for several months thereafter. On plots on
which a ton or more per acre was used, the fertilizing effects
were quite evident on crops planted four months later, and a
slight effect could be seen nearly a year later.
For most truck crops, then, in addition to the ton of cyan-
amid, it would be necessary to add only potash and acid phos-
phate. The latter not only serves as a plant food but it appar-
ently helps a little to counteract the scorching effect of the
cyanamid. At least, where moderate amounts of cyanamid and
about equal amounts of acid phosphate were used, there seemed
to be less scorching than on similar plots where no acid phos-
phate was used. However, its neutralizing effects are so slight
that it would not seem to be profitable under ordinary circum-
stances, to use it for that purpose alone. It is much cheaper
to allow the land to lie idle for a few weeks; then the farmer
will usually apply only the amount of acid phosphate desired
for fertilizing purposes. Under special circumstances, if for
any reason it is desired to plant the plot as soon as possible
158 Bulletin 136, Control of Root-Knot
regardless of cost, the addition of larger amounts of acid phos-
phate might be justified. The best results have been secured
by applying the acid phosphate about a week after the cyan-
amid. This gives the latter time to kill the nematodes before
being partly counteracted by the phosphate.
EFFECTS ON OTHER ORGANISMS IN THE SOIL
A striking difference is noticeable between treated and un-
treated plots in the amount of weeds that spring up. If plots
are treated during the warmer part of the year, when seed are
likely to germinate under the influence of the irrigation which
follows the application of the cyanamid, practically all weeds,
including most grasses, which have small seeds are killed. But
large weed seeds like beggar-weed and coffee-weed are not al-
ways killed. Neither are the underground stems of Bermuda
THE NITROGEN-FIXING BACTERIA
Apparently these very valuable organisms will stand no
larger doses of cyanamid than will the nematodes. At least on
the plots that received cyanamid at the rate of a ton or more
per acre, cowpeas were entirely devoid of nodules while those on
check plots had a normal supply. This may be due to the am-
monia derived from the cyanamid rather than to the calcium
cyanamide as it is known that legumes grown in soil highly
fertilized with ammonia may produce no nodules. It will prob-
ably be necessary to inoculate the seed if one wishes to rein-
troduce the nitrogen-fixing bacteria into treated soil.
WHERE CYANAMID WILL BE OF MOST VALUE
Because of the high cost of the treatment, the use of this
new method of controlling nematodes will probably be limited
largely to land on which particularly valuable and highly sus-
ceptible crops are raised and to which large amounts of nitro-
genous fertilizers are usually applied. Such lands are seed beds
and truck patches where the most intensive methods of cultiva-
tion are practiced.
It is evident, of course, that there is nothing to be gained
by treating the land if the contemplated crop is not commonly
damaged by the worms.
HOST PLANTS OF NEMATODES
The following list includes most susceptible crops commonly
grown in Florida. They are named in the order of the severity
Florida Agricultural Experiment Station 159
of the damage they usually suffer, which is not always that of
the severity of the infestation.
1. Okra 15. Roselle 30. Asparagus
2. Cucumbers 16. Dasheens 31. Cabbage
3. Tomatoes 17. Peppers 32. Cauliflower
4. Eggplant 18. Squash 33. Collards
5. Cantaloupes 19. Lettuce 34. Soy Beans
6. Amaranth 20. Beans 35. Mustard
(careless weed) 21. Rape 36. Pecans
7. Celery 22. Papaya 37. Japanese Persimmon
8. Tobacco 23. Carrot 38. Violets
9. Peas 24. Pineapples 39. Old World Grapes
10. Peaches 25. Sunflowers 40. Sugar Cane
11. Figs 26. Bananas 41. Kudzu
12. Irish Potatoes 27. Cotton 42. Catalpa
13. Watermelons 28. Radishes 43. Quince
14. Beets 29. Sweet Potatoes
On land which has been heavily infested it is impossible to
grow profitably the plants at the head of this list. They may
grow well at first but soon become stunted and fail to bear well.
Nematodes however, are less active during the cool and dry
weather of winter. Therefore, many plants in the foregoing
list may be profitably grown during the winter on heavily in-
fested land. Others may be planted in late winter and get such
a start that the nematodes are not able to prevent a satisfac-
tory crop from being harvested in late spring or early summer.
It is such susceptible plants as early lettuce and celery, which
must be started in the early fall or late summer, that suffer
most on infested land and will be benefitted most by the new
STARVING THE NEMATODES
On land where less intensive truck farming or general farm-
ingis practiced, the cyanamid treatment would be too expensive.
Under these circumstances the old method of starving the nema-
todes will be the more practicable. In brief, this method con-
sists of growing on the infested land for three years, crops on
which the nematodes do not thrive.
Among such immune or partly immune plants are: Most of
the true grasses, including crab-grass, Bermuda, etc.; most of
the varieties of corn and wheat; rye; some varieties of oats;
velvet beans, and beggar-weed. Iron and Brabham varieties of
cowpeas are usually resistant. Peanuts, onions, parsnips, straw-
berries, and turnips are but slightly affected.
While growing any of these crops to free the land of nema-
todes, it is important that weeds should not be allowed to grow
160 Bulletin 136, Control of Root-Knot
there as nematodes are abundant on many of them. This is
especially true of some species of Amaranth or careless weed."
OTHER METHODS OF FREEING THE SOIL
Among other chemicals which are sometimes used to destroy
nematodes in the soil are sodium and potassium cyanide, car-
bon bisulphide and formalin. Potassium cyanide, like cyanamid,
is also a fertilizer but adds to the soil a comparatively small
amount of potash instead of nitrogen.
Carbon bisulphide can be used with some success in killing
nematodes in land bearing living plants, but it requires con-
siderable experience to get just the proper amount. If too
much is used the plants will be killed and if too little is used
the nematodes will escape destruction. The quantity required
will vary with the type of soil. Altho sometimes used on truck
crops, the greatest value of this method is to infested trees and
shrubs like figs, peaches on peach roots (peaches on plum roots
are not injured by nematodes), mulberries, roses, etc. A hole
is made slanting under the tree and the proper amount of the
liquid poured in and the hole closed at once by tamping the soil
solidly over it.
In greenhouses where steam heat is available, nematodes
may be exterminated by turning live steam into the beds.
AVOID REINFESTING THE LAND
Whichever method is employed to free the land of nematodes
one should carefully avoid carrying the worms back onto the
treated land if he would get the full benefit of his work.
These minute worms move quite slowly by their own efforts,
probably not more than a few feet each year. They are usually
carried from one field to another by the transplanting of in-
fested plants. They are commonly distributed over a field and
often carried into new fields in soil clinging to the hoofs of
horses, the shoes of workmen, or the tools used in cultivating.
Water is also a common agent for distribution. In running
thru an infested field it may gather worms or their eggs and
carry them far into uninfested soil.
To avoid reinfesting new land, or a field once cleaned up,
carefully remove the soil from the tools as well as from the
feet of the horses and the shoes of the men before going into
the field. See that water does not wash over the field from an
infested one. And above all, be careful not to transplant into
the clean field any infested plants.