Cotton diseases in Florida

Material Information

Cotton diseases in Florida
Series Title:
Bulletin - University of Florida Agricultural Experiment Station ; 214
Walker, M. N.
Place of Publication:
Gainesville, Fla.
University of Florida Agricultural Experiment Station
Publication Date:


Subjects / Keywords:
City of Leesburg ( local )
City of Belle Glade ( local )
Diseases ( jstor )
Cotton ( jstor )
Bolls ( jstor )

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Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.


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Wilmon Newell, Director



Fig. 1.-Diplodia boll rot. Only five out of 25 bolls escaped injury. The
leaves have been removed for photographing the bolls.
Bulletins will be sent free upon application to the
Agricultural Experiment Station

May, 1930

Bulletin 214



P. K. YONGE, Chairman, Pensacola RAYMER F. MAGUIRE, Orlando
A. H. BLENDING, Leesburg FRANK J. WIDEMAN, West Palm Beach
W. B. DAVIS, Perry J. T. DIAMOND, Secretary, Tallahassee

JOHN J. TIGERT, M.A., LL.D., President IDA KEELING CRESAP, Librarian
WILMON NEWELL, D. Sc., Director RUBY NEWHALL, Secretary**
S. T. FLEMING, A.B., Asst. Director K. H. GRAHAM, Business Manager
R. M. FULGHUM, B.S.A., Asst. Editor


W. E. STOKES, M.S., Agronomist
W. A. LEUKEL, Ph.D., Associate
G. E. RITCHEY, M.S.A., Assistant*
FRED H. HULL, M.S., Assistant
J. D. WARNER, M.S., Assistant
JOHN P. CAMP, M.S.A., Assistant
A. L. SHEALY, D.V.M., Veterinarian in
E. F. THOMAS, D.V.M., Asst. Veterinarian
R. B. BECKER, Ph.D., Associate in Dairy
W. M. NEAL, Ph.D., Assistant in Animal
C. R. DAWSON, B.S.A., Assistant Dairy

R. W. RUPRECHT, Ph.D., Chemist
R. M. BARNETTE, Ph.D., Associate
C. E. BELL, M.S., Assistant
H. L. MARSHALL, M.S., Assistant
J. M. COLEMAN, B.S., Assistant
J. B. HESTER, B.S., Assistant
W. A. CARVER, Ph.D., Assistant
E. F. GROSSMAN, M.A., Assistant**
RAYMOND CROWN, B.S.A., Field Assistant

C. V. NOBLE, Ph.D., Agricultural Economist
BRUCE McKINLEY, A.B., B.S.A., Associate
M. A. BROOKER, M.S.A., Assistant**
JOHN L. WANN, B.S.A., Assistant

L. W. GADDUM, Ph.D., Biochemist
C. F. AHMANN, Ph.D., Physiologist
J. R. WATSON, A.M., Entomologist
A. N. TISSOT, M.S., Assistant
H. E. BRATLEY, M.S.A., Assistant

A. F. CAMP, Ph.D., Horticulturist
M. R. ENSIGN, M.S., Assistant
HAROLD MOWRY, B.S.A., Assistant
A. L. STAHL, Ph.D., Assistant
G. H. BLACKMON, M.S.A., Pecan Culturist

W. B. TISDALE, Ph.D., Plant Pathologist
G. F. WEBER, Ph.D., Associate
A. H. EDDINS, Ph.D., Assistant
K. W. LOUCKS, M.S., Assistant
ERDMAN WEST, B.S., Mycologist


R. R. KINCAID, M.S., Assistant Plant Pathologist (Quincy)
JESSE REEVES, Foreman, Tobacco Experiment Station (Quincy)
J. H. JEFFERIES, Superintendent, Citrus Experiment Station (Lake Alfred)
W. A. KUNTZ, A.M., Assistant Plant Pathologist (Lake Alfred)**
B. R. FUDGE, Ph.D., Assistant Chemist (Lake Alfred)
W. L. THOMPSON, B.S., Assistant Entomologist (Lake Alfred)
GEO. E. TEDDER, Foreman, Everglades Experiment Station (Belle Glade)
R. V. ALLISON, Ph.D., Soils Specialist in charge Everglades Experiment Station (Belle Glade)
R. N. LOBDELL, M.S., Assistant Entomologist (Belle Glade)
F. D. STEVENS, M.S., Sugarcane Agronomist (Belle Glade)
H. H. WEDGWORTH, M.S., Associate Plant Pathologist (Belle Glade)
FRED YOUNT, Office Assistant (Belle Glade)
E. R. PURVIS, B.S., Laboratory Assistant in Soils (Belle Glade)
L. O. GRATZ, Ph.D., Associate Plant Pathologist (Hastings)
A. N. BROOKS, Ph.D., Associate Plant Pathologist (Plant City)
A. S. RHOADS, Ph.D., Associate Plant Pathologist (Cocoa)
STACY O. HAWKINS, M.A., Field Assistant in Plant Pathology (Homestead)
L. R. TOY, B.S.A., Assistant Horticulturist (Homestead)
D. G. A. KELBERT, Field Assistant in Plant Pathology (Bradenton)
R. E. NOLEN, M.S.A., Field Assistant in Plant Pathology (Monticello)
FRED W. WALKER, Assistant Entomologist (Monticello)**
D. A. SANDERS, D.V.M., Associate Veterinarian (West Palm Beach)
M. N. WALKER, Ph.D., Associate Plant Pathologist (Leesburg)
W. B. SHIPPY, Ph.D., Assistant Plant Pathologist (Leesburg)
C. C. GOFF, M.S., Assistant Entomologist (Leesburg)
J. W. WILSON, Ph.D., Assistant Entomologist (Pierson)
*In cooperation with U. S. Department of Agriculture.
**On leave of absence.



G EN ERAL ............................ .. .. ........... .......... 5

WILT OR "BLACK ROOT"............................................... 7

ROOT-KNOT OR NEMATODE DISEASE .................................. 10

BACTERIAL BLIGHT OR ANGULAR LEAF SPOT .......................... 13

RUST ............... ...... ..................................... 16

SORESHIN ...................................................... 18

DIPLODIA BOLL ROT .................. ........................... 29

ANTHRACNOSE ................................................... 22

BOLL ROTS ............. ... ................... .................. ... 24

LEAF SPOTS ............... ..................................... 27

DIRECTIONS FOR DELINTING COTTON SEED ............................ 30

Fig. 2.-Cotton stems cut to show the blackened vascular elements of
plants infected with wilt in contrast with the stem of a healthy plant at
the left.

The trend of modern agriculture is toward intensification. In
the case of cotton the need for this has been especially empha-
sized by the appearance of the boll weevil, and in the effort to-
ward intensification a number of minor factors causing losses
have become relatively more important. Among them are cotton
diseases which, in the aggregate, annually cause from 15 to 25
percent loss of cotton in Florida, and for the entire United States
from 15 to 20 percent, or between 2,000,000 and 3,000,000 bales
annually. It is the purpose of this bulletin to describe the more
important diseases of cotton occurring in Florida and to give
such methods of controlling them as are known.

There are a number of diseases causing loss of cotton in Flor-
ida. Most of them are caused by fungi, though one of them,
"rust", is caused by an unbalanced or deficient food supply, and
another, "root-knot", is caused by nematodes. Cotton diseases
are manifested in different ways and may or may not be injuri-
ous, depending on the time, location, extent, and severity of the
attack. Certain diseases, as boll rots and anthracnose, may at-
tack one or more parts of the plant, while others, as wilt and
rust, may be of a general or systemic nature, affecting the en-
tire plant. Some diseases are limited to a particular stage in the
development of the plant, as, for instance, the soreshin disease,
whereas others like anthracnose may attack the plant at any
stage of its development. Environmental conditions strongly in-
fluence the severity of plant diseases, but conditions favorable to
one disease may be entirely unfavorable to another, and unfav-
orable weather conditions alone may at times inhibit certain
diseases. Abundant moisture and rather high temperatures are
most favorable to the majority of the cotton diseases, and, as
such conditions usually prevail during the growing season, dis-
eases of cotton are common in Florida. The condition of the
plant may predispose it to disease, since a weakened plant is
more susceptible to injury by parasites than a healthy one; for
this reason the soil type and its management are factors influ-
encing the seriousness of some diseases. Some diseases, how-
ever, are worse when the plant is in a succulent, rapidly grow-
ing condition. Bacterial blight may be mentioned as an exam-
ple of this.

Florida Agricultural Experiment Station

The control of cotton diseases is a matter of preventing infec-
tion rather than of fighting it after it has appeared, since one of
the-most effective means of combatting plant diseases, spraying
or dusting, has not proved feasible on cotton. To devise satisfac-
tory means of controlling a disease of cotton it is necessary to
understand the disease and the conditions favorable to it. The
chief means used in controlling cotton diseases really pertain
to good culture and are relatively easy to carry out. They are
the use of good, disease-free or resistant seed, proper fertilization
and cultivation and suitable rotations. The application of these
methods to particular diseases will be taken up under the discus-
sion of the diseases, but it is well to explain them in a general
way at this point.
Good seed denotes viable seed of a productive variety that is
well adapted to the area in which it is to be grown. In addition
to these characters, the seed should be as free as possible of seed-
borne diseases, or if they are to be used on wilt infested soil they
should be resistant to wilt. Reliable seed dealers have selected
seed only from uniform, vigorous, productive, and disease-free
plants. Resistant seed have been saved from plants of the fore-
going type grown on soil heavily infested with the wilt organ-
ism, in order that plants showing the slightest susceptibility can
be eliminated. By doing this year after year some extremely re-
sistant varieties have been developed. A fact that should be men-
tioned here is that wilt is the only disease for which resistant
varieties have been developed; therefore, claims of resistance
to other diseases should be regarded with suspicion. On the
other hand, gin-run seed, the type generally used by Florida cot-
ton growers, offer none of these advantages. They are from
plants of varying uniformity, vigor, and productiveness, and
they have not been especially selected for resistance to the wilt
disease, nor for freedom from seed-borne diseases. Even if the
farmer has taken special precautions in saving his seed, his seed
will usually be mixed with poor seed at the gin, or contaminated
with diseases. It is, therefore, evident that seed should be pur-
chased at frequent intervals from seed companies of established
reputations, and seed saved should be ginned separately in order
to avoid admixture with undesirable seed.
Cotton that is in a vigorous, healthy condition is less liable
to attack by fungi than cotton that is weakened by poor cultural
methods and insufficient fertilization. Consequently, proper

Bulletin 214, Cotton Diseases in Florida

cultural methods are very important in lessening the damage from
various cotton diseases. Furthermore, many of the parasites
causing boll diseases are unable to attack uninjured bolls. There-
fore, the loss resulting from these diseases can be reduced by con-
trolling the boll weevil, and thus lessening the number of punc-
tured bolls.
By rotating cotton with other crops, as is recommended for
maintaining the soil in the best condition, many diseases caused
by parasites that live in the soil are reduced. Most cotton para-
sites are limited to cotton alone, consequently, the growing of
crops other than cotton deprives them of their food with the result
that they die out. Long rotation of cotton with resistant crops
alone are recommended for the control of root-knot.

Cotton wilt or "black root," as it is commonly called, is caused
by a soil-borne fungus, Fusarium vasinfectvm Atk. The disease
is widespread over the entire cotton belt, being more or less re-
stricted to the lighter soil types, and is especially severe where
the nematode or root-knot disease occurs. The losses attributed
to this disease vary somewhat from year to year, but for the en-
tire United States they amount to approximately 400,000 bales
annually. It is one of the worst diseases that the Florida cotton
farmer has to combat, but fortunately it is rather localized in its
distribution, and is rather easy to control by the use of resistant
varieties. It is very difficult to estimate the losses caused by wilt
in Florida on account of the lack of uniformity in its distribution
but fields have been observed in west Florida abandoned on ac-
count of this disease and in certain areas it is not uncommon to
find 50 percent of the plants killed. Cotton may be attacked at
any time after it is well out of the ground and the losses in young
cotton are often very serious.
The fungus lives in the soil on decaying cotton stalks, and
probably on other plant material, and is capable of surviving in
fields planted to crops other than cotton for a number of years,
though it gradually dies out after the culture of cotton has been
discontinued. It may be spread from field to field on the feet of
workmen and animals, on cultivation implements, and by wind
and rain. After plants are killed by wilt, the fungus forms spores
in great numbers around the bases of the plants. These spores
are extremely small and are borne by-wind and rain to infest

Florida Agricultural Experiment Station

new areas. If cotton is repeatedly grown, small infested areas
in a field will increase in size from year to year until the entire
field is infested. The disease is also reported as being carried
in the seed, but this is probably only an occasional occurrence.
The fungus enters the plant through the roots and makes its
way to the water-carrying vessels of the cotton plant where it
develops. Infection develops most readily at rather high temper-
atures, 85F. or above, closely agreeing with the optimum tem-
perature for the growth of cotton. The presence of the fungus in
the water-carrying vessels of the plant causes injury in two ways;
the excretion or secretion of a substance toxic to the plant, and
by the actual obstruction of the vessels, the former probably being
the more important. As a result of these injuries the plant mani-
fests certain characteristic evidences or symptoms of infection.


The name "wilt" accurately describes one of the principal symp-
toms of this disease, and the disease may be suspected where
wilting of plants occurs. Shortly after a cotton plant is attacked
by the disease, the leaves show a tendency to become flaccid and
dull green in color. At first the plant wilts in the middle of the
day and recovers somewhat over night. In a day or so, however,
the wilted condition becomes permanent; the leaves dry out and
become brown and shriveled, the browning first becoming evident
in the areas between the main veins of the leaves, and soon fall
off. During moist weather the period of alternate wilting and
recovery may be somewhat prolonged, but once a plant is attacked
by the disease its productiveness is either greatly impaired or is
entirely destroyed. New growth may occur, but it is limited to
the tips of the stem or branches and the older leaves are shed;
this, with the fact that the new growth is dwarfed and weak,
gives a tufted appearance to the plant that is characteristic. Such
a plant develops few bolls and most of these are shed. In some
cases there is a rather vigorous development of lateral branches
that is also characteristic of the wilt disease. This type of growth
is illustrated in Fig. 3. The principal diagnostic character of wilt,
however, is the brown or black appearance of the water-carrying
vessels of the plant, which may be observed by making a diagonal
section through the stalk. The manner of cutting and the appear-
ance of the cut stems of wilted and healthy plants are shown in

Bulletin 214, Cotton Diseases in Florida

Fig. 3.-A cotton plant showing the wilt disease. Note the almost entire
absence of bolls, and the galls on the roots, caused by nematodes.

Fig. 2. This discoloration of the vascular tissue of the cotton plant
is conclusive evidence of the presence of the wilt disease.

Fortunately, the wilt disease may be rather easily controlled
by the use of resistant varieties. Quite a number of wilt-resistant
varieties have been developed and several of them are satisfactory
for Florida conditions. There is a tendency for the wilt resistant
varieties to be a little later than some of the non-resistant varie-
ties, but this is a point of minor importance where wilt is abund-
ant. Only wilt-resistant varieties should be planted on infested
soil, and seed of such varieties should be obtained from only relia-
ble seedsmen who have grown their seed on wilt-infested soil. In
saving his own seed the farmer should select seed only from the
healthiest plants in the wilt soil and should gin them separately
to avoid mixture with less desirable seed. In any case, new seed
should be obtained every two or three years, as admixture occurs
unless special facilities to prevent this are available. Resistance

10 Florida Agricultural Experiment Station
to wilt is sometimes lessened in fields also infested with nematodes
or root-knot. Some varieties of cotton seem to be resistant to
nematodes as well as to wilt but no definite recommendations can
be made on this score at this time. Consequently, it is better not
to plant cotton at all in fields heavily infested with both wilt and
nematodes. Such fields can be used satisfactorily for small grains,
corn, Iron or Brabham cowpeas, or other crops that are not sus-
ceptible to root-knot.
Applications of potash are sometimes said to be effective in con-
trolling wilt, but in a number of experiments at Gainesville no
great difference could be seen in plots that had the usual amount
of potash, 4 percent, and those that had extremely large amounts
of potash. Since wilt can be easily controlled by the use of resist-
ant varieties of cotton, of which there are a large number to select
from, it is not advisable to content oneself with makeshifts.
Some wilt-resistant varieties of cotton suitable to Florida con-
ditions are: Willis, Lightning Express No. 7, Rhyne's Cook,
Cook 307-6, Miller, Cleveland 54, and Council Toole. This list of
varieties contains representatives of all the principal types of
cotton grown in Florida, and substitutions of resistant varieties
can be made without sacrificing a favorite type.


The root-knot disease is caused by minute worms or nematodes
which are ordinarily very slender and thread-like, though the
adult female becomes almost spherical in shape. These worms
are known scientifically as Caconema radicicola (Greef) Cobb,
formerly as Heterodera radicicola (Greef) Muller.
Root-knot is a widespread and injurious disease of cotton as
well as of a large number of other plants, particularly the truck
crops. In addition to severe damage caused by the disease itself,
other parasites gain entrance through the galls on the roots, and
further the injury. Cotton wilt is much worse where root-knot
occurs. Root-knot of cotton occurs in Florida and, though cotton
is not so badly attacked as some other hosts, considerable damage
is done in some fields. The loss for the state as a whole, however,
probably does not exceed 1 percent. For the entire cotton belt,
the United States Department of Agriculture estimates the loss
at between 100,000 and 150,000 bales a year. Root-knot is more
common and injurious on the lighter soils, but it may also occur
in the heavier soil types. The application of large amounts of

Bulletin 214, Cotton Diseases in Florida

stable manure seems to especially favor the multiplication of the
worms. The presence of nematodes on cotton should indicate a
special handling of the soil to prevent loss of more susceptible
crops, such as many of the garden or truck crops, and to prevent
the worms from multiplying to such an extent as to become a
serious factor in the growing of cotton. Cotton grown after an
especially susceptible crop is much more severely injured than it is
when grown after an immune crop.
The young worms are capable of surviving several months of
a non-parasitic existence in the soil. When susceptible hosts are
available, however, the worms bore into the roots just back of
the growing tip, and some toxic substance formed by them stim-
ulates the roots to the development of galls. Young galls are
white in color, but later they become darker in color and irregular
in shape on account of attacks by insects and fungi. Where the
field is heavily infested practically all of the roots are covered
with galls which, in the case of cotton, usually do not exceed a
half inch in diameter, though in certain extremely susceptible
crops the galls may become as large as two inches in diameter.
The female lays eggs in the roots which hatch into the larvae.
The larvae migrate through the roots, causing other galls, or they
may escape into the soil to attack other plants. A female may lay
as many as 500 eggs and under favorable conditions a number of
generations may occur during a year. The injury to the plants
results from the disturbance of the normal water-carrying ca-
pacity of the roots, and the degree of injury is proportional to
the number of galls.
Nematode injury to the roots may be manifested above ground
by a yellowing and stunting of the plants. The degree of yellow-
ing or stunting is determined by the severity of the attack on the
roots and varies from an unnoticeable condition to the death of the
plant. The final proof of the presence of this disease is the
finding of galls or knots on the roots of suspicious looking plants
that have been pulled up. The root injury of cotton plants by
nematodes is illustrated in Fig. 4.
The only means of controlling root-knot feasible of execution
by the cotton farmer is suitable rotation of crops. Soil infested
with nematodes should not be planted to cotton or any other sus-
ceptible crop. There are a number of crops that are not suscep-

Florida Agricultural Experiment Station

Fig. 4.-Root-knot on the root system of a cotton plant infested with

tible to nematodes and such crops should be planted until the
worms die out or are greatly reduced in numbers. To entirely
kill out an infestation even by the use of immune crops is very
difficult, since there are many weeds that may serve to carry the
worms over from year to year. The infestation can, however, be
reduced greatly by suitable rotations largely made up of immune
or resistant crops. Some of the more common crops that are not
susceptible to attack by root-knot are beggarweed, chufas, corn,
cowpeas (Brabham, Iron and Monetta varieties only), most
grasses, peanuts, rye, sorghum, velvet beans, winter oats and
Crotalaria. It has been found that there is considerable varia-
tion in the susceptibility of different varieties of cotton to nema-
'tode injury but as yet no definite recommendations can be made
in this regard.

Bulletin 214, Cotton Diseases in Florida

Bacterial blight, caused by Pseudomonas malvacearum EFS.,
is a very common disease of cotton in Florida, and injures cotton
in all stages of its development. It is present in practically every
cotton field in Florida, and its direct and indirect injuries are
sufficiently severe to class it as one of the most serious of Florida
cotton diseases. It is practically impossible to properly evaluate
the losses caused by this disease, since its worst damage results
from its association with other parasites; in fact, much of the
damage attributed to other diseases, particularly the boll rots,
might properly be referred to bacterial blight. The United States
Department of Agriculture, however, estimates the losses due to
this disease for 1927 as 2.6 percent of the crop of the entire cotton
belt, or approximately 500,000 bales. During wet seasons the dis-
ease is much worse than it is during dry seasons. This is ex-
plained by the fact that wind-blown rain is one of the chief factors
in spreading this disease in the field, though insects and other
factors also play some part in its dissemination.
The most frequent and serious attacks of bacterial blight are
on the leaves and bolls, though the seedlings and the stems and
branches of older plants are also injured. The names "black-arm"
and "angular leaf spot" are often used to designate the disease
on the stems and leaves, respectively. The spots on the leaves
are particularly characteristic, and are the most commonly ob-
served symptoms of bacterial blight. Since the symptoms of the
disease on the seedlings and on the bolls are less distinctive, they
have not been designated with special names. The attacks on the
bolls constitute the most serious phase of the disease, because,
in addition to the direct injuries to the bolls, bacterial blight opens
the way for a number of secondary parasites that are themselves
unable to penetrate the uninjured tissues of cotton bolls. Conse-
quently, it is usually very difficult to distinguish blight lesions on
bolls a few days after infection because secondary parasites enter
them shortly after they are formed. Some of the secondary par-
asites after entering outgrow the blight organism and bring about
an even more rapid and complete rot of the bolls than P. malvac-
The disease is carried over winter on the seed and on diseased
parts of the cotton plant. From these sources of infection the bac-

Florida Agricultural Experiment Station

teria attack the cotyledons of the seedlings and later spread to
the new growth as it develops.
The disease appears on the cotyledons and leaves as dull
green, water-soaked areas. The spots on the leaves are bounded
by the veins of the leaf and are definitely angular in shape.
The spots later dry out, becoming brown in color, surrounded
by a reddish border. The individual spots rarely become a
quarter of an inch in diameter and they are usually con-
siderably smaller. The lesions may be scattered over the entire
surface of the leaf or may be concentrated in the neighborhood
of the main veins. A number of the spots may coalesce (run to-
gether), causing the rapid death and shedding of the leaves. Un-
der especially favorable conditions the disease may move down
the pedicels of the leaves and attack the young, tender shoots,
causing their death. The leaves and stems killed by this viru-
lent attack become black and shriveled in appearance and remain
on the plant. The name "black-arm" is applied to this type of in-
jury. These lesions on the leaves furnish excellent openings for
the entry of fungi that are unable to attack the uninjured leaf,
and in Florida the greatest defoliation of cotton occurs where a
fungus, Alternaria sp., accompanies angular leaf spot. Com-
plete defoliation has been observed in wet years under such cir-
cumstances, but defoliation from angular leaf-spot alone is rarely
so severe.
The most serious form of the disease, however, occurs on the
young bolls, where small spots similar to those on the leaves may
occur. These spots enlarge, unlike those on the leaves which are
bounded by the small veins, and a few of them may cover the
entire boll. Such bolls become dry and do not open, or if they do
the lint is usually discolored and rotten. Ordinarily, however,
other fungi get into the lesions and outgrow the angular leaf spot
organism, causing a more rapid rot than would otherwise occur.
This is the indirect injury done by the disease. In fact, the dam-
age from all boll rots would be greatly diminished if angular leaf
spot were controlled, since most of the boll rot fungi are unable
to attack a healthy boll, and even in the case of those that can
penetrate the boll themselves infection is much more abundant
and severe if angular leaf spot lesions are present. In Fig. 5 are
shown two types of injury to cotton leaves caused by the bacter-
ial blight organism.

Bulletin 214, Cotton Diseases in Florida

Fig. 5.-Two types of bacterial blight injury to cotton leaves. The leaf
on the left exhibits the angular leaf spot type of injury.

Angular leaf spot can be greatly reduced by carefully selecting
the seed from disease-free fields or from parts of fields least at-
tacked by the disease. It has been found that by delinting the
seed with sulphuric acid the disease can be practically eliminated,
since over-wintering in debris in the field seems to be unimport-
ant. The method is rather dangerous for persons inexperienced
in handling the acid, which is very caustic, and it is not recom-
mended as a general practice, though county agents will be glad
to help where it is desired to delint, and full directions for de-
linting are given in the back of this bulletin.
Delinting, in addition to helping in the control of cotton diseases,
makes planting much easier, since the lint-free seed can be planted
in an ordinary corn planter through a peanut plate. Where sev-
eral farmers can work together the delinting can be cheaply and
satisfactorily done. There is no doubt but that within a few years
there will be many seed houses handling delinted seed on account
of its convenience in planting and its great help in eliminating cer-
tain diseases.
By treating cotton seed with various poisonous dusts, angular
leaf spot has been controlled to some extent, but at the present
time it is not possible to make definite recommendations as to their
proper use.

Florida Agricultural Experiment Station

Rust, also called black rust, yellow leaf blight, and potash hun-
ger, unlike the other Florida cotton diseases, is not caused by par-
asites, but has its origin in a disturbed nutritional condition
brought about by a number of factors. The most important of
these factors is an actual deficiency of potash in the soil. Contrib-
utory to this are poor cultural conditions due to poor drainage, de-
ficient moisture, lack of humus, improper mechanical condition,
and worn-out soils. In fact, rust is practically synonymous with
poor farming, since fields where this disease occurs, worst have
been abandoned on account of failure to use fertilizer or to keep
down grass and weeds. It is true, however, that rust also appears
in fields that apparently have received good care. In such cases
the disease is usually in spots in the field characterized by poor
drainage, or by thin or rocky soil, and it will recur from year to
year if something is not done to improve conditions in these
Rust is a common disease in Florida and does a great deal of
damage on the lighter and poorer soils where practically total de-
foliation has been observed. The disease varies in severity in
different localities and even within the same field. This fact makes
estimates of loss for the state as a whole difficult and of little value,
because often where the disease is'worst the fields are abandoned
and are not considered in the computation of yields for the state.
If such fields were considered, the estimated yield per acre for
cotton for Florida would be even less than it is now, and the
percentage loss attributed to this disease would be greater. The
United States Department of Agriculture estimates the loss for
the entire cotton growing area of the South as 4 to 5 percent of
the crop. The loss from the disease in Florida probably exceeds
these figures somewhat, since the proportion of lighter soils used
for cotton in Florida is greater than it is in other states.


Plants suffering from rust are usually small and of an unthrifty
appearance. About the middle of the season the leaves assume a
mottled yellow color, the areas around the veins maintaining their
green color the longest. They later become rusty red in appear-
ance, curl up and shed. The weakened leaves are particularly
subject to the attacks of a number of parasites too weak to attack

Bulletin 214, Cotton Diseases in Florida

Fig. 6.-Cotton leaves showing two types of rust in-

them when in full
vigor, and defol-
iation is often
hastened in this
manner, especial-
ly in wet weather.
The Alternaria
disease mention-
ed in connection
with bacterial
blight is the most
common of the
secondary para-
sites aggravating
rust injury. Two
types of rust in-
jury are shown
in Fig. 6.

Fields showing
rust must be built
up if cotton is to
be grown success-
fully. This may
be done by rota-
tions in which or-
ganic matter or
humus is added to
the soil, and by
proper tillage,
drainage of low
areas, and proper
fertilization. Pot-
ash often acts al-
most as a specific
in controlling
rust, but without
proper attention

Florida Agricultural Experiment Station

to other details full benefit from its use cannot be obtained. It
is probable that there are but few cotton lands in Florida on which
potash can be safely omitted, and 3 or 4 percent of the fertilizer
used on cotton should consist of this element.

The soreshin disease is caused by the fungus Corticium vagum
solani Burt, the mycelial stage of which is known as Rhizoctonia
solani Kuhn; and the disease is still often spoken of as the Rhi-
zoctonia disease. The soreshin disease is the most common cause
of poor stands of cotton in Florida. Its injuries are ordinarily at-
tributed to cold, damp weather in the spring, but if it were not for
the presence of the causal fungus in the soil, the young cotton
stems and roots would remain white and healthy except for oc-
casional plants attacked by some other fungus. The fungus, how-
ever, is extremely widespread throughout the United States, and
foreign countries as well, and attacks a great many plants
other than cotton. On account of the nature of injury it is
impossible to make estimates of loss, but poor stands mean low
yields per acre.
The fungus causing soreshin lives in the soil from year to
year on decaying plant material and under favorable conditions
is capable of attacking a kreat many different kinds of plants
when they are young. The pathogenicity of the fungus is en-
tirely dependent on the temperature of the soil, and after the
soil has become thoroughly warmed the fungus is incapable of
attacking the plants, but at temperatures below about 80F. the
disease attacks young plants, the extent of injury increasing to-
ward the lower temperatures. If favorable temperatures are
constantly maintained 100 percent killing of the cotton seedlings
is common, but comparatively brief periods of exposure to unfav-
orable temperatures, that is, high temperatures, are sufficient to
reduce greatly the severity of the disease. This is the reason that
greatest injury from the soreshin disease occurs during damp,
cool, cloudy periods during which the soil maintains uniformly
low temperatures. Since, on account of the boll weevil, it is nec-
essary to plant cotton earlier than it would be ordinarily, the
prevalence of this disease has increased. The soreshin fungus
is also capable of rotting cotton bolls, but the rot occurs rather
infrequently and only on bolls close to or in contact with the soil.

Bulletin 214, Cotton Diseases in Florida

Fig. 7.-Cotton plants showing varying degrees of injury from the
soreshin disease.
The soreshin disease of cotton is characterized by a breaking
over of the young plants just at the soil level, where they have
been rotted by the causal fungus. Before this stage is reached the
plant assumes a dull green color and the leaves become limp. If
such plants are pulled up large dark brown cankers will be ob-
served just below the soil level. These cankers may girdle the
plant and bring about the falling over of the plants noted above.
When the cankers do not completely girdle the stem, the plants
may recover, but as a result of the injury they usually remain

Florida Agricultural Experiment Station

stunted and weak for some time. After the plants attain a little
size the fungus is unable to attack them even though the weather
becomes favorable to the disease. By the time the plants have be-
come large enough to be chopped danger from the soreshin dis-
ease is past and a stand has or has not been established. Young
cotton plants injured by the soreshin disease are illustrated in
Fig. 7.
The damage caused by the soreshin disease in reducing stands
can be lessened by the planting of a bushel of seed to the acre, by
not planting too early, and by cultivating to allow the soil to dry
out and warm up more rapidly. Planting in ridges helps in drying
out and warming up the soil, since more area is exposed to the
sun's rays. So far as is known there is no successful means of
treating the seed to control this disease.

The name Diplodia boll rot is derived from the name of the fun-
gus causing the disease, Diplodia gossypina Edg. This boll rot is
the most serious one occurring in Florida. Many fields in this
state have been observed where 50 percent of the bolls were worth-
less from this cause, and there is hardly a cotton field in the state
where it cannot be found. The damage to the crop as a whole in
the State of Florida during the wet season of 1928 was conserva-
tively estimated at 20 percent.
The fungus is unable to penetrate uninjured tissue, but the
slightest wound or abrasion is sufficient to allow the fungus to en-
ter. Diplodia, after once entering a boll, develops very rapidly,
and only two or three days of humid weather are sufficient for the
fungus to completely rot the boll. The lesions caused by bacterial
blight and anthracnose on the bolls, especially the former, are com-
mon points of entry for Diplodia, as are also the punctures of boll
weevils and of other insects.
Diplodia is capable of living in the soil for indefinite periods of
time on the decaying debris of cotton and other plants. From this
original source of infection the spores of the fungus are scattered
by the wind or other agencies to the bolls, where they germinate
and grow into the bolls, if they are the least bit damaged. The
rotted bolls produce great numbers of spores that are scattered
over the field and serve to infect other bolls. The seed produced
in such bolls are usually rotted and do not germinate. In germina-

Bulletin 214, Cotton Diseases in Florida

tion tests on large numbers of gin-run seed, a high percentage of
those that failed to germinate were found to contain Diplodia in
a viable condition.
The early stages of infection by Diplodia offer no distinguish-
ing characteristics. In Gainesville, where most of the work on this
disease has been done, a large percentage of the primary infec-
tion of the bolls seems to be caused by bacterial blight, and it has
been impossible to bring in blight lesions on the bolls early enough
to avoid infection by Diplodia. As a consequence of this it has
been hard to distinguish between the two until the rot was rather
far advanced. However, the diseased areas seem to enlarge much
faster in the case of secondary infection by Diplodia, since almost
half of a boll will appear to be water-soaked and darkened after
24 hours during moist weather. After another 24 hours the entire

Fig. 8.-Cotton bolls showing injuries caused by Diplodia.
boll will be darkened, rather soft and somewhat shrunken, with
small tufts of dirty white mycelium occasionally appearing. After
this the boll becomes hard and the fruiting pustules of the fungus
appear. Vast numbers of spores are extruded by these pustules,
the pycnidia. In wet weather the spores at first are white in color
but become black after a short while. When the boll is thoroughly
dry the masses of black spores give a sooty appearance to the boll
that is very characteristic. The lint of such bolls is badly rotted,
very dark in color, and utterly worthless. Bolls infected with
Diplodia usually do not open, and if they do only expose lint that
is badly stained and of very inferior quality. Bolls that have
been rotted by Diplodia are shown in Fig. 8.

Florida Agricultural Experiment Station

The injuries from Diplodia may be lessened by not growing
cotton repeatedly in the same field, and by reducing, as far as pos-
sible, all injuries to the bolls caused by bacterial blight, anthrac-
nose, the boll weevil and other insects, and by cultural implements.

Anthracnose is caused by the fungus Glomerella gossypii
(South.) Edg., or, as it was formerly known in its asexual stage,
Colletotrichum gossypii South. Anthracnose occurs in Florida
and was formerly the cause of a great deal of damage to cotton,
as high as 90 percent loss of bolls having been reported from some
fields. During the past three years, however, it has been ex-
tremely hard to find, and losses from it have been negligible.
Though varying widely in severity from year to year in individual
localities, the annual loss from this disease for the entire South,
as reported by the United States Department of Agriculture, av-
erages about 150,000 bales. The fungus over-winters in or on
the seed or in decaying cotton debris in the field. The latter meth-
od of over-wintering does not now appear to be of the importance
once attributed to it, and the fact that the disease is largely seed-
borne renders control an easier matter. From over-wintered fun-
gus material in or on the seed the disease is spread to the young
seedlings. As later growth appears the fungus attacks leaves,
stems and bolls, the greatest injury occurring on the bolls. The
fungus forms spores in large numbers on diseased bolls and often
on the seed themselves. The spores are scattered to the lint and
seed of healthy bolls in the field. Furthermore, the lint from a
few diseased bolls is sufficient to contaminate a great many seed
at the gin. Thousands of spores have been found on seed which
to the naked eye appeared healthy. The spores are comparatively
short-lived, however, and only a few survive longer than one year
in stored seed.

The young seedlings which develop from seed affected with an-
thracnose may damp-off and die or may merely show lesions on the
cotyledons. The damping-off by anthracnose resembles the damp-
ing-off caused by Rhizoctonia and other fungi, and refers to the
rotting off of the young seedling at or below the ground level.
Oftentimes the seed fail to germinate or the seedling is entirely

Bulletin 214, Cotton Diseases in Florida

rotted before reaching the surface. The spots on the cotyledons
are dead areas of irregular outline and are of less importance than
the damping-off, though they may spread to involve the whole
top of the seedling, which is thus killed. The lesions on the stems
and leaves of large plants are not a serious manifestation of the
disease and usually follow the attacks of the bacterial blight or-
ganism. The most injurious manifestation of anthracnose occurs
on the bolls, where the symptoms vary somewhat, depending on
the time and nature of the infection. Infection may take place
through the dead pistils of the flowers, in which case the entire
contents of the boll may be rotted with but minor external evi-
dences of disease at the tip of the boll. The most commonly de-
scribed type of anthracnose injury follows infection on the side
of the boll with or without the aid of injuries to the surface of the
boll from other causes. Infection often also occurs along the lines
of dehiscence of the boll. Following penetration of the boll, brown-
ish spots are formed which are somewhat sunken and surrounded
by a reddish border. The spots may enlarge under favorable con-
ditions to involve half of the boll, and by the coalescence of a
number of spots the whole boll may be destroyed. The centers of
the spots become covered with the orange-pink, slimy masses of
spores during wet weather, but may be gray and very similar in
appearance to bacterial blight lesions in dry weather.
When the infection occurs in young, succulent bolls a general rot
often occurs and the lint and seed become dark brown and dry


Fig. 9.-Bolls showing different degrees of anthracnose injury.

Florida Agricultural Experiment Station

down into a brittle, worthless mass. Bolls attacked later may
have but one or two locks infected. The infected locks fail to de-
velop and the bolls become lop-sided, a condition characteristic of
anthracnose. The lint of such locks becomes somewhat darkened
in color and of low quality. When bolls somewhat rotted by bac-
terial blight are attacked by anthracnose a general, uncharacter-
istic rot develops. Other fungi often accompany anthracnose and
further its injuries, and it is possible that secondary fungi are
often credited with damage really due to anthracnose. Bolls dam-
aged by anthracnose are shown in Fig. 9.

Since cotton anthracnose is largely a seed-borne disease and
since the spores and mycelium are comparatively short-lived, the
control of the disease is a relatively easy matter. It has been
found that the disease dies out in the seed if they are kept for two
years or more and that the germination of the seed is not impaired.
A period of only one year is sufficient to greatly reduce infective
material in the seed, but longer periods of storage entirely destroy
it. The seed should be stored in a dry place, otherwise, they will
heat or rot and much of their germinative power will be lost. It
is probable that seed houses are able to furnish seed that have
been kept a sufficient time to eliminate the anthracnose fungus.
If, in connection with the planting of disease-free seed, a ro-
tation is practiced to obviate the possibility of the disease carry-
ing over in debris in the field the disease can be entirely eradicated.
Where a farmer desires to save his own seed, the seed should be
selected only from healthy bolls in fields or sections of fields show-
ing the least disease, anthracnose as well as other diseases. The
seed should be ginned separately from the main crop in clean
gins in order to prevent the contamination of the seed to be saved
with spore or fungus material from the main crop.

Although there are a number of species of Fusarium causing
boll rots in Florida, by far the most common one is caused by
Fusarium moniliforme Sheld. This fungus is extremely widely
distributed in the United States, as well as in foreign countries,
and causes losses on a number of hosts, one of the more important
being corn. The fungus is seemingly unable to penetrate unin-

Bulletin 214, Cotton Diseases in Florida

jured bolls, but the wounds caused by insects and the lesions of
other diseases furnish ample means of entry. In some fields in
Florida the Fusarium boll-rot has been found in almost as great
abundance as the previously discussed Diplodia, though ordinarily
it is of much less importance than Diplodia.
F. moniliforme is also capable of causing a seedling rot and a
root rot. The general importance of these two types of injury is

Fig. 10.-Bolls showing different types of Fusarium injury. Bolls infected
with Fusarium offer no characteristic appearance, as the fungus usually
enters bolls already injured by other causes.

as yet not determined. The fungus can maintain itself in the
soil for indefinite periods of time, and can remain viable in the
seed for several months at least, though infected seed do not
usually germinate.
The damage to the bolls is the most serious type of injury.
Bolls attacked by this fungus rot and soon become covered with a
velvety mass of mycelium and spores, varying from pink to al-
most white in color. The spores are formed in extremely large
numbers and serve to further spread the disease. The lint of bolls
rotted by this fungus becomes stained a pink or yellow color, the
fibers stick together tightly, and are abundantly covered with the
fruiting stage of the fungus. Such lint is weak, easily broken, and
of little value. Probably the greatest injury from the disease
results from the fungus growing into the lint of partially open
bolls, or those that have been somewhat injured by other causes.
Rotting of the lint in the manner described above then follows.

Florida Agricultural Experiment Station

Fig. 11.-Rhinotrichum boll rot.

Bolls attacked by F. moniliforme
are shown in Fig. 10. The in-
juries caused by this disease may
be lessened by following the sug-
gestions made for the control of
the other boll rots.
A large number of other fun-
gi have been reported as caus-
ing rots of cotton bolls, but they
are usually of uncommon occur-
rence or only appear abundantly
on bolls rotted by more vigorous
parasites, and as a whole are of
little economic importance. Rhi-
notrichum tenellum B. & C oc-
curs commonly in Florida and is
conspicuous on account of a
dense felty growth of the gray
to dirty white mycelium, as
shown in Fig. 11. Another fun-
gus that resembles Rhinotrich-
um, though occurring less com-
monly, is Olpitrichum carpophi-
lum Atk. The extremely com-
mon soil organism, Sclerotium
rolfsii Sacc., which causes se-
vere losses on some other crops,
occasionally occurs on cotton
bolls in Florida. The bolls at-
tacked by this fungus are usual-
ly in contact with or near to the
soil, and are of a very character-
istic appearance as they become
covered with large numbers of
the sclerotia of the fungus
which resemble mustard seed. A
boll of this type is shown in Fig.
12. Injuries caused by these
fungi may be reduced by the
measures recommended for con-
trolling other boll diseases.

Fig. 12.-A cotton boll covered with
the sclerotia of Sclerotium rolfsii.

Bulletin 214, Cotton Diseases in Florida

There are a con-
siderable number
of fungi causing
leaf spots on cot-
ton, but most of
them are of small
or occasional im-
portance. The
m'o s t commonly
observed and im-
portant of these
leaf spots is caus-
ed by an Alterna-
ria sp. This fun-
gus attacks cot-
ton leaves that
are weakened by
rust or which
show bacterial or
Cercospora le-
sions. The spots
are usually ir-
Fig. 13.-A cotton leaf showing the type of injury regularly circu-
caused by Alternaria sp. Note concentric ringing in
certain of the spots. lar in shape and
may reach a size
of one-half inch in diameter. The spot is brown in color, of papery
consistency, and is usually marked by a series of concentric rings.
The spores are borne on these spots, sometimes in sufficient
quantity to give a black cast to the spot. By the coalescence
of several spots the whole leaf may become involved and soon
shrivels and falls off. Under moist conditions, defoliation may
be severe; and late in the season the fungus is extremely abun-
dant on the mature leaves and causes them to be shed earlier
than would normally occur. In Fig. 13 is shown a leaf attacked
by Alternaria.
Another extremely common leaf spot in Florida is that caused
by the conidial stage (Cercospora gossypina Cke.) of Mycos-
phaerella gossypina (Atk.) Earle. The Cercospora leaf spot, as it
is commonly called, is extremely common in Florida cotton fields,
but usually does not cause serious defoliation unless accompanied
by Alternaria. The fungus is capable of attacking uninjured tis-

Florida Agricultural Experiment Station

sue, and thus furnishes abundant facilities for the entry of the
more rapidly growing Alternaria. The spots caused by Cercospora
are usually small, rarely as large as a quarter of an inch in diam-
eter, and are rather characteristic in appearance, due to their pur-
ple border and the bleached, whitish appearance of their centers
which often fall out, giving the leaf a ragged appearance. The

Fig. 14. Cercospora
leaf spot. Note the whit-
ish centers of the spots.

spores are borne on clumps of dark-colored conidiophores that may
sometimes be seen with naked eye in the center of the spots, and
later in the season the perithecia of the perfect stage may appear.
In Fig. 14 are shown Cercospora spots on a cotton leaf.

Bulletin 214, Cotton Diseases in Florida

Another rather common leaf spot in Florida is known gener-
ally as areolate mildew, and is caused by the fungus Septocylin-
drium areola (Atk.) P. & C. The disease causes little damage,
but because of its conspicuousness should be mentioned. The

Fig. 15.-A leaf attacked
by Septocylindrium arcola.
Note the white color and
angular shape of the spots.

spots are angular in shape, being limited by the veins of the leaf,
and are white in color, though darkening somewhat with age. The
spots may become as large as one-half inch in diameter, but are
usually considerably smaller. A leaf attacked by this fungus is
shown in Fig. 15.
A true rust, Kuhneola gossypii Arth., has been reported from
Florida on cotton leaves, but it is rare and of no economic impor-
A disease that occurs in Florida, though usually to a small ex-
tent, is the Ascochyta disease of cotton caused by Ascochyta gos-
sypii Sydad. On at least one occasion, however, this disease

Florida Agricultural Experiment Station

caused considerable damage in a limited area. The disease may
attack all of the parts of the cotton plant above ground and may
cause the death of the entire plant. The injury to the stem is
the most severe manifestation of the disease, though leaves and
bolls may also be seriously injured. The disease on the stem us-
ually occurs around the axils of the leaves where a lesion or canker
forms that soon brings about the death of the leaf. The cankers
become sunken and the diseased tissue becomes ragged and often
falls out. This type of attack is characteristic of the Asochyta
disease. Measures recommended for controlling other diseases,
particularly rotation, will probably prevent this disease from
reaching serious proportions.

The process of delinting cotton seed with sulphuric acid consists
of dissolving the lint on the cotton seed with concentrated sul-
phuric acid and then washing off the acid, leaving the seed with
a smooth brown coat without any fuzz. This treatment will kill
most of the disease organisms carried on the seed, resulting in
healthier seedlings and a better stand. The process will also aid
germination materially in light dry soils.

The equipment necessary for delinting consists of two large
wooden tubs, which can easily be made by cutting a water-tight
barrel in half, wooden paddles with long handles, some hardware
cloth with one-eighth inch mesh, and a supply of commercial sul-
phuric acid containing at least 75 percent acid. (Acid ordinarily
used by fertilizer companies in making acid phosphate can be
used). Construct a strainer from one of the tubs by boring a large
number of inch-holes in the bottom and covering the bottom, in-
side, with hardware cloth tacked in place; a convenient strainer
may also be made by replacing the bottom of a stout box with
hardware cloth supported by lath slats. The strainer should be
placed over a hole in the ground deep enough to drain away the
acid and wash water. The inside of the tubs may be covered with
hot roofing pitch to prevent the acid from acting on the wood.

Bulletin 214, Cotton Diseases in Florida

Place about a bushel of seed in a tub and add about 15 pounds*
(4 to 41/2 quarts) of the concentrated sulphuric acid and stir with
wooden paddles until the seed and acid have formed a sticky mass
and the lint has been entirely dissolved. The seed should be
stirred vigorously and continuously, as the rubbing of the seed
together aids materially in the process. In stirring be sure to get
the acid mixed up thoroughly with the seed, as it tends to settle
to the bottom when first poured onto the mass of seed. Delinting
should be complete in about 20 minutes or less. If one is doubtful
concerning the progress of the reaction, it can easily be deter-
mined whether the fuzz has been dissolved by removing a few
seed and washing them in water (use a wooden paddle to remove
the seed-do not get your hands in the acid).
The seed will usually retain a tiny tuft of fuzz at one end with
any ordinary delinting, and with some varieties of seed it is not
desirable to attempt to remove the fuzz completely on account of
the time necessary. It is important that the seed and acid be
kept warm as this hastens delinting a great deal. Work in the
sun and avoid carrying on the work on a cold day. When delint-
ing is complete fill the tub quickly with water; keep an extra tub
or other large container at hand filled with water to be poured over
the mass of seed and acid, as it is very important that this be done
very rapidly in order to prevent heating of the seed mass due to
the combination of the water and the acid. Stir the seed up
thoroughly in the water and pour seed and water into the strainer
which has been placed over the drainage hole. The seed should
now be washed thoroughly while still in the strainer (stirring
vigorously), after which they can be spread out and dried, prefer-
ably away from direct sunlight.
There is no particular danger of damaging the seed by this
treatment if instructions are followed. The seed can remain in
the concentrated acid for 30 to 50 minutes without danger of in-
jury, but they should not be left standing in the wash water
long enough to soak them up much.

*-The amount of acid will vary somewhat with the grade obtained, but
the above amount is approximately correct. If it is desirable to save time,
more acid may be used, but the time saving is rather small.

32 Florida Agricultural Experiment Station

It is necessary to be careful in handling the acid, as it will
burn or blister the skin very easily and eat through cotton clothes
with great rapidity. Keep your hands out of it, and do not allow
it to splash or spatter. Have at hand some water which has been
saturated with baking soda and use this to put on any acid which
you may get on your skin or clothes.
Do not use sulphuric acid in metal utensils; use glass or wood
and replace the hardware cloth on the strainer when it becomes
badly damaged.