Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; 166
Title: Tobacco diseases in Gadsden County in 1922
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Permanent Link: http://ufdc.ufl.edu/UF00026406/00001
 Material Information
Title: Tobacco diseases in Gadsden County in 1922 with suggestions for their prevention and control
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: p. 73-118 : ill. ; 23 cm.
Language: English
Creator: Tisdale, W. B ( William Burleigh ), 1890-
Publisher: University of Florida Agricultural Experiment Station, 1922.
Place of Publication: Gainesville Fla
 Subjects
Subject: Tobacco -- Diseases and pests -- Florida -- Gadsden County   ( lcsh )
Tobacco -- Diseases and pests -- Control -- Florida -- Gadsden County   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references.
Statement of Responsibility: by W.B. Tisdale.
General Note: "Contribution no. 1 from the Tobacco Experiment Station."--T.p.
 Record Information
Bibliographic ID: UF00026406
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000922814
oclc - 18171375
notis - AEN3323

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







December, 1922


UNIVERSITY OF FLORIDA
Agricultural Experiment Station



TOBACCO DISEASES IN GADSDEN

COUNTY IN 1922

WITH SUGGESTIONS FOR THEIR PREVENTION
AND CONTROL

By
W. B. TISDALE


Fig. 14.-A field of healthy Big Cuba tobacco after
second priming

(Contribution No. 1 from the Tobacco Experiment Station)


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


Bulletin 166












BOARD OF CONTROL
P. K. YONGE, Chairman, Pensacola
E. L. WARTMANN, Citra
J. B. SUTTON, Tampa
W. L. WEAVER, Perry
J. C. COOPER, JR., Jacksonville
J. T. DIAMOND, Secretary, Tallahassee
J. G. KELLUM, Auditor, Tallahassee

STATION STAFF
WILMON NEWELL, D. Sc., Director
JOHN M. SCOTT, B. S., Vice Director and Animal Industrialist
J. R. WATSON, A. M., Entomologist
R. W. RUPRECHT, Ph. D., Chemist
O. F. BURGER, D. Sc., Plant Pathologist
W. E. STOKES. M. S., Assistant Grass and Forage Crop Investi-
gator1
A. H. BEYER, M. S., Assistant- Entomologist
C. E. BELL, B. S., Assistant Chemist
J. M. COLEMAN, B. S., Assistant Chemist
G. F. WEBER, Ph. D., Assistant Plant Pathologist
HAROLD MOWRY, Assistant Horticulturist
RUBY NEWHALL, Secretary
T. VAN HYNING, Librarian
RALPH STOUTAMIRE, B. S. A., Editor
MARY E. Roux, Mailing Clerk
A. W. LE4AND, Farm Foreman
K. H. GRAHAM, Auditor
RETTA MCQUARRIE, Assistant to Auditor
W. B. TISDALE, Ph. D., Assistant Plant Pathologist, Tobacco Ex-
periment Station (Quincy)
JESSE REEVES, Foreman, Tobacco Experiment Station (Quincy)
J. H. JEFFRIES, Superintendent Citrus Experiment Station (Lake
Alfred)





ERRATA
Note the following corrections in Bulletin 166 of the University
of Florida Agricultural Experiment Station:
1. Page 99, line 1: The expression "(see footnote 27)" should
read "(see footnote 24)."
2. Page 105, underline of fig. 21: In the third line the expres-
sion "the plant on the left" should read "the plant on the right."
3. Page 115, line 3: The expression "After the spots have
dried out somewhat" should read "After the leaves have dried
out somewhat."





















DISEASES OF TOBACCO

OCCURRING IN GADSDEN COUNTY

IN 1922


WITH SUGGESTIONS
PREVENTION AND


FOR THEIR
CONTROL


(Contribution No. 1 from the Tobacco Experiment Station)








CONTENTS
PAGE

INTRODUCTION ..............---------------- ---------------..... 77
i MOSAIC DISEASE ......... ... ........... ...... ....-....--....--- 80
Plants Affected by Mosaic .................------- ............ 81
Appearance of Mosaic .................... ..................... 81
Cause of Mosaic .................. -..............---.---.--- 83
Control. of Mosaic ....... ....................................... 84
J/ROOT-KNOT ................ -.. .. ...........- 85
Appearance of Root-Knot ..... .......... .......................... 86
I Plants Attacked by, R.-.-t-.-. I .. ... ....:.. .. ............. ............ 87
Cause of Root-Knot .................................. .. .... 88
Control of Root-Knot .....--......-.:..... .............. 89
S! WILDFIRE ................................----- ------. -- 90
Plants Affected by Wildfire ................................... 91
S Appearance of W wildfire ........................... .............. ........- 91
Cause of W ildfire ........................... ......... .. ... ...... 94
Control of W wildfire ...... ...... ............. ........ .............. 94
GRANVILLE W ILT ...... ............ ................ ..----..----...- 96
Appearance of W ilt ............. ....... .... -- ----.... --. -------... 97
Plants Attacked by W ilt ....... ............. .......... ........ 98
Cause of Wilt ............................ ................. ... 98
Control of W ilt .... ......................................... ........ 98
LEAF SPOT .............. ........... ..... .... ... .---. ..... ....- --- .......... 99
Appearance of Leaf Spot .... ........ ..-. .... ....... ........... .... 99
Cause of Leaf Spot ................................. ..... ..... .... ......100
Control of Leaf Spot ....................... .. .................. 100
FROG-EYE OR "SPECKING" .................. ....... .........................101
Appearance of Frog-Eye ......... ..............................101
(L / Cause of Frog-Eye .............. ......... ..................102
Control of Frog-Eye .... ...... ............ ........ ..............103
ROOT-ROT ....... .................. ..... ....................... ........103
Plants Attacked by Root-Rot ............................ ....-- ......104
Symptoms of Root-Rot ..................... ............ .....................105
Cause of Root-Rot .....................-.................. 106
Control of Root-Rot .......... ............................ .................107
BLACK SHANK ..................-......... ..... ............ ........108
Plants Affected by Black Shank ..................................... .. ...... 110
Symptoms of Black Shank ................................. ........-...1 11
Cause of Black Shank ...................... ................115
Inoculation Experiments ............................. ..............116
Control of Black Shank .............................. .. ........... ............117


V








TOBACCO DISEASES IN GADSDEN COUNTY
IN 1922
WITH SUGGESTIONS FOR THEIR
PREVENTION AND CONTROL
By W. B. TISDALE

INTRODUCTION
The culture of tobacco under shade in Gadsden County, Flor-
ida, was begun in 1889. Since that date it has been the practice
to grow tobacco on the same land year after year for indefinite
periods; that is, the continuous-culture system is employed. In
contrast with this, it is the practice in some other tobacco-grow-
ing sections to grow only one or two crops of tobacco on the land
and then to allow a period of several years to elapse before
cropping to tobacco again.
There is usually good reason on the part of growers for adopt-
ing any one system. In some sections the cultural practices are
determined by the area of land available and the type of tobacco
grown. In the shaded section of Florida and Georgia the great
overhead expense of constructing shade is the main reason for
practicing the continuous-culture system. Because of the short
life of the shade material, especially the cloth used in combina-
tion with the slats, the high initial outlay is distributed over only
a few years. Furthermore, no other crop has as yet proved to
be as profitable under the shades as tobacco, so it is the practice
to grow this crop year after year as long as the land will yield
favorable returns.
The length of time this system can be profitably employed is
shorter now than during the earlier years of tobacco culture.
It is reported that in the beginning of the industry in Gadsden
County a good yield of fine quality tobacco was produced on the
same land from ten to eighteen consecutive years. Now the com-
mon practice is to grow tobacco under a shade from two to four
years. When the yield and quality begin to decrease, then corn or
some other crop is grown from one to three years before crop-
ping the land to tobacco again.
Most growers are aware that this situation has been brought
about by certain diseases, and they have taken many steps to




Florida Agricultural E.i'xpi( it; nt Station


remedy it. Much more needs to be done to prevent fiirther spread
and to successfully combat the diseases already prevalent. Each
year seems to have brought forth new complications which, dur-
ing the last few years, have caused growers and others directly
interested in the culture of tobacco to make numerous inquiries
of the University of Florida Experiment Station and of the
United States Department of Agriculture. This, of course, indi-
cates an increasing recognition of the importance of the diseases
and a desire for information concerning their prevention and
control.
As is true of other crops, some diseases of tobacco are para-
sitic-that is, caused by specific germs or other microscopic or-
ganisms-whereas certain others are non-parasitic and may be
attributed to weather conditions or improper soil and fertilizer.
The latter class of diseases appeared to be of minor importance
in 1922 and will not be included in this paper.
Various popular ideas exist in the county as to the cause of
different diseases of tobacco. Because the underground parts
of a plant are diseased, growers frequently conclude that the
trouble is due to improper fertilization or some obnoxious chem-
ical in the soil. If a disease appears-on the leaves during or
immediately following a rainy period, it is concluded that the
trouble is due to rain and sunshine. Such conclusions are in a
way justifiable because the parasites which cause the diseases
are, in a large measure, dependent upon the soil and weather
conditions for their distribution and development. These para-
sites are living organisms and are as sensitive to changes in soil
and weather conditions as the tobacco plant itself, but they do
not always respond to the changes in the same way. Conditions
which are unfavorable for the healthy growth of tobacco are
ideal for certain species of germs to enter and cause diseases
in the plant. On the other hand, certain other germs find the
healthy and vigorous plants more favorable for their entrance.
Once introduced into a new locality, the parasitic organisms
may be carried from field to field by several different agencies;
namely, seedlings for transplanting, farm implements, men, ani-
mals, insects, wind, drainage and irrigation waters. Frequently
a grower is unable to understand how his visit to a neighboring
diseased field may be the means of introducing the disease into
his shade. This inability to understand the various agencies of
distributing germs is probably due to a misconception of their
size, nature and methods of reproduction. These germs are so





Bulletin 166, Tobacco Diseases in Gadsden County


extremely small there is ample room on the minute quantity of
soil which adheres to the feet of man or animal to harbor thou-
sands of them. Under favorable conditions a relatively small
number is all that is necessary to start the disease in a new field.
Because of this fa-t it is often difficult or even impossible to
determine the exact means of distribution. Furthermore, it is
difficult for some growers to realizethe seriousness of a disease
until it appears in their own shade. Under such circumstances,
therefore, it seems almost too much to expect a grower to care-
fully guard against every possible means of distribution. One
or more of the diseases discussed in this bulletin appeared on
every farm visited in the county in the season of 1922, so the
main problem has resolved itself into methods for growing a
profitable crop in spite of the diseases.
Organisms which cause disease in tobacco live during winter
in different ways. Some live on the seed of diseased plants,
others live in some related wild plant or weed, while others
exist on organic matter in the soil. The latter group of or-
ganisms accumulate in the soil from year to year until it can
no longer produce a profitable crop of tobacco. In such cases
we say the soil is "sick" or "tobacco sick."
Organisms which cause disease in plants can be eradicated
from "sick" fields by steaming or soaking the soil with formalde-
hyde solution or by keeping off susceptible plants for several
years. By the latter method the germs are gradually starved
out because the soil does not supply sufficient food to keep their
reproduction rate above the death rate. The length of time re-
quired to rid the soil of germs by the starvation process (rota-
tion) is in most cases too great to be practical for shade tobacco.
Sterilizing the soil with steam or formaldehyde also seems im-
practical except for plant beds. The main hope for controlling
some of the diseases, then, is to develop strains of tobacco which
resist the disease in question. When-only one disease is con-
cerned the problem of developing a resistant strain is often a
simple matter, but when two or more diseases are involved the
problem becomes very complex.
A survey of Gadsden County has been made to determine the
distribution of the different diseases and the relative importance
of each. It was learned that most of the diseases occurring in
this county are common in other sections where tobacco is grown
and, consequently, they have been carefully investigated. How-





80 Florida Agricultural Experiment Station

ever, because of the different types of tobacco and the peculiar
climatic and cultural conditions in Florida, it seems that some of
the recommendations for controlling the diseases in other sec-
tions will prove more or less impractical in this section. One
or two diseases have not been reported ini other sections of
the United States, and consequently very little is known
about them. Some experimental work has been done this year
with one of these diseases and more is in progress. The reader,
therefore, should understand at the outset that there are many
unavoidable limitations in the treatment of the subject at this
time. Therefore, this may be considered a preliminary report
upon the various diseases, and not a final treatment following
exhaustive investigation.
It is the purpose of this bulletin to assemble, primarily for the
grower, facts available in various publications on the parasitic
diseases of tobacco occurring in Florida. Each disease will be
described and illustrated with photographs, in so far as possible,
and accompanying these there will be an account of the causal
organism. Suggestions will. also be offered for the prevention
and control of the disease; in so far as they appear practical.

MOSAIC
Mosaic is a peculiar disease of tobacco which is said to occur in
all countries where this plant is grown. It is known in different
sections as "calico," "gray-top," "mottled-top," balloonn," and
"brindle."1 The seriousness of the disease apparently varies in
different countries and in different sections of this country.
Only a few growers in Gadsden County seem to recognize mosaic
as having any economic importance, and they claim that it is
more serious some years than others. In 1922 it was found in
only a few fields before the plants were topped. After the plants
were topped it appeared on the suckers in practically every
field. Since the sucker leaves usually are not harvested, the
disease caused little or no damage. The late occurrence of mosaic
is probably due to the fact that the tobacco is kept free from all
insects until the plants are topped. After being topped the plants
'are poisoned less frequently, if at all, so some insects feed on
the sucker leaves before the stalks are cut.

1Wolf, F. A. and Moss, E. G.: "Diseases of Flue-Cured Tobacco with
suggestions for Application of Palliative, Preventative and Remedial Mea-
sures," in The Bulletin, N. C. Dept. Agri., vol. 40, No. 12, pp. 1-45, 1919.





Bulletin 166, Tobacco Diseases in Gadsden County


PLANTS AFFECTED BY MOSAIC
Tobacco mosaic is known to affect several plants related to
tobacco; namely, tomato, pepper, petunia, jimson weed, horse
nettle, ground cherry, and nightshade. The pokeweed is affected
by a mosaic disease which appears similar to tobacco mosaic, but
so far as known the two diseases are quite distinct.
The horse nettle and ground cherry are perennial by means
of a deep rootstock which sends up new shoots every year. Once
these weeds become infected with mosaic, the rootstockssend
up mosaic shoots the next year which constitute a source of in-
fection for crops of tobacco in the vicinity. It has been proved
that plant lice, or aphids, and flea-beetles can transmit the mosaic
from these weeds to tomatoes." Careful experimentation has
shown that plant lice are the most important agents in the trans-
mission of tobacco mosaic.' After feeding on a mosaic plant, in-
sects become carriers of the mosaic virus and may cause infection
when they feed on a healthy plant.

APPEARANCE OF MOSAIC
Symptoms of tobacco mosaic are influenced by the age of the
plant and weather conditions. Usually only the youngest parts
of the plant are capable of becoming diseased, or, at least, of
showing external symptoms of the disease. In young plants at
the two-leaf or three-leaf stage the first visible symptoms of
mosaic are a downward curling and distortion of the smallest,
innermost leaves, which are at this stage chlorotic or yellowish-
green in color." As these leaves increase in size, small, abnor-
mally dark green spots appear. If the plants are growing rap-
idly, these dark green portions of the leaves develop rapidly into
large, irregular, crumpled swellings or blisters, and the affected
leaves become narrow, distorted or irregular (see fig. 15). On the
other hand, if the plants are growing less vigorously, the green
color of the affected leaves may be only slightly mottled. Plants
affected with mosaic when young do not outgrow the disease.
Plants which become infected with mosaic after they are prac-
tically mature develop a characteristic symptom known as "mot-

'Gardner, Max W., and Kendrick, James B.: "Tomato Mosaic," in Purdue
(Ind.) Univ. Agri. Exp. Sta. Bul. 261, pp. 1-24, 1922.
"Allard, H. A.: "The Mosaic Disease of Tobacco," in U. S. D. A. Bul. 40,
pp. 1-33, 1914.





Florida Agricultural Experiment Station


tied top." The lower leaves in such cases may never show
symptoms of the disease and the grower does not realize any loss.


Fig. 15.-Leaves of tobacco affected with mosaic. Note the characteristic
mottling and the raised dark green spots on a yellowish-green background.
(Courtesy of James Johnson)






Bulletin 166, Tobacco Diseases in Gadsden County


It has been proved that all leaves and flower parts of "mottled
top" plants contain the mosaic virus.'
Mosaic affects the pink color of the blossoms in much the same
manner as it does the green color of the leaves; that is, the nor-
mal uniform pink color may show only in lines, specks or
blotches. In some cases the blossoms remain small and become
greatly misshapen. Likewise the seed pods are small and develop
few or no viable seeds. Such distorted flowers and seed pods
sometimes develop on otherwise apparently healthy plants, and
the reverse has been found to occur.
Mosaic symptoms in horse nettle and ground cherry are usually
much less conspicuous than in tobacco and may not be easily
recognized. Nishimura" says that one species of ground cherry
may act as a carrier of the mosaic disease attacking tobacco, to-
mato and other plants without itself showing any symptoms of
the disease. Both horse nettle and ground cherry are common
around the tobacco fields of Gadsden County and some plants
have been found infected with mosaic. It has not been proved
that they are the source of infection for the tobacco. However,
it has been proved that insects transmit the disease from these
weeds to tomatoes and it seems probable that the same thing can
happen with tobacco, especially since mosaic does not appear, as
a rule, until dusting has been discontinued and insects begin to
feed on the tobacco.
CAUSE OF MOSAIC
So far no organism, such as a fungus or bacterium, has been
found which causes mosaic. The disease, however, is highly in-
fectious, and the infectious principle is known as a virus. Just
what the nature of this virus is still remains a debatable ques-
tion. There are mosaic diseases of cucumbers, beans, and sugar
cane which seem to be separate and distinct from tobacco mosaic.
The juice of mosaic plants is extremely infectious even after it
has passed thru a bacteria-proof filter, or in dilutions of 1 to
1000. The virus increases very rapidly when injected into
healthy plants. It has been known to live in dry mosaic leaves for

'Allard, H. A.: "Distribution of the Virus of the Mosaic Disease in Cap-
sules, Filaments, Anthers, and Pistils of Affected Tobacco Plants," in Jour.
Agri. Res., vol. 5, No. 5, pp. 251-256, 1915.
"Nishimura, Makoto: "A Carrier of the Mosaic Disease," in Bul. Torrey
Bot. Club 45, No. 6, pp. 219-223, 1918.






Florida A t! iicl/ti aul Experiment Station


18 months, but is not known to live over winter in the soil or in
seed from diseased plants. It is killed by heating."
Mosaic may be spread from diseased plants to healthy ones
while transplanting,' poisoning the buds, topping, and by in-
sects. It seems that a slight wound of some kind is necessary
for infection to take place. It has been shown" that merely break-
ing off the hairs on the leaves offers adequate wounds to permit
mosaic infection. Mosaic symptoms usually appear in plants
within ten days or two weeks after the virus has been rubbed or
inserted into their tissues.
Because of these properties the virus is believed by some to
be an exceedingly small organism invisible under the microscope
and small enough to pass thru the filters.

CONTROL OF MOSAIC
In experiments in Massachusetts' it was found that many of
the field outbreaks of tobacco mosaic can be traced to the plant
bed. Plants which become infected in the beds not only are
worthless themselves but serve as a source of infection for other
plants. It is important, therefore, that the disease be kept out
of the plant beds.
Inasmuch as the virus is not known to live over winter in the
soil or in the seed, it appears evident that it is introduced into
the plant bed from some outside source. Experimenters in In-
diana' have found that the mosaic virus lives over winter in the
rootstocks of horse nettle and perennial ground cherry and that
plant lice and flea-beetles transmit the disease from these plants
to tomato. These weeds are common in Gadsden County and
probably serve as a source of infection for tobacco plants." Flea-
beetles have been found feeding on ground cherry and horse
nettle early in spring before tobacco is transplanted and after
the tobacco stalks are cut in summer. The common practice in

'Allard, H. A.: "Some Properties of the Virus of the Mosaic Disease of
Tobacco," in Jour. Agri. Res., vol. 5, pp. 251-256, 1915.
'Chapman, G. H.: "Mosaic Disease of Tobacco," in Mass. Agri. Exp. Sta.
Bul. 175, pp. 72-117, 1917; and Clinton, G. P.: "Chlorosis of Plants with
Special Reference to Calico of Tobacco," in Cbnn. State Sta. Rpt., pt. 6,
pp. 357-424, 1914.
'Allard, H. A.: "Further Studies of the Mosaic Disease of Tobacco," in
Jour. Agr. Res., vol. 10, No. 12, pp. 615-631, 1917.
'Gardner, Max W., and Kendrick, James B.: "Tomato Mosaic," in Purdue
(Ind.) Uni. Agri. Exp. Sta. Bul. 261, pp. 1-24, 1922.





Bulletin 166, Tobacco Diseases in Gadsden County


Florida of covering the plant beds with cloth protects the seed-
lings from insects and, no doubt, thus prevents mosaic infection.
Most growers also cut the stalks as soon as they have finished
priming, which reduces the number of infected plants for the
insects to feed on. Even so, the insects have had opportunity to
feed on some infected plants and after the tobacco stalks are cut
they return to the weeds and inoculate them with the virus.
Since it has been found that mosaic may be carried several hun-
dred feet among the weeds, it seems that tobacco growers could
further insure their crop against the disease by destroying horse
nettle and ground cherry weeds around the plant beds. Clearing
out the edges of shades, as is practiced by some growers, destroys
insects and the source of mosaic infection. Eradication of these
weeds from extensive areas around the fields would, however,
be a big undertaking and, unless the disease becomes more se-
vere than at present, this would probably not be practical.
If any mosaic plants are detected in the plant bed they should
be pulled out and the hands thoroly washed with soap and water
before handling healthy plants. Also, if a few infected plants
are detected in the field early in the season, they should be pulled
out and destroyed, since they may serve as centers of infection.
Several instances were observed this year where it was apparent
that mosaic was spread from plant to plant by laborers while
poisoning for budworm. Finally, the employment of any sani-
tary measures which will reduce the number of insects during
the winter and spring will lessen the chances for transmitting
mosaic from weeds to tobacco.

ROOT-KNOT
A disease of tobacco, known in this county as "knot-root" and
in other sections of the country as "root-knot," "root-gall," or
"big-root," is very prevalent on the light sandy soils. It has not
been observed to cause much damage on heavy clay soils, altho
infected plants have been found under these conditions. It does
not occur in northern states except in greenhouses.
Root-knot is the cause of serious damage to other crops besides
tobacco. In some parts of Florida and other southern states it
is impractical to grow certain vegetable crops because of this
disease. Since it is so prevalent in the county it probably causes
more damage to tobacco than is usually attributed to it. Some of
the fields are infested when first planted to tobacco and the





Florida Agricultural Experiment Station


growers think the reduced yield is the normal one. Under exist-
ing conditions it would be difficult to estimate accurately the
total damage caused by root-knot.

APPEARANCE OF ROOT-KNOT
Tobacco plants badly infected with root-knot are dwarfed, wilt
readily in dry, hot weather; and are usually of a paler green
color than normal ones. Badly infected plants may be entirely
killed, especially during a dry season. However, except in badly
infested areas, there is only a slight amount of dwarfing and
the yield is only slightly reduced. This slight checking of
growth is especially unnoticeable if there is no near-by, non-
infested field which may be used for comparison. It is very
probable that many tobacco growers in the county unknowingly
suffer a material annual reduction in yield because of root-knot,
or if the damage is noticed it may be attributed to some other
cause. Fields of tobacco infested with nematode usually show
























Fig 16.-Tobacco roots showing typical root-knot injury. The swellings or
knots on the roots cut off the water supply to the leaves and are subject
to invasion by insects and bacteria or fungi and, therefore, of decay
(Courtesy of F. A. Wolf)





Bulletin 166, Tobacco Diseases in Gadsden County


irregular growth of plants. The stunted plants in such fields
usually show root-knot or root-rot infection.
The roots of an infected plant are greatly enlarged or knotted
at various points (see fig. 16). The distribution of these enlarge-
ments varies somewhat with the different species of plants.
They are scattered on some species, while on others they may be
so close together that the whole root system is abnormally thick-
ened. In some plants the fine lateral rootlets are the principal
points of attack, while in others, as coffee weed, the attack is
limited almost entirely to the main root. These enlargements on
the roots interfere with the transfer of water from the fine feed-
ing roots to the stalks and leaves, with the result that in dry, hot
weather the plants wilt because of their inability to secure
enough water.. The knots are quite watery and tender, and are
readily attacked by insects and fungi or bacteria which cause
them to decay. As a result of this secondary invasion and con-
sequent decay of the roots, many plants die prematurely or
produce an inferior crop. This type of indirect injury from root-
knot occasionally occurs in plants where the knots are too few to
be harmful by themselves.
Root-knot enlargements on legumes cowpeas, beans, and
clovers-are sometimes confused with the beneficial nodules
caused by nitrogen-fixing bacteria that live in the roots of these
plants. Nodules produced by nitrogen-fixing bacteria are usually
more or less spherical or lobed, relatively small, and attached to
the side of the rootlet, while knots of root-knot are swellings or
thickened portions of the roots.

PLANTS ATTACKED BY ROOT-KNOT
In addition to tobacco, root-knot attacks a large number of
plants belonging to unrelated families. About five hundred kinds
of plants are known to be attacked. Practically all weeds com-
mon in tobacco shades are attacked, but in some cases they show
only slight root-knot symptoms. There are some plants which
develop numerous galls or knots on the roots, yet with no ap-
parent damage to the crop.
Since the number of susceptible plants is too great to list in
this bulletin, the agricultural crops which are immune or highly
resistant to the disease will be given instead. These include beg-
garweed, Brabham and Iron cowpeas, peanut, velvet bean, corn,
rye, barley, broom-corn millet, pearl millet, sorghum, timothy,





Florida Agricultural E., 1., ii t Station


wheat and oats. It is safe to assume that all weeds occurring in
tobacco shades, except beggarweed and crab grass, are more or
less susceptible to root-knot.
Numerous fields were observed in the fall of 1922 in which the
bean plants were shedding leaves and blossoms. A high per-
centage of the plants died, either directly or indirectly from root-
knot injury. Most of these fields, it is claimed, will not be cropped
to tobacco next year; but, even so, the purpose of keeping to-
bacco off for several years will have been defeated by growing
the susceptible bean plants. At any rate it seems bad practice
to grow beans or crops susceptible to root-knot on land where
tobacco is to be planted the following year.

CAUSE OF ROOT-KNOT

Root-knot is caused by a minute animal, technically known as
Heterodera radicicola. It belongs to the group of animals com-
monly called nematodes or eelworms. Many members of this
group attack plants, while others attack animals. At the time
it hatches from the egg the worm-like nematode is from about
one-eightieth (1/80) to one-fiftieth (1/50) of an inch in length,
while in thickness it is about one-thirtieth (1/30) of its length.
Thus, because of its minuteness, the nematode is invisible to
the naked eye. It moves about in the soil and on coming in con-
tact with a root bores its way into it. Once inside, the young
nematode ceases its active movements and, by means of a hollow,
spear-like organ within its mouth, absorbs its nourishment from
the root tissues. It grows while feeding on the root and increases
in thickness more rapidly than it does in length, so that even-
tually the mature female is from one-fortieth (1/40) to one-
twenty-fifth (1/25) of an inch in diameter and almost pear-
shaped. In this stage the nematode is visible to the naked eyes
as a minute, pearly white, rounded body. It requires about four
weeks for the female to reach full development and begin laying
eggs. The females are capable of laying about five hundred eggs,
each of which may hatch into the minute worm described above.
In Florida it is possible for the nematodes to produce as many
as ten generations in a year.'1 The male increases in size but
never attains the size of the female.

'Bet-v y. Ernst A., and Byars, L. P.: "The Control of Root-Knot,"
in Farmers' Bulletin 648, pp. 1-19, 1915.






Bulletin 166, Tobacco Diseases in Gadsden County 89

The presence of the nematode in the root irritates the tissues
in such a way that the root enlarges, forming a swelling that
may be several times the diameter of the root above or below. If
many nematodes are in the root, the swellings become very large
and numerous.

CONTROL OF ROOT-KNOT
Whenever land becomes infested with nematodes, it can be
freed of them only by sterilization or keeping off all susceptible
plants for some time. Since sterilization is considered expensive,
except for plant beds, eradication can be accomplished only by
growing immune plants and by clean and constant cultivation.
The nematode can be carried into the field on plants from in-
fested plant beds. Plants infested when transplanted are doomed
to suffer injury themselves and to infest the soil in which they
grow. Therefore, it is important to sterilize the bed before plant-
ing the seed and then to dig a ditch around it to prevent rein-
festation. Practically all growers in Gadsden County sterilize
their plant beds, either by steaming or burning, but many fail to
dig a ditch around the beds to prevent drainage water running
into it from the outside. Laborers are permitted to enter the
beds to remove weeds without disinfecting their feet. This is
another probable means for reinfesting the beds.
It has been known for several years that the nematodes can
be eradicated from infested land by practicing a rotation system
which will keep susceptible crops and weeds off the land for two
or three years." This method is more or less impractical for the
tobacco growers of Gadsden County. The Florida Agricultural
Experiment Station recently reported" that the same result can
be accomplished in one summer by constant cultivation and
eradication of all susceptible weeds. This means that the land
must be cultivated once a week, or after each rain, to prevent the
formation of a crust. Since it is injurious to the land to keep it
free from vegetation during summer, velvet beans, Brabham,
Victory or Iron cowpeas should be grown to furnish shade and to
add humus and nitrogen to the soil. The bunch velvet bean
serves best for this purpose because it allows cultivation dut iing
the growing period and is more nearly immune to root-knot than

"Bessey, Ernst A., and Byars, L. P.: "The Control of Root-Knot,' in
Farmers' Bulletin 648, pp. 1-19, 1915.
"Watson, J. R.: "Bunch Velvet Beans to Control Root-Knot," in Fla.
Agri. Exp. Sta. Bul. 163, pp. 55-59, 1922.






Florida Agricultural Experiment Sftfion


cowpeas. All weeds must be kept out of the beans by occasional
hoeings, if necessary, otherwise they will act as host plants for
the nematodes and thus defeat the purpose of the treatment.
This method is based upon the fact that air and a favorable
temperature are necessary for the nematode eggs to hatch." If
a crust is allowed to form on the soil, sufficient air cannot enter
and the eggs will not hatch but will remain dormant for a long
time and then hatch when the soil is broken. On the other hand,
if the soil is kept broken and loose 'during the summer months
the eggs will hatch and, if there are no suieptible )plants grow-
ing on the land, the nematodes will die.
The great unevenness in height of tobacco plaiit s in badly in-
fested fields indicates a difference in degree of susceptibility as be-
tween individual plants. This condition suggests the possibility
of developing a strain of tobacco which is resistant to root-knot.
Several of the most vigorous plants. selected in a badly infested
field this year, were self-pollinated, and the progeny will be
tested in 1923 on infested soil.
WILDFIRE
Wildfire is a bacterial or germ disease of tobacco which was
first reported in 1917 from North Carolina." Since that date it
has been reported from Connecticut, Kentucky, Massachusetts,
Ohio, Virginia, Wisconsin" and South Africa." In some states
the disease has been local, while in 1921 it was reported to
be quite widespread in plant beds and fields in Massachusetts
and Connecticut. The disease was reported in Florida in 1921
but no specimens were collected and the person who made the
report was not quite sure of the diagnosis. Since the disease
appeared in 1922, it seems probable that the report of last year
is correct. The disease appeared in three two-acre fields in 1922,
and the source of this infection was traced to two small plant
beds both owned by the same person. One of these beds was lo-
cated on April 20 and about 75 percent of the plants were in-
fected at that time. The other bed was free from the disease on
"Watson, J. R.: "The Control of Root-Knot, II," in Fla. Exp. Sta. Bul.
159, pp. 31-44, 1921.
"Wolf. F. A., and Foster, A. C.: "Tobacco Wildfire," in Jour. Agri. Res.,
vol. 12, No. 7, pp. 449-458, 1918.
"Wolf, F. A., and Moss, E. G.: "Diseases of Flue-Cured Tobacco with
Suggestions for Application of Palliative, Preventative and Remedial Mea-
sures," in The Bulletin, N. C. Dept. Agri., vol. 40, No. 12, pp. 1-45, 1919.
"Pole-Evans, I. B.: "Tobacco Wildfire (Bacterium tabacum)," in Jour.
Dept. Agri., Union S. Afr., pp. 4-57, 1922.






Bulletin 166, Tobacco Diseases in Gadsden County


that date but became infected a few days later. The owner had
been passing from the infected bed to the healthy one, thus it is
probable that the organism was carried on his clothes, or on
boxes which were used for carrying the plants.
The source of this plant-bed infection is not definitely known
but second-hand cloth from Connecticut is strongly suspected.
The seed was grown in the county in 1921 and many other beds
were planted from the same lot but only the one bed showed in-
fection. This bed was covered with cloth which was said to have
been used in Connecticut in 1921. The other bed that became in-
fected later in the season was covered with cloth from a different
source, but as stated previously the owner had been passing from
one bed to the other and, no doubt, carried the germs to the one
from the other.
The seriousness of this small outbreak indicates that wildfire
may become of great importance in Florida, provided it becomes
widespread. The usual heavy rains of the growing season favor
the rapid spread of the disease from the lower to the upper
leaves, thereby making them valueless as wrappers. Data col-
lected in all states where wildfire occurs show that practically all
outbreaks of the disease in the field originate in the plant beds;"
hence it behooves every grower to endeavor to grow healthy seed-
lings.
PLANTS AFFECTED BY WILDFIRE
Inoculation experiments conducted at the Massachusetts Ex-
periment Station (see footnote 17) have shown that besides to-
bacco, petunia, eggplant, pokeweed, and tomato are more or less
susceptible to wildfire. The organism has been isolated from dis-
eased spots around insect injuries on cowpea leaves but it is not
considered an active parasite of this plant." When a water sus-
pension of the wildfire organism was sprayed on pepper, potato,
horse nettle and jimson weed plants, the disease did not develop.
APPEARANCE OF WILDFIRE
The symptoms of wildfire are conspicuous and easily recog-
nized. Leaves, flowers and seed pods may be attacked, but the
disease has not been found on the stalks and roots. The or-
ganism enters the plant by way of wounds, stomates (breathing
"Chapman, G. H., and Anderson, P. J.: "Tobacco Wildfire," in Mass.
Agri. Exp. Sta. Bul. 203, pp. 67-81, 1921.
"Wolf, F. A., and Foster, A. C.: "Tobacco Wildfire," in Jour. Agri. Res.,
vol. 12, No. 7, pp. 449-458, 1918.






Florida Agricultural Experiment Station


pores), and hydathodes (water pores). It multiplies very rapidly
inside of the plant and soon kills the tissues immediately sur-
rounding the point of entrance. This dead area is recognizable
as a small, brown speck about the size of a pin point surrounded
by a circular, yellowish-green area varying in size from less
than a fourth to
half an inch in di-
ameter (see fig.
17). Within two
or three days the
brown specks will
have enlarged
from an eighth to
a fourth of an
inch in diameter,
but the yellowish-
green halo will not
have increased in
1 i k e proportion.
This halo is the
most constant and
dependable char-
acteristic for use
in a field diagnosis
of wildfire. During
rainy, cloudy
weather the brown
areas rot out,
which gives the
leaves and plant
a ragged appear-
ance. Any number
of spots may ap-
pear on a leaf, and
when they are nu-
merous they run
together and form
Fig. 17.-Leaf of young tobacco plant showing large, irregular,
typical early symptoms of wildfire. Note the brown areas.
small white spots surrounded with a halo. In
living plants the small spots in the centers are When the lower
light brown and the halo yellowish-green. (Cour- leaves are badly
tesy of F. A. Wolf)





Bulletin 166, Tobacco Diseases in Gadsden County


affected the up-
per ones may
turn yellow.
Because of the
rapidity of spread
from leaf to leaf
and from plant
to plant during
rainy periods the
name "wildfire"
was appropriate-
ly given to this
disease. The age
of the plant and
weather condi-
tions modify the
appearance of
the spots. The
brown centers of
old plants may
not be uniformly
brown but may
consist of several
concentric rings
of different
shades of brown
(see fig. 18).
During periods of
Fig. 18.-Leaf of tobacco showing symptoms of old w e t c 1 o u d y
wildfire infection. Note the zonated markings and weather the
dark borders of the spots. In the field the borders
appear water-soaked. (Courtesy of F. A. Wolf) young spots may
not show the
characteristic yellowish-green halo but instead the affected tis-
sues may appear water-soaked and develop a soft rot. In the
very early seedling stage the disease is also typical of a wet rot,
and a translucent line is noticeable between the living and the
dead tissues.
Wildfire usually makes its appearance in the plant bed before
the plants are ready for transplanting. With warm weather and
favorable rainfall 100 percent of the plants in a bed can become





Florida Agricultural Experiment Station


infected in a very short time. IPants infected when set in the
field have little chance of making a marketable crop, especially
if rainfall is abundant.

CAUSE OF WILDFIRE
Wildfire is caused by a specific bacterial organism or germ
technically known as Bacterium tabacum Wolf & Foster. An
individual organism is so small that more than 7500 of them
placed end to end would form a chain only one inch long. It
reproduces by fission; that is; the body, a single cell, increases in
length and divides into two. With a favorable supply of food and
a moderately high temperature this organism divides at a very
rapid rate. Some of the new cells remain attached to each other,
thus forming short chains.
During rains wildfire germs are washed out of the diseased
tissues of the host plant and are splashed on healthy leaves above
and on healthy plants nearby. It passes into the tissues of the
healthy leaves while the water is on them and within a few days
the spots begin to appear. It is because the spots appear during
or immediately after a rainy period that some growers are in-
clined to attribute the disease directly to the rain.

CONTROL OF WILDFIRE
Observations in North Carolina, Virginia, Massachusetts and
Connecticut show that wildfire invariably begins in the plant bed
and is introduced into the fields at the time of transplanting.
The most important factor in the control of wildfire, then, is the
production of healthy seedlings. The organism lives over winter
on seed of diseased plants and on the cloth used for shade."
Available data indicate that it does not live over winter in the
fields in Massachusetts." However, it has been found to live over
winter in North Carolina21 in old plant beds which bore infected
plants the previous season. The greatest attention possible
should, therefore, be given to obtain clean seed and to protect
the seedlings until they are transplanted. As yet Florida growers

"Fromme, F. D., and Windgard, S. A.: "Blackfire and Wildfire of Tobacco
and Their Control," in Va. Agr. Exp. Sta. Bul. 228, pp. 1-19, 1922.
2oChapman, G. H., and Anderson, P. J.: "Tobacco Wildfire," in Mass.
Agri. Exp. Sta. Bul. 203, pp. 67-81, 1921.
"Wolf, F. A.: "Tobacco Wildfire," in N. C. Agri. Exp. Sta. Bul. 246, pp.
1-26, 1922.






Bulletin 166, Tobacco Diseases in Gadsden County


have no reason to fear that their home-grown seed are infected,
because no outbreaks of the disease have been found in this
county, except the cases already mentioned. When seed are im-
ported from some other section of the country, the following
recommendations should be observed in order to insure healthy
seedlings.
First, disinfect the seed before planting. Tobacco seed can
be most conveniently disinfected by tying them loosely in a
muslin bag and immersing them for ten minutes in a solution of
corrosive sublimate (1 part to 1000 parts of water) or formalde-
hyde (1 fluid ounce to 1 pint of water). Stir them about during
the treatment in order to remove air bubbles from around the
seed. After removing the seed from the solution wash them
thoroly in running water or in several changes of water, and
then spread them out to dry in the shade. The seed can also be
treated loose in a glass jar but usually they are handled easier
in a cloth bag.
Second, do not use second-hand cloth over the beds at any
time, if it comes from an area where wildfire is known to occur.
It may be used over the fields with less danger of introducing
wildfire, but should be disinfected before being used for either
purpose. Other diseases than wildfire may also be introduced on
cloth from other sections. While the cloth is being rolled up on
the ground, dirt and trash adhere to it and on being unrolled
the adhering material falls off or is washed off later by rain.
Even if the plant bed is sterilized before planting the seed, this
dirt and trash may serve to reinfest the bed.
Third, watch the plants in the bed and, if the seed are from
another state or of doubtful purity, spray or dust them once a
week until they are set in the field. The Massachusetts Experi-
ment Station recommends22 freshly prepared bordeaux (4-4-50)
or a dust, such as Sanders'.
If the disease appears in the field early in the season, the in-
fected plants, if only a few, should be pulled out when dry and
replaced with healthy ones. If a field shows heavy infection,
remove and destroy all the plants and reset the field ten days or
two weeks later with healthy ones. This method is impractical
after the plants are several weeks old.

"Chapman, G. H., and Anderson, P. J.: "Tobacco Wildfire," in Mass.
Agri. Exp. Sta. Bul. 203, pp. 67-81, 1921.





Fli, ;dol Agricultural E., p,. i I'l t Station


The latter method was employed with good results this season
in one of the two-acre fields mentioned above. This field was lo-
cated on April 20, about two weeks after the plants were set, and
60 percent of the plants were found infected. On that date all of
the plants were pulled and burned, and ten days later the field
was reset with healthy plants. This crop of plants remained
free from wildfire until early in June when a small center of
infection appeared on the edge of the field. All of these infected
plants were removed when found, and no other signs of infection
developed during the remainder of the season.
The other two fields were not located until June 10 when the
plants were from three to five feet high. At this time 100 percent
of the plants in each field were infected, and the lower leaves
were very ragged and yellow. The plants in one field were cut by
the owner and turned under. In the other field the plants were
cut off a few inches above the ground (the leaves below the cut
were broken off) and the entire tops carried out of the field and
burned. Suckers developed upon only about half of the stubbles,
and the leaves on the plants which developed never attained nor-
mal size. About ten days after the stalks were cut wildfire ap-
peared on the lowest leaves of a few of the plants. These infected
leaves were pulled off and no subsequent infection developed.
If there had been a good stand of plants, the yield would have
been almost up to normal. Because of the great amount of labor,
the poor stand, and inferior quality of tobacco resulting from
this method of control, it does not promise to be very practical.

GRANVILLE WILT

Granville wilt, or wilt, of tobacco is a serious disease wherever
it occurs. The disease was first reported in this country in 190323
when it was causing serious damage in Granville County, North
Carolina. Because of the possible existence of other tobacco wilts
at that time, this disease was designated as Granville wilt, from
the name of the county in which it was first definitely recognized.
Extensive investigations have established the fact that the dis-
ease has long existed in Japan and the Dutch East Indies."
Since the wilt first came under observation in North Carolina
it has continued to spread in that state, South Carolina, Georgia,
"Smith, Erwin F.: "The Granville Tobacco Wilt," in Bur. of Plant,Ind.,
U. S. D. A. Bul. 141, pt. II, pp. 17-24, 1908.
"Garner, W. W., Wolf, F. A., and Moss., E. G.: "The Control of Tobacco
Wilt in the Flue-Cured District," in U. S. D. A. Bul. 562, pp. 1-20, 1917.







SBulletin 166, Tobacco Diseases in Gadsden County 97

and to some extent in Florida. The rate of spread and extent of
distribution in Florida apparently has not been very great, for it
does not appear as prevalent as when reported in 1908 (see
footnote 23). This decreased prevalence may be because grow-
ers, realizing its seriousness and the persistence of the causal
organism, in the soil, abandoned infested plantations. On the
other hand, one field was observed, during the season of 1922,
where the crop was damaged only slightly, yet the owner says
that the land had been infested for several years. It seems to
be the general observation. of growers that the seriousness of
the disease varies from year to year. However, in the Carolinas,
Java and Sumatra only one crop of tobacco can be grown suc-
cessfully on infested land every five to seven years.

APPEARANCE OF WILT
Granville wilt affects the entire tobacco plant. It usually ap-
pears from two to four weeks after the plants are set in the
fields and continues to develop during the season. Its presence
is indicated by the drooping of one or more leaves. The wilted
leaves may straighten up for the first night or two, after which
they become permanently wilted. At first there is no discolora-
tion of the leaves, but they soon turn pale green and then yellow,
gradually. At this stage the leaves will have drooped on the
stem in an umbrella-fashion, in which condition they remain,
even after the leaves become brown and dry. In some cases the
leaves on one side of the plant wilt first, and occasionally only
half of a leaf is affected, in which case it becomes curled and
distorted.
If in the early stages of wilt the stalk is cut in two, yellowish
specks may be seen in the woody portion. In more advanced
stages the cut end will appear brownish, and dark cavities may
be found in the pith. When the bark is stripped off or the stalk
split lengthwise, the discoloration will appear as streaks in the
woody portion. One of the surest signs of wilt is the appearance
of a dirty-white, sticky ooze on the cut end of the stalk a few
minutes after being cut. This ooze can also be forced out by
pressing the stem near the cut end. The inner bark decays and
blackened areas appear on the surface of the stalk.
The roots of wilted plants are discolored also. Only a few
roots may be affected when the leaves first begin to wilt, but









finally the whole root system may die and turn brown. Discol-
oration of the roots may be produced by other diseases and,
therefore, cannot be relied upon entirely for the diagnosis of
Granville wilt.
PLANTS ATTACKED BY WILT
Granville wilt does not confine itself to tobacco but attacks
tomatoes, Irish potatoes, peppers, eggplants, peanuts, garden
beans, velvet beans and soybeans of cultivated plants, and castor
oil bean, jimson weed, black nightshade, horse nettle, dahlia,
cosmos, ragweed, croton, and fleabane -or horseweed of the com-
mon weeds."2 Possibly there are many other susceptible wild
plants. Thus, it may be understood why the organism is able to
persist in the soil indefinitely even when tobacco is not grown.
CAUSE OF WILT
Granville wilt is caused by a germ or bacterial organism, Bac-
terium solanacearum E. F. S. When plants are set in infested
soil this organism enters the plant thru wounds in the roots
made in transplanting or by subsequent cultivation. Having
gained admission to the plant tissues, the bacteria increase in
number very rapidly and soon plug the water vessels, thus cut-
ting off the water supply to the leaves. This bacteral growth is
what appears as white ooze on cut ends of diseased stalks.
CONTROL OF WILT
Numerous strains and species of tobacco, both wild and culti-
vated, have been tested in an effort to find a wilt-resistant
strain." None of the strains tested showed any promising degree
of resistance, so the hope for developing a resistant strain has
practically been abandoned. Since the organism can enter the
plant tissues only thru wounds and since wounds are unavoidable
during transplanting, there seems little hope of finding a wilt-
resistant strain of tobacco. It does seem probable. however, that
a method of shallow cultivation could be worked out whereby a
minimum number of roots would be broken, thereby reducing
the chances for the organism to enter the plhnt.
"Wolf, F. A., and Moss, E. G.: "Disea.-, ..f Fl1ie-Cured Tobacco with
Suggestions for Application of Palliative, Pr .e- itdt i, and Remedial Mea-
sures," in The Bulletin, N. C. Dept. Agri., vol. 40, No. 12, pp. 1-45, 1919.
0"Honing, J. A.: "Experiments on the Virulence of B,, ;Ill,. solanacearum
Against Different Nicotiana Species and Varieties," in Bul. Deli Proefata-
tion Medan, No. 2, pp. 1-15, 1914.


Florida _4fjrirdtmit7 A', p. i;wtiit Sfol;oil






Bulletin 166, Tobacco Diseases in Gadsden County


Experimental workers in North Carolina (see footnote 27)
have treated the soil with various chemicals and fertilizers in
an effort to kill the organism, but no treatment of milder nature
than steaming or soaking with formaldehyde solution has proved
successful. The only method which they have found practical is
a rotation in which tobacco is grown on the land once in five to
seven years. Such a long rotation would be impractical for
Florida. In the light of this information it seems that in Gads-
den County it is most important to prevent the further spread
of the disease. This can be accomplished only by prohibiting the
passage of people and animals from infested to non-infested
fields, by not setting tobacco or any related plants from unster-
ilized beds, and by preventing drainage water from running into
the plant beds and fields from the outside.

LEAF SPOT

So far as known, leaf spot is very limited in distribution
and of minor importance in tobacco culture. Very little was
known about the disease until it was reported from North Car-
olina" as occurring on seedlings in plant beds and on older
plants in fields of that state. Apparently it has not been reported
from any other state in the United States, except Ohio," or from
any foreign country. The disease was found in two plant beds
in Gadsden County in 1922, but so far has not been identified
in the field. These beds were on new land which had been
burned before the seed was planted. The spots were most con-
spicuous on slow-growing plants under crowded conditions. Only
an occasional spot was found on vigorous plants.

APPEARANCE OF LEAF SPOT
This disease manifests itself as brownish, irregular, zonate
spots which vary in size from minute specks to a fourth of an
inch in diameter (see fig. 19). The spots are surrounded by a
ring or halo of yellowish-green tissue, which may involve a
greater portion of the small leaves. The pycnidia (spore cases)

7Wolf, F. A.: "A Leaf-Spot Disease of Tobacco Caused by Phyllosticta
nicotiana E. & E.," in Phytopath, vol. 12, No. 2, pp. 99-101, 1922.
"Selby, A. D.: "A Brief Handbook of the Diseases of Cultivated Plants
in Ohio," in Ohio Agri. Exp. Sta. Bul. 214, p. 445, 1910.






Florida Agricultural Experiment Station


of the fungus are sparsely scattered over the dead tissue in the
spot, but are not easily visible to the naked eye, because their
color is so nearly that of the dead tissue. These spore cases con-
tain numerous spores which come out during rains and are
splashed on near-by healthy plants.















Fig. 19.-Phyllosticta leaf spot on leaves of tobacco seedlings. Note the
characteristic zonated markings in the spots

CAUSE OF LEAF SPOT
These spores are the reproductive bodies of a fungus known
technically as Phyllosticta nicotianae E. & E. Soon after the.
spores land on a healthy tobacco leaf they germinate and the fun-
gous threads grow into the tissues to obtain food. About a week
afterward the characteristic spots become visible. In a week or
ten days more spore cases will have developed in the spots; thus,
the fungus passes thru its life cycle in less than 20 days. It is
not known how the fungus lives during winter. Because of the
hitherto minor importance of the disease, this phase of the life
history of the organism has not been investigated.

CONTROL OF LEAF SPOT
No definite preventative or control measure can be recom-
mended until more is known about the life history of the causal
organism. The conditions under which the disease was observed
in 1922, however, suggest that the injury may be lessened by
sowing the seed thinner, or thinning the stand on the poorer
spots of soil. Very little infection has been found in healthy
plants in Florida.







Bulletin 166, Tobacco Diseases in Gadsden County 101

FROG-EYE OR SPEAKINGG"
Frog-eye is the name used to designate a certain leaf spot of
tobacco which is reported29 widespread in the bright-leaved to-
bacco section and in several foreign countries. In Florida the
disease is known as speakingg." Apparently this disease has
not been of any great importance in other sections, since it is
merely mentioned among the minor diseases. It is also usually
considered of little or no importance in Florida, as the crop can
be harvested in advance of the speaking. At one time tobacco
buyers and manufacturers are said to have preferred tobacco
leaves affected with frog-eye, and as a result the growers en-
couraged its development.
In 1922 frog-eye was very prevalent in Gadsden County, but
in fields where the leaves could be primed early the crop suf-
fered very little damage. On the other hand, in fields where
rains delayed priming frog-eye caused considerable loss. This
unusual occurrence of the disease is attributed by growers to
the excessive rains which fell early in June. The direct injury
caused by these rains varied from the slight checking of growth
to the complete drowning of the plants. This checking of growth
together with the high humidity were favorable for the develop-
ient of frog-eye. It was most severe in plants affected with
root-rot. Very little of the disease was noticed in any field prior
to June 1.
APPEARANCE OF FROG-EYE
When the leaves begin to ripen they are subject to attack by
frog-eye, especially if a rainy period of several days occurs. The
lower leaves are, therefore, the first attacked. The spots appear at
first as minute brown specks and enlarge very rapidly. \Vithin
a few days they become more or less circular, brownish spots
with a grayish-white center and a dark brown border (see fig.
20). They are from a fourth to half an inch in diameter. When
the spots are numerous they run together and form irregular
spots of larger dimensions.
If the leaves are primed when the specks are small, narrow
greenish rings remain around the specks after the leaves are

"Wolf, F'. A., and Moss, E. G.: "Diseases of Flue-Cured Tobacco with
Suggestions for Application of Palliative, Preventative and Remedial Mea-
sures," in The Bulletin, N. C. Dept. Agri., vol. 40, No. 12, pp. 1-45, 1919.







Florida Agricultural Experiment Station


cured. Such spots or blotches are commonly seen on cigars on
the market. The white centers of the smaller spots usually do
not break out during the curing process, which makes the disease
less objectionable. Indeed, wrapper tobacco affected with these
spots was at one
time in demand
by buyers and ci-
gar manufactur-
ers.
CAUSE OF
FROG-EYE
T h e grayish-
white spots de-
scribed above are
usually marked
with minute
black dots which
are the fruiting
bodies of a fun-
gus, Cercospora
nicotianae E. &
E. These black
bodies become
v e r y noticeable
during rainy
weather or when
diseased leaves
are kept in a
moist chamber
for 36 hours. It
appears, ho w -
ever, that no one
has actually
proved that this
fungus is the
cause of frog-eye,
but its pathogen-
icity has been as-
Fig. 20.-Cured leaf of tobacco showing typical sumed because of
symptoms of frog-eye or speakingg:" Note that the the constant as-
spots do not break out very badly after the leaf is
cured sociation of the






Bulletin 166, Tobacco Diseases in Gadsden County 103

fungus with the disease. The lack of such proof is due, no doubt,
to the relative minor importance of frog-eye in tobacco culture.
Some growers are inclined to believe that the trouble is due to
an excess of certain fertilizers, while others believe that it is
caused by excessive moisture in the soil. It is apparent that any
factor which checks the growth or causes premature ripening
of the leaves predisposes them to frog-eye. Investigations are in
progress to determine the exact cause of the disease.

CONTROL OF FROG-EYE
Extensive observations in Gadsden County have indicated that
frog-eye does not occur on vigorous, rapidly growing tobacco
plants. Whenever growth is checked, either by normal ripening
processes or by unfavorable weather and soil conditions, frog-eye
appears on the lower leaves and advances toward the top of the
plant. In 1922 a rainy period of two weeks in June appeared to
be the predisposing factor for the prevalence of frog-eye. Very
little of the speaking was observed prior to this period. Of
course, weather conditions cannot be controlled, but the follow-
ing suggestions may help to reduce injury from frog-eye: (1) Do
not plant the variety known as Big Cuba, which is susceptible
to root-rot, on "root-rot sick" soils. The stunting of the plant
caused by root-rot predisposes the leaves to frog-eye. (Connecti-
cut Round Tip should escape injury from speaking on root-rot-
sick soils because of its resistance to root-rot.) (2) Avoid deep
cultivation late in the season, as this tends to check the growth
and thus causes premature ripening of the leaves.

ROOT-ROT

Root-rot of tobacco has been known in some foreign countries
since 1897. According to reports"0 it probably occurred in the
United States long before that date, altho it was not recognized
as a parasitic disease. Tobacco growers in some sections of the
country believe that by cropping the land to tobacco continuously,
certain fertilizing elements of the soil become exhausted, which
condition is known as "running out."" The disease is now known
to occur in practically all sections of the -United States where

"oJohnson, James, and Hartman, R. E.: "Influence of Soil Environment on
the Root-Rot of Tobacco," in Jour. Agri. Res., vol. 17, No. 2, pp. 41-86, 1919.
"Johnson, James: "The Control of Diseases and Insects of Tobacco," in
Wis. Agri. Exp. Sta. Bul. 237, pp. 1-34, 1914.






Florida Agricultural Experiment Station


tobacco is grown on the same land for two or more years in
succession, the shaded area of Florida being no exception. In
some of the northern states where the growing season is short
the disease becomes very serious in that it retards the maturity
of the crop to such an extent that frost may injure or ruin it. In
Kentucky it has been reported"8 to cause considerable annual loss
to the crop of Burley tobacco.
In 1922 root-rot was widespread in Gadsden County. A few
small fields were almost a total loss because of the disease.
Gradations occurred from this condition up to an unnoticeable
amount of damage. Growers report that during average years
the plants finally outgrow the disease and produce a fairly good
yield, altho the affected crop may be from two to four weeks late
in maturing. Even tho the quality were as good as that of a
healthy crop, the additional cost of cultivating and poisoning for
the longer period would be objectionable. Consequently, local
growers have adopted the practice of growing tobacco on the
land for from two to four years when symptoms of root-rot be-
come quite noticeable. They then grow corn for from one to
three years before returning to tobacco. This rotation is rather
expensive because the shade deteriorates very rapidly and is of
no value to the corn crop.
Root-rot may occur in the plant beds or in the field. Since
most of the growers sterilize the plant beds every year, they are
not troubled with the disease in the beds. If plants infected with
root-rot are set in the field, the disease is certain to continue to
a greater or less extent, depending upon weather and soil con-
ditions." Furthermore, if healthy plants are set in infested
fields, results will be practically the same.

PLANTS ATTACKED BY ROOT-ROT

Besides tobacco, root-rot attacks a great number of other
plants, many of which are unrelated to tobacco. It is reported"
that it attacks peanuts, cowpeas, garden peas, vetch, red clover,
alsike clover and several weeds belonging to the Leguminosae

3"Valleau, W. D., and Kinney, E. J.: "Strains of Standup White Burley
Tobacco Resistant to Root-Rot," in Ky. Agri. Exp. Sta. Cir. 28, pp. 1-16,
1922.
"Jenkins, E. H.: "Studies on the Tobacco Crop of Connecticut," in Conn.
Agri. Exp. Sta. Bul. 18.0, pp. 1-65, 1914.
"Johnson, James: "Host Plants of Thielavia basicola," in Jour. Agri.
Res., vol. 7, No 6, pp. 289-300, 1916.






Bulletin 166, Tobacco Diseases in Gadsden County 105

family. It also attacks cotton, watermelon, beet, carrot, and sev-
eral of the common weeds. Most of these plants are attacked
less severely than tobacco, yet their presence on the land will
enable the fungus to persist in the soil for several years.
SYMPTOMS OF ROOT-ROT
Plants attacked by root-rot appear as if they were suffering
from drouth or malnutrition. In severely infested fields the
plants may be of uneven height with occasional ones appearing
practically normal. Plants infected with root-rot may stand un-
til late in the summer without making any apparent growth and
































Fig. 21.-Tobacco plants grown in "root-rot sick" soil (left) and in soil free
from root-rot (right). These plants were grown under identical conditions,
except that the soil in which the plant on the left was grown was sterilized
to kill the parasite causing the disease. Note the contrast in root system
and tops. (Courtesy of James Johnson)






Florida Agricultural Experiment Station


then, after the soil is worked to them and with favorable rains,
start suddenly into rapid growth. On the other hand, if the rainy
period should be of several days duration, the hew roots rot and
the plants fail to start this rapid growth. This happened in Gads-
den County in 1922.
When roots of such stunted plants are examined, they will be
found to have dark brown or black areas on them. In advanced
cases the roots rot in two, so that when the plants are pulled
out of the soil only a small portion of the root system remains
attached to the stem (see fig. 21). Tobacco attempts to over-
come the attack of root-rot by sending out new roots above the
diseased ones; but, if the ground is wet and cold, the new roots
are attacked as fast as they develop. When plants are set slightly
below the level, which is common practice with some growers,
and the earth is worked to them gradually, roots continue to
develop higher up the stem until finally when the soil warms up
some of them escape attack and serve as feeders for the plant.

CAUSE OF ROOT-ROT

Root-rot is caused by a fungus known technically as Thielavia
basicola (B. &. Br.) Zopf. This organism lives as a parasite on
the roots of tobacco and other susceptible plants. It grows into
the roots and obtains nourishment from them which causes them
to decay. In the absence of tobacco and other usce.eptible plants
the fungus can live for a number of years on the dead organic
material in the soil, but it gradually dies out. The exact time
required to rid the soil of the organism by growing resistant
plants on it has not been determined, but beneficial results have
been obtained in Gadsden County by growing corn on infested
soil for from two to four years. The results obtained in this time
will probably vary with the different types of soil.
The disease is spread from field to field by the same means as
other diseases of plants caused by organisms inhabiting the
soil and attacking the underground parts. The most common
means of dissemination is the transference of infested soil, either
by wind, water, farm implements, men and animals, or by trans-
planting diseased plants to healthy soil.







Bulletin 166, Tobacco Diseases in Gadsden County 107

CONTROL OF ROOT-ROT
All attempts to control root-rot by applying large quantities
of fertilizer to the soil have failed." In certain sections of the
United States where land is available, growers have succeeded
in reducing the amount of damage by growing one or two crops
of tobacco and then allowing the land to "rest" for a number
of years." Root-rot has probably been present in Florida for
years but until very recently the growers have had no accurate
means of determining the amount of damage it causes.
During the last two years many of the growers have planted
a small acreage of Connecticut Round Tip, a strain of tobacco
highly resistant to root-rot. Unfortunately, only a few of them
have grown this resistant strain beside the susceptible Big Cuba
for comparison. Wherever the two strains were grown together


















Fig. 22.-Big Cuba (left) and Connecticut Round Tip (right) growing in
"root-rot sick" soil in Gadsden County in 1922. The plants were set on the
same date and received the same treatment


in badly infested fields the contrast was very striking (see fig.
22). The Connecticut Round Tip, however, does not seem to
meet all the requirements of the Florida grower for wrapper to-

"Gilbert, W. W.: "The Root-Rot of Tobacco Caused by Thielavia basi-
cola," in Bur. of Plant Ind., U. S. D. A. Bul. 158, pp. 1-55, 1909; Johnson,
James, and Hartman, R. E.: "Influence of Soil Environment on the Root-Rot
of Tobacco," in Jour. Agri. Res., vol. 17, No. 2, pp. 41-86, 1919.
"Johnson, James, and Milton, R. H.: "Strains of White Burley Tobacco
Resistant to Root-Rot," in U. S. D. A. Bul. 765, pp. 1-11, 1919.






Florida Agricultural Experiment Station


bacco. Strains of White Burley have been reported by investi-
gators as being resistant to root-rot."
The difference in growth of Big Cuba plants in badly infested
fields indicates a difference in degree of resistance between
plants. Some plants appear very vigorous and healthy, while
adjacent plants may be greatly stunted and have a yellowish-
green color. Such differences have been the basis for developing
strains of tobacco resistant to root-rot in other states, and it is
very probable that they can be used with equal success in Flor-
ida. A few growers have already started selections for resistance
but in most cases they have failed to set the plants from the
selected seed beside plants from general stock seed for compari-
son. The most important factor that must be considered in con-
nection with the development of a resistant strain of tobacco
is the correlation of desirable qualities with resistance. Selec-
tions were made in 1922 in badly infested fields and the plants
from the selected seed will be tested on the same soil in 1923.

BLACK SHANK

During recent years a disease of tobacco which appears to be
new in the United States has been gaining foothold in Gadsden
County. Because of the conspicuous black rot of the lower por-
tion of the affected stalks the disease is called "black shank."
According to the growers, this disease first appeared in 1915 on
a plantation in the southern part of Decatur County, Georgia.
Since that date it has become widely distributed in Gadsden
County, Florida, and one infested field has been found in Leon
County, Florida. The extent of its distribution in Georgia has
not been ascertained. The total acreage infested has not been
determined, but it is estimated that an, area equal to from 5 to 7
percent of the land devoted to tobacco culture in Gadsden County
is infested. Since the common practice has been to abandon a
field for tobacco culture the year following the first appearance
of the disease, the percentage of land showing infestation each
year is less than the above figures. The disease made its first
appearance in several fields this year, some of which were widely
separated from other infested ones.
As to the original source of the causal organism and by what
"Valleau, W. D., and Kinney, E. J.: "Strains of Standup White Burley
Tobacco Resistant to Root-Rot," in Ky. Agri. Exp. Sta. Cir. 28, pp. 1-16,
1922.







Bulletin 166, Tobacco Diseases in Gadsden County 109

means it was introduced into this section, it is not the province
of this publication to speculate. Furthermore, it has not been
established that the infested field in Georgia was the source of
infestation for the fields in Florida. However, the proximity of
other infested fields and the direction of spread of the disease in
the county indicates that it may be.
A -disease was described and illustrated in Java in 1896,"
which was at that time, and is yet, causing great damage to to-
bacco on that island. From the illustrations and description of
the disease and causal organism this disease appears to be identi-
















Fig. 23.-Connecticut Round Tip in a "black shank sick" field 22 days after
the plants were set. None of the plants in this field lived to the blossoming
stage

cal to black shank. The same organism has been reported"
among the parasitic molds of tobacco in New South Wales. Aside
from these reports no other record has been found of its occur-
rence in any other country.
Black shank was the most serious disease of tobacco in Gads-
den County in 1922. It probably did not cause as great a total
loss for the entire area as some of the other diseases, but where
it occurred it took a heavier toll than all other diseases com-
bined. The losses in individual fields varied from less than 1 to
100 percent, depending upon the time the disease appeared and
38de Haan, J. Van Breda: "Bibitziekte in de Deli Tabak," in Mededeelin-
gen Uit 'S Lands Plantentuin-Buitenzorg, No. 15, pp. 1-107, 1896.
-"A New Disease of Tobacco," abs. U. S. D. A. Exp. Sta. Rec., pp. 8-237,
1896-97.
"Darnell-Smith, G. P.: "Diseases of Tobacco Plants: Blue Mold and
Bacterial Diseases," in Agri. Gaz., N. S. Wales, 29, No. 2, pp. 82-88, 1918.






Florida Agricultural Experiment Station


to some extent upon the variety of tobacco. Big Cuba, the va-
riety most generally grown in this county, is the most resistant
of the few varieties tested. Connecticut Round Tip and White
Burley are the most susceptible. Several growers set Connecti-
cut Round Tip on infested soil hoping that it would be resistant
to black shank also, but in all such cases observed the crop was a
complete failure. In one infested field five acres of Connecticut
Round Tip was set on April 27. Twenty-two days later 95 per-
cent of the plants were dead (see fig. 23). None of the plants in
this field lived to the flowering stage. No fields of Big Cuba
were observed under similar conditions, but in several fields
where the disease appeared early in the season the yield was
reduced by a third to three-fourths of the normal yield. Data col-
lected to date indicate that the severity of the disease is not
greatly influenced by type of soil or cultural practices.
The first symptoms of black shank appeared this year in pre-
viously infested fields about April 15-about two weeks after
the average date for transplanting. Growers, who have had op-
portunity to observe the development of the disease during the
last several years, say that this date is the earliest they have
known the disease to appear. It is probable that the unusually
warm spring weather is responsible for this early development
of the disease. It appeared at intervals during the season in
hitherto non-infested fields, even up to the end of harvest. As
a rule, it appears first in a single spot in a field and then spreads'
very rapidly in all directions. The owner often remembers that
upon this spot laborers or implements from an infested field
began work. Other cases have been observed where the disease
first appeared near a gate, thus indicating that the parasite
probably was carried into the field on the feet of visitors or on
some implement. The infested area enlarges so rapidly that-if
the first signs of the disease appear as late as June 1 the damage
may be very appreciable by the end of the season.

PLANTS AFFECTED BY BLACK SHANK
At present tobacco is the only plant known to be affected by
black shank. Inoculation experiments with young Kentucky
Wonder bean plants, one variety of tomato, and young Irish
potato plants have shown that the blac;k-hank fungus is not
actively parasitic on these plants. Small brown areas appeared
around the point of inoculation on some of the potato stems but





Bulletin 166, Tobacco Diseases in Gadsden County 111

the typical symptoms of black shank did not develop. None of
the many species of weeds which grow under the shades after
tobacco is harvested has shown symptoms of the disease.
SYMPTOMS OF BLACK SHANK
The symptoms of black shank vary somewhat with the age of
the plant. In young plants the disease causes a typical damping-
off or wet-rot of the stalk, while in older plants the characteristic
symptom is a dry, black rot of the lower portion of the stalk
(see fig. 24). Sudden wilting of the leaves is also a conspicuous
symptom (see fig. 25) but this does not differ greatly from that

































Fig. 24.-Typical symptoms of black shank showing different stages in the
destruction of the root system. Note that the point of attack on the stalk
at the left is at the surface of the soil





Florida Agricultural Experiment Station


caused by Granville wilt. Affected plants soon lose the normal
green color but they do not turn yellow rapidly. A few plants
have been observed to straighten up at night after the first
symptoms of wilt developed, but, as a rule, they remain perma-
nently wilted from the beginning and dry out gradually. In some
cases the affected
plant wilts before
any lesion ap-
pears above
ground. S u c h
specimens might
be confused with
Granville w i 1 t
except that no
bacterial ooze ap-
pears on the cut
end of the black-
shank stalk. The
root system of
such plants will
be found to be
partially or en-
tirely dead and
have a brown or
black color. On
the other hand
plants have been
observed which
had an apparent-
Fig. 25. Typical wilt of young tobacco plants af- ly healthy root
fected with black shank. In this stage the wilt does
not differ greatly from "Granville wilt" sy stem when
the stalk was
damped-off or entirely girdled by a lesion at the surface of the
soil. As a rule the lesions appear on the stalk at the surface of
the soil and advance in both directions. It is not unusual to see
plants late in the season with the stalk black half way to the
top, especially in the Connecticut Round Tip variety. Such
plants may still retain a few small green leaves in the top and
bloom prematurely.
Figure 26 shows a field of Big Cuba tobacco late in the season
after the plants have been topped. All stages of the disease from






Bulletin 166, Tobacco Diseases in Gadsden County 113

plants which died early in the season to the ones showing in-
cipient stages of wilting, and even a few apparently healthy ones
(marked "X" in figure 26) are evident.
A cross section of the stalk above the dead black area shows
brown spots in the woody tissue. When the stalk is split length-
wise or if the bark is stripped off, this discoloration shows as
brown streaks. These streaks often extend almost to the bud
of the affected plant. Mycelial threads of fungi are usually



















Fig. 26.-Big Cuba on "black shank sick" soil as it appeared almost at the
end of the season. Note that some plants died when young, while some
mature ones are just beginning to wilt. Also note that occasional plants
(marked "X") are still apparently healthy. Seed were obtained from a
few such plants and will be tested next year on "sick" soil for resistance

present in the brown tissue. The pith within the black portion
of the stalk is dry and brown, and is usually split into plate-like
discs, so that when the stalk is split lengthwise each half re-
sembles a ladder.
Black shank also attacks the leaves of tobacco. Large brown
blotches varying from one to three inches in diameter appear
on the leaves during periods of rainy, cloudy weather. On leaves
of Big Cuba these blotches are more or less circular and marked
with concentric bands of different shades of brown, the lighter
color being in the center (see fig. 27). The lesions are not
numerous on an individual leaf and do not develop on those very
high above the ground, but affected leaves are usually worthless






Florida Agricultural Experiment Station


for wrappers. In contrast with this, the spots occurring on the
leaves of Connecticut Round Tip and Wisconsin No. 1207 are dark
brown and at first have the consistency of a wet rot. The spots
may occur on any portion of young stalks, petioles (stems) and
leaf blades, and
thus cause the
stalks or leaves to
break over at the
point of attack.
In this condition
the diseased
plants appear
similar to Irish
potato plants af-
fected with late
blight. Conidio-
phores (spore
stalks) and coni-
dia (spores) of
the causal organ-
ism have been
observed in small
numbers in the
leaf lesions dur-
ing periods of
cloudy weather.
After the lesions
are a few days
old spores of an-
other fungus
(Fusarium) ap-
Fig. 27.-A leaf of Big Cuba showing typical black pear in them, es-
shank lesions as they appear in the field. Note the pecially in the
zones of different colors and the gradual blending of
the spots into the normal color of the leaf ones on the stalks
and petioles.
Large blotches have been observed to develop on the leaves
from infested fields after being hung in the barn. In one case 20
percent of the first priming was affected in this manner. The
lowest or sand leaves were primed this season during a period
of cloudy weather, and it was these which developed the blotches
in the barns. Leaves primed subsequently were not affected. The






Bulletin 166, Tobacco Diseases in Gadsden County 115

blotches develop very rapidly, and attain their maximum dimen-
sions within a few days after the leaves are placed in the barns.
After the spots have dried out somewhat, enlargement of the
blotches ceases.
Occasionally more than half of the leaf may be involved by
one or more blotches, and, of course, the affected ones are worth-
less for wrappers. These blotches have a greenish color mottled
with different shades of brown in contrast with the uniform
light brown color of the normal cured leaf. The diseased areas
remain brittle and wrinkled after the leaves have been subjected
to the sweating process. Since the affected leaves are destroyed
and since no further development of the blotches has been ob-
served to occur in the packing house or even on cured leaves in
the barns, there seems to be no danger of the disease developing
on cured tobacco.
CAUSE OF BLACK SHANK
Since its first appearance in Gadsden County, various popular
ideas have been entertained as to the cause of black shank. Be-
cause of the time of occurrence and the part of the plant af-
fected, some growers believe that the disease is caused by the
use of the wrong fertilizer or by fertilizing at the wrong time.
Certain insects have been found around the roots and inside of
stalks affected with black shank, and these are thought by other
growers to be the cause of the disease.
A specific fungous organism has been isolated from typical
black-shank plants and it has been proved that this organism is
the cause of the disease. It has been shown by repeated inocula-
tions that none of the several forms of Fusaria, always present
in diseased stalks under field conditions, will produce black
shank in tobacco plants. On the other hand, the black-shank
fungus proved to be very pathogenic when inoculated into
healthy tobacco plants.
The morphology of the black-shank organism corresponds
very closely with the description and illustrations of Phytoph-
thora nicotianae de Haan"4 and it is very probably the same or-
ganism. The organism grows vigorously on potato-dextrose agar
and on cooked bean pods, but poorly on nutrient agar. Its growth
4"de Haan, J. Van Breda: "Bibitziekte in de Deli Tabak," in Mededeelin-
gen Uit 'S Lands Plantentuin-Buitenzorg, No. 15, pp. 1-107, 1896; Jensen,
H. DeLanasziekte in de Vorstenlanden en Hare bestrijding. Proefstation
voor Vorstenlandsche Tabak, Mededeeling, No. 1, pp. 1-35, 1913.






Florida Agricultural Experiment Station


on these media resembles closely that of Phytophthora terrestrial
Sherb. Phytophthora terrestrial, however, proved to be non-
pathogenic when inoculated into tobacco stalks.
The conidia (spores) are very irregular in size and shape.
They are mostly ovoid and apiculate, averaging 25 by 33 microns
in diameter (a micron is about 1/25000 of an inch), and the con-
tents are granular, and olivaceous in color. They begin to germi-
nate in distilled water in about fifteen minutes, producing from
ten to twenty zoospores. The zoospores appear oval to bean-
shaped, and average about six and a half microns in diameter.
After about fifteen minutes they cease activity, enlarge and ap-
parently disintegrate.

INOCULATION EXPERIMENTS

Healthy tobacco plants have been inoculated by inserting frag-
ments of the fungous growth from pure culture into the stalks
at the surface of the ground. Other plants have been inoculated
by placing bits of the growth against the stalks at a similar
point. In all cases the inoculated plants began to wilt within
from three to five days, and the characteristic black-shank symp-
toms had developed at the end of eight days. Some of the plants
were completely dead ten days after inoculation, while others in
the same series
lived 18 days.
Check plants, un-
inoculated, in the
same box were
healthy at the
end of the period
(see fig. 28). A
culture of the
fungus was re-
isolated from one
of these plants
and, when inocu-
lated into other
healthy plants, it
caused typical
Fig. 28.-Tobacco seedlings 18 days after they were black shank with-
inoculated with Phytophthora nicotianae. All four in five days. In
inoculated plants (left) are dead, while the two
uninoculated ones (right) are healthy t h e s e experi-







Bulletin 166, Tobacco Diseases in Gadsden County 117

ments the disease developed as quickly in plants three feet high
as in those six inches high but the older plants died less quickly,
especially when they were growing slowly at the time of inocu-
lation.
Young Kentucky Wonder bean plants and Acme tomato plants
were inoculated with pure cultures of the fungus in the same
way as the tobacco plants. No signs of black shank developed in
any of the plants within 20 days after the inoculation. Several
Irish potato plants about three inches high were also inoculated.
A small brown spot developed around the point of inoculation on
two plants within five days but the spots were no larger after
two weeks.
CONTROL OF BLACK SHANK
As yet no definite and practical method can be offered which
will enable one to grow a crop of tobacco on "black shank sick"
soil. So far it has been the practice in Gadsden County to move
to new fields. In Java, where the Phytophthora disease has been
under investigation since 1896, no entirely successful method of
controlling the disease in the fields has been worked out." It is
claimed,2" however, that beneficial results have been obtained by
removing and burning diseased plants as soon as they appear
in the fields and then treating the soil in which the plants stood
with quicklime or a combination of lime and ammonium sulphate.
It is further recommended that all stalks be collected and burned
after harvest, but for several reasons this has proved imprac-
tical for them. Several strains of tobacco which resist the dis-
ease have recently been reported from Java (see footnote 41).
It appears, however, that none of these resistant strains or
varieties possess the most desirable quality of leaf.
Results obtained this year from two trial plots, and observa-
tions made in several infested fields, indicate a difference in re-
sistance between individual plants and varieties. Connecticut
Round Tip, Haliday Havana, White Burley, Wisconsin No. 1207
(a binder type), and five different strains of Big Cuba were
planted in two plots of "black shank sick" soil. The plants were
*'d' Angermond, A.: "Onderzoekingen tot het vinden van een tegen Phy-
tophthora nicotianae de Haan, weerstandskrachtig Tabaskras," Proefstation
voor Vorstenlandsche Tabak, Medeeling No. 37, pp. 1-29, 1919.
"Jensen, H.: De Lanasziekte en Hare Bestrijding. 11. Proefstation voor
Vorstenlandsche Tabak," in Medeeling, No. 29, pp. 5-118, 1917; d' Anger-
mond, A.: "Bestrijding van Phytophthora nicotianae in de Vorstenlanden.
Proefstation voor Vorstenlandsche Tabak. Medeelingen, No. 39, pp. 3-59,
1920-21.







Florida Agricultural E, in ,in at, Station


set on April 17, about two weeks later than the average date for
setting in the county. By June 9 practically every plant of all
varieties except the Big Cuba were dead or badly diseased. On
that date 35 percent of the best strain of Big Cuba was apparent-
ly healthy. These plants, however, one by one developed the
disease so that on August 21 when the seed was ready to har-
vest only 4 of the original 968 plants were apparently healthy.
Even so, about 20 percent of the plants did not wilt until after
the leaves were harvested. A small percentage of Big Cuba
plants in other badly infested fields also remained apparently
free from the disease until the seed matured. These instances
are at most only indications of resistance and further trials are
necessary to establish the facts. Seed from several plants which
reached maturity in an apparently healthy condition in infested
fields will be tested on infested soil in 1923.
One experiment of steaming several acres has demonstrated
that the organism can be eradicated froni the soil by this method,
but as yet it is generally considered too expensive to be prac-
tical. Furthermore, since the soil around the edges of the in-
fested field is also very probably infested, the chance for rein-
festation seems great. So far as known, no grower has returned
to infested soil with tobacco after it had once been abandoned
because of black shank. It is not known, therefore, how long the
black-shank organism can live in the soil. Until more can be
learned about the disease, growers will do well to use every pos-
sible means to prevent its further distribution.
The following suggestions should prove beneficial: (1) Visits
from infested fields to clean ones should be strictly forbidden at
all times. (2) Do not use plants from another plantation, espe-
cially if the disease is in nearby fields. (3) Do not buy or borrow
farming implements,, mules or wagons from other plantations
unless they are disinfected before being brought to the farm.
(4) Prohibit laborers going from one plantation to another,
unless they first change their clothing. (5) Do not allow water
to drain fromif roads into tobacco fields. (6) Water from streams
which drain infested fields should not be used for irrigation.
(7) Manure from animals which have pastured on infested soil
should not be used for tobacco, unless first sterilized.




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