Group Title: Bulletin University of Florida. Agricultural Experiment Station
Title: Some diseases of cabbage and other crucifers in Florida
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00026441/00001
 Material Information
Title: Some diseases of cabbage and other crucifers in Florida
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 62 p. : ill. ; 23 cm.
Language: English
Creator: Weber, George F ( George Frederick ), b. 1894
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1932
Copyright Date: 1932
 Subjects
Subject: Cabbage -- Diseases and pests -- Florida   ( lcsh )
Cruciferae -- Diseases and pests -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by George F. Weber.
General Note: Cover title.
 Record Information
Bibliographic ID: UF00026441
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 - AEN4722
oclc - 18204836
alephbibnum - 000924117

Full Text





HISTORIC NOTE



The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida






Bulletin 256 December, 1932
UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA
Wilmon Newell, Director



SOME DISEASES OF CABBAGE
AND OTHER CRUCIFERS IN
FLORIDA
By GEORGE F. WEBER












r











Fig. 1.-Bottom rot of cabbage. The foliage leaves in the foreground have
been broken down to show the disease. (Bul. 242.)



Bulletins will be sent free upon application to the
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA








EXECUTIVE STAFF BOARD OF CONTROL
John J. Tigert, M.A., LL.D., President of the P. K. Yonge, Chairman, Pensacola
University A. H. Blanding, Bartow
Wilmon Newell, D.Sc., Director Raymer F. Maguire, Orlando
H. Harold Hume, M.S., Asst. Dir., Research Frank J. Wideman, West Palm Beach
J. Francis Cooper, M.S.A., Editor Geo. H. Baldwin, Jacksonville
R. M. Fulghumi B.S.A., Assistant Editor J. T. Diamond, Secretary, Tallahassee
Ida Keeling Cresap, Librarian
Ruby Newhall, Administrative Manager
K. H. Graham, Business Manager BRANCH STATIONS
Rachel McQuarrie, Accountant
NORTH FLORIDA STATION, QUINCY
S L. 0. Gratz, Ph.D., Plant Pathologist in Charge
MAIN STATION, GAINESVILLE R. R. Kincaid, M.S., Asst. Plant Pathologist
"W. A. Carver, Ph.D., Associate Agronomist
AGRONOMY R. M. Crown, B.S.A., Assistant Agronomist
W. E. Stokes, M.S., Agronomist Jesse Reeves, Farm Superintendent
W. A. Leukel, Ph.D., Agronomist
W. A. Leukel, Ph.D., Agronomist CITRUS STATION, LAKE ALFRED
G. E. Ritchey, M.S.A., Associate* CITRUS STATION, LAKE ALFRED
Fred H. Hull, M.S., Associate John H. Jefferies, Superintendent
J. D. Warner, M.S., Associate Geo. D. Ruehle, Ph.D., Associate Plant Pathol-
John P. Camp, M.S., Assistant ogist
W. A. Kuntz, A.M., Associate Plant Pathologist
ANIMAL HUSBANDRY B. R. Fudge, Ph.D., Associate Chemist
A. L. Shealy, D.V.M., Animal Husbandman** W. L. Thompson, B.S., Assistant Entomologist
R. B. Becker, Ph.D., Specialist in Dairy Hus-
bandry EVERGLADES STATION, BELLE GLADE
W. M. Neal, Ph.D., Associate in Animal Nutri-
tion R. V. Allison, Ph.D., Soils Specialist in Charge
E. F. Thomas, D.V.M., Assistant Veterinarian R. N. Lobdell, M.S., Entomologist
W. W. Henley, B.S.A., Assistant Animal Hus- F. D. Stevens, B.S., Sugarcane Agronomist
bandman G. R. Townsend, Ph.D., Asst. Plant Pathologist
P. T. Dix Arnold, B.S.A., Assistant in Dairy In- B. A. Bourne, M.S., Sugarcane Physiologist
vestigations J. R. Neller, Ph.D., Biochemist
A. Daane, Ph.D., Agronomist
CHEMISTRY AND SOILS R. W. Kidder, B.S., Asst. Animal Husbandman
R. W. Ruprecht, Ph.D., Chemist"* Ross E. Robertson, B.S., Assistant Chemist
R. M. Barnette, Ph.D., Chemist
C. E. Bell, Ph.D., Assistant SUB-TROPICAL STATION, HOMESTEAD
J. M. Coleman, B.S., Assistant H. S. Wolfe, Ph.D., Horticulturist in Charge
H. W. Winsor, B.S.A., Assistant W. M. Fifield, M.S., Assistant Horticulturist
H. W. Jones, M.S., Assistant Stacy O. Hawkins, M.A., Assistant Plant
ECONOMICS, AGRICULTURAL Pathologist
C. V. Noble, Ph.D., Agricultural Economist**
Bruce McKinley, A.B., B.S.A., Associate
M. A. Brooker, Ph.D., Associate
Zach Savage, M.S.A., Assistant FIELD STATIONS
ECONOMICS, HOME
Ouida Davis Abbott, Ph.D., Specialist** N. W eesburgt P t
L. W. Gaddum, Ph.D., Biochemist M. N. Walker, Ph.D., Plant Pathologist in
C. F. Ahmann, Ph.D., Physiologist Charge
W. B. Shippy, Ph.D., Associate Plant Pathol-
ENTOMOLOGY ogist
K. W. Louck?. MS Asst. Plant Pi 'I:*r.J._+t
J. R. Was-on. A.M.. Entomologist** J. W. ..,li..n. As . antr Er, ,noli
E. F. cr,o:r:i., RI .\.. Entomologist C. C. Crl, I ..\. .ihlrr Erton.1loit
A. N. Tissot, Ph.D., Associate
H. E. Bratley, M.S.A, Assistant Plant City
P. W. Calhoun, Assistant, Cotton Insects A. N. Brooks, Ph.D., Plant Pathologist
A. N. Brooks, Ph.D., Plant Pathologist
HORTICULTURE R. E. Nolen, M.S.A., Asst. Plant Pathologist
A. F. Camp, Ph.D., Horticulturist** Cocoa
Harold Mowry, B.S.A., Horticulturist A. S. Rhoads, Ph.D., Plant Pathologist
M. R. Ensign, M.S., Associate
A. L. Stahl, Ph.D., Associate Hastings
G. H. Blackmon, M.S.A., Pecan Culturist H
C. B. Van Cleef, M.S.A., Greenhouse Foreman A. H. Eddins, Ph.D., Asso. Plant Pathologr:t

PLANT PATHOLOGY W'I1 Palm Beach
W. B. Tidsle, Ph.D Prr Pai-. i D. A. Sanders, r, V' M.. Veterinarian
George P. \\eber. PIh. '. P'l;nt P-url,..i,:r Monticello
R. K. oorr: R'. FM . A-:dltanr.
E.dn, n \\..t. M1. Mlkcol.-izr Fred W. Walker, Assistant Ert.r,.:logist
*In cooperation with U.S.D.A. Bradenton
"**Head of Department, David G. Ketbert, Asst. Plant Pathologist







SOME DISEASES OF CABBAGE AND
OTHER CRUCIFERS IN FLORIDA
By GEORGE F. WEBER*

CONTENTS
Page Page
Black rot ............................. 4 W hite rust ............................ 44
W atery rot .......... ................ 12 Anthracnose .......................... 46
Downy mildew ........ ............ 1 Soft rot .............................. 49
Powdery mildew ....................... 23 Mosaic ............................. 49
Rhizoctoniose ......................... 24 Blackroot of radish.................... 51
Damp-off ......................... 27 White spot ........................... 53
W ire-stem ........................ 27 Cercospora leaf spots................... 54
Boot rot ......................... 29 Cercospora leafspot of water cress..... 56
Stem lesions ...................... 31 Mold .................................. 56
Bottom rot ........................ 31 Other diseases ......................... 58
Control of rhizoctoniose ........... 33 Physiological disturbances .............. 58
Blackleg .............................. 35 Seed treatment ........................ 61
Gray mold ............................ 36 Fungicides ........................... 62
Alternaria leafspot .................... 39

The crucifers, or members of the mustard family, of which
there are about 2,000 species, include a large number of the
economically important crops cultivated throughout the year in
Florida. The most important species of this group grown in the
State are cabbage, collards, brussels sprouts, kohlrabi, cauliflower,
broccoli, turnips, chinese cabbage (Petsai), rutabaga or swede,
mustard, radish and cress. Each of these is divided into numer-
ous horticultural varieties and strains. For example, there are
green or purple, early or late, flat, round or pointed, solid or loose,
smooth or wrinkled cabbage.
Plants of the crucifer group are closely related to each other
and as a result many of them are attacked by the same parasites,
although the degree of injury resulting from the attacks may
vary among the different species. Because of this fact, the group
of plants attacked in common by a disease is treated in this bul-
letin rather than giving a separate discussion for the same disease
under each crop. The specific disease is described on the plant
which is most often and severely attacked and the crops known
to be attacked by the disease are listed. Mention is made in the
proper places concerning certain of these diseases which are of
considerable importance in transit, although this bulletin is pre-
pared primarily for the benefit of growers.
The information given herein was obtained from the literature,
field and laboratory elJerimerntls and observations. The purpose
of this bulletin is to make available to the growers of the State
information concerning symptoms of these diseases in the field
so that they may be recognized and control methods, where known,
intelligently applied.

*Photos by D. G. A. Kelbert.






4 Florida Agricwultural E.rperih ett Statioii

BLACK ROT

Black rot caused by Bacterium coiiipistrOe (Pam.) E.F.S. is
probably the most common, widespread and destructive disease
of this group of plants in the State. It causes the most damage
to cabbage and will be described on that plant, although the fol-
lowing plants are susceptible to it and are often partially or totally
killed: cauliflower, turnips, rutabagas, mustard, radish, collards.
kale, brussels sprouts, broccoli and kohlrabi.
This disease occurs in most sections of the United States and is
generally distributed in Florida. It is found in commercial fields
of most of the crops mentioned above from September to IMay and
in collards and cabbages in home gardens during the remaining
months of the year. Thus. the disease is present in living plants
during the entire year and the causal parasite sur\'vies in the soil
from one season to the next. It is not known how many years
the parasite will survive in the soil without contact with suscep-
tible host plants, but it is known to survive in this manner from
one season to the next in Florida. It is also carried on the seed
and particular care should be exercised in securing disease-free
seed and in seed treatment. The seedlings may be infected in
the seedbed from the infested soil in which they are planted or
from infested soil blown into the beds by wind or washed in by
running water. The seedlings may be killed or they may carry
the disease throughout the season. Transplanting diseased seed-
lings from infected beds is the most common artificial way of
disseminating the disease in the field. Such a practice should be
avoided and growers should insist on using black-rot-free seed-
lings for planting.
The organism lives in old infected plants left in the field and
after they decay it may survive in the soil for a year or more.
Cabbage heads selected for storage or shipment should be free
from the disease because it continues to develop in diseased heads
and is usually followed by soft rot producing organisms with dis-
astrous results. The disease is very similar on all cultivated
crucifers and can be distinguished by the following character-
istics.
Symptoms: The first indication of black rot on the small seed-
lings is wilting and drying out of a portion of one or both of the
cotyledons, beginning at the margins. This infection is believed
to originate mostly from infected seed, although it may also be
caused by the organism being splashed by rain upon the leaf from







Bulletin 256, Some Diseases of Cabbage and Other Crucifers 5

the soil or from other diseased plants. The organism enters the
cotyledons and leaves of the cabbage plant through the natural
openings (water pores) at the ends of the veins along their mar-
gins. It invades and kills the vascular tissues and the tissues



































Fig. 2.-Cabbage leaf showing blackened veins and marginal infections
caused by black rot.

surrounding them. As the disease progresses the veins become
more or less blackened (Fig. 2) downward toward the main stem
and the diseased part which is at first marginal, enlarges in a
V-shaped area with the point toward the stem (Fig. 3). The leaf







6 Florida Agricultural Experiment Station

blade becomes more or less yellow and usually drops from the
plant. The stem becomes invaded and a rapid spread of the dis-
ease occurs in both
Si- directions from the
point where the par-
asite enters the stem
through the leaf
4- .petiole and passes
out into other leaves.
S When the stem of a
diseased plant is cut
across, the black-
ened vascular tissue
can be observed
(Fig. 4). This con-
dition can also be
observed in the
midrib of infected
leaves.
If infection is se-
vere on the seed-
lings, they may be
killed before new
leaves develop or
they may develop
new leaves and not
show any noticeable
symptoms until
Fig. 3.-Black rot of turnip leaf, showing mar- after transplanting
ginal infection with yellow zones around the when they suffer
dead areas.
severely under con-
ditions favorable for the parasite. In such instances the disease
is centered in the growing tip of the stem and the youngest leaves
are killed first. The infection spreads from there to the leaves
of other plants where it produces local infections which enlarge
rapidly and soon kill the plant (Fig. 5).
When conditions are not so favorable, the disease develops
more slowly and may not become conspicuous until the plant
heads, at which time the lower leaves shed and the head becomes
stunted and never develops into a marketable product. The in-
fection may occur only on one side of the plant stem and in such







Bulletin 256, Some Diseases of Cabbage and Other Crucifers 7







































r,.






Fig. 4.-Sections of cabbage stems showing typical lesions and
blackening of tissues caused by black rot.







8 Florida Agricultural Experiment Station


















,hI,




A 'irA





ta



























Fig. 5.-Three stages in the development of black rot on young
cabbage plants.







Bulletin 256, Some Diseases of Cabbage and Other Crucifers 9

cases a lopsided head may develop (Figs. 6 and 8). Heads from
infected plants should never be shipped because they usually
result in losses due to the disease continuing to develop in transit
and the diseased tissue becomes invaded with secondary organ-
isms that cause a soft rot. These secondary organisms are the



















A-




















Fig. 6.-Black rot infection causing one-sided development of the cabbage
head.







10 Florida Agricultural Experiment Station

gas former and the cause of the disagreeable odor always asso-
ciated with decaying cabbage. The black rot organism does not
produce the offensive odor.
These characteristics of the disease are applicable to most of
the other crucifers such as mustard, turnips, etc., but vary some-
what on cauliflower, broccoli, and kohlrabi. The disease on these
plants may show the marginal infections, darkened veins and





































Fig. 7.-Black rot of kohlrabi leaf, showing characteristic symptoms that
are different from those on cabbage and turnip leaves.







Bulletin 256, Some Diseases of Cabbage and Other Crucifers 11

V-shaped development, or the lesions may be very irregular in
shape, often quite linear, following the veins. The leaf tissue
involved is killed rapidly and becomes brown in contrast to the
gradual yellowing of the diseased tissue of cabbage leaves. The
lesions are not confined to the leaf margins but may appear any
place over the surface of the blade, varying from minute infec-
tions not easily detected to lesions which are more or less united
and occupying most of the entire blade (Fig. 7). This type of
infection is common on these plants during conditions favorable
to the development
of the disease.
Control: The
first step in control
of black rot is to
secure seed free
from the bacterial
organism that
causes it. If seed
cannot be secured
with this guaran-
tee, they should be
disinfected with
corrosive sublimate
1:1000 for 15 min-
utes or in hot water
at a constant tem-
perature of 122' F.
for 18 minutes. The
seed should be
planted in new
seedbeds known to
be free from black
rot or in seedbeds
sterilized by live
steam or formalde-
hyde.
Diseased plants
should never be set
in the field, or even
plants from seed- Fig. 8.-Black rot of cauliflower, showing diseased
beds in which dis- stem and head.







12 Florida Agricultural Experiment Station

eased plants have been found. Diseased plant material should be
collected in fields and buried or disposed of otherwise outside the
limits of cultivation.
Fields that show black rot should be planted to other crops for
a few years in order to reduce the amount of infection that may
occur in the soil.
Do not pack for shipment any heads that were cut from plants
that showed the disease.
WATERY ROT
Watery rot is a common disease in Florida caused by the fun-
gus Sclerotinia sclerotiorum Fckl. It has been found in almost
all of the truck-growing parts of the United States. It is com-
monly found in greenhouses in Northern states during the Winter
on lettuce and other plants. It is more common in the Southeast-
ern states, where it is of first importance. It is generally distrib-
uted in Florida on cabbage, cauliflower, mustard and other related
plants, and is known to attack a large number of plants of other
families. Some of the more common and important diseases it
causes are pink rot of celery, nesting of beans, drop of lettuce,
timber rot of cucumbers, stem blight of eggplant and tomatoes,
damp-off of seedlings and watery soft rot of fresh vegetables in
transit.
The disease in Florida is always more plentiful during the Win-
ter months when large acreages of cabbage and other truck crops
are being cultivated. During this time of the year, it is favored
by heavy rainfall. Usually the Winter seasons are comparatively
dry so that the disease does not cause extensive damage. The
fungus causes a damping-off of seedlings, which is not common,
a girdling of the stem of heading plants and a watery rot of the
heads (Fig. 9).
The fungus survives unfavoirale periods or seasons as scle-
rotia. These sleirotia are irregularly shaped structures usually
more or less flattened, slightly flexible when wet or immature
and hard and horny when dry. They are white when immature,
gradually becoming brown, and finally a glossy black (Fig. 10).
The outer coat is thin and black and the interior is white. They
remain viable for a year or more under favorable conditions but
decay whenitoo wet. They germinate in the spring and produce
small mushroom-like fruiting structures an inch or less in diam-
eter close to the surface of the soil. These bodies forcibly shed
large numbers of microscopical spores that are carried by air
currents and disseminated widely. The spores germinate and







Bulletin 256, Some Diseases of Cabbage and Other Crucifers 13

grow for certain periods in the soil and are capable of infecting
plants if they come in contact with them. The infections are
usually at the soil line, where leaves of the plant touch the soil,
or where the fungus grows up the stem of the plant causing very
little infection until it comes in contact with the foliage. The
sclerotia are produced by the fungus on the cabbage heads as























IF.

















Fig. 9.-Watery rot of cabbage, showing the white, fluffy growth of the
parasite.






14 Florida Agricultural Experiment Station

decay advances. In addition to the dissemination of the spores,
the fungus is spread by the sclerotia which may be moved con-
siderable distances, during plowing and cultivation, by running
water and scattering of dried infected plant debris by the wind.
The fungus grows very well at low temperatures and, conse-
quently, is very important as the cause of transit diseases. It
will grow quite well in refrigerator cars sent out of the State





































Fig. 10.-Sclerotia of the watery rot fungus, about natural size.






Bulletin 256, Some Diseases of Cabbage and Other Crucifers 15

under ordinary conditions. Pre-cooling is much desired in ship-
ping cruciferous plant products from the State.
Symptoms: Early symptoms of watery rot are very inconspic-
uous and usually are unobserved, except when damping-off occurs
under humid conditions. In such instances, young plants become
weakened at the soil line and fall over; the fungus grows over
them and attacks others in close proximity. The fungus may
also cover the surrounding soil with a white cottony growth that
is particularly conspicuous in the early mornings before the dew
is dissipated. On older plants its spread usually is checked by
the advent of less favorable growing conditions before it becomes
noticeable or causes much damage.
The fungus may be first observed on the stem at the soil line or
on the foliage leaves at their bases when the soil is close around
the stem of the plants or any place on the leaf blades where the
foliage comes in contact with the soil. As the fungus invades
the plant the leaves become weakened where they are attached
to the stem and droop until they rest upon the soil but do not
become detached until they are well invaded and almost dead
(Fig. 11). The fungus then grows up the stem to the next leaf
and gradually all of the foliage leaves become involved and rest
one upon the other on the soil around the base of the plant. The




















Fig. 11.-Watery rot of cabbage, showing a diseased plant (left) in
contrast with a healthy plant.






16 Florida Agricultural Experiment Station

head leaves may become detached from the main stem but are
held in place because their edges lap over the top of the head.
The head becomes overgrown with the fungus and a soft watery
rot develops. The fungous mycelium may or may not be con-
spicuous, depending on weather conditions. However, there are
often numerous tufts of white mycelium scattered over the head.
The leaves that fall on the soil are rapidly overgrown and the
sclerotia begin to form over them. The sclerotia are most often
located along the larger veins of the leaf on either surface. On
the head they are scattered, forming under the tufts of mycelium
(Fig. 12). They develop in great numbers, often as many as
several ounces develop on one head. They vary considerably in
shape and size, some attaining one inch in length. The disease
can be readily identified and the fungus determined by the pres-
ence of these sclerotia.
In transit the disease develops on the heads in much the same
way as in the field, except that it is much more rapid, the my-
celium is more abundant and unless in the final stages of decay,
the sclerotia are fewer.























Fig. 12.-Cabbage plant killed by the watery rot disease. Sclerotia are
shown scattered over the outer leaves of the head.






Bulletin 256, Some Diseases of Cabbage and. Other Crucifers 17

Control: Because of the soil-inhabiting characteristic of the
casual fungus and the type and manner of infecting plants,
watery rot is very difficult to control in the field. The application
of fungicides is of very little value since the fungus attacks the
plant while under cover, so to speak. Sanitation offers the best
way of holding the disease in check. In this type of control all
plants that show infection from this disease should be pulled up
and carefully deposited in some container and removed from the
field. In most instances this can be done easily without leaving
any of the infected material on the soil. Care should be exer-
cised to collect these plants before the sclerotia have fully de-
veloped. If the plant is more or less disintegrated and the ma-
ture sclerotia are scattered on the ground, a thin top. layer of
soil should be removed so that the sclerotia will be collected.
Rotation should be practiced. Crops not attacked by this fungus,
such as corn, crotalaria, cotton, peanuts, or sweet potatoes, should
be planted alternately with crops that are susceptible, such as
lettuce, celery, beans or peppers. Seedbeds should be disinfected
before the seed are planted.

DOWNY MILDEW
Downy mildew is a common disease of crucifers. It is caused
by the fungus Peronospora parasitica (Pers.) DeBy. The dis-
ease has been reported on cabbage from all parts ;of the United
States and it is generally distributed in Florida wherever cabbage
is grown. It attacks a number of related crucifers grown com-
mercially in the State, the most important of which are cauli-
flower. mustard. collards, kohlrabi. and turnips. It causes the
most damage to cabbage in comparison with the susceptible
crops (Fig. 13).
The plants may be attacked in the seedbed as soon as the first
true leaves begin to develop and the disease may continue to
develop throughout the growing. season until the head is har-
vested.
There are two periods when real loss is incurred, the first and
more important one being with the seedlings in the seedbed. the
other after the plants have headed (Fig. 14). In the latter case
the mildew lesions become infected with soft rotting organisms.
especially in transit, and often result in considerable loss. The
spores of the fungus which are produced in. large numbers are
easily detached from the plant on which they grow and may be






18 Florida Agricultural Experiment Station
carried considerable distance by wind. They germinate in water
after a few hours and cause infection of other cruciferous plants
upon which they fall. After 10 days or two weeks the fungus
has developed sufficiently to be producing more spores. The dis-








































Fig. 13.-Cabbage leaf showing typical infection by downy mildew. The
parasite cannot be found easily except in early morning.







Bulletin 256, Some Diseases of Cabbage and Other Crucifers 19






















Fig. 14.-Downy mildew infection on cabbage head that is usually overlooked
at harvest time. This head should not be stored or shipped because of
danger of secondary soft rot.

ease occurs in the seedbeds in early fall and continues to develop
throughout the Winter and Spring as long as commercial crops
are grown. It has not been found in the Summer months but is
undoubtedly present on wild host plants which grow profusely
during this season. The fungus is favored in its development by
cool moist weather accompanied by heavy dews.
Symptoms: Downy mildew is first evident on the true leaves
of the seedlings in the form of pale green or yellow spots scat-
tered over the blade. These spots are very inconspicuous in the
early stages and do not increase rapidly in size and numbers.
When a slight yellowing is evident, the fungus has usually de-
veloped enough to be producing spores. The spores and the fine
fungus threads upon which they are produced are not easily
seen, except when the plants are wet with dew in the morning
(Fig. 15). During the day they seem to disappear and cannot
be observed with certainty except with the aid of a magnifier.
During the night, when humidity is high, they grow rapidly and
produce a crop of spores which are mature by morning and when
the dew dries, they dry and become detached and are dissem-
inated. Often the conditions are so favorable for the develop-







20 Florida Agricultural Experiment Station

ment of the fungus that the seedlings become severely infected
and are badly stunted or killed.
When infected seedlings are transplanted they carry the dis-
ease until mature and often healthy plants become heavily infect-
ed in the field. The lower leaves become overgrown with the
fungus and they become mottled, green and yellow. The center of
the yellow areas, where the plant cells have been killed, is often
dark brown. Badly infected leaves are often thickly spotted by
these brown areas and in the morning the entire lower surface of
such leaves is thinly covered with the "down" of the fungus.
Leaves thus infected deteriorate rapidly, become brown and drop
from the plant.
In contrast to the above symptoms on cabbage and collard































Fig. 15.-Downy mildew on seedling cabbage leaf. Slightly enlarged to
show the fungus.






Bulletin 256, Some Diseases of Cabbage and Other Crucifers 21

plants in the field, the spots formed on cauliflower and turnips
are somewhat different. The infections are first evident by a
slight yellowing (Fig. 16). This color fades rapidly almost to
white and becomes bleached and dies. These spots enlarge rap-
idly and are very conspicuous on plants in the field. The fungus
develops on them as has been described on cabbage.
In many cases on cabbage in the field all of the foliage leaves
and also the exposed head leaves become infected. Usually the
head is not prominently marked and will escape notice, but oc-



































Fig. 16.-Downy mildew on cauliflower leaf, showing symptoms different
from those on cabbage (see Fig. 13).






22 Florida Agricultural Experiment Station

casionally heads are badly infected and are unmarketable (Fig.
17). Those that are infected and packed for market are often
attacked by secondary organisms resulting in soft decay in tran-
sit. The spots on cabbage heads caused by the downy mildew
fungus are very much the same as those on the foliage leaves
and likewise the fungus sporulates over the exposed leaves.
Control: The control of downy mildew can be obtained best
by spraying the seedlings in the seedbed with bordeaux mixture,
to which a spreader and sticker, such as calcium caseinate, has
been added. Spray the seedlings as soon as the first leaves begin
to develop. Reject all heads that show any spotting at packing
time to prevent losses developing in transit.






























Fig. 17.-Cabbage head heavily infected with downy mildew.







Bulletin 256, Some Diseases of Cabbage and Other Crucifers 23

POWDERY MILDEW
Powdery mildew is caused by the fungus Erysiphe polygoni
DC. This disease is found on certain members of the mustard
family wherever they are grown. It is common in the United
States and everywhere in Florida where these plants grow. The
disease is probably most severe on rutabagas, collards, mustard
and turnips and is not of special importance on cabbage, cauli-
flower and certain
other species of
this group, except
under conditions
most favorable for
its development.
Thefungus is found
on a large number
of plants belonging
to other families
and since the spores
are small, produced
in abundance and
wind-carried, they
may be widely' dis-
tributed. The se- u
verity of the dis-
ease may vary only
with the presence
of favorable or un-
favorable weather
conditions. Plants 7 ,.
are very seldom
killed by the fun-
gus, but in most
cases they are more
or less stunted and
often partially de- Fig. 18.--Powdery mildew on rutabaga leaf.
foliated. The dis-
ease appears any time during the year when host plants are grow-
ing, but is probably more plentiful in late Winter, Spring, and
early Summer.
Symptoms: The powdery mildew fungus can be seen in patches
casually placed and unevenly distributed on the top surface of






24 Florida Agricultural Experiment Station

the leaves (Fig. 18). When it is producing spores, it resembles
white powder, which is more or less granular and will adhere
to the fingers when touched. The fungus is difficult to find be-
fore it sporulates because of the fineness of the mycelium. It
attacks the host in a mild manner and does not cause a yellow-
ing of the leaves until after they are quite mature. Often the
fungus develops on the underside of the leaf and in such in-
stances it usually will be overlooked until after it is well estab-
lished, sporulating, and causing a faint yellowing of the leaf tis-
sue which it covers. When the host plants are not growing rap-
idly, it causes leaves to shed and stunts the plants severely.
When the spots are numerous they coalesce (run together) and
soon cover the leaves completely.
Control: No control methods are recommended because pow-
dery mildew is seldom severe, except on plants that are too old
to be of much value. Should the disease become severe, dusting
with flowers of sulphur is suggested.

RHIZOCTONIOSE
Rhizoctoniose is the common name applied to the several dis-
eases of cabbage and related plants caused by the parasitic fun-
gus Rhizoctonia solani Kihn, which is the sterile form of the
sporiferous saprophytic fungus Corticium vagum B. & C. This
disease is known to all parts of the civilized world to a greater or
lesser extent. In the United States it is common and causes con-
siderable losses not only to cabbage but also to a large number of
other cultivated plant-. In Florida, the disease causes damage
throughout the entire year and is generally distributed over the
State in its various types of soil. The losses resulting from its
attacks include plants in all stages of growth, from germinating
seed to mature plants ready for harvest (Fig. 19). The annual
damage caused by the disease averages from 5 to 10 percent of
the crop, amounting to from $50,000 to $75,000. Certain precau-
tions taken during the growing season can reduce this annual
loss by half. Suggestions in this relation will be made under
the heading of control.
The .fungus is extremely virile and might almost be called
omnivorous because of the wide range of plants that it attacks.
It lives in the soil, usually in the top layers, tolerates extremes
of acid and alkali, appears to be as plentiful in light sands, if
not too dry, as in heavy muck, grows at temperatures ranging







Bulletin 256, Some Diseases of Cabbage and Other Crucifers 25

from almost 0 to 900F. and is not killed by temperatures of 0 or
1000F. In the soil, the fungus produces brown mycelium that
grows among the soil particles and attacks plants with which it
comes in contact. It kills portions of roots and stems of plants
and produces sclerotia on the dead tissue. These dark brown
sclerotia remain viable over unfavorable seasons and function in
perpetuating and disseminating the fungus. They are usually
somewhat flattened and more or less elongate, varying in size
from 1/16 to 1/8 of an inch in width and about twice as long.















Fig. 19.-Cabbage heads affected with bottom rot. (Bul. 242.)

Often they are formed on the host close to each other and coal-
esce, forming large irregular crust-like structures. The scle-
rotia are very resistant to environmental changes, particularly
those unfavorable for the development and growth of the fungus
such as high temperature and dryness.
The perfect stage of the fungus is not parasitic and develops
under most favorable conditions where the parasitic stage is
growing luxuriantly on susceptible plants (Fig. 20). The fungus,
when in the proper conditions to produce spores, grows up ele-
vations above the soil surface such as plant stems, sticks, straws,
soil clods, etc., where the whitish spore-producing network of
hyphae develops. On cabbage plants this stage of the fungus
usually occurs on the main stem 1 to 3 inches above the soil line
or on either surface of some of the lower leaves. The spores
which are microscopic in size are carried by air currents and
when deposited in favorable environments germinate and pro-
duce the parasitic stage of the fungus.






26 Florida Agricultural Experiment Station

The fungus, Rhizoctonia solani Kiihn, is responsible for a num-
ber of manifestations of the disease, each of which is designated
by a specific common name depending primarily on the age of the
cabbage plant when it is attacked. When seedlings are attacked
the disease is known as damp-off. If they are not killed follow-
ing infection by damp-off but continue to grow and show stem






Arc























Fig. 20.-Corticium vagum, the sporulating stage of the fungus causing
Rhizoctoniose, showing sporulating area, sclerotia and mycelium, (Bul.
242.)

discoloration, or if the stems are attacked after they become
woody, the disease is known as wire-stem. Occasionally lesions
develop above ground on the stems of half-grown plants. They
may or may not kill or stunt the plant or girdle the main root,
causing decay. This disease is known as root rot or stem lesions.
Finally the fungus may grow up on the outer surface of the stem






Bulletin 256, Some Diseases of Cabbage and Other Crucifers 27

when the plants begin to head and infect the foliage leaves and
head from the lower side. This manifestation of the disease is
known as bottom rot. The symptoms of all of these diseases will
be given briefly.

DAMP-OFF

Symptoms: Seedlings of all crucifers are attacked more or less
by Rhizoctonia solani when they are in the cotyledon stage. The
attacked seedlings first show a slight drooping at the tips of the
cotyledons similar to that caused by the lack of soil moisture.
Examination of the stems of these plants at the soil line will
reveal a soft, flabby, water-soaked area. The water-soaked con-
dition becomes more pronounced and is usually followed by the
enlargement of the lesions on the stem to such an extent that
the stem is no longer strong enough to hold the plant erect. It
falls over on the soil and is rapidly overgrown by the fungus.
This condition is known as damp-off. From this seedling, the
fungus grows out on the top of the soil in all directions, coming
in contact with other plants, and repeating the process. If the
seed have been planted broadcast, the area of killed plants is
more or less circular and enlarges in all directions. If the seed-
lings are in rows, the disease spreads in both directions from
the place it first started and each infected area is usunilly con-
fined to a single row. There may be a number of them. however,
in a small seedbed or the whole bed may be attacked at almost
the same time, if the soil is badly infested. Often weather con-
ditions change after infection occurs or the plant stems may be
quite hard before they are attacked and the fungus fails to kill
them but stunts them severely, in which case the disease is known
as wire-stem.

WIRE-STEM
Symptoms: Wire-stem, caused by Rhizoctonia solani Kiihn,
usually can be found in all cabbage seedbeds that have previously
shown any damp-off caused by this parasite. A typical wire-
stem cabbage seedling appears to be stunted and the leaves are
more or less mature and hard. Diseased seedlings often lack the
amount of "leaf-bloom" or waxy covering that healthy plants
possess. They are also more or less "shanky," that is, they are







28 Florida Agricultural Experiment Station

long stemmed, probably because a number of the lower leaves
have been shed. Upon removing such plants from the soil one
finds a dark area on that portion of the stem in contact with the
top half-inch of soil and above, when the plant is growing. On
newly-infected plants, or at least those that are not severely
diseased, the discolored area frequently is confined to the space
on the plant stem between the cotyledon scars and the shallowest
rootlets (Fig. 21). On more severely-infected plants this dark-
ened area may extend higher up the stem and lower in the
ground.








Mb M
























Fig. 21.-Wire-stem of cabbage plants slightly enlarged to show the
characteristic symptoms. (Bul. 242.).






Bulletin 256, Some Diseases of Cabbage and Other Crucifers 29

When the roots become involved by the disease the plant
withers and dies. The browning that occurs is caused by in-
vasion of the cortex of the stem by the fungus. The outer cells
are killed at first, but, if conditions are favorable for plant
growth, the seedlings may overcome the disease before further
damage is done. This will result.in cracks that run lengthwise
of the stem as the stem increases in diameter. In severe cases,
however, the enlargement of the stem is prevented because the
fungus kills all the cells to the cambium or growing part of the
stem. Plants showing any discoloration of the stem should not
be transplanted.

ROOT ROT

Symptoms: Root rot cannot be determined with any degree of
accuracy without removing the plant from the soil, except when
the disease is well developed. Cabbage plants growing in wet soils
















Fig. 22.-Wilted cabbage plants affected with root rot. (Bul. 242.)


are the most frequently attacked. The earliest distinguishable
symptoms are a yellowish-green color of the leaves and their lack
of turgidity (Fig. 22). The yellow or sickly green color is quite a
contrast to the normal green of healthy plants and can be easily
distinguished. The wilting of the leaves is certain evidence that
the plant is diseased and that it is infected by this parasite. Fol-






30 Florida Agricultural Experiment Station

lowing the wilting, which gradually involves more and more of
the leaves, the leaves turn yellow and eventually shed. Exam-
ination of the stems of plants that have developed these symp-
toms shows a girdled stem at, or slightly below, the soil line and
dead roots. The cortex is killed and sloughs off, leaving only
the central woody tissue (Fig. 23). Plants showing any of the
symptoms never recover.


















--















Fig. 23.-Cabbage plants killed by root rot, showing where the cortex
has been killed and sloughed off. (Bul. 242.)







Bulletin 256, Some Diseases of Cabbage and Other Crucifers 31

STEM LESIONS
Symptoms: Stem lesions on cabbage are not common in the
State. They occur on the portion of the stem above ground and
below the lowest leaves. The fungus penetrates the stem in lim-
ited areas, either through leaf scars or other opening, and dis-
color portions of it. The disease is more conspicuous on radishes
and turnips. The spots
on radishes are at first
small, originating from
infected rootlets
through which the fun-
gus grows up into the
radish. The lesion in-
creases in size and may
cover a whole side of --
the root (Fig. 24). It
becomes brownish-
black and is slightly
sunken, being deeper
in the center than near
the margins. As the Fig. 24.-Stem lesions of radish caused by th.
bottom rot fungus.
affected radish en-
larges it becomes irregular in shape and the spots crack open.
When infection takes place other than through rootlets the sur-
face is usually slightly roughened and discolored. The disease on
radishes cannot be detected by leaf symptoms until the plant
is almost killed.

BOTTOM ROT
Symptoms: The early stages of infection on cabbage heads and
the development of the disease up to certain stages is decidedly
inconspicuous. In most cases the fungus has invaded the lower
portion of the head and killed portions of the leaf blades before
its presence can be detected, except by careful examination (Fig.
1). The outer foliage leaves hide the diseased portions of the
head. The foliage leaves usually are not severely infected them-
selves in the early stages of the disease, except at their bases,
where the fungus invades and kills tissue of the leaf blades on
either side of the midrib from one to several inches. The outer-
most head leaves usually are affected more than the inner ones.
Where the foliage leaves enclose the head closely, the invasion






32 Florida Agricultural Experiment Station

of the head leaves is more complete than where the foliage leaves
are loose.
The fungus grows up the main stem of the plant from the soil,
passing between the leaf petioles. The outside head leaf always
is the most severely affected (Fig. 25). The lower portion of the
blade is killed and deep le-
sions are produced on the
petioles, finally destroying
them entirely. This killing
of the entire leaf through
invasion of the petiole is the
most typical symptom of
gthe disease on turnips and
"Chinese cabbage (Fig. 26).
Turnip and Chinese cabbage
leaves are involved succes-
sively and killed directly or
by secondary invasion of
soft rot organisms. As the
leaves of cabbage heads are
killed, they turn yellow,
then brown, and become
loosened from the main
stem. The foliage leaves
drop off, but the head leaves
Fig. 25.-Bottom rot of cabbage, showing
how the fungus grows up the stem and are held in place by lapping
attacks cabbage heads from the bottom over the top of the head or
side. (Bul. 242.)
by the fungous mycelium

which grows over the outer surface as well as on the interior
portions.
In the final stages of the disease the affected cabbage plants
stand erect, consisting of a main stem terminated by a capitate
knob (Fig. 27). The outer leaves are brown and dry on top and
usually wet below. This rot continues to develop in storage and
transit and all heads should be inspected carefully before they
are packed for storage or shipment to distant markets.





Bulletin 256, Some Diseases of Cabbage and Other Crucifers 33
CONTROL OF RHIZOCTONIOSE
Sterilization of the seedbeds before planting the seed and ap-
plication of bordeaux mixture containing calcium caseinate to
seedlings often enough to keep new growth covered with the
fungicide serve to reduce the losses from Rhizoctoniose.
Discard all plants that show discolored stems at transplanting
time.















I W










Fig. 26.-Stem lesions of (A) turnip and (B) pe-tsai, caused by
Rhizoctonia solani.






34 Florida Agricultural Experiment Station

Careful cultivation to prevent the banking of soil too close to
heading plants is suggested.
Inspection at harvest to prevent packing for storage or ship-
ment of diseased heads is desirable.









Fig. 27.-Last stage of Rhizoctoniose or bottom rot of cabbage. (Bu 242.








'I
























Fig. 27.-Last stage of Rhizoctoniose or bottom rot of cabbage. (Bul. 242.)






Bulletin 256, Some Diseases of Cabbage and Other Crucifers 35

BLACKLEG

Blackleg is a disease of cabbage caused by the fungus Phoma
lingam (Tode) Desm. It has been known a long time and occurs
in most places in the United States and in foreign countries Where
cabbage is grown. In Florida, however, this disease is of very
little consequence, except during the Winter and Spring months
if they are exceptionally wet. It has been found on cabbage and
all of the other crucifers that are cultivated in the State.
The disease is usually introduced into seedbeds in this State
through infected seed, the most common method of dissemina-
tion. Seed become infected while growing and, as no cabbage
seed are grown in the State, it must come from the outside.
Few seedling plants are imported, most plants are grown from
seed. Infected seedlings usually will die before maturity under
average conditions. The name of the disease implies a blackening
of the stem which is the most characteristic symptom. Close
examination usually reveals small black specks scattered over the
surface of the dark diseased area. This diagnosis can be easily
made and in most cases will be correct.
Disease-free seed are not always available, although they are
grown in quantities in the vicinity of Puget Sound. Because of
certain weather conditions which are unfavorable for the de-
velopment of the disease in that locality, the seed mature quite
clean and free of the disease.
Symptoms: Cabbage plants may be affected by blackleg at
any time during their growth, from the seedlings in the seedbed
to the old plants in the field up to harvest. The earliest infection
found on seedlings is a brownish spot near the base of the stems.
This spot enlarges rapidly and soon girdles the stem. The af-
fected stem becomes blackened and is very conspicuous.
The cotyledons of diseased seedlings yellow rapidly and are
shed, followed by the death of the young plants. On older plants,
the lesion is at first confined to parts at or below the soil surface
(Fig. 28). Later it develops up the stem. The tap-root and most
of the fiberous; feeding roots are killed. The leaves wilt and
drop off, producing a shanky plant.
The fruiting structures of the fungus consist of small black






36 Florida Agricultural Experiment Station

specks which develop
in large numbers,
irregularly scattered
on the affected parts
of the host plant.
Brownish spots also
appear on the leaves
and are distinguish-
able by the presence
of pycnidia (black
specks referred to
above) scattered
over them. Early
infection results in
the killing of plants
during the season,
while the late ap-
pearance of the dis-
ease may not cause
extensive damage.
Control: Secure
disease-free seed if
possible. Treat all
seed for 15 minutes
in 1:1000 corrosive
sublimate or give
them a hot water
treatment by soak-
ing seed for 25 min-
utes in water at
1220 F.
Sanitation and
rotation should be
practiced to avoid
Fig. 28.--Blackleg of cabbage. blackleg.

GRAY MOLD
Gray mold is caused by the fungus Botrytis cinerea Pers. This
fungus has been found on a large number of different plants, such
as squash, tomato, carrot and lettuce, in addition to most of the
crucifers. It is distributed over the United States wherever
these plants are grown. In Florida it is state-wide in its distri-






Bulletin 256, Some Diseases of Cabbage and Other Crucifers 37

bution and has been found on almost as riiy different plants as
have been found attacked by it in the remainder of the country.
In this State the losses resulting from it vary according to the
seasons and weather conditions during these seasons. "It becomes
most destructive during wet, rainy, foggy,days in Fall, Winter,
or Spring, when certain crop plants are growing luxuriantly.
Cabbage is most often attacked in the late Winter and early
Spring following wet periods.
The fungus develops spores in abundance over the surface of
the attacked leaves. They are easily detached by wind and rain
and transmitted to other plants which they may attack. The dis-
ease does not cause epidemics except under most favorable con-
ditions, but it is often well distributed in cabbage fields, causing
rot on the heads in all stages of maturity. The fungus occurs
more or less promiscuously on the borders of rotted places on
cabbage heads in the form of whitish mycelium or olive-gray,
spore-bearing areas. It forms sClerotia of various sizes and
shapes in the rotted tissue. These sclerotia areusually small and
always germinate by producing spores in loose clumps instead of
the small mushrooms, as is the case with watery rot. The scle-
rotia aid in maintaining the fungus over periods of unfavorable
environment. They remain viable from season to season and
their dissemination through cultivation aids materially in the
spread of the fungus. The fungus lives for certain periods in
the soil and crop debris, where it serves as a source of infection
for susceptible plants.
Symptoms: Gray mold is not often encountered on young
plants that have not produced heads. Heading plants are at-
tacked anywhere over their surface but most often on the lower
parts of the outside foliage leaves where they come in contact
with the soil, or on the inner leaves close to the head. The infec-
tions first appear as inconspicuous, wilted and watersoaked por-
tions of a leaf along the margin, later becoming discolored. The
disease spreads slowly and the fungus produces whitish tufts of
mycelium and sporulates abundantly. The entire head may be-
come involved, resulting in a wet, brown mass. Or only portions
of the head may become invaded. Diseased areas may develop
among the inner foliage leaves (Fig. 29) extensive enough to
involve half of the head and yet pass unobserved. The disease
always can be distinguished by the gray moldy-appearing my-
celium and spores bordering on the rotted areas.
The disease continues to develop in storage and transit. Con-







38 Florida Agricultural Experiment Station































4W










Fig. 29.-Gray mold infection of cabbage head. The foliage leaves
have been removed to show the diseased area.

sequently careful inspection should be made at harvest time so as
to remove all diseased heads.
Control: Gray mold is very difficult to control because the
spores are produced so abundantly and are so easily disseminated
and its development is often very inconspicuous until after con-






Bulletin 256, Some Diseases of Cabbage and Other Crucifers 39

siderable damage is done. However, it is not always sufficiently
important to warrant spraying entire fields to prevent its oc-
currence.
Sanitation and rotation should be practiced.

ALTERNARIA LEAFSPOT
Alternaria leafspot is caused by the fungi Alternaria brassicae
(Berk) Sacc. and Alternaria herculea (E. & M.) Elliott, and ap-
pears annually more or less commonly on all of the cultivated
crucifers. It is worldwide in its distribution and is found in all
parts of the United States and wherever these plants are grown
in Florida. Cabbage and cauliflower are probably the most af-
fected, although it is destructive on turnips, radish, Chinese cab-
bage, Brussels sprouts, collards, broccoli, kohlrabi and others.
The exact losses caused by these parasites is difficult to judge,
because the disease is mostly on the leaves. Cauliflower and
broccoli, however, are attacked on the flower buds which consti-
tute the commercial product and suffer considerable loss both in
the field and in transit. A black discoloration is produced by
these fungi that necessitates the culling out of the diseased heads.
These heads, being very tender, are easily bruised in handling.
Bruises of this kind are quite ideal locations for the fungi to
gain entrance and cause a black decay. The decay continues to
develop in transit and in storage and may spread to adjacent
heads.
Plants may become infected at any time during their develop-
ment. If infected when young, considerable damage is done to
the seedlings, and they are often retarded in growth due to de-
foliation. The disease is probably most prevalent when the
plants are about half grown, at which time a large percent of the
older leaves may be badly spotted, resulting in their early yellow-
ing and shedding (Fig. 30). Under certain conditions cabbage
heads show a black decay on the stem or lower part of the head
resulting from infections by these parasites. Spores of these
fungi are produced in abundance over the lesions on the leaves.
They are easily detached from the spots on the plant leaves and
are scattered by wind, rain, insects and cultivators. The thick-
walled, many-celled spores are able to live for a long time during
unfavorable conditions. Also, the mycelium of these organisms
survives in old plant parts in the fields from one season to an-
other. The disease is quite characteristic on the foliage of the






40 Florida Agricultural Experiment Station






























Fig. 30.-Alternaria leafspot of broccoli, showing typical lesions.

crucifers and can be definitely distinguished in the field from
other diseases by the dark sooty clusters of spores that will rub
off easily, over the surface of the larger spots (Fig. 31).
Symptoms: The first signs of Alternaria leafspot on young cab-
bage or cauliflower plants are manifest as small dark-brown or
black spots, about 1/8 inch in diameter, on the leaf petioles and
blades. The spots are irregularly scattered and when very nu-
merous they do not become very large before the leaf turns yel-
low, becomes lifeless, and eventually sheds. When fewer of
them are present, the spots enlarge and become light colored and
the dark border widens and becomes lighter colored. The spots
show a definite zonation that is characteristic of the disease.
The centers of the older spots produce spores in abundance which






Bulletin 256, Some Diseases of Cabbage and Other Crucifers 41


































Fig. 31.-Lower surface of cabbage leaf showing alternaria spots.

give the sporulating area a brownish color and later a black sooty
appearance. The above symptoms are typical of the disease on
cabbage and cauliflower foliage. The infections on turnip, radish
(Fig. 32) and Chinese cabbage are quite similar except that the
spots enlarge more rapidly, produce fewer spores and cause the
leaves to become yellow and die more rapidly.
On cauliflower and broccoli heads the first indication of the dis-
ease is the appearance of numerous very minute sunken black
specks. On cauliflower these specks enlarge slowly and when the
infections are numerous they finally coalesce, producing a black,






42 Florida Agricultural Experiment Station


































Fig. 32.-Alternaria leafspot of radish.

dry decay of the entire surface of the head. Broccoli plants show
infection of the leaves only slightly, although the clusters of
flower buds are often seriously affected. The fungus infects the
individual buds of each of the flower clusters successively and in
a short time all of them turn brownish-black in color, shrivel
and die (Fig. 33). Under average conditions, the damage caused
on broccoli is not serious, but when conditions favor development
of the parasites, namely, warm humid days, entire fields may be-
come infected and suffer heavy losses. Since infections of cauli-
flower and broccoli Which occur in the field continue to develop







Bulletin 256, Some Diseases of Cabbage and Other Crucifers 43
















Fig. 33.-Alternaria flower blight of broccoli (left) and healthy flower
(right).

in transit and in storage, infected heads should be discarded at
harvest time.
Alternaria leafspot occasionally occurs on cabbage heads grow-
ing in the field, resulting in an irregular development of the
head and in black decay. The decay is most frequently located on
the petioles of the lower leaves or on the stem (Fig. 34). Such
infected heads
should be dis-
carded at harvest
time as the decay
will continue in
transit or in stor-
age.
Control: Under
ordinary condi-
tions Alternaria
leafspot is found
only on the older -.
foliage leaves and
is not severe
enough to require
the application of
control measures.
However, it be-
comes of consid-
erable importance
Fig. 34.-Early stage of Alternaria headrot of
during rainy pe- cabbage.






44 Florida Agricultural Experiment Station

riods and fungicides should be applied to prevent serious loss. An
effective spray consists of 4-6-50 (hydrated lime) bordeaux mix-
ture to which has been added 1 pound of calcium caseinate per 50
gallons of spray. All infected heads should be eliminated when
the crop is graded for packing and shipment.

WHITE RUST
White rust is the common name of the disease of crucifers
caused by Albugo candida (Pers.) Ktz. The disease is worldwide
in its distribution, has been found commonly over the United
States, and in Florida is known to all growers of these plants at
all seasons of the year. In this State, it is most often found on
mustard, turnips and radishes and is seldom seen on cabbage,
cauliflower and the numerous other cultivated plants of this
group. It is not considered of great importance as a destructive
disease and has not been feared by growers. The disease lives
over periods, when crops are not being produced, on wild plants
and mustard that has escaped from cultivation along the edges
of fields and ditch banks. The susceptible crops grown for mar-
ket are produced during the Winter and Spring seasons, which
are least favorable for the development of white rust. Volun-
teer plants are almost always severely infected in late Spring
and Summer and often killed during blooming.
The disease is easily identified by the masses of chalky-white
spores which are produced mostly on the lower surface of the
leaf blade, occasionally on the upper side and on some of the
smaller stem and the floral parts. These spores are easily spread
by wind, insects and meteoric waters. The fungus also produces
other. thick-walled spores that are resistant to unfavorable con-
ditions and remain viable from season to season in old decaying
plant refuse in the soil. They germinate when favorable condi-
tions surround them and may reproduce the disease.
Symptoms: The first symptom of white rust is the appearance
of yellowish spots on the leaves. No indication of any parasite
can be distinguished until light-colored areas begin to appear un-
der the epidermis on the lower surface of the leaves. These
areas enlarge, become lighter colored and produce a raised area
before they finally cause the epidermis to crack open. The edges
of the ruptured epidermis dry and shrivel, exposing more and
more of the white spore mass. The spots enlarge, producing
single more or less circular pustules, or the epidermis is ruptured






Bulletin 256, Some Diseases of Cabbage and Other Crucifers 45

in several places often resulting in more or less circular rows of
small pustules surrounding the original one (Fig. 35). The pus-
tules are almost always on the lower surface. The leaf tissue
directly over them becomes yellow, dies and turns brown and the
white spores disappear, leaving dark-brown killed spots. The
fungus develops readily in dry weather, requiring only enough
moisture furnished by dew for the germination of the spores and
infection of plants.
Control: Control methods are usually not necessary but should





































Fig. 35.-White rust of mustard.






46 Florida Agricultural Experiment Station

white rust become destructive it is suggested that the affected
plants and those growing in the rows close to them be destroyed.

ANTHRACNOSE
Anthracnose is caused by the fungus Colletotrichum higgins-
ianum Sacc. The disease is not widespread nor destructive in
the United States as a whole. It is more or less common in the
Southeastern Atlan-
tic and Gulf States,
Where it causes at
certain times consid-
erable damage. In
Florida it is present
in almost every
planting of turnips
and Chinese cabbage
and is frequently
found on radishes
and mustard. The
disease may attack
Chinese cabbage
when the plants are
young and follow
through the entire
season. Lesions de-
velop on the leaf
petioles and when
p they are numerous
the leaves are killed
(Fig, 36). The leaves
are often badly
spotted at heading
time, the outer head
leaves being killed
and turning brown
while still in place
over the head. Dur-
Fig. 36.-Anthracnose lesions on petioles and ing wet periods, a
leaf blades of pe-tsai.'
soft rot develops
which involves the inner parts of the heads and renders them
worthless.






Bulletin 256, Some Diseases of Cabbage and Other Crucifers 47

Anthracnose may be found on plants of all ages, but is most
often found from the time the plants are about half grown until
harvest time (Fig. 37). The fungus produces spores in abund-
ance in clusters that are so small they can be observed with diffi-
culty even with a good hand lens. The spores are readily dis-
seminated by wind and rain and may be carried on the seed.
Seed transmission is not important in Florida because mustard
and turnip plants
are usually grow-
ing in the differ-
ent parts of the
State during ev-
ery month of the
year and young
plants become in-
fected from the
old ones. The
losses are heavier
on Chinese cab-
bage than on tur- .
nips. This is prob-
ably because the
turnip is grown
mostly for greens
and is removed
from the soil and ,
prepared for mar-
ket when it is '
young and before
it has had oppor-
tunity to become ,
badly diseased.
Symptoms: An-
thracnose always
appears first as
small water-
soaked spots spar-
ingly scattered
over the leaves.
As these spots in-
crease in size they
develop a definite
brownish-black Fig. 37.-Late stage of anthracnose of pe-tsai.






48 Florida Agricultural Experiment Station

border and the centers become light colored and dry parchment-
like (Fig. 38). As the spots enlarge they often crack across and
portions fall away, leaving holes in the leaves. The spots are few
in number at first, but after secondary infection takes place the
leaves may become thickly spotted. The spots coalesce and cause
a rapid yellowing of portions of the entire leaf. The fungus also
infects the petioles and midribs of the leaves, forming elongated
sunken brown or gray spots surrounded with brownish borders.
These lesions are usually about as deep as they are wide. The
epidermis cracks
and drying takes
place rapidly.
.The leaves be-
come yellow, wilt
and die. When
such heavy infec-
tion occurs on
plants that are
half grown or less,
usually they are
killed before they
develop fully.
Control: No
control is neces-
sary under aver-
age conditions,
but if anthracnose
should be detected
early, the affected
plants should be
removed from
the field and de-
stroyed.
Rotate so that
crucifers do not
follow in succes-
sion on the same
Fig. 38.-Anthracnose of turnip leaf. soil.






Bulletin 256, Some Diseases of Cabbage and Other Crucifers 49

SOFT ROT
Soft rot may be caused by any of a number of bacterial organ-
isms, but Bacillus carotovorous Jones is the one most often found
associated with the rot of crucifers in the field, transit and storage.
Plants are susceptible to rot caused by this organism at any time
during their life. Soft rot has been found on all of the cultivated
plants listed in this bulletin and a large number of others, such
as carrots, celery, squash and potatoes. It is nationwide in dis-
tribution and of statewide occurrence in Florida. It is extremely
destructive in transit and storage but is considered less important
in the field.
The disease is more or less secondary in nature; that is, its
beginning is dependent upon open wounds such as cultivator in-
j u ries, harvesting bruises, insect injuries and other diseases. The
principal loss from soft rot comes from injuries at harvest time
that become infected and later result in a soft, slimy decay of the
vegetable in transit or storage. Washing may also be the cause
of considerable decay because the bacteria are washed into the
water from a diseased plant and all injured ones that are washed
later became inoculated. Consequently, products that are being
washed in preparation for market should be washed in running
water and not in tanks or buckets. Injury to young plants by
tools is not of importance. Insect injury, however, is very impor-
tant because it leaves open roads for infection by this parasite.
Handling at harvest time should be done carefully so as to avoid
bruises and cuts that may become infected.
The decayed parts are soft and slimy without much discolora-
tion and give off a foul odor. The decay is more rapid and com-
plete in the tender parts of the plant.
The bacteria causing the decay are spread by wind, water and
insects and occur in practically all cultivated areas. The best
means for preventing loss is sanitation around packinghouses
and fields, rotation with field crops, careful cultivation and han-
dling, adequate refrigeration during transit and storage. If
products are washed, use a mild disinfectant or at least running
water.
MOSAIC
Mosaic is a disease of plants caused by a so-called virus; other-
wise, little is known as to the exact cause. Research workers
have discovered and learned certain properties of the virus and
symptoms of the disease resulting from infection. It has been
found in all parts of the world and in all states of the United
States on most of the cultivated plants. In Florida it is well






50 Florida Agricultural Experiment Station

known and widely distributed. It has been found on tomatoes,
peppers, celery, lettuce, sugarcane, petunias, tobacco, beans, roses,
wandering jew, pokeweed, cucumber, flowering annuals and a
number of others belonging to families separate from the cruci-
fers. Turnips, mustard, rutabagas and chinese cabbage are the
members of the crucifer family most often affected in the State.
The disease is of minor importance on these plants as it causes
negligible losses.
The infective agent is contained in the sap of diseased plants
and is carried
from plant to
plant, mostly by
mechanical means
such as sucking
insects, cultiva-
tors and pickers.
The principal car-
rier of the infec-
wl tive virus is the
green plant louse
or aphid. These
insects are almost
always associated
with the disease.
Other insects such
as jassids and red
spider may be re-
sponsible. The
first infections on
cultivated plants
probably come
from aphids that
have fed on mosa-
ic plants else-
where, either cul-
tivated or wild,
and thus carried
the infection to
the next healthy
Fig. 39.-Mosaic of turnip leaf. plant upon which
they fed. If a
turnip or mustard plant once shows symptoms of the disease, it
will not recover and may or may not produce a salable product.






Bulletin 256, Some Diseases of Cabbage and Other Crucifers 51

The disease can also be transmitted by rubbing vigorously a leaf
from a mosaic plant orto an attached leaf of a healthy plant.
Symptoms: The early symptoms of mosaic on half-grown plants
are indicated by the appearance of new leaves that are more or
less yellowish and stunted. These leaves usually become mottled
later, showing light and dark green patches over the blade with
irregularities in structure or outline. The midrib and principal
veins are often distorted and pouch-like areas appear over the
leaf blade with the other malformations (Fig. 39). Finally they
become yellow and die prematurely.
Control: On cruciferous plants mosaic has not been serious
enough to warrant control measures. Control of insects, espe-
cially aphids, and the eradication of affected plants are suggested.

BLACKROOT OF RADISH

Blackroot of radish is caused by the fungus Aphanomyces
raphani Kend. This disease is not widely spread in the United
States and has been found only in certain localities in Florida.
It has been found only on radishes of which the White Icicle is
the most susceptible variety. The disease is very conspicuous
on this white variety because it forms a black area on the under-
ground portion of the hypocotyl and the main root and renders
then unfit for table use. The lesion may be large, irregular in
outline and shallow or deep. The radish is not deformed except
when it has been attacked early in its growth, in which case its
growth may be restricted through the central portion or other-
wise deformed. The fungus is not carried on the seed, but lives
in the soil from season to season. It attacks the radish through
injured roots or through the openings made in the epidermis or
cortex by the emerging rootlets. The mycelium of the fungus
grows in between the lho:t cell., causing them to become black.
Spores are 1rod nuced in aunliidaince. e-pecially in wet weather, and
cause secondary infection. Thick-\\ aled spores, very resistant
to unfavorable environmental conditions, are also produced in the
tissue of the plant. They remain in the dead plant material and
are freed when it disintegrates. They germinate under favorable
conditions and reinfect radishes.
Symptoms: The blackroot fungus enters the young radish plant
through wounds on roots and causes first a browning and finally
a blackening of the outer tissue. The spots are at first small and
circular, later becoming large and irregular. If the plant is young
when attacked, the unaffected portion continues to grow and






52 Florida Agricultural Experiment Station

enlarge while the affected parts increase very little in size. This
causes an uneven development, very often found where the dis-
ease is plentiful. The disease usually cannot be detected unless
the plants are removed from the soil.
Control: Rotation; plant resistant varieties or plant the White
Icicle on new soil.









































Fig. 40.-White spot of pe-tsai leaf.






Bulletin 256, Some Diseases of Cabbage and Other Crucifers 53

WHITE SPOT
White spot is caused by the fungus Cercosporella albomaculans
(E. & E.) Sacc. This is a disease of the leaves of petsai, turnips
and radishes and has not been found on other crucifers in this
State. It is widespread and common in Florida wherever turnips
are grown, but it is not so plentiful on the other two listed hosts
(Fig. 40). The leaf spotting is not often severe enough to cause
any damage except in certain instances where it has prevented
turnip greens from being marketed. The disease is conspicuous




































Fig. 41.-White spot of turnip leaf.






54 Florida Agricultural Experiment Station

on the leaves and develops rapidly during favorable weather con-
ditions. The spores are produced in large numbers and they are
disseminated by wind and water.
Symptoms: Tiny, water-soaked spots on the leaves are the first
indication of infection; they dry out, the host cells die and bleach
to almost white. The process is rapid and shortly the leaf blade
is speckled with white, mostly circular, slightly sunken spots 1/4
inch or less in diameter. They increase in size by coalescing.
The leaf tissue does not appear to be seriously affected except
when the white spots are numerous; then it turns yellow and cer-
tain areas may die and become brown (Fig. 41).
Control: No recommendations. Remove affected plants.

CERCOSPORA LEAF SPOTS
A leaf spot of radish is caused by Cercospora cruciferarum
E. & E. and a leaf spot of chinese cabbage (petsai) is caused by
Cercospora bloxami Berk. & Br. These two leaf spots are not
common in Florida, although they have been found in certain
localities causing some damage to small plantings. The petsai is
attacked when the
plants are small
and the leaves are
often badly spot-
ted and occasion-
ally killed, but en-
tire plants are sel-
dom killed (Fig.
42). The spots are
very distinctive
because they are
ash gray in color
and lack a definite
border. They are
more or less cir-
cular and average
about 1/2 inch in
diameter.
The spots on
radish are deci-
dedly different
from those on
petsai. They are
Fig. 42.-Leaf spot of young pe-tsai, caused by
Cercospora bloxami. small, circular or






Bulletin 256, Some Diseases of Cabbage and Other Crucifers 55

irregular in shape and black, showing no definite center color or
border. They are seldom more than 1/4 inch in diameter. Radish
leaves have been observed that were thickly spotted but none
have been seen that have been killed by the disease. Because of
the scarcity of these leaf spots, no control methods seem necessary.






































Fig. 43.-Leaves of water cress showing diseased areas typical of
Cercospora leafspot.






56 Florida Agricultural Experiment Station

CERCOSPORA LEAFSPOT OF WATER CRESS
Water cress, a cruciferous plant, Radicula nasturtium-aquatic
(L.) Britt. & Ren., although not commercially grown in Florida,
is used in the preparation of salads and as garnishes.
Occasionally plants are severely affected with a conspicuous
leafspot caused by the fungus Cercospora nasturtii Pass. This
fungus is apparently distinct from those causing leafspots on
radish and chinese cabbage. The disease, although not frequently
found or reported in the United States, may appear at any season
in Florida but is apparently more common during the cooler parts
of the year at which time the host plant grows best. When infec-
tion is severe the leaves become spotted, turn yellow and die
almost as rapidly as new ones develop. In such instances the
green leaf area of the plants is greatly reduced but the plants
are not killed.
Symptoms:-The disease is first evident by the appearance of
minute, dirty-white specks less than a millimeter in diameter.
The margin is not distinct but blends into the normal green of
the leaf blade. These spots enlarge rapidly and when widely
scattered often become one-half centimeter in diameter. When
numerous they coalesce, causing certain areas of the leaf blade
to become yellow, shrivel and die (Fig. 43). After the leaflets
are killed, the fleshy stems collapse and leaflets and petiole remain
attached to the stem of the plant. This development of the disease
results in an exposed, leggy stem with dead leaves attached and
terminated with a tuft of green developing leaves. The spots
are slightly sunken on both surfaces and often somewhat reti-
culate because of the dark colored veins in the light colored papery
area in the center of the large spots.
Control:-No recommendations. Might be advlisa1)le to remove
affected plants if the disease is detected before many plants be-
come involved.
MOLD
Mold caused by the fungus Rhizopus nigricans Ebrhr. is not an
important disease in Florida except in storage. It has never
been found in the field, but occurs often in market places where
cabbage is sold that has been kept in storage. The fungus causes
practically all of the damage attributed to it during transit and
storage. It is widely distributed and occurs as a rot of stored
perishables in all parts of the United States. The spores are
always present and infect truck-crop products, especially follow-
ing bruises.






Bulletin 256, Some Diseases of Cabbage and Other Crucifers 57

The outer leaves of the cabbage head are the first attacked and
they often become entirely covered with 'the fungous mycelium
and black speck-like clusters of spores before the inner leaves
show any indication of infection. The fungus spreads from one
head to those adjacent to it and thus infects a large number of
them. The damage resulting is dependent upon the length of
time and temperature in transit or storage. The disease develops
slower at the lower temperatures. It can always be identified
by the beadlike clusters of spores and the abundant mycelial
growth of the fungus (Fig. 44). Diseased cabbages taken from
storage can be made to look like new by peeling off several of the
outer leaves, provided, of course, that the rot has not penetrated
too deeply.





























Fig. 44.-Mold on cabbage head. Developed in storage.







58 Florida Agricultural Experiment Station

DISEASES OF CRUCIFERS NOT FOUND IN FLORIDA
There are several very important diseases of cabbage and other
cultivated crucifers caused by virulent parasites that have not
been found in Florida. Whether it is only a matter of time until
they appear or whether environmental conditions are not favor-
able to their development is not known.
Club Root: This disease is caused by the fungus Plasmodiophora
brassicae Wor. and is characterized by the rough irregular devel-
opment and growth of the roots.
Yellows: Yellows is caused by the fungus Fusarium congluti-
nans Woll. The yellowing and shedding of the leaves and general
stunting of the plants are typical symptoms.
Ringspot: The fungus Mycosphaerella brassicicola (Fr.) Lind.
causes this disease which is characterized by more or less circular
spots from 1/4 to 1 inch in diameter. The spots are dotted in
more or less concentric circles with small black specks.
Bacterial Leafspot: This cauliflower disease is caused by Bac-
terium maculicolum McC. and is identified by the large number
of small spots formed on the leaves; it is sometimes referred to
as peppery leafspot.
Ramularia Leafspot: The disease is caused by Ramularia
armoraciae Fckl. and it is identified by the numerous more or
less circular spots on the leaves.
Pythium Head Rot: Head rot caused by the fungus Pythium
debaryanum Hesse is a more or less dark colored, soft, wet decay
occasionally found in transit.

PHYSIOLOGICAL DISTURBANCES
This type of disease is due primarily to unfavorable environ-
mental factors, water being the principal one. There are un-
doubtedly other agents such as sunshine, moisture, soil types and
fertilizers that are conitilitors to the cause, but very little is
known of the exact cause and the proper application of corrective
measures. Those listed herewith are not of much importance in
the State; consequently will not be fully described.
Oedema is the name applied to malformation, bursting and dis-
tortion of the veins in leaves of cabbage.
Tipburn (Fig. 45), as the name implies, is the browning, wrink-
ling and shrinking of the margins of the leaves which finally turn
black. This disease is attributed usually to unfavorable soil and
water relations and to varietal susceptibility.







Bulletin 256, Some Diseases of Cabbage and Other Crucifers 59



































Fig. 45.-Tipburn of bearing brussels sprout plant.

Enlarged lenticels and hypertrophied cells are troubles occa-
sionally encountered in cabbage fields occurring on the leaves dur-
ing continuously rainy and muggy days.
Growth cracks (Fig. 46) appear in cabbage fields at about har-
vest time in which the head bursts open and are attributed by
most growers to too much water for the plant. The inner por-
tion of the head swells or enlarges too rapidly for the outer leaves
to stretch themselves and thus the head bursts.






60 Florida Agricultural Experiment Station















Fig. 46.-Growth cracks or splitting of cabbage on right; normal plant
at left, both same variety and age.

Variegated leaves occur frequently in cabbage fields. The leaves
are margined with a white or yellow band and the center is green
or the edge of the leaf may be green and the interior portion light.
It appears to be associated with individual plants and is probably
hereditary.
Premature seeding (Fig. 47) likewise is supposed to be linked
with hereditary tendencies of individual plants, as these seeders
usually are widely scattered in fields.

















Fig. 47.-Cabbage plants of the same variety and age, showing seeding
tendencies of center plant.






Bulletin 256, Some Diseases of Cabbage and Other Crucifers 61

SEED TREATMENT
Seed of crucifers should be disinfected before being planted, as
there are several seed-borne diseases that are very important in
growing these plants. Blackrot is the most important seed-borne
disease in the State, while blackleg and others are of less impor-
tance. Two treatments are given in detail in general practice in
this country.
Mercuric Chloride Treatment: This is the simpler of the two
methods and naturally is the one most used. The poison mercuric
chloride may be purchased at any drugstore and can be secured
in tablet and crystal form. The tablets are so prepared that a
1:1000 solution can be obtained by dissolving 1 tablet in 1 pint
of water. The same strength solution can be prepared by dis-
solving 1 ounce of crystals in 71/2 gallons of water. Solutions of
this strength are recommended for use. The solution is poison
if taken internally and never should be prepared in metal con-
tainers, because the solution is weakened. ALWAYS USE
EARTHEN OR WOODEN CONTAINERS. After the solution is
prepared and ready for use, place the seed to be treated in a
cheesecloth bag, filling it 1/3 full; use sacks of such size that they
can be floated easily in the solution in the container. Submerge
the bag of seed in the solution and agitate it with a short stick so
as to separate the seed from each other and remove all air bubbles.
Soaking for 15 minutes is sufficient to kill all parasitic bacteria
adhering to the outside of the seed, although the seed will stand
30 minutes in the solution without setiou ;s detrimental effects.
This treatment will not entirely elimniate blackleg, but this dis-
ease has not been of importance in the State and further treatment
is probably not warranted. After the specified time, the seed
should be removed from the disinfectant and washed in several
changes of fresh water and spread out to dry in the shade.
Hot Water Treatment: When treating seed with hot water, one
should be equipped first with a standardized thermometer. The
water bath should be large enough to hold plenty of water and
the temperature should be so regulated that it will not exceed
1220 F. and be kept constant by the addition of either steam or hot
water. The seed after being placed.in cheesecloth bags as stated
above should be placed in the bath (it is recommended that a small
sample be given a trial treatment before the regular treatment,
for practice) followed by adequate agitation. Soak the seed for
25 to 30 minutes, then remove them, rinse in cold water and spread
out to dry. Do not add the steam or hot water'close to the seed.






62 Florida Agricultural Experiment Station

They should be removed from the bath at such instances. This
is a very exact treatment and should not be attempted unless well
understood and fully equipped.


FUNGICIDES
The application of sprays and dusts is not generally recom-
mended, except in the seedbed; here they should be used especially
for downy mildew. If dust is to be applied, a 25-75 or 20-80
copper-lime mixture containing 7 to 10 percent metallic copper
should be applied in early morning while dew is heavy on the
plants. Of the liquid fungicides, 3-5-50 bordeaux mixture pre-
pared with hydrated lime to which has been added a spreader such
as calcium caseinate at the rate of one pound to 50 gallons of pre-
pared spray has given the best. results.





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