Group Title: Bulletin University of Florida. Agricultural Experiment Station
Title: Control of root-knot, II
Full Citation
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 Material Information
Title: Control of root-knot, II
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Alternate Title: Control of root knot, II
Physical Description: p. 29-44 : ; 23 cm.
Language: English
Creator: Watson, J. R ( Joseph Ralph ), 1874-1946
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1921
Copyright Date: 1921
Subject: Root-knot   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
Statement of Responsibility: by J.R. Watson.
General Note: Cover title.
 Record Information
Bibliographic ID: UF00026940
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: ltuf - AEN3300
oclc - 18171140
alephbibnum - 000922791

Full Text

Bulletin 159 April, 1921


Agricultural Experiment Station


Fig. 3.-Root-knot on watermelon (Bull. 136)

Bulletins will be sent free upon application to the Experiment Station,

1. For the general farmer and trucker with plenty of land:
The cheapest method of treating nematode-infested land
is to grow on it immune or resistant crops for three
2. For truckers with limited acreage who cannot spare the
land long enough for the starvation method: The num-
ber of nematodes in a case of this kind can be reduced
a. By growing during the summer resistant or immune
cover crops in rows which can be constantly culti-
vated; or
b. By summer fallowing, if loss of soil fertility is of
minor importance; or
c. By applying fresh cyanamid at the rate of a ton to
the acre a month or two before the land is to be
planted; or
d. By flooding the land with water for a week or two.
3. For Seedbeds:
a. Plant on newly cleared land; or
b. Treat the land with sodium cyanide at the rate of
600 to 800 pounds and with ammonia sulphate at
the rate of 900 to 1200 pounds to the acre. This is
too expensive for a large acreage.
4. For the small home garden:
Combine fallowing with the yarding of chickens.
5. For growing perennial plants:
a. Plant on newly cleared land;
b. Mulch heavily and do not cultivate; water well;
c. For figs, plant near a building;
d. For peaches, graft on plum roots.
Be sure that the seedbed is free from nematodes.
Do not set out in nematode-free land plants from a seedbed
showing any trace of nematodes.
Thoroly clean all dirt from plows and other tools before tak-
ing them into a nematode-free field.
Take the same precautions with horses' feet and workmen's
Do not allow water to wash soil from an infested field over
an uninfested one.


Root-knot is one of the most widespread and destructive
diseases with which the Florida trucker has to contend. The
parasite causing the disease is so abundant thruout the well
drained sandy soils of the state that it is found in practically
every field cleared for even a few years. Newly cleared land is
usually free from the worms, root-knot nematodes. However,
this is by no means always true. On stiff clay soils or any wet
soils they are not nearly as destructive as on well drained sandy
The entomologist of the Florida Experiment Station has been
working on this problem for several years and has published a
bulletin (number 136) and several reports (An. Repts. Fla. Agri.
Exp. Sta., 1916, 1917, 1918).
The aim of this bulletin is to present to farmers and truckers
only those details essential to the intelligent treating of infested
fields and to make public the main results of recent experiments.
A more detailed account of the experiments upon which these
recommendations are based may be obtained from the reports
listed above.
In all these experiments the method of testing the absence,
presence or abundance of the nematodes in the soil has been by
planting plots, after treatment, to highly susceptible crops and
noting the presence or absence of the characteristic knots on the
roots, as well as their abundance, compared with crops planted
the same day on adjoining untreated plots.
The worms are too small to make direct observations in the
soil practicable. The direct effect of the reagents used has been
observed on the worms under a microscope. The roots with the
galls on them have been dipped directly into the solution used
and the effects noted. Field conditions, however, are so different,
with the worms imbedded in the roots in the soil, that apparently
little of a practical value as to dosage, etc., can be learned from
laboratory experiments.
Root-knot derives its name from the large, irregular, swollen,
knotted appearance of the roots of affected plants. These should

32 Florida Agricultural Experiment Station

not be confused with the nodules of nitrogen-fixing bacteria
which grow on the roots of legumes and a few other plants.
Nodules are usually smaller and on any given plant are approxi-
mately uniform in size and shape. They are attached loosely to
the root and may be pulled off easily. The galls of root-knot-in-
fected plants, on the other hand, are swellings in the root itself
and vary greatly in size and shape.
Severely affected plants soon turn yellow, cease growing and
die prematurely. Those less severely affected, may remain alive
for some time, appearing sickly and stunted and producing but
little fruit and that of small size and poor quality.
The minute worm, Heterodera radicicola (Atkinson), which
causes this peculiar root disease, bores into the roots to feed upon
the sap. As it feeds it gives off a poison which stimulates the
root to form the gall or knot. The worm is a member of a large
group, including the hookworm, "vinegar eel" and many in-
testinal worms. All are known as "round worms," or "eel
worms," and as nematodes technically. The males and young are
long and slender and can make their way thru the soil from
plant to plant; but the adult females are pear-shaped and capable
of little or no motion. Even the young can make their way but
slowly thru the soil, only ten or fifteen feet a year.
These worms are very small, even the adults being barely
visible to the naked eye. Most of them are found in the top foot
or two of soil. However, they may occur in small numbers con-
siderably deeper, particularly in loose soils. Only in small num-
bers are they ever found in the surface of dry soils. It has been
determined that soil dry enough to blow about contains few or
no living nematodes. Wind is, therefore, not much of a factor in
the spread of the disease.


Many plants are more or less immune to root-knot, i.e., the
worms do not find their roots a suitable medium in which to
grow and reproduce. Probably there are substances in the sap
which poison the worms. As a whole plants of the true grass
family, including corn, oats, rye, canes, sorghums and millets, as
well as Crab and Bermuda grasses, etc., are quite resistant. Still
some varieties of corn, oats and cane are sometimes seriously at-
tacked. Velvet beans and beggarweeds are practically immune.

Bulletin 159, Control of Root-Knot, II 33

Generally speaking, trees and shrubs are not as apt to be at-
tacked as herbs. There are numerous exceptions to this rule.
Other plants seem to be more or less tolerant, i.e., they are
able to make satisfactory growth and produce a good crop of
fruit altho they are heavily attacked and their roots are badly
knotted. Mulberry trees and sunflowers are such plants.
Unfortunately, most truck and garden crops are severely
injured by the worms. There are, of course, all gradations be-
tween highly susceptible and practically immune plants. The
following list includes most of the susceptible plants commonly
grown in Florida, given in the approximate order of their sus-
ceptibility to damage, which is not necessarily that of the abun-
dance of nematodes in their roots:

1. Okra 16. Irish potatoes 31. Radishes
2. Tomatoes 17. Watermelons 32. Sweet potatoes
3. Eggplant 18. Lettuce 33. Asparagus
4. Cucumbers 19. Careless weed 34. Soybeans
5. Cantaloupes 20. Beets 35. Pecans
6. Celery 21. Pineapples 36. Sugar cane
7. Beans 22. Cotton 37. Mustard
8. Dasheens 23. Cabbage 38. Violets
9. Peppers 24. Cauliflower 39. Japanese persim-
10. Squash 25. Collards mons
11. Figs 26. Sunflowers 40. Catalpa
12. Peas 27. Carrots 41. Kudzu
13. Peaches 28. Bananas 42. Quince
14. Roses 29. Papaya 43. Peanuts
15. Old World grapes 30. Rape

On land which is heavily infested it is impossible to profitably
grow okra, tomatoes, eggplants, and others near the head of this


Nematodes are least active during the cooler and drier
weather of winter. In the latitude of Gainesville they generally
do comparatively little damage between November 1 and April 1.
Further south they are more destructive in winter. They are
most destructive in all sections during summer. Therefore,
many plants in the above list may be profitably grown during
winter on heavily infested land. Others may be planted in winter
and given sufficient start before the nematodes become active to
produce well. Such susceptible plants as celery and early lettuce
which must be planted in the fall or late summer, suffer most on
infested land.

34 Florida Agricultural Experiment Station

Sometimes the number of nematodes in the soil will markedly
decrease without any active measures being taken against them.
Like all other animals, root-knot nematodes have their enemies.
The principal enemies in this case are other nematodes, species
which prey upon those herein discussed. Doubtless the presence
in the soil of these and other enemies often reduces the trouble.
It is never safe, however, to depend on this natural control.
Generally, if the grower wishes to reduce the infestation, he must
take active measures to combat the worms.
On old, heavily infested farms, control rather than eradica-
tion has been the aim in these experiments. By means of the
procedure herein recommended, control, but not complete eradi-
cation of the nematodes, has been secured. In other words, the
result has generally been to reduce the pests to the point where
susceptible crops can be grown for a season. If the nematodes
are reduced to only a few spots here and there over a field, leaving
98 percent or more of the crop uninfested, the control is consid-
ered satisfactory. It takes many months for the worms to reach
again all parts of a field from a few infested spots in it, probably
as long as it would take them to make their way in from untreated
fields. On the other hand, if the worms remain generally dis-
tributed thruout the field, even tho greatly reduced in numbers,
the control is not considered satisfactory, as the rapid breeding
of the remaining worms will soon result in heavy reinfestation.
Complete eradication is expensive. On a heavily infested
farm the nematodes are usually so quickly reintroduced, after
being eradicated from a single field, that the attempts are not
profitable for the average farmer or trucker. It would seem that
in many cases a cheaper procedure, which will enable the crop
to be kept reasonably free for a season, would better meet his
In the case of a small infested area in an otherwise clean
farm, which often occurs on recently cleared land, much more
thoro measures are desirable. The grower can well afford to go
to a higher proportionate expense to stamp out a small infesta-
tion than he can a large one. In experiments on small greenhouse
benches and on plots in the open, where the reinfestation of the
land is prevented by cement walls extending to a depth of four
feet, the worms have been repeatedly and completely eradicated.

Bulletin 159, Control of Root-Knot, II 35

In general, however, this has required doses of chemicals twice
as great as herein recommended for average conditions, or, as in
the case of fallow, twice as long a time. If it were possible to
secure an absolutely uniform distribution in the soil, it is prob-
able that the chemicals, in amounts recommended below, would
result in the complete destruction of the worms. In actual field
work such distribution is not practicable.

The old standard method of reducing the nematodes in the
soil is to grow on the land for three consecutive years crops that
do not harbor the worms, or which are highly resistant to them.
Such crops are corn, oats, rye, wheat, most of the true grasses,
beggarweeds and velvet beans. True Iron, Brabham and Victory
cowpeas are usually highly resistant. Peanuts, onions, straw-
berries and turnips are but slightly affected. By the continuous
planting of these crops for two or three years most of the nema-
todes are starved out. However, this method seldom secures com-
plete eradication. While growing any of these crops to starve the
nematodes it is of the utmost importance that no weeds be al-
lowed to grow on the land. This is because many weeds are
host to the worms and, if allowed to grow, will prevent the at-
tempted eradication. A good rotation is oats or rye during the
winter and corn and velvet beans during the summer and fall.
This is by far the cheapest method of bringing the nematodes
under control. But on high-priced and intensively cultivated
land the time necessary to devote to growing relatively low-priced
crops is a drawback that often renders this method impracticable.
Furthermore, it cannot be depended upon to be sufficiently thoro
for seedbed preparation, and other important phases of trucking.
During the last four years experiments with summer fallow,
as a means of controlling nematodes, have been conducted by the
Florida Experiment Station. In order to appreciate the manner
in which the summer fallow works, one should understand the
conditions necessary for the hatching of the eggs, and the growth
of the worms. As in the case of most organisms, plant or animal,
these conditions are: (1) heat, (2) water, (3) food, and (4) air
(oxygen). If any one of these four factors is lacking or present
in insufficient amount, growth is impossible. This does not
necessarily mean that the organism will die. It may be able to lie

36 Florida Agricultural Experiment Station

dormant for a long period. The eggs of nematodes are capable of
lying dormant in the soil for months or even years in an "en-
cysted" stage. They are inclosed in a thick coat which resists the
action of the weather and preserves the organism. But, if mois-
ture, the proper amount of heat, and air are present in the soil, the
eggs sooner or later hatch. During a greater portion of winter
the necessary heat and moisture are lacking sometimes; but
during summer there is ample heat, and usually ample moisture.
but sometimes insufficient air in the soil. The heavy rains of
summer often compact the surface and fill the pores of the soil
with water until air cannot readily enter. This is shown by the
acid reaction and the general growth of the inch-high sedge,
Eleocharis, often called "moss."
In these experiments, therefore, the soil has been kept well
supplied with air by constant cultivation so as to insure hatching
of the eggs. The plots are cultivated at least once a week and
more often, in the case of heavy rains, the aim being to maintain
a constant soil mulch and to break up crusts as soon as formed.
At the same time the ground was kept free of all vegetation so
as to starve the nematodes. This has been tried out during both
winter and summer. Some of the plots were kept fallow from
May to October, others from May to August, others from June to
September, others from July to October, and others from October
to April. The winter fallow considerably reduced the infestation
as compared with plots kept in truck crops but not nearly as well
as did the summer fallow. The latter greatly reduced the in-
festation. In no case, however, was there anywhere near com-
plete eradication. In most cases there were more nematodes in
the fallowed soil than in soil treated with "cyanamid" or sodium
cyanide and ammonium sulphate.
As was to be expected this fallowing treatment proved de-
structive to soil fertility. Not only was much of the humus in the
soil destroyed but the bacterial content doubtless was reduced
greatly. The soil was "dead" as the result of the action of the hot
sun on the bare ground and the leaching effects of the heavy sum-
mer rains. This deleterious effect on the soil is a serious objection
to this method of combating nematodes. Nevertheless, it should
be useful under some circumstances, as on lands rich in humus or
on small truck farms where the owner can afford to restore the
fertiliy and soil organisms by the liberal use of manure and other

Bulletin 159, Control of Root-Knot, 11 37

In the small home garden a modification of the summer fal-
low is one of the best and cheapest methods of combating nema-
todes. It consists of combining the fallowing with the penning
of chickens. The fowls by their scratching and wallowing, will
help to maintain the soil mulch; and their manure, incorporated
into the soil, will not only prevent the soil's deterioration but will
leave it much more fertile than before. The same precautions
should be taken as with summer fallow; viz., keep down all
vegetation and break up at once crusts that form on the soil after
heavy rains. The writer has for several years employed this
method of combating root-knot in his home garden. Penning
the hens on the ground for six months during the summer has
usually reduced the nematodes to such an extent that they did
little damage to following crops. Penning for a year practically
exterminated them.
This method is, of course, practicable for a small kitchen
garden only, but it is exactly in such situations that root-knot
does its most destructive work.
It is possible that penning hogs on the ground would result
in much the same benefit, and could be practiced on a larger
In an attempt to overcome the deleterious effects of summer
fallow on soil fertility, another modification of the fallow method
has been tried during the last two years. This is in effect a com-
bination of the summer fallow and the growing of resistant crops.
It was hoped that in this way the humus could be preserved by
shading the ground with a cover crop which could be plowed
under when planting time arrived. Even if the destruction of
the nematodes is not as thoro as with the complete summer fal-
low, due to the partial interference of the crop with cultivation
and the increased chances of weeds escaping destruction, the
saving of soil fertility by this method might more than com-
pensate the planter.
Brabham cowpeas and velvet beans were planted in rows
and cultivated at least once a week; and, if it rained, more often.
Absolutely every weed was destroyed by hoeing frequently. It
will be noticed that this method differs from the old method of
growing resistant crops in that the cultivation is more thoro and
frequent, the crop never being "laid by."

38 Florida Agricultural Experiment Station

Altho the results already obtained need to be checked by
further trials, they appear very promising. The destruction
of nematodes has appeared to be nearly as thoro as with the
summer fallow method and the soil is left in better condition.
Velvet beans are superior in three respects to cowpeas. They
furnish better shade, have never been observed to harbor root-
knot, while even Iron or Brabham cowpeas sometimes do so, and
there is no danger of getting any susceptible plants in the plot
thru impure seed. They are, however, more troublesome to cul-
tivate because of their vines. It is hoped that the new bunch
variety may prove more satisfactory in this respect.
Nematodes can be greatly reduced in number, if not com-
pletely eradicated, by flooding. Indeed, in some fields usually
flooded during part of the summer, as with some tomato fields on
the lower East Coast, nematodes are seldom noticed. There is
much yet to be learned as to the length of time a field should be
covered with water, especially at different seasons, and as to the
resistance of the eggs to water. Generally a week or two is con-
sidered necessary. Of course, comparatively few fields are so
situated as to render flooding practicable.
In northern greenhouses where the protection from frost
sometimes enables nematodes to become troublesome, it has long
been the custom to sterilize the soil by turning live steam into it.
The beds are covered with straw, mats, building paper, or other
material, and the steam then turned on. A raw potato is placed
on top of the bed furthest from the pipes. When the potato is
thoroly cooked the sterilization is considered complete. When
steam is available this is undoubtedly one of the quickest, most
thoro and cheapest methods of eradicating nematodes.
Hot water also is an efficient killing agent. The soil is satur-
ated with boiling water to the depth of two feet. But much the
same objection would apply here as in case of the steam treat-
ment. Unless one is equipped with apparatus for quickly and
cheaply heating water this method is slow and expensive, con-
sidering labor.
There are a number of chemicals that can be used to exter-
minate root-knot in the soil. The objection to most of them is

Bulletin 159, Control of Root-Knot, II 39

that they are too expensive or the cost of application is too great
to make their use on a large scale practicable. But, at least, the
two mentioned below are cheap enough to justify their use on a
small area of especially valuable land devoted to intensive truck-
ing. The practicability of their use depends partly upon the
fact that they are both rich, nitrogenous fertilizers and much of
their cost may be charged to the fertilizer bill.
In Bulletin 136 of this station are recorded the results of
treating the land with "cyanamid." This is a trade name for a
mixture consisting chiefly of calcium cyanamide (about 45 per-
cent), hydrated lime (27 percent), carbon (13 percent), calcium
carbonate (4 percent) and calcium sulphate (2 percent). It is a
black powder, the color being due to the carbon. It is a concen-
trated nitrogeous fertilizer, analyzing from 15 to 24 percent am-
monia. The ingredient which kills the nematodes is the calcium
cyanamide (CaCN,). It is a strong poison, but in the soil most
of it goes quickly into urea and other harmless compounds. Some
of it may go to dicyanamide and other polymeric compounds
which decompose more slowly and are highly poisonous to plant
These chemicals produce serious "burning" effects for weeks
and months after treatment. The edges of the leaves of plants
set in such soil, turn white, shrivel and die. The whole plant
may die quickly or it may remain stunted. The first symptom is
an abnormally dark green color. The earliest tests with this
substance were all satisfactory, but some later ones have resulted
in the total loss of crops of lettuce and celery as long as four
months after treatment; whereas, in our early experiments we
were able to plant most crops within a month or six weeks after
treatment without serious burning. During the war it was
found difficult to obtain fresh cyanamid and these later tests
had been conducted with material which had been in storage for
many months. Experience has taught that after the material
cakes in the bag it is no longer safe to use, even if broken up be-
fore it is used. It should be in the form of a dry fine powder.
Cyanamid is applied at the rate of one ton to the acre and
carefully and uniformly mixed with the dry soil. The soil is
then thoroly irrigated. The treatment should precede the
planting of the crop by six or eight weeks, during which time the
soil should be frequently stirred to break up any crust which may

40 Florida Agricultural Experiment Station

form. Letting the air into the soil hastens the decomposition
of the poison.
Tho not as safe as the following treatment, it would seem
that the cyanamid method of dealing with the nematodes should
still have a place in Florida agriculture. When the grower is
not in a special hurry to plant the land it can safely be used; or
the field may be planted soon after treating with some cover
crop, the possible loss of which will not be a serious matter. The
material is much less costly than sodium cyanide and ammonium
sulphate, recommended below.
Some crops are more easily injured by cyanamid than others.
A list of the more resistant plants, as well as full directions for
applying the material, is given in Bulletin 136. An excellent
plan would be to treat an infested field with cyanamid after the
spring crop is off and plant it to corn for summer crop three or
four weeks later. If there is sufficient time, Iron or Brabham
cowpeas could be planted between the rows of corn at the last
cultivation. This should leave the land in good condition for the
fall truck crop.
During the last four years the Florida Station has been ex-
perimenting with a method used first by Professor Woodward of
the California Station. It consists of treating the soil with a
solution of sodium cyanide which is carried down to a depth of
about 18 inches by irrigation water. Then the soil is at once
treated with a solution of ammonium sulphate, which is also
washed down. The ammonium sulphate reacts with the cyanide
and breaks it up, forming hydrocyanic acid gas which has the
killing effect. The amount of the sulphate used should be one
and a half times by weight that of the cyanide.
This is, on the whole, our most satisfactory method of treat-
ing seedbeds and other particularly valuable tracts of land, which
it is desired to plant within a week or two after treatment.
The material is too expensive to warrant its use on any except
the most valuable and intensively cultivated truck lands. A
week or two after application the land may be planted without
danger of the serious burning sometimes experienced in the use
of cyanamid. Both of the chemicals are, like cyanamid, rich,
nitrogenous fertilizers; and, in the seedbed, where large amounts
of nitrogenous fertilizers are regularly used, much of the cost of
the material can be charged as fertilizer. All of the ammonium

Bulletin 159, Control of Root-Knot, II 41

sulphate can be so charged, but sodium cyanide is an expensive
source of nitrogen.
Potassium cyanide will work as well as sodium cyanide but
one must use a third more of it. Moreover, it is more expensive
than the sodium salt. On the other hand, it is even more valu-
able as a fertilizer as it contains potassium as well as nitrogen.
The dosage will depend on the thoroness of eradication de-
sired. Professor Woodward recommended 600 pounds of the
cyanide and 900 pounds of the ammonium sulphate to the acre.
Usually that amount has been found to reduce the nematodes to
a point where they will not become sufficiently abundant to do
serious damage for nearly a year. But to secure complete eradica-
tion a dose of at least twice that strength is necessary.
It is evident that the thoroness of eradication will depend
upon the evenness of the distribution. Perhaps, if the material
could be distributed with abolute uniformity thruout the soil,
600 to 800 pounds to the acre would suffice for complete eradi-
cation; but absolute uniformity is not practicable for field work.
Complete eradication has been secured, even on beds in the open,
from doses of twice that amount. Beds in greenhouse benches
six inches deep, treated with 900 pounds sodium cyanide and
1350 pounds ammonium sulphate to the acre, remained free
from nematodes, indicating complete eradication. Beds treated
at the rate of 400 pounds cyanide and 600 pounds sulphate to the
acre were much freer from nematodes than check plots. But
plots treated with less than 300 pounds to the acre showed little
improvement over untreated plots.
In order to produce plants reasonably free of nematodes as
in the case of plants to be set in a field already somewhat in-
fested, it is generally recommended that 600 to 800 pounds of
cyanide and 900 to 1200 pounds of ammonium sulphate to the
acre be used. If nematodes appear at all in such seedbeds, they
will be in isolated spots which can be rejected at planting time.
If, on the other hand, the desire is for plants that can be de-
pended upon to be absolutely free, as for setting in uninfested
ground, application of at least 1200 pounds cyanide and 1800
pounds ammonia sulphate to the acre should be applied.
The proper quantity of sodium cyanide is first dissolved in
water and the solution is then poured over the ground, which

42 Florida Agricultural Experiment Station

should have been previously plowed. Pains must be taken for
an even distribution of the liquid. The irrigation water is then
applied and the soil soaked to a depth of 18 inches or more. The
ammonium sulphate, one and a half times the weight of the
cyanide, is then dissolved in water which also is poured evenly
over the ground; a little irrigation water is applied again, just
enough to carry the sulphate down.
It is important that the sulphate be applied as promptly as
possible after the cyanide, certainly the same day. The killing
of the nematodes is accomplished by hydrocyanic acid gas given
off by decomposition of the cyanide. Ammonium sulphate has-
tens decomposition by reacting with the cyanide. Hence, it is im-
portant that the sulphate be applied soon after the cyanide. The
two substances must not, however, be mixed before applying.
It is important that reaction between these two materials takes
place in the soil.*
The material should be placed in a sprinkling can to which
water is then added. When all is dissolved (it dissolves readily)
the solution can be sprinkled evenly over the ground. There is
no need of touching it with the hands.
The cost of 600 pounds of cyanide and 900 pounds ammonium
sulphate at present prices is about $200. While this cost is high
the treatment is well worth while for seedbeds, particularly of
such plants as celery and lettuce, peppers and other fall crops
started in late summer or early fall when nematodes are most
If these plants can be carried thru until cooler weather in a
nematode-free bed, they may make satisfactory growth, even if
set out in a field with considerable nematodes, after cool weather
has checked the growth of the worms. Furthermore, it is par-
ticularly important that a plant be kept free from nematodes in
its early life. Growth is now slower and the root system
smaller than at any time in its life, and an infestation that
would not disastrously affect a larger plant, might kill it. More-

*Cautions: Persons applying this material must bear in mind that
sodium cyanide is an extremely poisonous substance. The balls (a con-
venient form is one in which the material is put in ounce "eggs") can be
handled with the bare hands, if the skin is dry and there are no abrasions.
It is always safer to use rubber gloves or a pair of forcepts or tongs in
handling. The solution should not be allowed to come in contact with the
The fumes are very poisonous to breathe, but there is little danger
from this in the open air. In a greenhouse or other inclosed space care
must be taken to avoid inhaling much of the fumes.

Bulletin 159, Control of Root-Knot, 11 43

over, the shorter time a plant stands in nematode-infested land
the fewer will be the generations of worms dwelling on it and,
hence, the lighter the infestation.
As stated above the value of the material as a fertilizer
should be deducted from the cost, when figuring the cost of the
treatment. Indeed, on some seedbeds, such as celery, larger
amounts of nitrogen to the acre are regularly applied than is
contained in 600 pounds of cyanide and 900 pounds of ammonium
sulphate. Ordinarily it will be necessary for the grower to apply
only potash and phosphoric acid after treatment.
Sodium cyanide alone does not seem to be nearly as efficient
as when used in combination with ammonium sulphate. The lat-
ter is necessary to hasten the decomposition of the cyanide and
thus free the hydrocyanic acid gas. When used alone, the cya-
nide remains in the soil a long time and greatly lengthens the
time between treatment and planting.
In addition to nematodes this treatment will free the land
from many other pests; such as, ants, wireworms, white grubs,
mole-crickets and, indeed, all insect life and possibly some fungi.
Of course, many of these pests will come back after treatment.
Most weeds also are killed out, altho those with large seeds, like
coffeeweed, will spring up after treatment.
All the chemicals cited above are, of course, applied to fallow
land and not living plants. At the present time no chemical is
known that is entirely safe to use on living plants and, at the
same time, will kill nematodes. Of all well tried chemicals carbon
bisulphide comes nearest to being such a compound. If the dosage
is properly regulated, it can be used to fumigate the soil about
the roots of plants without killing them. It is not practicable
by this means, however, to kill all the nematodes; and except,
perhaps, in the case of very valuable plants, such as choice roses,
the result hardly justifies the trouble and expense.
A slanting hole is made under the plants and a little carbon
bisulphide is poured into it, after which the soil is tramped solid
over the hole to confine the fumes. These holes should be from
a foot to 18 inches apart. The shorter distances are for clay
and other stiff soils; the longer for loose sandy soils thru which
the fumes can penetrate readily.
It is particularly important that susceptible species of long
lived plants, such as trees and shrubs, should be planted in soil

44 Florida Agriculturql Experiment Station

absolutely free of nematodes; for, if there were even a few
present, they would in time give rise to a heavy infestation.
Among trees and shrubs particularly susceptible to nema-
tode attacks are peaches, figs and roses. In general, peaches (on
peach roots) and figs should, when possible, be planted in new,
uninfested land.
All tools and shoes going into the orchard should be thoroly
cleaned, and by ditching and terracing, if necessary, any water
that might wash over the land from adjoining, old infested fields
should be diverted. Refrain particularly from carrying infested
plants into the field.
It is well to avoid planting between the rows of trees such
highly susceptible plants as cowpeas. These will not introduce
root-knot but will greatly increase the number of any of the
worms that may, in spite of precautions, be introduced.
When possible, peaches should be grafted on plum roots, as
plums are immune. Figs do best in a dooryard and near a build-
ing under which the roots can run. Constant tramping keeps
the soil compact and thus, by excluding the air, makes conditions
unfavorable for root-knot.
The growth of root-knot can be checked by heavy mulching.
Pile about the trees, straw, weeds, Spanish moss and other mulch-
ing material to a depth of a foot or more. Do not cultivate or
otherwise disturb the soil. During a dry period water the plants.
Under these conditions the nematodes do not thrive and the life
of the plants can be prolonged.

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