Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; 117
Title: Tomato diseases
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Permanent Link: http://ufdc.ufl.edu/UF00026408/00001
 Material Information
Title: Tomato diseases
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: p. 33-48 : ill. ; 23 cm.
Language: English
Creator: Rolfs, P. H ( Peter Henry ), 1865-1944
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1913
 Subjects
Subject: Tomatoes -- Diseases and pests -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
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Statement of Responsibility: by P.H. Rolfs.
General Note: Cover title.
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Bibliographic ID: UF00026408
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000921873
oclc - 18161072
notis - AEN2341

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HISTORIC NOTE


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

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida





BULLETIN 117 NOVEMBER, 1913


UNIVERSITY OF FLORIDA

Agricultural Experiment Station




TOMATO DISEASES

BY

P. H. ROLFS


Fig. 4.-RUST.-Leaflet in an advanced stage of the disease. The tips are
attacked first.

The Station bulletins will be sent free upon application to the Experiment
Station, Gainesville, Fla.

Pepper Pub. & Ptg. Co., Gainesville, Fla.












BOARD OF CONTROL


P. K. YONGE, Chairman, Pensacola, Fla.
T. B. KING, Arcadia, Fla.
E. L. WARTMANN, Citra, Fla.
F. E. JENNINGS, Jacksonville, Fla.
W. D. FINLAYSON, Old Town, Fla.

STATION STAFF
P. H. ROLFS, M.S., Director.
J. M. SCOTT, B.S., Animal Industrialist and Assistant Director.
B. F. FLOYD, A.M., Plant Physiologist.
J. R. WATSON, A.M., Entomologist.
H. E. STEVENS, M.S., Plant Pathologist.
S. E. COLLISON, M.S., Chemist.
JOHN BELLING, B.Sc., Assistant Botanist, and Editor.
O. F. BURGER, M.S., Assistant Plant Pathologist*.
S. S. WALKER, M.S., Assistant Chemist.
JOHN SCHNABEL, Assistant Horticulturist.
A. C. MASON, B.S., Laboratory Assistant in Entomology.
JULIUS MATZ, B.S., Laboratory Assistant in Plant Pathology.
E. G. SHAW, Secretary.
B. V. GLOVER, Stenographer.
K. H. GRAHAM, Auditor and Bookkeeper.
M. CREWS, Farm Foreman.

FARMERS' INSTITUTE STAFF
P. H. ROLFS, M.S., Director Extension Department.
A. P. SPENCER, M.S., Vice-Director Extension Department.


*Granted one year leave of absence.




























CONTENTS
PAGE
Rust .--. ----....----..... .... --.---------..----------------- 37
Fungus Blight..------. _----- .-------------------.----- 38
Sclerotium Blight .---.------------------------.-.------------ 40
Bacterial Blight, Wilts------------------------- 42
Dropping of Bloom Buds. ---------------------------------------- 44
Leaf Curl, or Roll Leaf ..----------.------ .------------------------ -45
Damping Off....----.....--..----- .--------------------------- 45
Hollow Stem----...-----...--- .---- .. ------------------------. 47
Scab, Black Spot ---- -------- ----------------------- 47
Blossom-End Rot-...--- .----------... ---------------------- 48













SUMMARY
(1) RUST may be prevented by using Bordeaux mixture. Dry
Bordeaux is less effective.
(2) FUNGUS BLIGHT may be avoided only by rotation of crops,
or the field may be abandoned.
(3) SCLEROTIUM BLIGHT may be controlled by avoiding the
use of manure or similar organic materials, by spraying
about the roots and cultivating close to the plants.
(4) BACTERIAL BLIGHT is difficult to control when once start-
ed in a field. Some good may be done by destroying in-
fected plants.
(5) DROPPING OF BLOOM BUDS (a) cannot be remedied when
due to continued cold weather. (b) When due to too
vigorous growth it may be controlled by checking the
growth. (c) When due to the minute green fly it is diffi-
cult to secure an effective remedy.
(6) When LEAF CURL is caused by too much moisture, the
remedy is to relieve the soil of the superabundant mois-
ture; if a result of too drastic pruning, this should be dis-
continued.
(7) DAMPING OFF is remedied by letting in sunlight, drying
off the seedbed, and applying a soluble fungicide.
(8) HOLLOW STEM may be prevented by hardening plants off
before setting out.
(9) SCAB, or BLACK SPOT may be prevented by spraying with
Bordeaux mixture.
(10) BLOSSOM-END ROT is not easily controlled.











TOMATO DISEASES
BY P. H. ROLFS



RUST

This disease has been known to inflict serious damage on the
tomato fields in the State of Florida ever since the cultivation of
this crop has been taken up. From time to time different com-
mon names have been given to it. Among these is the name rust,
which is now almost the only one used by the tomato planters;
spot, black spot, blight, leaf blight, and other terms have also been
used.
GENERAL APPEARANCE.--The general appearance of this
disease in the advanced stage is well illustrated by Figure 4. The
leaflet there shows its end infected and dried up, while the cen-
tral portion and the part near the stem are still green, but spotted
with brown areas of various sizes. The first visible appearance
of the disease on the leaf is a minute brown speck, which is fre-
quently so minute that it can scarcely be made out with the un-
aided eye. These minute specks may occur on seedlings in the
seed-bed, but more frequently the plants are well advanced in the
field before they are plainly noticeable.
CAUSE.-The cause of this disease has been known for many
years, and the fungus has been carefully studied. Botanically it
is known as Macrosporium (Alternaria) solani. The disease has
its beginning from a minute spore which may have been borne to
the plant by the wind. Frequently the diseased plants are so
evenly and so widely distributed in a field that it is really difficult
to see how any other agency could have disseminated the spores
so promiscuously. Usually rust originates in certain portions of
the field and is distributed to other parts.
The fungus spore falling upon the leaf germinates, and the
germ tube penetrates the tissues. The fungus grows within the
leaf-blade, and after a shorter or longer period begins to mature
spores of the same kind that originally infected the leaf. Whilst
producing spores the fungus continues to spread in the leaf tissue,






Florida Agricultural Experiment Station


and thus the diseased area becomes daily larger. A number of
these diseased areas may grow together, producing larger areas.
(See Figure 4.) Finally the entire tissue of the leaf is destroyed.
(In some cases the fungus produces more or lest concentric rows
of dots; these, however, are not always present.)
REMEDY.-In the case of rust, as in the case of almost every
other disease, prevention is much cheaper than cure. This dis-
ease can be most effectively prevented in the beginning by spray-
ing the plants with Bordeaux mixture while they are still in the
seedbed. Though it is not practicable to cover all the leaves, yet
the spraying should be done as thoroughly as possible in order
to fortify the plants against infection at the time they are set out
in the field.
As the disease does not have a regular time for occurring, and
is not always disastrously severe, most tomato growers prefer to
wait and see whether the plants are going to be affected. Every
tomato grower should, however, keep a very careful lookout to de-
tect the first signs of the presence of this fungus. Spraying
should then be begun at once and carried out vigorously and thor-
oughly. While in some years the climatic conditions are such as
to enable the tomato plants to produce a fair crop without spray-
ing, the probability is that the presence of this disease in a field
will practically ruin the crop if not controlled during its earlier
stages.
Where dry Bordeaux is used, it should be applied at least as
frequently as once every week. The dry Bordeaux is about a half
or a third as effective as ordinary Bordeaux mixture.*

FUNGUS BLIGHT

The term blight has been applied to so many different dis-
eases that it has no distinctive significance. In fact, it is not in-
frequently applied to insect pests. The disease which is known
as fungus blight has probably caused a greater loss to the toma-
to growers in the State of Florida than any other disease.

How to make Bordeaux mixture.--Solution No. 1: copper sulphate
(bluestone), 6 pounds; water, 50 gallons. Solution No. 2: caustic lime
(quicklime), 4 pounds; water, 50 gallons.
It is advisable to have three kerosene barrels of about fifty gallons ca-
pacity in the field. Dissolve 6 pounds of copper sulphate in a barrel of water
(50 gallons). The copper sulphlate will be dissolved slowly in cool water
if it is suspended near the top of the barrel in a feed sack or other coarse
cloth. If it is desirable to dissolve it quickly, this may be done by placing it






Bulletin 117


For a considerable number of years its true nature was
not understood, and the difficulties in the field were ascribed
to improper fertilization, drought, moisture, too much ferti-
lizer, too little fertilizer, too much cultivation, want of cultiva-
tion, or almost any other adverse condition. Later scientific in-
vestigations, however, have shown that the disease is due to a
specific fungus which occurs in the soil, and from this attacks the
plant.
DESCRIPTION OF THE DISEASE.-The fungus blight(Fusarium)
may attack the most vigorous growing plants in any portion of
the field or it may attack those of low vitality. Since the fungus
is found in the soil, it is impossible to tell beforehand whether
there is any of the disease present or not. The first symptom
that is noticed is that the lower leaves (usually the largest ones)
turn rather pale, and finally quite yellow. The leaves usually dry
up from the tip, and where the disease is not accompanied by rust
no spots are seen. By cutting the leaf stalk with a sharp knife
darkened veins can frequently be seen. If the tomato plant is
pulled up and the stem cut across the darkened veins are usually
found in this portion, especially on the side to which the diseased
leaf is attached. The rapidity with which the disease develops
in a plant depends on climatic conditions and on the condition of
the plant. If the plant has been growing rapidly and is rather
soft the fungus is apt to make considerable headway, especially

in a barrel and pouring on hot water. After the 6 pounds of copper sulphate
have been dissolved, the barrel may be filled to the 50-gallon mark. Tin or
iron vessels should not be used in connection with Bordeaux mixture or the
copper sulphate solution; always use copper or wooden vessels.
Slack the 4 pounds of lime in just enough water to cover it. Be careful
to stir it well and see that it does not burn dry. This is best done in a
wooden vessel, as there is considerable heat generated by the lime in slack-
ing. If the stone from which the lime is made contains much sand, it will
be necessary to increase the number of pounds of lime used. If there is a
quantity of air-slacked lime also present, it will be better to reject this and
simply use the part that has not been air-slacked. After the lime has
been slacked add water to make 50 gallons.
Stir the copper sulphate solution (No. 1) thoroughly, and take out about
one-half as much as the spraying apparatus will hold. Pour this in the
third barrel; then stir the lime water thoroughly and take out just as much
lime water (No. 2) as already taken of copper sulphate solution; pour this
into the third barrel and stir the two together immediately and briskly for a
minute or two. You will then have formed a greenish-colored substance,
which is Bordeaux mixture. Put it into the spraying pump and apply it at
once. Bordeaux mixture is not so good after it has settled, and after it is
twenty-four hours old it had better be poured away and fresh Bordeaux made.
The lime water and copper sulphate solution may be kept separately for an
indefinite time without deterioration.





Florida Agricultural Experiment Station


if some dry weather follows the infection. Not infrequently the
first leaf dries up completely, only the leaf stalk being left green,
and this may fall off or not as the conditions determine. After
the first leaf has shown considerable distress, the second and third
leaves, and finally the entire plant may show the presence of the
disease.
All varieties of tomato obtainable on the American and Euro-
pean markets were tried with a view of securing a resistant one,
but in vain. Tomatoes from Cuba and Mexico were also tried
without success.
TREATMENT.-About the only practical method of treating
this disease at the present time is that of rotation of crops. Us-
ually there is a sufficient amount of land present in the tomato
growing sections to allow a crop of tomatoes to be grown and the
land to be abandoned, or planted to some other crop, for two or
three years. After the lapse of this time, the field may again be
planted out to tomatoes with a fair degree of certainty that the
fungus will not make cropping unprofitable.

SCLEROTIUM BLIGHT

This disease of the tomato was discovered by the writer dur-
ing the spring of 1892. At that time it was found to be very
widely distributed, and in many tomato fields almost completely
destroyed the crop. Immediate steps were taken towards discov-
ering a remedy for this-trouble and means of preventing it. With
our present knowledge of this disease it is by no means so difficult
to handle as some of the others. For the most part this disease
is prevented by methods of clean culture, and by not using stable
manure or other decaying vegetable matter for fertilizer where
this may be avoided.
DESCRIPTION OF THE DISEASED PLANT.-In the case of sclerot-
ium blight the first symptom is the wilting of the terminal
portion of the plant. This characteristic distinguishes the
sclerotium blight rather sharply from the fungus blight; since
with the former the top of the plant is the portion that shows the
disorder, while the presence of the fungus blight is shown by the
yellowing and dying off of the lower leaves.
CAUSE.-The cause of the disease is a fungus (Sclerotium
rolfsii). The disease is carried over from year to year by means
of small bodies, which in their mature state resemble mustard






Bulletin 117


seeds. Sometimes these sclerotia are more minute than the finest
mustard seed. Sometimes a number of them grow together into
a larger body and make up a somewhat irregular mass. The color
of the mature sclerotia varies from very dark-almost black-to
mahogany red. The young sclerotia are milk white. This fun-
gus, like the preceding one, lives in the soil; but it differs from
the fusarium fungus in requiring a considerable amount of vege-
table matter to enable it to continue to exist from year to year.
REMEDY.-Plants attacked by this fungus rarely show the
presence of the sclerotia, excepting when the disease has de-
veloped to an advanced stage, and then the sclerotia are found
only under certain conditions. They, however, form on the stems
of dead tomato plants, and by the cultivation of the soil are dis-
tributed rather widely in an infected field.
As the fungus attacks the plant from the soil, either at the
base of the stem or in some of the larger roots, it is manifestly
impracticable to prevent it by spraying the top of the plant. The
writer has, however, shown that it is readily treated by using
some soluble form of fungicide; such as Eau celeste or ammonia-
cal solution of copper carbonate.*
One of these fungicides, preferablytheammoniacal solution of
copper carbonate, should be sprayed on the soil about the stem
of the plant. By spraying on a half teacupful at this point the
plant is usually perfectly protected against infection. In using
this remedy it should be remembered that where the fungus has
gained entrance into the tissues of a plant before the fungicide
has been applied, the remedy will be of no avail. So many tomato
growers, however, have used this remedy effectively against the
fungus, that we must conclude that it is a first-class remedy for
this form of blight.

Ammoniacal Copper Carbonate.-
Copper carbonate .................................. 5 oz.
Ammonia water 26 degrees Beaume.................. 3 pts.
For use dilute to fifty gallons.
Pour one gallon of water in a wooden or earthen vessel. Pour in the 3
pints of ammonia and stir so !as to mix evenly. Take the 5 ounces of copper
carbonate and shake it in the ammonia water, stirring the liquid all the
while. If the copper carbonate all dissolves, put in an additional amount of
it until a small quantity remains undissolved. When the undissolved copper
carbonate has settled to the bottom, pour the clear, blue liquid off into some
vessels that can be tightly corked, such as jugs, or bottles. The writer's
experience has been that this stock solution does not keep well for more than
from a few days to a week or two, even in tightly corked vessels; consequent-
ly, the material should be made up just at the time when it is to be used.





Florida Agricultural Experiment Station


In addition to the use of the fungicide, the ravages of this dis-
ease are very greatly reduced by pruning and staking the plants.
This should be done in such a way as to allow the air to circulate
freely around the base of the plant, and the "vines" should be
kept off the ground. Cultivating the soil so as to keep it loose
and dry around the plants kills much of this fungus and further
protects the tomatoes.
PLANTS AFFECTED.-The sclerotium blight of the tomato is,
unfortunately, a very wide-spread disease, attacking many other
plants. In addition to tomatoes, we find egg-plants, Irish pota-
toes, beans, cowpeas, summer squashes, cabbages, beets and mel-
ons among the garden plants that are often severely attacked.
Even fig trees from one to one and a half inches in diameter have
been attacked and killed by it. Hydrangeas and Daphnes are
among the ornamental plants that succumb to the disease. In
addition to these, there are many weeds and some of our forage
crops that may be affected. The sclerotium blight grows in al-
most any kind of decaying vegetable matter. It has been found
especially abundantly in compost heaps, and in heaps of decaying
comptie pulp.

BACTERIAL BLIGHT, WILTS
(Bacillus solanacearum.)

The bacterial blight of the tomato is rather widely distributed
in the United States, and during some years it has been extremely
severe in Florida. During other years it has been almost absent
from the State. It usually becomes very severe in fields where it
makes its appearance; especially if this is during the early part
of the growing season.
CAUSE.-Dr. E. F. Smith proved conclusively that the disease
is due to a bacterium which gains an entrance into the tissues of
its host plant, where it develops, and that it may be transferred
from one plant to another, especially by biting and sucking in-
sects. It is impossible in practice to eliminate the insects from a
vegetable field, yet it can be readily understood that the severi-
ty of an attack of this disease in a very large measure depends
upon the numbers and kinds of insects present.
TREATMENT.-As the biting and sucking insects are the main
carriers of this disease, so far as we know, it is manifestly im-
possible to prevent the disease by using fungicides; such as





Bulletin 117


Bordeaux mixture and ammoniacal copper carbonate. We can,
however, do a great deal towards reducing the disease after it
has made its appearance by reducing the number of insects as
much as possible. It is possible for insects to transmit the dis-
ease from one diseased plant to a great number, and as it takes
some days for the development of the disease, a very large per-
centage of our plants may become inoculated before we discover
its presence. It has been the writer's experience with this dis-
ease that it almost invariably spreads over the field from certain
centers. Sometimes the disease has been so general that it was
difficult to find exactly the first point of infection; but this can
usually be located by the dead plants being more numerous in
some points than in others.
As soon as a plant in the field is discovered to be diseased by
a bacterial blight, it should be pulled out at once, and destroyed
either by burying, or by carrying from the field and putting it in
such a place that insects will be unable to migrate from the dis-
eased plants to the healthy ones.
OTHER PLANTS AFFECTED.-While it has not been definitely
proved that this bacterium may live in the soil from one tomato
season to another in Florida, it is possible, in any case, for the
disease to be carried over from one year to another on some of our
wild plants which are subject to it. Consequently, a field that has
been severely affected by the bacterial blight one year, should not
be planted either to tomatoes, Irish potatoes, or egg-plants dur-
ing the succeeding year. In addition to these vegetables, the
Jamestown weed, black nightshade, and several weeds of this
family (Solanaceae), are affected by this bacterium.
DESCRIPTION OF A DISEASED PLANT.--In some cases it is rath-
er difficult to distinguish between plants that are affected with the
bacterial blight and those that are diseased with the sclerotium
blight. Typical cases of each form have many points of similari-
ty. As a rule, a plant that is suffering from the bacterial blight
becomes infected through a leaf. This leaf shows that it is in-
fected by wilting. Next, that portion of the plant to which the
leaf is attached begins to wilt; and finally the entire plant will be-
come involved. In the case of the sclerotium blight the whole
plant usually shows the distress at once, and does not, as a rule,
die off as quickly as a plant attacked by bacterial blight. In the
case of bacterial blight a dark gummy substance is apt to be de-
posited in the woody portion of the stems. Sometimes these dark





Florida Agricultural Experiment Station


streaks also grow in the leaf stalks. In this respect the bacterial
blight may be confused with the fungus blight. It is not usual
for this dark, gummy substance to be deposited in the stems of
the plant or in the leaf stalks, when the plant is attacked by the
sclerotium blight.
These three forms of blight may be easily diagnosed by the
plant pathologist with his microscope in the laboratory, but they
have so many points of similarity that it is very difficult to de-
scribe them in such a way as to enable the tomato grower to dis-
tinguish them beyond a question of doubt. The plant pathologist,
however, who comes in contact with the three forms of blight
regularly has no difficulty in diagnosing them in the field.

DROPPING OF BLOOM BUDS

During some years this trouble occasions a greater loss to the
tomato growers than any of the diseases that are caused by micro-
organisms. The plant puts out the bloom hands or clusters, but
after the blooms have opened they drop off, leaving no fruit set.
The plant continues to grow and produce new blooms, but these in
turn may be shed.
CAUSES.-There are a number of causes which bring about
this condition.
First,-and among the most general and widespread causes
for the dropping of bloom buds is the sudden occurrence of cold
or cool weather, coming at a time when the plants in the tomato
field are in active blooming condition.
Second.-Just the opposite condition may sometimes occur.
Plants may grow too rapidly, especially if the formula of the fer-
tilizer used is high in ammonia and the weather is favorable to
the most rapid growth. In this case the tomato plant grows very
rapidly and grows to weed instead of producing fruit. When this is
the case the vegetative function of the plant is carried on too rapid-
ly to allow fruiting. Where the bloom buds are shed on account
of too rapid growth of the vine, this condition may be checked
almost immediately by cutting out the growth buds at the termi-
nals of the plants. Care should be taken to leave at least two
"hands" of bloom buds. This makes the process of disbudding a
little more tedious, but if all the bloom buds are removed the
plants will not be able to set any fruit. In disbudding rapidly-
growing plants to make them set fruit, care must be taken not to






Bulletin 117


carry this operation to an extreme; otherwise, we introduce a dis-
ease which is known as leaf curl or roll leaf, and is described in
subsequent pages.
Third.-The shedding of bloom is also caused by thrips, and
by the suck-fly. (See Florida Agr. Exp. Sta. Bul. 112, pp. 26 and
38.)
LEAF CURL, OR ROLL LEAF

There are a number of causes which lead up to this difficulty.
The most important one in Florida is the presence of too much
moisture in the soil. Another very prolific cause of this disease is
the too severe pruning of the tomato plants. Where this is caf-
ried on rather drastically, it is almost certain to produce the dis-
ease. As disbudding is practiced by many of our growers, and
staking of tomatoes is also customary, we find this disease not at
all uncommon. The bad effects of it, however, are as a rule not
recognized, since the leaves usually remain green and the plant
continues to grow. A plant, however, that has been pruned or
disbudded to the extent of producing leaf curl is less productive.
REMEDY.-Where leaf curl is due to too much moisture in the
soil, care should be taken to plow the field in such a way as to re-
lieve it of the superabundance of moisture. Where leaf curl is
due to pruning, the pruning should be discontinued, or deep plow-
ing, and plowing rather close to the plant, followed. This plow-
ing will in a measure relieve the soil of the surface moisture, and
at the same time do a considerable amount of root pruning. In
this way we cut off a portion of the moisture that would otherwise
be taken up from the soil.

DAMPING OFF

This disease rarely occurs, excepting in the seedbed. It
manifests itself by the plants falling over, and looking very much
as if they had been gnawed off by some insect. These apparently
gnawed-off areas occur at different points in the seedbeds, and the
fungus which causes the trouble spreads out from these points in
all directions. The disease occurs usually when the plants are
covered, as in a cold frame, or when the seedbed is located in a
moist hammock. Damping off is specifically caused, for the most
part, by one or more fungi which inhabit the soil.
REMEDY.-In case the seedbed is located in a moist hammock
it should be ditched around so as to draw the water off and dry






























































Fig. 5.-LEAF CURL, OR ROLLED LEAF.





Bulletin 117


the bed thoroughly. If the plants are very thick set in the bed, it
would be best to remove a portion of them so as to let in the sun-
light on the ground. In addition to this, a great deal of good can
be done by spraying the soil thoroughly with an ammoniacal solu-
tion of copper carbonate. (See foot-note on a former page.)
Stirring the soil between the seedlings is a further aid towards re-
ducing the loss from these fungi. Seedlings in rows can be easily
handled in this way.

HOLLOW STEM

This diseased condition of the plants manifests itself in the
field shortly after they have been set out. The plants at the time
of setting out may look perfectly healthy and normal, but after
some days or a week, they begin to fall over, remaining green aft-
er they have fallen over, but making no growth. Even the plants
that do not fall make only an indifferent growth and many of
them do not recover. Those that are so weakened as to fall over
almost never recover. On examining such plants the stems will
be found to be hollow. Many of the plants that are still standing
will also be found to have hollow stems.
CAUSE.-The cause of this trouble is that the plants have
been grown in a seedbed that has been overfed with nitrogenous
material, and which has been given more moisture than is neces-
sary to produce vigorous plants. In short, they are extra forced
plants.
TREATMENT.-Less difficulty is now experienced from this
trouble than formerly. The plants are now generally hardened
off before being transplanted to the field. Less of the stimulat-
ing fertilizer which causes a quick growth, is being used. Slowly
grown plants well hardened off in the seedbeds do not suffer from
this trouble.

SCAB, BLACK SPOT

This disease is well described by the name usually applied to
it. It is easily distinguished from blossom-end rot in that the
affectation may occur on any portion of the fruit. The spots
vary in size from very minute to a fraction of an inch across, and
are rough to the touch. Frequently a large percentage of the
fruit will be affected without any of it rotting, and this fruit
would be good for consumption. The unsightliness, however,





Florida Agricultural Experiment Station


makes it unsalable. This disease also gives the rot fungi an
opportunity to infect the fruit, causing a large portion, or all of
it, to decay, either in the field or in transit.
TREATMENT.-The disease is caused by a fungus, Alternaria
solani, and can be prevented by spraying with Bordeaux mix-
ture. The fungus that causes this disease is the same as causes
rust on the leaves. Unfortunately the trouble is usually over-
looked until a large percentage of the fruit has become affected.

BLOSSOM-END ROT

This disease has caused a considerable amount of loss in the
tomato fields. It may occur on fruits of various sizes, but is
usually not noticed excepting on fruits that are more than half
grown. It is characterized by a darkening and drying down of
the blossom-end of the fruit, and later by rotting at this place.
Careful investigations have been made as to the cause of the dis-
ease. It seems probable that a number of different species of
fungi and a species of bacterium may produce conditions that are
very similar in appearance.
REMEDY.-Some experimenters have found fungicides effect-
ive in controlling the disease, but others have been unable to see
any advantage from their use. This contradiction of observat-
ions is probably due to different agents causing indistinguishable
diseases. Bordeaux mixture is usually recommended as a pre-
ventive.

(ROOT KNOT, "MOLD," and INSECT PESTS are treated
of in Bulletin 112 of this Station.)




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