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
site maintained by the Florida
Cooperative Extension Service.
Copyright 2005, Board of Trustees, University
COOPERATIVE EXTENSION WORK IN
AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30, 1914)
UNIVERSITY OF FLORIDA, DIVISION OF AGRICULTURAL EXTENSION,
AND UNITED STATES DEPARTMENT OF AGRICULTURE,
WILMON NEWELL, Director
SOME IMPORTANT DISEASES OF
TRUCK CROPS IN FLORIDA
By C. D. SHERBAKOFF
FIG. 75.-Bean pods spotted with anthracnose.
A reprint of bulletin 139, Agricultural Experiment Station, University
of Florida, Gainesville.
INTRODUCTION ..................-......-.......- ----...- ....- ... -- .-- -------------.. 3
MATERIALS USED IN CONTROL OF TRUCK DISEASES..----...........--...------------- 4
Bordeaux Mixture .............------...- ... ....................... ------- 4
Making the Mixture..................---------------------- 5
Using the Mixture.-........ ...... ............ .. .......------ .--.-------.. --. 6
Soda Bordeaux Mixture.....................----------- --......------...---...... 8
Ammoniacal Solution of Copper Carbonate---........ --..---....... ....... 8
Rosin-Salsoda Sticker ..-------............. ----- ........- -- 8
Sulphur .....------..............------------- ------ 9
Formalin ............. .........--- .------.-------..... 9
Corrosive Sublimate ....---......----....................---- 9
SPRAYERS .............- .....--.... ------.............-- ...... ..-. .--- ----------- 10
GENERAL MEASURES FOR CONTROL OF TRUCK DISEASES................-.......--...... 11
Cultural Methods ..--............-- ... -- ..........--........----...... 11
Sanitation ......--......... ....--........----.....-- .... -------. 11
Importance of Healthy Seed-............ ------------------. 12
SedDsneton----------------- ... -----------------------12
Seed Disinfection ........................-- .......-- 12
Crop Rotation ..........--- .......... ........ --- ---------------------------- 14
Spraying --- ---...................----- ------- ---... 14
Care of the Seed Bed------............. -----.-------.-------. 15
Damping Off .....................-- .....---...---------------- 15
Soil Sterilization ..........................--------------- ---- 17
Sterilization with Formalin................. ... ----------- 17
Steam Sterilization ......................... ---..-. ---- --------------- 18
Disease Resistant Varieties ....----...........................-------------- 19
DISEASES OF TRUCK CROPS AND THEIR CONTROL................------------ --- 20
Bean Diseases ..................................----------- ------- 21
Cabbage Diseases .-.... -------......................-- 33
Cantaloupe and Cucumber Diseases---.......--. ---------------- 36
Cauliflower Diseases .---.......----.---- --------------- 37
Celery Diseases ..-......--------------------------
Eggplant Diseases ...- .-----.----------------------------42
Lettuce Diseases ............--------------.--- -------- 48
Pea Diseases .....................--------------- ----------------- 50
Pepper Diseases ........-----.---------------------5
Potato Diseases ...................--------- ----------- 53
Sweet Potato Diseases---....-...--..------- ---------------- 68
Tomato Diseases ...------------.....----------- --- 0
Watermelon Diseases .. --.....----. ----------------------
SOME IMPORTANT DISEASES OF TRUCK CROPS
BY C. D. SHERBAKOFF
Truck growers often sustain great losses from diseases
which attack their crops. Sometimes the grower is unaware of
the fact, or underestimates the damage done by the diseases. It
may be that he does not know how to control them, or, knowing
how, prefers to take a chance at growing a profitable crop in
spite of the diseases rather than to take the trouble of applying
the remedies. For the control of a disease is often a trouble-
some and expensive operation and may be discouraging when
attempted without proper knowledge. Nevertheless, many dol-
lars can be saved in profits thru the proper application of dis-
ease-control measures at a small cost. An acre of Irish potatoes
costing the grower from one to several hundred dollars, threat-
ened with ruin by the late blight, can be saved by an expendi-
ture of from four to ten dollars an acre for spraying. Consid-
ering the fact that blight occurs here on an average of probably
not less than once every three years, it is evident that the ex-
penditure of money for its control is a necessary and profitable
investment. In fact, some of Florida's most profitable crops
could not be grown profitably without due measures against
certain diseases. Among celery growers it has become a general
practice to spray with bordeaux mixture celery plants in the
seed bed and in the field for protection against early blight or
rust. This spraying costs considerable money but the growers
find that only by spraying can they make money.
Spraying or any other single measure of plant-disease con-
trol, is not effective against all diseases. For instance, if tomato
or pepper plants are attacked by the fungus wilt, then any
spraying of the plants will be entirely useless. Dusting with
flowers of sulphur is a good measure against powdery mildews
of various plants, but it will not help in the case of most other
diseases. Seed disinfection will protect Irish potatoes from
scab, and other plants from other diseases, but this process is
worthless when applied to cucumbers to prevent downy mildew
or rust, to peppers to prevent leaf drop, to tomatoes to prevent
French rust (Alternaria or brown spot), etc.
Florida Cooperative Extension
Therefore, to control diseases one must know what disease
is present and what measures should be used against it. Then,
knowing what to do, it should be done thoroly, because half
measures do not pay.
MATERIALS USED IN CONTROL OF TRUCK DISEASES
BORDEAUX MIXTURE.-This is a precipitate produced when
water solution of copper sulphate (blue stone) and water-slaked
lime (in the form of lime milk) are brought together. Besides
the timely and thoro application of bordeaux mixture, its ef-
ficiency depends on its chemical composition and physical prop-
erties. Copper is the element of fungicidal value in the mix-
ture; lime is added to neutralize the caustic property of copper
sulphate and to transfer the copper from copper sulphate, which
is easily soluble in water, to other substances which are almost
insoluble in pure water. Thus the lime makes bordeaux mixture
harmless to most of the plants and at the same time makes it
lasting; that is, not easily washed off by rains that may follow
the spraying. Hence the use of copper sulphate, not copperass,"
and quicklime unslakedd rock), not air-slaked lime, is essential.
In regard to the physical properties of bordeaux mixture,
it should be kept in mind that the mixture when properly made
is a water suspension of light, fluffy, jelly-like, minute, particles.
These physical properties of bordeaux mixture make it spread
and stick well, which attributes are very important for a good
spray mixture. On standing for a day, or even less, the sub-
stance begins to crystallize, becomes heavier and quickly settles,
thus losing its original spreading and sticking properties.
Therefore, it is always best to make bordeaux mixture fresh
for each spraying. This explains why a freshly home-made
bordeaux mixture is recommended in preference to various
commercial fungicides of similar composition.
Bordeaux mixture is used in different concentrations which
are designated by formulae. The first number in a formula
shows pounds of copper sulphate, the second, pounds of quick-
lime unslakedd), and the third number, gallons of water. Thus,
5-5-50 bordeaux mixture means 5 pounds of copper sulphate, 5
pounds of quicklime, and 50 gallons of water; and formula
4-4-50 means 4 pounds of copper sulphate, 4 pounds of quick-
lime, and 50 gallons of water. A 4-4-50 bordeaux mixture is
commonly used for spraying, but there are some cases where
other concentrations of the mixture should be used. Such cases
are stated when needed.
Some Important Diseases of Truck Crops in Florida 5
Each grower must devise the details for making bordeaux
mixture which will best suit his conditions. But he must keep
in mind these things which have been proved either essential
or convenient in making the best bordeaux mixture:
1. Prepare stock (concentrated) solutions of copper sul-
phate and lime beforehand.
2. Use only quicklime unslakedd or rock) ; air-slaked lime
is unfit for making bordeaux mixture. Fresh hydrated or water-
slaked lime can be used in amounts 20 percent greater than re-
quired in the formula.
3. Mix diluted copper sulphate and diluted lime milk; be-
cause if concentrated copper sulphate solution and concentrated
lime milk are poured together, the result is a heavy, coarse,
inferior mixture. It is best to dilute the required amount of
copper sulphate in half the required amount of water, also to
dilute the required amount of lime in the other half of the water
and then pour the diluted solutions together. When bordeaux
mixture is made on a large scale it is more convenient to dilute
one of the substances in nearly the whole amount of water and
then to add to it the other substances in concentrated form.
The writer finds that the mixture made in this way is, for
practical use, about as good as when each of the two substances
are first diluted in half the required amount of water.
4. Immediately after the two solutions are poured to-
gether, stir the mixture vigorously for a few minutes.
5. Make bordeaux mixture fresh for each spraying.
6. If the lime milk has not been strained, pour the mix-
ture into the spraying machine thru a copper strainer of about
18 meshes to the inch or thru cheese cloth. Then proceed with
Making the Mixture.-The following procedure has been
found convenient for making bordeaux mixture for spraying a
field of from 5 to 15 acres:
1. To make stock solution of copper sulphate, weigh out
80 pounds of copper sulphate into a coarse bag and suspend it
in a barrel containing 40 gallons of water, just below the water
surface. This should be done in the evening before the day of
spraying, or at an earlier date, in order that the copper sulphate
will have time to dissolve. Each half gallon of the solution will
then contain 1 pound of copper sulphate. Stir it before using.
2. To make a stock of lime milk, weigh out 80 pounds of
unslaked lime and slake it with a small amount of water in a
Florida Cooperative Extension
trough. When the lime is thoroly slaked, add enough water to
make a thick milk. Run this milk thru a wire strainer of about
18 meshes to the inch into another barrel and add to it enough
water to make 40 gallons of the lime milk. Each half-gallon of
the lime milk will then, if thoroly stirred before using, contain
lime equivalent to 1 pound of unslaked lime.
Both of the stock solutions will keep indefinitely but they
should be covered to protect them against dust and a possible
excess of rain water. If any amount of stock solution be left
unused, its surface level should be marked on the container so
that the amount of water which evaporates before the next
spraying can be added. In this way the concentration of the
stock solutions will remain unchanged; that is, 1 pound to a
half-gallon. Copper sulphate will corrode iron, therefore, do
not mark the level of copper sulphate solution with an iron nail,
but with a copper nail or wooden peg. In handling copper sul-
phate solution or bordeaux mixture do not use any iron ware.
3. To make bordeaux mixture, pour into a half-barrel of
25 gallons capacity, as many half-gallons of the stock solution
of copper sulphate as the number of pounds required by the for-
mula, and then fill the half-barrel up to the rim with water.
Next pour into a similar barrel as many half-gallons of the
stock lime milk as the number of pounds of lime required in the
formula, and add water sufficient to fill the barrel to the rim.
Pour simultaneously the entire amounts of diluted copper
sulphate and lime solutions into a 50-gallon barrel or into the
spray tank, if it is large enough. If a small sprayer is to
be used, pour into it equal amounts of the two diluted solutions
sufficient to fill it; stir thoroly and spray. Make fresh mixture
each time as it does not keep well for more than a day.
Bordeaux mixture is the best known fungicide with which
to spray truck crops to protect them against various diseases
caused by fungi, when these parasites are affecting leaves, stems,
and fruits, by means of the spores lodging and germinating on
the surface of the plants. This is true in the case of celery
early and late blights, known also as rust and scab; also in the
case of various tomato leaf and fruit spots, pepper leaf spot
(rust) and in many other instances.
Using the Mixture.-Bordeaux mixture when sprayed on
the plants does not penetrate their tissues and does not kill the
parasites that have already grown into the tissues. Therefore,
spraying with bordeaux mixture, or any other fungicide, will
Some Important Diseases of Truck Crops in Florida 7
not protect the plants against parasites attacking them from the
soil or from the seed and from those working within the plants.
But the continuous film of bordeaux mixture with which sur-
faces of the thoroly sprayed plants are covered kills the spores
when they germinate on it, and is thus an effective protection
against the diseases.
Spraying is most efficient, and hence most profitable, when
it is done before the appearance of the disease. This does not
mean, however, that it is useless to spray against diseases after
they have appeared; on the contrary, the more of the disease
found on your plants the more urgent is the need of spraying
to save them. It means only that if the spraying had been
started earlier, the fight would be easier and more successful.
Do not spray with bordeaux mixture for "bugs" and va-
rious insects because it has no insecticidal value, that is, it is
not poisonous to them.1 But when you are spraying with
bordeaux mixture for a fungus disease and know or suspect that
certain insects are also attacking the plants, then add to the
bordeaux mixture, as if it were merely that much water, the
required amount of the insecticide needed to kill the "bugs."2
In this way a separate spraying for insects can be obviated.
The ordinary, or lime, bordeaux mixture, of which the
method of making has just been given, while being the best
material for spraying is sometimes objectionable for two rea-
sons: (1) The lime solution always contains coarse, insoluble
particles and therefore requires extra work of straining it, or
the bordeaux mixture, and even then it causes an occasional
clogging of the nozzle. (2) Bordeaux mixture leaves conspic-
uous spots on the fruit and plants which is often objectionable
when spraying shortly before marketing them.
To avoid these disadvantages of lime bordeaux mixture,
either soda bordeaux mixture or ammoniacal solution of copper
carbonate may be recommended. It should be remembered
that these two fungicides have certain disadvantages when
compared with the lime bordeaux mixture; namely, they cost
much more under ordinary market conditions, they are more
soluble in water and therefore present a greater chance of
injuring the plants, and they do not last as long as the lime
SFlea beetles are controlled by spraying with bordeaux mixture.
SFor detailed information of what to use for insects, see Florida Agri-
cultural Experiment Station Bulletin 134.
Florida Cooperative Extension
SODA BORDEAUX MIXTURE.-Dissolve commercial caustic
soda in the proportion of 1 pound to 1 gallon of water. The
amount of the soda needed will usually not exceed one third
that of the copper sulphate to be used.
Make a stock solution of copper sulphate as recommended
for the lime bordeaux mixture.
In case a mixture is wanted about equal in strength to
that of 4-4-50 lime bordeaux mixture, measure into a 50-gallon
barrel 2 gallons of the stock solution of copper sulphate and
pour into the barrel about 45 gallons of water, stir and add
from 1 to 11/ gallons of the concentrated solution of caustic
soda. While adding the soda stir the contents of the barrel
continuously. No exact amount of caustic soda to use can be
given because of the great variation in strength of the differ-
ent commercial sodas. One should add enough of it to make
the mixture slightly alkaline. This can be determined by dip-
ping into the mixture a piece of red litmus paper. When the
paper begins to turn blue, there is enough soda. Then pour in
enough water to fill the barrel.
When a stronger mixture is needed, use more copper sul-
phate and soda in proportion to the desired increase in the
strength, keeping in mind that a pound of copper sulphate in
both lime bordeaux and soda bordeaux mixtures has about the
same fungicidal value.
AMMONIACAL SOLUTION OF COPPER CARBONATE.-Measure
3 pints of concentrated ammonia (260 Baum6) into a wooden
bucket and add to it enough water to make 21/2 gallons of di-
luted ammonia. To this add 6 ounces by weight of copper
carbonate and stir the contents of the bucket until the copper
carbonate has had time to dissolve. Usually some of it will
remain undissolved, but if all the copper carbonate dissolves,
add more in small amounts until no more will pass into solu-
tion. Then the stock solution is ready for use. Use only the
clear solution, carefully leaving out the sediment. For spray-
ing, dilute the stock solution of ammoniacal copper carbonate
20 times with water.
For making and handling the concentrated copper carbon-
ate solution do not use any metal utensils. Use wooden,
earthen or glass ware. Never leave any of the solution in the
sprayer longer than is necessary for the work. As soon as the
spraying is over empty the sprayer and rinse it thoroly.
ROSIN-SALSODA STICKER.-In spraying plants which have
Some Important Diseases of Truck Crops in Florida 9
waxy surfaces of the foliage to which ordinary spray mixtures
will not stick, such as cabbage and onion plants, add a sticker
to the spray mixture. A good sticker can be made as follows:
Pour into an iron vessel 1 gallon of water and add to it 1
pound of salsoda (crystals) and 2 pounds of rosin. Boil until
the contents become a clear brown color. Do this in the open
and watch it because it may easily boil over. Add one gallon
of the sticker to each 50 gallons of bordeaux mixture or am-
moniacal solution of copper carbonate.
SULPHUR.-This is used in the form of either flowers of
sulphur or sulphur flour of the finest grade to control pow-
dery mildews on various plants. A power or hand duster
(blower) should be used to apply the sulphur. Make the ap-
plication as light as you can but see that the plants are
thoroly dusted. The best time for dusting is when the plants
are wet with dew or rain. Dusting with sulphur is also effec-
tive against some insects, such as red spiders and mites.
Liquid spray mixtures containing sulphur, such as com-
mercial lime-sulphur and solutions of various polysulfids, can
be used to control powdery mildews, but spraying with them
is more expensive than the dusting and gives no better results
in the control of powdery mildews.
Recent information shows that lime-sulphur solution can-
not, so far as it has been tried, replace bordeaux mixture for
spraying vegetables against various fungus diseases.
FORMALIN.-Under this patented name goes a 40 percent
solution of formaldehyde gas. The same substance and of the
same concentration but without the patented name is known
as "40 percent formaldehyde" and is much cheaper than the
"formalin." It can be obtained from most of the houses
dealing in spray materials and chemicals or small amounts
can be had at any drug store.
Formalin or formaldehyde solution is a very strong dis-
infectant. In connection with plant-disease control it is used
in a diluted form for disinfection of seed (see seed disinfec-
tion) and soil (see soil disinfection).
CORROSIVE SUBLIMATE.-This is one of the most deadly
poisonous substances to plants and animals alike, and therefore
must be handled with care. The substance should be kept in
a secure place inaccessible to children and prominently labeled
"poison," and any solution made and not used should be poured
into a hole in the ground. Plants or the parts treated with it
Florida Cooperative Extension
should not be fed to animals nor be used for human food. For
disinfection of seed, plant parts, agricultural implements,
clothes, etc., it is ordinarily used in a 1 to 1000 concentration.
For its use in seed disinfection see "seed disinfection."
To make 1:1000 solution, dissolve 1 ounce of corrosive
sublimate (crystals) in 71/2 gallons of water; or, if corrosive
sublimate is in tablet form, dissolve 1 tablet in 1 pint of water.
In the case of trucking on a loose muck soil which is not
firm enough to permit the use of a heavy field sprayer or
where the trucking operations are not extensive, a knapsack
sprayer is generally used and is perhaps best for the work.
But when the soil is firm enough and the trucking is done on
a large scale-five or more acres-then a field sprayer with
either horse, engine or hand operated pump, would be the most
profitable implement. When good nozzles are used and high
pressure is maintained, such a machine sprays much better
and uses less of the spray material than does a knapsack
sprayer. A considerable acreage can be sprayed in a short
time. This is highly important in controlling plant diseases
because very often the spraying must be done in a very short
time if it is to be effective.
A sprayer that maintains high pressure-at least 100
pounds while the nozzles are open-without needlessly over-
taxing the power operating the pump, that has a convenient
attachment for spraying four or more rows of plants, and has
also a device by which each row can be sprayed with either
single or double nozzles, and that has its working parts easily
accessible, simple and substantial-such a sprayer, and only
such, should be considered satisfactory for the work. Of
course, it should be supplied with first-class nozzles. See
that the working parts have good finish, which indicates care-
ful workmanship, and then test the apparatus under working
conditions. A good nozzle should give a fine mist evenly dis-
tributed over the area it sprays.
There are many different sprayers and it is impossible to
recommend any one particular make. Every grower should
get catalogs from as many different firms as practicable and
compare the machines for himself. Then he should not miss
any opportunity to see the sprayers at work in various ex-
hibits, county fairs, and in neighbors' fields. Get a sprayer
Some Important Diseases of Truck Crops in Florida 11
which you know beforehand will be satisfactory and thus avoid
disappointment. A sprayer is as important a machine on your
truck farm as any other machine used there.
GENERAL MEASURES FOR CONTROL OF TRUCK DISEASES
CULTURAL METHODS.-Plants might be "sick" directly or
indirectly on account of the poor condition of the soil-poor
drainage, poor aeration, the presence in it of some poisonous
substance, or its poor mechanical condition-and on account,
of a lack or excess of light, heat, food, and water. Plants vary
greatly in their requirements. Therefore, find out what truck
crops are best adapted to your soil and climate and choose
from them the ones to grow for profit or pleasure. Neither
soil nor climate is ever perfect, so it will be well to improve
these conditions where practicable by proper cultivation, fer-
tilization, drainage, irrigation, shading, etc., as needed.
Trucking in Florida with certain crops, such as celery and
lettuce, is a stable and dependable business only when a good
system of irrigation is used. Several methods of irrigation are
practiced. A discussion of their merits will not be entered into
here, except for this suggestion: When the overhead system
is used remember that the waterings should be few and each
one heavy enough to let water sink deep into the soil where
the roots grow. This is where the plants need it. They do not
require any water on the surface of their leaves. Frequent and
light waterings only help diseases to develop and bring the
roots close to the surface where they might easily be injured
by a short spell of dry and hot weather.
SANITATION.-Nearly all important diseases of truck crops
in Florida are due to the work of certain parasitic fungi and
bacteria. These parasites are first introduced into the field,
usually with contaminated seed, plants, plant parts, and with
the soil, or are brought in by the wind. Once these parasites
begin to grow on the plants, they usually multiply with great
rapidity. Their spores-minute special fungus cells serving
the purpose of seed in higher plants-and parts of their body
growth are carried by contaminated soil clinging to farm im-
plements and to the feet of animals and men, by insects, wind,
water, etc., from one infected plant to another. Therefore,
it is important that all infected plants and their parts should,
as far as possible, be immediately destroyed. No sick or de-
caying plants should be left in the field because they will serve
Florida Cooperative Extension
as an ever present source of infection to the neighboring
plants. Keep your field perfectly clean from all rubbish.
IMPORTANCE OF HEALTHY SEED.-Several truck diseases of
great importance are either entirely or to a considerable extent
carried with the contaminated seed. Such undoubtedly is the
case with bean anthracnose and bacterial blight; with Irish
potato scab, late blight, black leg, wilt, and mosaic; with egg-
plant foot rot (the same parasite which causes the foot rot is
also responsible for the fruit rot, leaf spot, stem canker, and
damping off); with cabbage and cauliflower black rot, water-
melon wilt; and with several other diseases.
New soil, that is, a soil never before cultivated to the crop
about to be grown or to one closely related to it, is, as a rule,
entirely free from the disease. But because parasites causing
some of these diseases, such as Irish potato scab and eggplant
foot rot, once introduced into the soil will remain there in an
active stage, the cultivated fields in course of time will almost
invariably become thoroly contaminated with the parasites and
be thus rendered unfit for the culture of like crops for a long
time, a few years or more.
Therefore, it is of great importance to use only healthy.
uncontaminated seed. This is true in all cases but is especially
true in the case of the seed of beans, Irish potatoes, tomatoes,
peppers, onions, cabbage, cauliflower, and eggplant. The best
way to get healthy seed would be to produce it yourself from
the fields and plants entirely free from the disease. This is
easy to do in the case of tomatoes, peppers, eggplant, water-
melons, and some other plants, but in some instances, as in the
case of Irish potatoes, it is at present hardly practicable for
the Florida grower to produce his own seed and he must look
for some other means to get clean seed. He must insist that
his seed dealer furnish certified seed. Such seed is available in
the case of Irish potatoes, but the demand for it must be made
before the Northern crop of seed is grown. By all means, try
to secure only healthy seed, for by its use you will save con-
siderable worry and money.
SEED DISINFECTION.-Certain diseases are so common in
the districts where the crops have been grown for some time,
that it is almost impossible to obtain seed of those crops free
from the disease. When the disease-producing germs are car-
ried only on the surface of the seed, as is the case of Irish po-
tato scab under ordinary soil conditions, seed disinfection is
the only measure to be taken against the disease. There are
Some Important Diseases of Truck Crops in Florida 13
many other instances in which seed disinfection is of great
service, and should be resorted to. In the present state of
knowledge of truck-crop seed and its disinfection, this much
can be safely recommended:
1. Irish potato seed should be disinfected against the
scab by soaking the tubers either in 1:1000 corrosive sublimate
solution for 11/2 hours, or in formalin (40% formaldehyde) di-
luted in water in the proportion of 1 pint to 30 gallons of
water, for two hours.
Corrosive sublimate solution should not be used more than
three times-twice would be safer-and then the old solution
should be discarded and a new one made, because it loses its
strength after repeated use. The solution of formalin can be
used over and over again indefinitely. If there is too little of
it, add to the old solution the needed amount of a new one.
Formalin solution loses its strength only thru evaporation.
Therefore, the solution should be prepared when needed and
Corrosive sublimate is the more efficient because, besides
killing the scab, it also kills the fungus Rhizoctonia of the
"black scab" which also causes sprout blight and little potato.
The formalin treatment does not kill this fungus. However,
the formalin treatment is more convenient and on a large
scale is somewhat cheaper.
It is best to treat seed just before planting. When it is
desirable to treat seed some time ahead of planting, the seed
immediately after treatment should be spread in a thin layer
on a clean floor or canvas in a shady and breezy place for quick
drying. The treated seed must be kept in a disinfected sack
or barrel, or anything that is known to be free from germs
causing the disease.
In some cases it was found that the treatment with corro-
sive sublimate caused some injury to the seed when treatment
was made during hot weather, therefore, avoid treatment when
the temperature is above 700 F.
2. Eggplant and pepper seed should be disinfected by
soaking in 1:1000 solution of corrosive sublimate for ten
minutes; tomato seed in a similar solution for three min-
utes; watermelon, cabbage, cauliflower, and onion seed for fif-
teen minutes. All of these small seed should be at once thoroly
rinsed in running water, or in several catches of fresh water,
and then planted immediately. When needed, the seed should
Florida Cooperative Extension
be dried enough for planting by mixing them with some harm-
less substance, such as dry sand taken from the sea shore or
heated in an oven, starch, etc.
The treatment of the seed, if the directions are closely
followed, does not injure them and does free them to a great
extent from the disease-producing germs with which they were
CROP ROTATION.-Many parasites causing certain diseases,
some of which are important, are capable of remaining in an
active stage in the soil for a long time. Most of them can feed
only on certain plants and will in the course of time die of
starvation if the plants on which they live (so-called "hosts")
are not grown there for the required time. By changing from
the growth of crops susceptible to the disease to those that are
resistant, the field might be freed from the parasites. If on
the contrary the same crop, or crops susceptible to the same
diseases, is continuously grown on the same land, the parasites
will finally so increase in number that the crop cannot be
grown profitably, if at all.
Crop rotation for disease control is also beneficial in the
maintenance of soil fertility. Rotate the crops so that no
closely related plants, which are susceptible to the same dis-
eases, will follow each other. Do not plant tomatoes, Irish
potatoes, eggplant, peppers, and tobacco in rotation because
they are closely related and are subject to some diseases com-
mon to all of them. Do not plant cabbage after cauliflower or
kohlrabi, for the same reason. Neither is it good practice
to plant watermelons after cucumbers or cantaloupes.
SPRAYING.-Many fungus diseases can be readily con-
trolled by covering the plants with certain substances poison-
ous to parasites and at the same time harmless to the plants.
This is done by means of spraying and dusting. Bordeaux
mixture is the standard fungicide for spraying, and for dust-
ing, sulphur is used. When it is necessary to control insect
enemies also, add to the fungicide the needed amount of the
Get your sprayer ready and test it thoroly before the time
for spraying. Have on hand plenty of bluestone, lime, and
other substances which you are likely to need for spraying,
or dusting. Spray before diseases appear. Avoid spraying
late in the day. Spraying during or just before a rain is not
advantageous, but a spray applied so far ahead of the rain
Some Important Diseases of Truck Crops in Florida 15
that it dries on the plants before rain comes will prove most
The strength of the solutions to use and the frequency of
application will be given under each disease that can be con-
trolled by spraying.
CARE OF THE SEED BED.-Young plants in the seed bed
are subject to many diseases. Because of the crowded condi-
tion of the plants, these diseases have ample opportunity to
spread from one plant to another and cause considerable dam-
age. Certain diseases attack plants with tender, succulent
roots and stems, so that young plants are more susceptible to
them than are the more mature plants. For these reasons, and
also because in the control of many truck diseases it is essen-
tial to transplant into the field only healthy plants, no care
nor expense should be spared for protecting plants in the seed
Damping Off.-The disease most generally known and
probably of most common occurrence in seed beds alone is
damping off. The name was probably given to the disease
because it is prominent only when there is plenty of moisture
in the air. While the trouble is not caused by "dampness" it
is necessary for the development of the disease. Damping off
of truck plants and others is due to an attack by fungi, the most
common of which in Florida is a soil-living fungus, Rhizoctonia
solani Kuhn. Several other fungi may cause the same trouble-
Pythium debaryanum, Phomopsis vexans, Sclerotinia libertiana,
several Fusaria, and some others.
The appearance of plants affected with damping off is that
of having been scalded, and one can often detect on the surface
of the soil and on the plants a thin cobweb-like growth of the
fungus causing the disease. As a rule, the disease begins its
work in only a few spots. Under favorable conditions the spots
increase in size quite rapidly and, if not checked, may destroy
all of the plants in the seed bed in a short time.
This scalding effect on the plants is produced by damping
off only when the plants are young and succulent. As the plant
stems become harder the disease causes them to decay slowly.
This decay may ultimately kill the plant but it often results only
in the producing of more or less deep scars on the stems just
at, or near the level of the ground. In some instances these
scars might be entirely harmless to the plants. Far more often,
however, the plants even slightly affected in this way are unfit
Florida Cooperative Extension
for transplanting into the field, because it is much cheaper to
discard an occasional good seedling than to grow a poor, unpro-
ductive plant in the field. Also, these innocent looking scars on
the young plants may, and often do, introduce into the field
some very destructive diseases, such as foot rot of eggplant, and
A seed bed even when prepared on new ground is not al-
ways free from damping off. This is due partly to the fact that
certain fungi, Rhizoctonia for instance, causing the disease are
sometimes present in the virgin soil, and partly to the fact that
damping off fungi are frequently brought into the seed bed with
the seed. In these or some other ways, the diseases become
more prevalent from year to year until, as it often happens, no
plants of the crop previously grown can longer be produced.
Much investigation is still needed to determine the best
methods for controlling this disease under Florida conditions,
yet some information at hand can be recommended:
1. Keep the surface of the soil and the plants as dry as
is consistent with their best growth. Do not water seed beds
too often and do not shade them more than is necessary.
2. It is often advantageous to have on the surface of the
seed bed a half-inch layer of pure, coarse sand. Damping off
fungi grow on the surface or in upper layers of the soil and
thrive best when the soil is well supplied with organic matter.
This layer of pure sand will hinder the growth of the fungi.
For the same reason it is better to fertilize seed beds entirely
with mineral, not organic (stable manure, blood, raw bone, etc.)
3. A frequent stirring of the soil around the plants is
beneficial for checking the disease.
4. Seed beds should be carefully examined each day for
the presence of damping off and every spot found should be
thoroly soaked with a good disinfectant. For this disinfection
use copper sulphate solution, 1 to 100 parts water, or a solution
of corrosive sublimate, 1 to 1000 parts water, or formalin, di-
luted 1 to 50 parts water. In case formalin solution is used, the
treated spot should be covered with a sack or piece of canvas
for a day or two. Treat somewhat more of the seed bed than
the visibly affected area because the disease is always some dis-
tance ahead of the sickly plants and the purpose of the treat-
ment is to get rid of the infection by killing all of the fungi.
5. When damping off is common, it would be best to ster-
Some Important Diseases of Truck Crops in Florida 17
ilize the soil either with formalin or with steam (see soil steril-
ization) or at least to locate the seed bed on a virgin soil. This
is also a good measure against several other diseases that might
have accumulated in the seed-bed soil.
As previously stated there are other diseases that affect
young plants. Many of them cannot be detected or are incon-
spicuous. The young plants may appear healthy and be trans-
ferred into the field, but they will not produce the expected
yields and will serve as a source of infection to the other plants
and to the soil. Therefore, the protection of plants against such
diseases is of special importance. In doing this the grower
should keep in mind that germs of the parasites of these dis-
eases come most commonly either with the contaminated seed or
from contaminated soil and manure, or with the wind.
Only healthy seed should be used; the soil and stable ma-
nure should be either sterilized (see soil sterilization) before
planting the seed or they must be known to be free from the
disease. Use new soil and a manure with which refuse of dis-
eased plants was not mixed. Finally, certain plants should be
sprayed with bordeaux mixture or some other good fungicide.
Spraying in the seed bed is especially important in the case of
celery, tomato, and pepper plants.
It is also a good policy to have the seed beds located if
possible in an isolated place, somewhere in the woods, because
plants grown there will be protected considerably from infection
with various diseases carried by the wind and insects.
The sprayings should be frequent, not less than once every
week, and they should be made with all precautions against
burning the plants. In this case it is safer to spray with 3-4-50
bordeaux mixture than with a stronger one, and it is also quite
necessary that the spray mixture be allowed to dry on the
plants in a short time, otherwise a burning may result.
SOIL STERILIZATION.-To free a soil from germs of various
parasites causing plant diseases, it is often necessary to treat it
either with a substance poisonous to the parasites or to heat the
soil sufficiently to kill them. Many different methods of soil
sterilization have been tried but so far only these two can be
safely recommended for treatment of seed beds, in which truck
plants will be grown.
Sterilization with Formalin.-Dilute 1 part of 40 percent
formaldehyde (see formalin) in 50 parts of water and apply
this solution to the soil at the rate of 1/2 gallon to each square
Florida Cooperative Extension
foot of the seed-bed surface. The treatment should be given
after the seed bed is prepared for planting and at least 10 days
before plaiiting the seed. The soil should be well stirred before
the treatment so that it will readily absorb the required amount
of the solution. The surface of the bed should be level so that
the solution will not run off and also so that all parts may be
treated uniformly. This application can be made conveniently
with a sprinkler.
Immediately after the treatment the beds should be covered
with sacks or canvas for a period of 24 to 48 hours. This is to
prevent a too rapid evaporation of the poison. After this period
the covering should be removed and the poison allowed to es-
cape. An occasional stirring of the soil will promote quicker
evaporation. This is necessary because if the formalin has not
been sufficiently evaporated it will injure the plants.
Steam Sterilization.-Two methods of steam sterilization
are in common practice; a pipe method and an inverted-pan
method. For the first method a frame is made of perforated
pipes. The frame is buried about six inches below the surface
of the seed bed and then by means of a hose connecting the
frame with a boiler, live steam is let into the frame for a suf-
ficient time. By removing the frame from one part of the seed-
bed to another the entire bed may be treated.
For the inverted-pan method, provide a flat pan of gal-
vanized iron with sides about six inches high. The edges of the
sides should be sharp enough to permit sinking them readily
into the soil. The pan is provided with a short pipe to which a
hose from the boiler can be attached. The pan should be as
wide as the seed bed and of a length convenient to handle, usual-
ly about twelve feet. For sterilization, the pan is placed open-
side down over the seed bed and pressed down about four inches
into the soil. The steam is let into the pan for the required
time, after which the pan is removed to the next part of the
bed and the operation repeated.
Either of these steam sterilization methods requires a good
portable boiler capable of maintaining seventy-five pounds or
more pressure while the treatment is in progress. The pan
method is the less cumbersome and more generally used. In
each case the heating is considered sufficient when a potato
tuber placed in the soil is cooked.
After the soil is sterilized, special care should be taken not
to contaminate it again with the parasites. Seeds and tools are
Some Important Diseases of Truck Crops in Florida 19
the most common carriers of contamination and should be dis-
infected before using them.
Steam sterilization is more efficient by far than formalin
sterilization. It also kills insects and weeds. In Florida, where
one seldom finds a good boiler on a farm, steam sterilization is
not always practicable unless the growing of young plants is
conducted on a large scale or several growers will unite for the
purchase of a good boiler for this purpose. But because steam
sterilization is much more dependable and after all is much
cheaper than the formalin treatment, it is desirable that the
steam sterilization method should be employed whenever pos-
sible, in preference to the formalin method.
Sterilizing the seed-bed soil is especially important when
tomato, eggplant, cabbage, pepper, and perhaps, celery plants
are to be grown because these plants are subject to some very
destructive diseases which enter the plants from the seed-bed
soil. Sometimes entire fields are ruined on account of these
diseases, as has been observed in the case of tomato plants af-
fected by the wilt or blight and of the eggplant Phomopsis dis-
ease, the latter causing collar or foot rot, tipover, stem canker,
leaf spot, and fruit rot of the plant. Fields with some 5 to 20
percent of the plants affected with diseases are common in al-
most any part of the State where the plants are cultivated con-
Soil sterilization alone while important in itself, is, like
anything else, of no great value in the control of diseases unless
healthy seed and other means of protecting the soil and plants
against contamination with the germs of the parasites are used.
DISEASE RESISTANT VARIETIES.-It is a well-known fact
that in some cases different varieties of plants are affected dif-
ferently by certain diseases. A discussion of beans in regard
to their varying resistance to anthracnose is presented under
that disease name. Certain varieties of beans are resistant to
certain strains of the fungus causing bean anthracnose. Some
varieties of watermelons and of cotton are resistant to their
respective wilts; some varieties of cowpeas are resistant to the
root-knot; some cabbage varieties are resistant to the "yellows,"
etc. In this connection the points of special interest to the
grower are these:
1. In some instances it is nearly hopeless to search for a
variety resistant to certain diseases, in which case it would
Florida Cooperative Extension
probably be better for the grower to direct his attention toward
some other means of controlling the disease.
2. Invariably the resistance is to certain diseases only;
that is, an anthracnose-resistant variety of beans is not neces-
sarily, and usually is not, resistant to the blight.
3. As a rule, the resistance is only relative; that is, a
resistant variety is affected by the disease, but to a less extent
than some other variety.
4. The resistance is often local; the variety might prove
highly susceptible in another locality.
5. The resistance may also prove to be only temporary;
losing this property in course of time.
Points 3, 4 and 5 can probably be explained by the fact
that not only the host plants vary in their resistance to the
parasites, but the parasites themselves vary in their ability to
attack the plants.
6. It is often the case that resistant varieties are not fit
for cultivation, either because they are not accepted by the
market or because they have some inferior property.
7. Control of diseases by means of cultivating disease-re-
sistant varieties, if there are such varieties and they are ac-
ceptable to the market, is the cheapest and least troublesome
method. Therefore, watch the seed market and the literature on
this subject, also watch your own plants, especially in the case
of a severe attack by disease, and do not miss any opportunity
to obtain a disease-resistant variety.
DISEASES OF TRUCK CROPS AND THEIR CONTROL
Because of the purpose of this publication, only the diseases
of considerable consequence to the most important truck crops
grown in Florida are discussed here. The crops are named in
alphabetical order, without seeking to establish their relative
Other diseases are known to exist in the State, but because
of their secondary importance or because their attacks are con-
fined to relatively small areas, no discussion of them is given.
However, some of these diseases may prove of the greatest im-
portance under peculiar local conditions. If the symptoms show
that a disease not described in this bulletin is present, inquiry
should at once be directed to the College of Agriculture, Gaines-
ville. Such inquiry should always be accompanied by a liberal num-
ber of freshly collected and well wrapped specimens of the diseased
Some Important Diseases of Truck Crops in Florida 21
plants. The whole plants, including the roots, are usually neces-
sary for the proper diagnosis of the trouble.
Several bean diseases are of more or less general occurrence
in Florida. Some are of considerable importance and are de-
scribed here. Anthracnose seems, on the whole, to be the most
important one and, therefore, should receive greatest attention
from the growers, but the other diseases are not negligible.
Anthracnose and blight are both controlled chiefly or almost
entirely by using disease-free seed; powdery mildew may be
controlled by dusting with sulphur; root-knot is controlled by
either crop rotation or soil sterilization; proper cultural methods,
sanitation and local disinfection, are the methods of controlling
some other bean diseases, such as hollow stem and white
ANTHRACNOSE (RUST, SPOT, BLIGHT)
This disease, sometimes known as rust, spot, or blight, af-
fects all parts of the bean plant above ground. It is most no-
ticeable on the pods where it produces various sized spots (fig.
75). When well developed, the spots are often of a round or
oval shape with reddish margin. The spots are somewhat sunken,
dark brown to blackish in color, and on the older parts may be
found pinkish masses of spores of the fungus which causes the
The disease of the pod usually works its way thru the walls
and affects .the seed, causing yellowish to brown or black spots,
with the pinkish spores or without them, sunken or not, and of
great variation in size,-all depending on the extent of the de-
velopment of the disease.
On the leaves (fig. 76), the disease appears usually on the
under side where it affects only the veins, which turn black and
shrink. When young leaves are affected in this way they may
become slightly crinkled; on the larger veins and on the petioles
the spots sometimes resemble those on the pods.
On the cotyledons, the spots are similar to those on the seed,
the chief difference being that here the fungus is in an active,
The stems of young and well developed plants are also some-
times badly spotted with anthracnose. Here the spots vary
greatly in appearance. They are often of about the same type
as those on the pods, but they are usually narrow in form while
Florida Cooperative Extension
sometimes the spots appear as long streaks, brownish to blackish
Anthracnose causes its greatest damage by spotting the pods,
which renders them unmarketable. When very young plants are
FIG. 76.-Bean leaf, showing veins blackened by anthracnose.
(After H. H. Whetzel.)
attacked by the disease, they are often killed. The disease may
ruin an entire crop, and year after year it causes serious losses,
making profits from growing beans uncertain unless the growers
take the necessary steps to protect their crop against the
CAUSE AND DISSEMINATION.-The disease is caused by the
fungus Colletotrichum lindemuthianum. This fungus produces
Some Important Diseases of Truck Crops in Florida 23
great numbers of spores in the numerous minute pimple-like
bodies on the spots caused by the disease. The spores are sticky
and can be scattered readily only when moist. They are easily
carried by drops of rain water and dew running or dripping from
the infected parts of the plant or are carried from plant to plant
by men, animals and implements while cultivating and picking.
Introduction of the disease into the field is almost invariably
due to the use of diseased seed. When such seed germinates, the
disease develops on the infected cotyledons. Here the fungus will
soon begin to produce its numerous spores, by which the disease
In Florida, as well as in other states with a somewhat com-
parable climate during the time when the crop is grown, the
disease can be found during winter and spring in almost every
field. The extent of its injury varies with the condition of the
seed used for planting, weather conditions, especially during the
first half of the growing season, variety of the beans, and a few
other factors of minor importance. A badly affected field may be
observed side by side with one almost free from the trouble, or
one may have a field of beans nearly free from the disease one
year while the same variety of beans grown in the same way on
the same soil the next season might be badly affected.
VARIETAL RESISTANCE.-During recent years much careful
scientific work has been done in America by plant pathologists,
especially in New York and Louisiana, on resistance of different
varieties of beans to anthracnose. Their work developed this
While the anthracnose fungus collected from different lo-
calities and different varieties of beans appears to be the same, it
affects varieties of beans in different ways. Some strains seem
able to produce the disease on all varieties of beans while other
strains affect only certain varieties.
In spite of the fact that all varieties of beans seem to be
affected by some strains of the fungus, it may be worth while
for the grower to remember that certain varieties in certain lo-
calities will prove highly resistant to the fungus for a while.
Other varieties are readily susceptible to the fungus and their
planting is not to be encouraged. Plant only the most resistant
varieties if they are suitable for the particular market favored
and will prove profitable under the trucker's conditions for pro-
duction. Such varieties are not necessarily, and usually are not,
resistant to any other bean disease.
Florida Cooperative Extension
CONTROL.-Grow, if possible, a variety that is resistant to
Save seed for yourself from the pods that were perfectly
free from the disease. From the work of the Louisiana station
(La. Exp. Sta. Bul. 119) it appears that beans grown in Louisiana
during the continuous hot weather of summer or early fall will
not suffer from anthracnose. This should also be true under
Florida conditions. Such a crop should be grown and the seed
saved for the winter and spring plantings, or the clean pods may
be picked from any field and the beans thrashed and dried. In
order to keep the seed without loss of vitality, the following is
recommended (La. Exp. Sta. Bul. 139, p. 32) :
1. "Sun-dry the seed for about a week." Protect it while
drying by a glass frame or keep it under cover during rain.
2. "Fumigate the beans with carbon bisulphide." Place the
seed in an air-tight box and on the top of the seed place the re-
quired amount of carbon bisulphide-10 ounces for every hundred
cubic feet of space-in an open dish, then cover the box as tightly
as possible and seal all the cracks with putty. Leave the seed for
24 hours, then open the box and let the gas escape. When no
more of the gas is left, which can be determined by the absence
of its odor, the seed is ready for storing. Fumigation should be
made in a place where no animals are kept. Carbon bisulphide
is highly inflammable and no lighted pipes nor any other fire
should be brought near it. The purpose of this fumigation is to
kill the weevils.
3. "Store the beans in a tight, dry place. Examine them oc-
casionally for the weevils and if found, fumigate again."
Or, buy seed from a dependable dealer who will guarantee
them to be from pods not affected with anthracnose.
During the first period of the plant's growth avoid working
in the bean field when the plants are wet with rain or dew. By
working at such times the disease is easily spread over the whole
When there are indications that the young plants are affected
with the disease, spray once every other week or more often, de-
pending on the weather, with a 4-4-50 bordeaux mixture.
This disease affects bean leaves and pods. In either case the
spots are irregular in outline and water-soaked in appearance
when young. The leaf spots (fig. 77) in time spread over large
areas of the leaf, the affected parts dry up, the whole leaf may
Some Important Diseases of Tr:ck. Crops in Florida 25
become affected, and sometimes all leaves on a plant, are killed.
The spots on the pods (fig. 78) later become reddish in color
and sunken. As a rule they can readily be distinguished from
Spots by the ab-
sence of black
gins, and pink-
ish spore mass-
es. The disease
pod to the seed,
but usually does
not cause them
to rot altho,
the seed may
The blight is
caused by cer-
bacteria are in-
the field by
When the seed
plant to the sur-
FIG. 77.-Bean leaf, showing blight spots. (After H.
H. Whetzel.) face of the soil
the young leaves. From leaf to leaf and from plant to plant the
infection is carried by insects, possibly by the wind and other
means, to other plants. When the leaves are affected, the pods
will become affected; thru the pod walls the bacteria will work
their way to the seed and contaminate them also. On the seed,
26 Florida Cooperative Extension
the bacteria will live, tho dor-
mant, until planting time, when
they will begin work again.
The blight ranks next to an-
thracnose in importance. No bean
varieties seem to be immune to its
attack. The disease is common in
the fields where by killing parts
or all of the leaves and by spotting
the pods it nearly always causes
certain damage to the crops. When
infection is heavy and weather
conditions are favorable for its
development, which is not uncom-
mon, the damage caused by the
disease might amount to a nearly
total loss of the crop.
CONTROL.-Use only clean
seed, free from contamination
with the disease-producing bac-
teria. To be sure of this to some
degree, save the seed from select-
ed pods not showing spots. For
methods of taking care of the seed
thus obtained so that they will not
lose their vitality before planting,
see the suggestions given under
In addition to saving home-
grown seed free from the disease
it is recommended (La. Exp. Sta.*
Bul. 139, p. 32) to disinfect them
by soaking for 18 minutes just
before planting in either 1 to 50
benetol solution or 1 to 1000 solu-
tion of corrosive sublimate. After
the treatment, the seed should be
planted immediately. If they are
to be drilled with a planter, and Fbligh. -Bean p affected wthl.
therefore a preliminary drying be
necessary, do it by spreading the treated seed in a thin layer on a
canvas in a dry, breezy place where they will dry quickly. Allow
them to dry just enough to prevent their sticking in the planter.
Some Important Diseases of Truck Crops in Florida 27
HOLLOW STEM (STEM ROT, ROOT ROT, DAMPING OFF)
This disease, known also as stem rot, root rot, and damping
off, at first affects stems of the plants just at or below the surface
of the ground. Later, the infection spreads up and down the
stem. It produces a semi-soft, colorless to dark brown rot. The
affected plants, if young and succulent when attacked, soon tip
over and die; if older, they will remain erect and eventually either
die or wilt and lose vitality. In advanced stages of the disease the
stems are conspicuously hollow, giving rise to the name, "hollow
stem," by which it is commonly known among growers. If the
disease attacks well-developed plants an unimportant injury in
the form of brownish scars of various sizes is produced near
The cause of this disease is the same as that causing damping
off of plants in seed beds. The writer has had opportunity on
several occasions to determine the cause of the disease. In one
instance it was found to be Pythium debaryanum (?), while in a
few others it was Rhizoctonia solani. Both fungi, especially the
Rhizoctonia, are common causes of damping off. The disease is
spread by contaminated soil and infected seed.
Hollow stem has evidently been known for a long time tho
under some other name such as stem rot, root rot, and damping
off. It is of common occurrence and often causes considerable
damage by reducing the number of plants and their productivity.
Some fields have been practically ruined by it.
CONTROL.-Watch carefully for the disease and as soon as
a distinct, even if only slight, wilting or bending over of the
plants is observed, pull them out and destroy them. Drench the
ground to some distance around where the affected plants grew,
with a 1 percent solution of copper sulphate or with some other
Do not plant beans too close for the disease will have a good
chance thereby to spread from one plant to another. Use seed
from healthy pods, because it is a well-known fact that at least
one of the fungi producing this disease, the Rhizoctonia, can also
attack bean pods, producing a semi-soft, slightly brown rot of the
pod tip, and thru the pods invade the bean seed. These seeds
when planted will introduce the fungus into the field right where
it can cause much damage.
POWDERY MILDEW (RUST)
This disease affects bean leaves, pods and stems. In each
case it appears first in the form of minute brownish, cobweb-like
Florida Cooperative Extension'
spots affecting the tissue only superficially. These spots grad-
ually increase in size and, in time, cause considerable injury. On
somewhat old spots one can often plainly see a whitish, powdery
growth of the fungus Ery-
siphe polygoni, which
causes the disease; hence
the name, powdery mil-
dew. Affected pods fre-
Squently have a rusted ap-
pearance (fig. 79) and on
that account the disease is
known locally as "rust."
The disease is of long
m standing and is of common
occurrence on different va-
rieties of beans and on
many other plants. On
beans, it affects the leaves
causing them to die pre-
maturely and thus short-
ens the life and reduces the
productiveness of the
plant, but when beans are
grown for their pods its
worst damage is to the
pods which are rendered
unmarketable. In general,
the disease is not of a se-
there is a likelihood of the
presence or spread of the
disease, dust the plants
S- with sulphur flowers or
with a fine grade of sul-
FIG. 79.-Bean pods affected with powdery phur flour. Repeat the
mildew. dusting in about ten days
or two weeks if necessary.
Use as little of the sulphur as you can but take care that the dust
goes all over the plants. The addition of lime to sulphur increases
only the bulk of the material without increasing its effectiveness,
and in fact rather decreases it.
Some Important Diseases of Truck Crops in Florida 29
This disease affects plant roots on which it produces numer-
ous knots, galls or swellings (fig. 80) of various shapes and
sizes, from minute knots to those 1/4 inch or more in diameter.
The root-knot swellings can be readily distinguished from the
leguminous nodules which are common on bean roots and on roots
of other plants of the same fam-
ily, mainly by the fact that the
knots are swellings of the body
of the roots themselves and are
not detachable from them, while
the leguminous nodules are de-
veloped only superficially on the
roots, are easily detachable from
them and are not accompanied
by malformations of the roots
(fig. 81). Plants affected with
root-knot are more or less yel-
lowish, often wilted and stunted
in their growth. When the dis-
ease is severe, many plants will
Root-knot affects a great num-
ber of cultivated and wild plants.
All truck crops are subject to it
but there are several field crops,
such as corn and velvet beans,
that are free from attack. Plants
on heavy clay soils suffer little
from the disease. Lands that ------
St d L FIG. 80.-Bean roots affected with
are regularly under water each root-knot.
year for a month or longer are
free from root-knot nematodes. Light sandy soils are especially
favorable for its development.
CAUSE AND DISSEMINATION.-Root-knot is caused by the
activities of certain minute eel-worms or nematodes, Heterodera
radicicola, which are usually visible only under a microscope.
The nematodes feed on the roots, boring into them, and thus by
mechanical irritation, and possibly by the effect of certain sub-
stances produced by the nematodes, the roots are stimulated to
form the swellings. Parts of the roots affected sooner or later
decay, materially reducing and often entirely destroying the root
system of the plant.
Florida Cooperative Extension
From the hatching time of the nematodes to full maturity
and egg production requires about four weeks. In Florida, and
in other regions with a similar climate, probably from ten to
twelve generations are produced each year, and each female lays
more than 500 eggs. It is evident that the nematodes will in-
crease rapidly in number if conditions are favorable. The pres-
ence of live roots
of plants on which
the nematodes can
live, a proper com-
bination of airand
moisture and suf-
ficiently high tem-
perature are the
ments for the ne-
todes, before they
bore into plant
roots, can move
O thru the soil, but
tion by this meth-
od is almost neg-
ligible. They are
'N carried from one
place to another
mainly with par-
FIG. 81.-Bean roots, with nitrogen-fixing nodules
attached. Compare with figure 80. ticles of infested
soil clinging to the
feet of men and animals, to farm implements and to transplanted
plants. They are also carried with refuse containing infested
plant parts and by surface water running from a contaminated
soil. The root-knot organism is distributed from one locality to
another chiefly with diseased plants, bulbs, nursery stock and
CONTROL.-1. Keep the soil free from contamination with
the root-knot organism. A new field is free or nearly free from
the parasite. Any uninfested field can be kept in this condition
for a long time if these precautions are observed:
Some Important Diseases of Truck Crops in Florida 31
Before starting work in a field free from root-knot, see that
the cultivation implements, the feet of the working animals and
of the men are free from infested soil and, if practicable, are
well disinfected. In cultivating a valuable crop on high-priced
truck land this is often a profitable tho somewhat troublesome
thing to do.
Plant only such plants, trees and seeds as are entirely free
from contamination with root-knot.
Do not use any manure containing infested material, and
do not throw into the field garbage or any plant refuse contam-
inated with the nematodes.
2. When a soil becomes infested with the root-knot organ-
ism, free it from the parasite either by planting the land for at
least two years to some root-knot resistant crops such as barley,
beggarweed, corn, millet, peanuts, rye, sorghum, velvet beans,
winter oats, or most any of the grasses, or by flooding the soil
for about a month or more, or by soil sterilization. Planting
crops resistant to nematodes is the method used for starving
them out. Therefore, care must be taken that the land be kept
free from weeds as much as possible because many of them also
are susceptible to root-knot.
Flooding the land seems to be an efficient method for killing
the nematodes. The soil should be entirely under water for at
least 25 days, according to definite observations by reliable grow-
ers in Florida.
Soil sterilization means killing the parasites by treating the
soil either with a poisonous substance or with sufficient heat. The
two general methods commonly used, the formalin and steam
methods, are detailed earlier in this bulletin under soil sterilization.
The Cyanamid Method of Soil Sterilization.-J. R. Watson,
entomologist to the Florida Experiment Station, has been work-
ing for several years on the cyanamid treatment of soil to rid it
of nematodes. (Fla. Agr. Exp. Sta. Bulletin 136.) The
cyanamid which he employs is the one commonly used as a source
of ammonia (nitrogen) in many commercial fertilizers. At
present it costs about $75.00 a ton. A certain part of the cost of
the material should be considered as the cost of fertilizer needed
and used by the plants. Therefore that much of the treatment
is cheaper than other methods of disinfecting the soil with chem-
According to Watson, the cyanamid treatment when properly
given proved efficient in reducing the number of nematodes in
the soil to a practically negligible quantity. About two tons of
Florida Cooperative Extension
cyanamid per acre should be applied and the applications be
made in such way that the substance will be thoroly mixed with
the upper six or eight inches of the soil. It is recommended to
divide the quantity of cyanamid to be used into two equal parts
and to spread the first part broadcast over the unplowed ground
and plow it under. The remainder should then be spread in like
manner and the field immediately and thoroly disked. The suc-
cess of the treatment depends upon a heavy rainfall shortly after
the application of the cyanamid, or on a heavy irrigation of the
treated soil. Treat the soil about three months before planting
tomatoes, or one month before planting other crops, otherwise
the treatment may work injury to the plants.
Growers who are troubled with the root-knot should try the
cyanamid treatment on a small scale at first. This treatment is
probably not effective against damping off nor against other par-
asitic fungi present in the soil.
The first evidence of the presence of this disease is in the
appearance of large water-soaked, irregular spots on the stems
and leaves of the plants. These spots soon become covered with
an extensive white growth of the mold (fungus) Sclerotinia lib-
ertiana, which causes this disease.
Under favorable conditions the fungus grows quite rapidly
and causes a somewhat soft rot of all parts of the bean plant
above ground. Within a few days after the first appearance
of the mold there may be observed in and on the decaying parts
of the plant comparatively large oblong bodies, usually from 1/8 to
1/4 inch thick and from 1/8 to 3/% inch long, at first flesh colored
but soon turning black. After a period of cold weather and in
the presence of moisture these black bodies, if not buried too deep
in the soil, will give rise to small saucer-like mushrooms each of
which produces myriads of spores. When these spores mature
they are ejected into the air and, being extremely minute and
light, are carried by even the slightest breeze to some distance
from the place of their production.
When the spores fall on moist soil they soon germinate and
produce a rapidly-growing white mold capable of attacking beans
and many other cultivated or wild plants. After growing for a
short time the fungus will again produce the black bodies, thus
completing its life-cycle. Diseases produced by this fungus on
various plants differ somewhat in appearance and are frequently
known by different names. Its effect on young lettuce plants is
Some Important Diseases of Truck Crops in Florida 33
the production of damping off and on full-grown lettuce it results
in the so-called lettuce drop; when it attacks celery plants the re-
sult is celery foot rot. Its work is especially destructive to lettuce.
The fungus causing white mold is carried with plant rubbish.
with contaminated soil, and by the wind. It also spreads by
growing from plant to plant directly or by first growing on or
in the upper layer of the soil.
CONTROL.-White mold of beans is of importance only during
wet seasons when it frequently causes the plants to decay. At
such times watch the bean plants closely and as soon as the mold
is detected destroy all plants affected by it. Drench the soil where
the affected plant grew, and to some distance around it, with a
good disinfectant, such as 1 percent copper sulphate solution,
1:1000 solution of corrosive sublimate, 1:50 formalin, or ammo-
niacal copper carbonate of the strength recommended for spray-
ing. Then spray the field with 4-4-50 bordeaux mixture.
Several diseases of cabbage occur in Florida but the black
rot is of greatest importance. During some seasons the black
mold or black leaf spot
also causes considerable
damage to the crop.
Young plants in the seed
bed are quite generally
subject to damping off
and, frequently, to a se-
vere attack by the downy
FIG. 82.-Cross-section of cabbage leaf BLACK ROT
midrib showing blackened water-con- The first evidence of
ducting vessels due to black rot. En- isa a ack
large 3 times. this disease is a blacken-
larged 3 times.
ing of the veins on the
edges of the leaves. This blackening rapidly extends downward
thru the veins (fig. 82) to the stem and from there up and down
the plant, affecting its woody elements by which water and food
materials are distributed within the plants. Affected leaves turn
yellow and wilt, then dry up and fall off. (Fig. 83.) In time,
the entire plant will decay. Even if the attack is not sufficiently
severe to destroy the plant in the field, the growth of the disease
during transit and storage will finally ruin the cabbage before it
reaches the consumer.
Florida Cooperative Extension
The disease is caused by
-ertain bacteria Pseudo-
monas campestris, which
gain entrance into the
plant first thru the water
pores in the leaf. Early
in the morning one may
observe drops of water on
the leaf edges. These
drops are exuded from the
I water pores in which the
Sleaf veins terminate. The
gY bacteria get into these
drops and thru them enter
the leaf pores.
Contaminated soil, seed,
manure and plants are the
chief carriers of the bac-
teria causing this disease.
When once introduced into
a field the bacteria will re-
main in the soil for a long
time in a virulent state
ready to infect new crops
of cabbage, collards, tur-
nips, kale, kohlrabi, rape,
Brussels sprouts, rutaba-
gas and radishes.
Black rot frequently de-
stroys entire fields of cab-
bage and other related
plants. When the soil is
I infested with the parasite
profitable culture of these
Plants is either impossible
or uncertain. In many in-
FIG. 83.-Cabbage plant affected with stances the culture of cab-
bage is abandoned entirely.
CoNTROL.-Disinfect the seed by soaking for fifteen minutes
in corrosive sublimate (see seed disinfection).
A field affected with the disease should not be planted to
cabbage or any other plant of the cress family for several years.
Some Important Diseases of Truck Crops in Florida 35
Exact information as to the number of years necessary to free
the soil from the black-rot parasite is not available. Plant other
crops and keep the field free from weeds because many of them
are also subject to the trouble.
This disease spots the leaves. The spots are large (up to an
inch or more in diameter when old), circular, with concentric
rings, nearly black, and gradually shading into the healthy tissues.
The disease is caused by the fungus Alternaria brassicae. It
is not a new disease and occurs quite commonly on cabbage, col-
FIG. 84.-Cabbage downy mildew.
lards, cauliflower and some other related plants, causing consider-
CONTROL.-Spray with 4-4-50 bordeaux mixture to which
a sticker (see rosin-salsoda sticker) has been added. The disease
does not occur every season and therefore cabbage plants need
not be invariably sprayed against it. Spraying should be made
as soon as the black mold is detected on the plants and be re-
peated about two weeks later. If any of the trouble remains,
spray again about two weeks after the second spraying.
On a number of occasions this disease has been observed on
young cabbage plants in the seed bed. The affected leaves show
at first small, somewhat angular, pale yellow spots; soon the
leaves begin to curl up, shrink and dry. On the lower surface of
the affected leaves one can often observe a downy growth (fig. 84)
Florida Cooperative Extension
of the fungus Peronospora pasasitica which causes this disease.
Young plants are often severely injured by the trouble and entire
seed beds are sometimes ruined.
CONTROL.-Spray young plants frequently with 4-4-50 bor-
OTHER CABBAGE DISEASES
Other diseases affecting cabbage are: Damping off (see
under care of the seed bed) and root-knot (see under bean dis-
CANTALOUPE AND CUCUMBER DISEASES
Cucumbers and cantaloupes are subject to several diseases
of which the downy mildew or rust, as it is frequently called by
growers, is the most important one. This disease can be con-
trolled by spraying with a good fungicide such as a fresh home-
made bordeaux mixture. Root-knot is another disease very in-
jurious to these plants.
DOWNY MILDEW (RUST, BLIGHT, FIRE-BLIGHT)
This disease is known by different names, such as rust,
blight, fire-blight, and downy mildew. The first three are mis-
nomers being properly used for entirely different diseases from
the one discussed here. The name "downy mildew" should be
used because the disease is due to the fungus Peronoplasmopora
cubensis (B & C) Clint., belonging to the Downy Mildews.
The disease affects the leaves of cucumbers, cantaloupes,
squashes and some other related plants, on which it produces
characteristic spots most evident on the older leaves. The spots
are at first pale green or yellow and somewhat angular. When
the spots are older they turn pinkish-brown to brown and become
paper-dry. In time they increase in number and size until most
of the leaf is affected. On the under side of the spots one can
usually observe a faint violet to rusty violet powder which is
composed of numerous spores of the fungus causing this disease.
Downy mildew, or rather the spores of the fungus which
causes the disease, is disseminated chiefly by the wind. The
spores fall readily in great numbers from the spots produced by
the disease. Being minute in size and very light they are easily
carried by the wind, often to quite distant places. These spores,
if they fall on the moist surface of a cucumber leaf, germinate
and invade the leaf tissue. This will result in the production of
the spots on the underside of which the spores will soon form
Some Important Diseases of Truck Crops in Florida 37
again in great numbers. A slight breeze will carry these spores
from one part of the leaf to another, from leaf to leaf, and plant
to plant, soon infecting an entire field.
This disease affects cucumbers and other plants named above
at any season of the year and may at any time become very
destructive to the crops, especially to cucumbers. Squashes may
also suffer seriously from this trouble. During wet and cloudy
seasons the disease may ruin an entire crop of cucumbers, and
during even comparatively dry and bright seasons the disease is
almost always present in every field, causing more or less damage
to the crop by shortening the life of the plants. The affected
plants yield less fruit and of smaller size.
CONTROL.-The disease can be controlled by timely and thoro
spraying with a good fungicide. Spray first when the plants are
very young, that is when they form or begin to form the third
leaf. The spraying should be repeated once a week or once every
other week, depending on the weather conditions, rate of plant
growth, and on the seriousness of the disease. If the weather is
wet and cloudy, the growth of the plant rapid, and the disease is
gaining headway in the field, the plants should be sprayed often.
Spray thoroly so that every leaf will be covered with the spray.
While spraying, hold the nozzle in such manner that the underside
of the leaves also will be sprayed. A high pressure should be
maintained while spraying so that the mixture will be applied,
not in the form of coarse drops, but as a fine mist.
Do not stop spraying because the plants spread so much that
it is impossible to spray them without injuring some of the vines.
This is the important time to spray. If neglected, your plants
may be injured by the disease in a short time much more than by
the walking or riding over some of the vines while spraying.
Train the vines in such a way or have the rows so far apart that
the spraying can be continued. The last spraying should not be
more than one week before the last picking.
Bordeaux mixture 4-4-50 is recommended for spraying cu-
cumbers and cantaloupes to control the disease. Spray at such
time that the mixture when applied to the leaves will dry quickly.
Root-knot also attacks cucumbers and cantaloupes. A dis-
cussion of this trouble and remedies for it are given under bean
The most important diseases of cauliflower are the black rot,
Florida Cooperative Extension
black mold, damping off, and root-knot. The first two diseases
named are of the same nature and are controlled in the same way as
those described under cabbage diseases. For the control of damping
off see care of seed bed, and for root-knot see under bean diseases.
There are several diseases that cause more or less damage to
the celery crop in Florida. Of these the early blight, known also
FIG. 85.-Early blight of celery.
as rust, and the black heart are the most important. The first
one can be controlled by spraying with bordeaux mixture and
the second one by proper fertilization, irrigation and sanitary
EARLY BLIGHT (RUST)
This disease produces spreading ash-gray spots (fig. 85) on
the leaf blades and petioles; the affected parts soon dry and
shrink slightly. When weather conditions are favorable to the
Some Important Diseases of Truck Crops in Florida 39
disease nearly all the somewhat mature leaves of the plant will
become involved and be killed by it in a short time. Plants of an
entire field are often affected in this way and by their ash-gray,
scorched appearance can be seen readily.
The trouble is caused by the fungus Cercospora apii Fr. No
definite information as to how the disease is first introduced into
a locality is available. There is hardly any doubt, however, that
it is carried with plant rubbish and manures containing remnants
FIG. 86.-Late blight of celery.
of celery plants affected with the disease. It is also well known
that young plants in the seed bed are often attacked and, on
transplanting into the field, carry the disease there. It has been
observed that plants grown in a seed bed previously affected with
the trouble were all badly affected, while plants from the same
lot of seed but grown in a disease-free soil were all free from it.
Once the disease begins its work in the field, if the weather is
moist and warm, it will be spread rapidly over the field by rain
and wind; the wind easily carrying the minute light spores of
the fungus from one plant to another.
Florida Cooperative Extension
This blight is of old standing. It is almost invariably present
in the fields and causes great injury to the plants if proper control
measures have not been taken. The effect of the disease on the
plants is a great reduction in growth and an unattractive ap-
CONTRoL.-Plant the seed bed in a new or sterilized soil.
Do not use any manure containing
HL / remnants of diseased plants.
Spray celery plants in the seed bed
with 3-4-50 bordeaux mixture. Spray-
ing in the seed bed should begin when
the plants are well thru the ground,
and be repeated at least weekly. Give
the first spraying in the field as soon
as the plants begin to make a new
growth and repeat the spraying at in-
tervals of one or two weeks. Fre-
quency of spraying depends on weath-
er conditions and on the amount of the
disease present in the field. Spray
T more often if the weather is wet and
much of the disease is on the plants.
This disease affects the leaves and
petioles where it produces spots that
can be readily distinguished from those
of the early blight by the presence of
numerous minute black specks (fig. 86)
which are the fruiting bodies (pycni-
j dia) of the fungus Septoria petroselini
/ Desm. var. apii Br. & Cav., causing
FIG. 87.-Celery black heart. this disease. Besides producing a more
or less severe injury to the plants in
the field, the late blight continues its work in transit and storage,
causing the plants to rot.
CONTROL.-The disease can be controlled in the same way as
the early blight.
This disease produces somewhat soft, brown to black rot of
the bud and of the tender central leaves of celery plants. (Fig.
87.) Its cause is not yet clearly determined but there are strong
Some Important Diseases of Truck Crops in Florida 41
indications that it is at least greatly favored, if not caused, by
certain conditions of the plant's growth, due mainly to certain
fertilizers and soil conditions.
Certain bacteria, probably closely related to B. caratovorus,
are always associated with the rot and are evidently responsible
for the final rotting effect on the plant. These two factors, the
fertilization and care of the plants and the presence of the bac-
teria, should be kept in mind when efforts are made to control
How the disease first attacks the plants, which fertilizers
are most favorable to it, which ones are best to use to keep it
inacheck, and what other conditions are largely responsible for
the severity of the trouble, has been studied by R. Y. Winters,
formerly of the Florida Experiment Station. The results of his
work (Fla. Agr. Exp. Sta. Rep., 1908, pp. xcix-ciii) are briefly
His fertilizer experiments in the celery district of Sanford
showed that "to supply ammonia, dried blood and fish scrap
proved best. Plots on which nitrate of soda was used were usual-
ly uniformly affected by black heart. Plots upon which high-
grade sulphate of potash, low-grade and muriate were used, stood
in the order named. The plots on which kainit was used were
usually uniformly affected by black heart. Bone meal was found
to be the best source of phosphoric acid. The plots on which a
formula composed of bone meal, fish scrap, and high-grade sul-
phate of potash was used, gave best results."
In his laboratory studies of this trouble, he found that "a
bleaching of the tips and margins of the center leaves always
preceded the disease." From some experiments and field obser-
vations on the cause of this bleaching, he concludes that "an ad-
verse physical condition of the plants" caused bleaching and
therefore, indirectly at least, caused black heart. Among these
adverse conditions he mentions as important, too much or not
enough water in the soil, attack by early blight, either too heavy
or too light fertilization or poor mixing of fertilizers with the
soil, and attack by the foot rot. Over-irrigation is emphasized as
an especially frequent cause of the bleaching.
CONTROL.-From the preceding paragraph it is evident that
to control black heart one has first of all to give the plants the
best of care without overdoing it either in the way of fertiliza-
tion or irrigation. Especially, avoid over-irrigation. Avoid also
the use of nitrate of soda and kainit, applying instead fish scrap
and high-grade sulphate of potash correspondingly. For phos-
Florida Cooperative Extension
phoric acid, use bone meal. Then by properly spraying the plants
for blight and by adopting sanitary measures and proper crop
rotation for the foot rot, keep the field as free as possible from
Do not let any plants affected with the rot or any decaying
plant rubbish remain in the field, but destroy them immediately.
Plants affected with the rot even in the slightest degree
should not be sent to a distant market because they will not reach
it in good condition. Such plants should be used, if practicable,
for the home table or be disposed of on the local market for im-
This disease produces a semi-soft, colorless to slightly pink
or brown rot of the petioles, usually at the base and just under
or slightly above the surface of the ground. Quite often entire
plants are destroyed by the rot. It is common in celery fields but
as a rule is not as prevalent as the black heart. Foot rot is caused
by the same fungus that causes lettuce drop and white mold
CoNTRoL.-Control of this disease is rather difficult because
the fungus works from the soil where it can hardly be reached by
any fungicide. Methods of prevention and sanitation are the
chief measures against the disease. Examine the plants fre-
quently and pull out and immediately destroy all of the affected
plants and drench the spot and to some distance around it with
ammoniacal solution of copper carbonate of the concentration
recommended for spraying. Do not plant crops year after year
that are readily susceptible to this fungus, such as lettuce, celery,
beans and peas.
OTHER CELERY DISEASES
Other diseases affecting celery are: Damping off (see under
care of the seed bed) and root-knot (see under bean diseases).
Of the several diseases of eggplant occurring in Florida the
damage caused to the crop by the fungus Phomopsis vexans is the
greatest. This fungus produces leaf spots, stem cankers, fruit
rot, foot rot, fallover or tipover, and one form of damping off. Use
of seed and seed-bed soil free from this fungus, and setting the
plants in a field not infected with it are the chief measures for
its control. Some other diseases are also of importance.
Some Important Diseases of Truck Crops in Florida 43
PHOMOPSIS LEAF SPOT, FRUIT SPOT AND ROT, STEM CANKER,
DRY COLLAR OR FOOT ROT, TIPOVER, DAMPING OFF
On the leaves, this disease usually produces large, irregular,
gray to brown spots. These are covered with numerous minute,
dark specks which are fruiting bodies of the fungus causing the
disease. When the leaves
Share badly affected, they be-
S come torn and ragged in
On the fruit are produced
pale, sunken spots which in
time become covered wi h
Minute pimple-like struc-
tures, fruiting bodies of the
causal fungus. The fruit
spots gradually develop into
a dryish rot which often in-
volves the entire fruit.
On the stems are pro-
duced slightly sunken can-
kers of nearly normal color
or slightly brown areas (fig.
88). These are seldom ob-
served to be covered with
fruiting bodies of the fun-
gus and as a rule remain
On the main stem, the
disease is known as foot rot,
collar rot, or stem dry rot
and shows itself in the
form of a dry rot (fig. 89)
FIG. 88.--Phomopsis cankers on eggplant which can often be distin-
guished from healthy neigh-
boring parts only by a more or less noticeable sinking of the dis-
eased portion. The diseased areas, when old, often turn into a
very light rot of the stem "bark" which easily falls off, sometimes
leaving the woody part of the stem exposed. Quite commonly
new roots are produced just above the infected area and new buds
just below it. The woody elements of the stems often show a
Florida Cooperative Extension
Tissues affected by the fruit rot, stem canker, and foot rot
are white, or nearly so, and more or less dry.
As tipover, the disease affects stems of young plants near
the level of the ground in such way as to inhibit their normally
strong growth at that point (fig. 90). A stem affected in this
I L'I ESlHH'l
FIG. 89.-- homopsis foot rot of eggplant.
way is somewhat thinner at the region of attack than is the rest
of the stem. When such plants are transplanted into the field and
make a sufficiently heavy growth, the stems will break, "tipover,"
at the infected place. On cutting the stems that fall over in this
manner, one can hardly see any difference between the diseased
and the healthy tissues. Yet an extensive series of isolations
made by the writer from plants affected with tipover all resulted
in the production of pure cultures of the same fungus that causes-
the other troubles named.
Some Important Diseases of Truck Crops in Florida 45
On young eggplant seedlings, this fungus produces an effect
which resembles very much that of the common damping off. The
chief difference is that in the case of this damping off the trouble
is introduced with the seed and then with the affected plants into
the field. Therefore it will be necessary to use disease-free seed
in addition to the measures suggested for preventing the common
damping off. (See damping
off, under care of the seed
CAUSE AND DISSEMINA-
TION. The foregoing dis-
ease of eggplant stems,
leaves, fruit and seedlings
known by various names is
caused by the fungus Pho-
mopsis vexans (Sacc. &
Syd.) Harter. The common
type of the spores of this
fungus (pycnospores) are
produced in great abun-
dance on the diseased parts
of the plant, but because of
their sticky nature are prob-
ably not carried by the wind
to any great extent tho it is
possible for them to be
blown with drops of water
and particles of soil to some
History of the spread of
the disease and field obser-
vations also show that by
FIG. 90.-Eggplant stems affected with
its nature it is not readily tipover.
disseminated by the wind.
Moreover, these same field observations, the nature of the spores,
and the writer's isolations of the fungus from apparently healthy
seed obtained from a local seed house, show plainly that the dis-
ease is first introduced with contaminated seed, and that the seed,
thru the medium of infected young plants, is the chief carrier of
the disease from one locality to another. Contaminated manures
and soil probably also play some part in a gradual spread of the
Florida Cooperative Extension
Contaminated seed means infected seedlings. Many of the
seedlings when attacked by this fungus very early in their growth
are killed in a short time. The disease in this case has the ap-
pearance of common damping off. But some young eggplants
are only slightly affected; these plants might appear healthy and
be transplanted into the field. There some of them that had some-
what tender stems when infected will tip over, while others that
had somewhat hard and woody stems when attacked will continue
to grow, often for a long time, and even be able to produce some
fruits, but as a rule they also will be either killed or rendered
worthless by the foot rot.
The leaves and stems may be infected by the fungus in vari-
ous ways. It may be on the seed planted, or be carried to the
plant by insects, or the infection may come from contaminated
soil or from the hands in transplanting. In a new field where
eggplants were never grown before the plants are free from the
disease even if weather conditions are exceptionally favorable
for its development, but sooner or later the disease will appear,
maybe suddenly and in a severe form, due to the use of contam-
inated seed. Year after year the disease grows worse until egg-
plant culture becomes unprofitable.
It is evident that the disease-producing fungus remains
active in the soil from year to year, tho the results of actual ex-
periments to prove this are lacking. It is not known how long
the fungus will remain in a soil if eggplants are not cultivated
there. Judging from the fact that it does not attack any other
cultivated plants, it is reasonable to expect that it will not be
hard to free the soil from the fungus in a few years if the field
is planted to some other crops.
During rainy weather the disease is especially prominent on
the leaves, fruits and stems as damping off, but it is always
present in the form of foot rot and tipover.
This Phomopsis disease is the most important one attacking
eggplant and causes great loss to the growers. It kills seedlings
in the seed bed and reduces the stand in the field. It renders
some plants unproductive and on others it spots and rots the
fruit. Finally, the fields contaminated by the disease become en-
tirely unfit for the culture of eggplant.
CONTROL.-1. Use only disease-free seed. At present, the
only way to obtain such seed is to save it yourself from the fruits
that are known to be free from the fungus. The following pro-
cedure is suggested:
Some Important Diseases of Truck Crops in Florida 47
Pick out ripe, perfectly healthy fruits, preferably from a field
free from the disease and from heavily bearing and healthy plants
of the right variety. Bring the fruits into the house, break off
the calyx (the stem and leaf-like part), disinfect the fruits in
1:1000 corrosive sublimate solution for twenty minutes, and ex-
tract the seed in any convenient way, taking care that the seed
are not exposed to contamination by the disease. After the seed
are extracted they should be thoroly sun-dried for about a week
in a box with a glass top and a screen bottom, then put into a
jar or bottle, corked tightly and stored in a dry room.
When one must use seed from a seed house, the seed should
be soaked in 1:1000 corrosive sublimate solution for 10 minutes
and then rinsed at once in running water for about 15 minutes
and planted immediately. If a planter is to be used it will be
necessary to have the seed somewhat dry before planting them; in
which case after rinsing the seed spread them on a fine screen in
a thin layer and place it in an open breezy place for quick drying.
Dry just enough so that the seed will not stick to the planter.
To reduce their tendency to stick, clean starch can be added to
Treatment of the seed is desirable because it considerably
reduces the contamination by fungus, yet, as it has been found by
the writer, some of the contamination now and then escapes this
2. Make the seed bed on a soil where no eggplants were
previously grown or on a soil sterilized with steam or for-
3. Do not set eggplants into a field where eggplants were
grown within the last few years, especially if the disease was
present. Do not use just anybody's plants for transplanting
unless you are sure they are free from disease. It is better to
grow your own plants.
Another disease of importance is the bacterial blight. The
blight attacks tomato, tobacco, Irish potato, pepper, and several
wild plants also. In Florida it is of greater importance on toma-
toes and, therefore, is discussed under tomato diseases.
OTHER EGGPLANT DISEASES
Other diseases affecting eggplant are: Root-knot (see under
bean diseases) and damping off (see under care of the seed bed).
Florida Cooperative Extension
There are two very important diseases of lettuce in Flor-
ida-the drop and the black rot. A very important bacterial dis-
ease of lettuce has recently been reported from South Carolina
by Nellie A. Brown (Phytoph. 7:63, 1917). This disease causes
blue-green rot of lettuce stems and, as yet, has not been observed
in this State. For fear of its introduction all precautions must be
taken to avoid buying seed from suspected districts.
Lettuce drop and black rot are both hard to control, yet they
can be kept in check to a great extent if proper measures are
taken against them. These measures are, the use of healthy
plants only, good field sanitation, disinfection, and crop rotation.
This disease is first evident by a soft, colorless rot of the
leaves next to the ground; in a short time the rot penetrates the
stem and then the whole plant collapses, or drops. The disease
usually starts in a few isolated spots in the field. From these
spots it gradually spreads from one plant to another, and, if the
weather is moist, with great rapidity.
The disease is caused by the same fungus which causes white
mold of beans, foot rot of celery and other plants, and is dis-
seminated in the same way.
Lettuce drop is a disease of old standing and is almost always
present in Florida lettuce fields but it becomes disastrous only
after a period of prolonged cold, moist weather. During seasons
favorable for its development, the entire crop may be lost.
CONTROL.-Avoid a too close planting in the field.
Watch your plants for the first appearance of the disease
and immediately destroy every plant affected by it. Do the same
with all other plants subject to diseases caused by this same
fungus. Try to get the whole community to observe like precau-
tions. In this way much of the source of infection will be de-
stroyed not only for this season but chiefly for the next season.
Whenever practicable drench diseased spots and to some distance
around them with a good disinfectant, such as 1:1000 copper sul-
phate solution, or 1:1000 corrosive sublimate solution, or ammo-
niacal copper carbonate. Do not leave any decaying plants lying
in the field; destroy all such rubbish or plow them under deeply.
For transplanting into the field, use only plants that came
from a seed bed free from damping off. Some damping off is
Sime Important Diseases of Truck Crops in Florida 49
caused by the lettuce-drop fungus, and plants from an infected
seed bed may carry the disease with them.
Employ to as great an extent as possible a crop rotation that
will include some other crops that are free or nearly free from
attack by this fungus. Irish potatoes, tomatoes, eggplant, and
a few other important truck crops can be used in such a rotation.
This disease affects lettuce in the seed bed and in the field.
It appears at first in the form of small black or brown spots on
the leaves. These spots are sometimes nearly round, and some-
times in the form of irregular patches. They occur most often
on the edges of the leaf but can also be found anywhere on the
leaf blade or the midrib and at the base of the leaf. When there
is enough moisture and the weather is comparatively warm, the
spots will soon increase in size until either the whole leaf turns
black and drops off, as is the case when a young seedling is at-
tacked, or, in case the disease begins to work inside the lettuce
head, until typical black rot is produced. The final effect of the
disease on lettuce, a soft dark brownish rot of the head, is seldom
observed in the field where it is usually evident only by the above
described black or brown spotting of some of the leaves or by
blackening of leaf tips, sometimes deep within the head. But
when the plants are affected with this trouble the rot quite often
develops in transit.
CAUSE AND DISSEMINATION.-This disease was reported for
the first time, in 1908, by H. S. Fawcett, former pathologist of
the Florida Experiment Station (Fla. Agr. Exp. Sta. Rep., 1908).
His work and the work of O. F. Burger, former assistant plant
pathologist of the same station (Fla. Agr. Exp. Sta. Rep., 1912,
and press bul. 200), show that the disease is infectious and is due
to certain bacteria, Pseudomonas sp. During the last three sea-
sons the disease has been generally observed in the main lettuce
growing regions of the state and in a number of fields.
In the seed bed where plants are close to each other, the
bacteria causing this rot are readily carried from plant to plant
by insects, rain and irrigation water, and probably by other
means. The same takes place to some extent also in the field; but
the chief source of the trouble in the field is evidently from young
plants which were infected with the disease while in the seed bed.
Such infection may be slight or on account of dry weather may
not show itself to any considerable extent, and thus when the
young plants are transplanted they may appear healthy. Never-
Florida Cooperative Extension
theless, some living bacteria will be present and will start work
as soon as the conditions become favorable for their development.
Growers know that any lettuce head, even when only slightly
affected with the black rot, will be lost before it reaches the mar-
ket, therefore, it is a common practice to pull out affected plants
and throw them away, as a rule among other lettuce plants, thus
leaving in the field an ever present source of infection. Such
discarded plants should be destroyed.
No exact data on the amount of damage caused to the crop
year after year by the disease are available. It has been observed
during some seasons that whole seed beds and fields are ruined
by the rot. Even during some seasons somewhat unfavorable for
the disease it causes considerable damage. Therefore it is evi-
dent that the disease is important and that great care should be
taken to control it.
CONTROL.-Keep the plants in the seed bed as dry as is con-
sistent with their best growth, do not water them too often and,
if they are grown under canvas, keep them uncovered during
cloudy days and warm nights. If the seed bed shows any signs
of the disease, do not use any of the plants from it.
In the field, watch constantly for the disease and as soon as
any plants affected with it are detected, pull them out and destroy
them, either by burning or by dumping them into a hole in the
ground and pouring over them a sufficient amount of good disin-
fectant, such as 1:1000 corrosive sublimate solution, 1:100 copper
sulphate solution, or 1:200 formalin solution, or the diseased
plants may be covered with lime. Keep the field free of vegetable
In case a slight infection is observed on nearly or quite mar-
ketable plants, use them for immediate consumption at home or
on local markets; because the disease, as almost all other plant
diseases, is not injurious to man. The shipping of such plants
should be avoided.
OTHER LETTUCE DISEASES
Other diseases affecting lettuce are: Damping off (see care
of the seed bed) and root-knot (see under bean diseases).
Root-knot and powdery mildew are the most important dis-
eases of English or garden peas in Florida. Both of these dis-
eases are described fully under bean diseases. During a wet
Some Important Diseases of Truck Crops in Florida 51
season peas are seriously damaged also by the white mold (see
under bean diseases).
Peppers in Florida are often seriously damaged by the Cer-
cospora leaf spot and by the root-knot. Sometimes they are also
FIG. 91.-Cercospora spots on pepper leaves.
severely injured by fruit rot and by bacterial blight, which is
probably the same as the bacterial blight of tomatoes and other
CERCOSPORA LEAF SPOT (RUST, LEAF DROP)
This disease is also known as rust and leaf drop. It affects
the leaves most commonly but sometimes it affects also the leaf
petioles, stems, and fruit pedicels. It produces circular to oblong
spots (fig. 91) of gray-brown to brown in color. The spots are
usually surrounded by a dark to nearly black margin and often
have a pale halo surrounding them. They have a light gray to
Florida Cooperative Extension
nearly white center and are usually slightly bulged. When the
spots are numerous the affected leaves wilt slightly and fall. In
case of a severe attack, the plants may be entirely defoliated.
This leaf spot is caused by the fungus Cercospora capcici
Heald & Wolf, which is perhaps easily disseminated by the wind
and rain. Its sudden appearance in new localities in which pep-
pers free from the trouble were grown before, indicates that it
is probably introduced with either contaminated seed or diseased
young plants. The gradual increase of the trouble in a field in-
dicates that the disease can remain in the field from one season
to another on diseased remains of old plants.
The disease is common in Florida and can be found in nearly
all sections where peppers have been grown for several years.
So far as known, it does not attack any other truck crop here.
If not controlled, the disease quite often ruins the entire crop.
In less severe cases it causes only a reduction of the healthy
foliage which leads to less fruit and of poorer quality.
CONTROL.-Disinfect the seed. Do this in the same way as
recommended for eggplant seed disinfection.
Plant your seed bed in a new soil and, if possible, in an iso-
lated spot in the woods. If a new soil is not available, sterilize it.
Watch the field for the disease and, if practicable, pick and
destroy every leaf affected with the disease.
Spray young plants in the seed bed and in the field with
4-4-50 bordeaux mixture. Begin spraying in the seed bed when
the plants have two or three fully developed leaves and repeat it
once each week. In the field, begin to spray as soon as the plants
produce a new growth and repeat the spraying weekly or bi-
weekly. Spray more often if the weather is wet and the disease
is present. Spray thoroly with a fresh, well-made mixture.
FRUIT SOFT ROT
This disease produces a soft rot of pepper fruit, somewhat
watery in appearance. It spreads so rapidly that an entire fruit
may rot within three or four days after the first appearance of
The rot is caused by certain bacteria which by their behavior
and appearance in cultures and by their ability to produce soft
rot of many vegetables, such as tomatoes, carrots, turnips, etc.,
is probably Bacillus carotovorus Jones, the common cause of soft
rot of various vegetables. The bacteria causing soft rot of pep-
per fruit in all inoculation experiments made by the writer were
Some Important Diseases of Truck Crops in Florida 53
able to produce rot only when the epidermis (skin) of the fruit
was injured in some way. Uninjured fruit remained healthy for
ten days or more after it was placed in a water inoculated with
the bacteria. Under the same conditions, a fruit with the epi-
dermis pierced or cut entirely decayed in less than six days.
The bacteria are probably disseminated chiefly with con-
taminated water, manures and by insects. Insects are also re-
sponsible for wounding the fruit, thus giving the bacteria a
chance to invade it and cause the rot.
The first specimens of this rot were received by H. E. Ste-
vens, plant pathologist of the Florida Experiment Station, in the
summer of 1915. Since then the disease was often observed
by the writer in the neighborhood of Gainesville and elsewhere
in the state. Besides attacking bell peppers, it was found in 1915
on a number of different varieties of small peppers grown in a
plot on the Experiment Station grounds. On several occasions
the rot destroyed from a few to twenty percent of the fruit in the
field. In general, the trouble is of importance only in some iso-
CONTROL.-Watch the field for the rot and immediately de-
stroy every fruit affected with it. In this way the source of
infection will be materially reduced.
Keep in check all insects working on the plants, especially
the aphids, because they are responsible for introducing the bac-
teria into the fruit.
OTHER PEPPER DISEASES
Other diseases affecting peppers are: Root-knot (see under
bean diseases), bacterial blight (see under tomato diseases), and
damping off (see under care of the seed bed).
POTATO DISEASES *
A number of important diseases of Irish potatoes occur in
Florida. The State has no monopoly on them for all may be found
outside the State, from whence they were introduced into Florida.
This process of disease introduction is still going on and the
growers must carefully guard against further introductions.
Most of the diseases are carried with the seed potatoes, therefore
growers should be careful in buying seed because certain of the
diseases under favorable conditions are able to ruin an entire
crop. Any of them will materially reduce the grower's profit. If
disease-free seed is used such losses may be greatly reduced or
Irish or white potatoes-not sweet potatoes.
Florida Cooperative Extension
The following named Irish-potato diseases can be carried
with the seed: Mosaic, blackleg and rot, black scurf, common
scab, dry rot and wilt, bacterial blight, and late blight and rot.
With the exception of the late blight and rot none of these diseases
can be controlled by spraying.
It should be remembered that only in extreme cases can the
presence of these diseases be detected on the seed even by an
expert. The only sure way to obtain seed free from disease is to
get them from fields that were not infected. This condition
should be guaranteed by the seed dealer or certified by some de-
pendable agent who personally inspected the fields. Seed can
hardly be guaranteed free from certain of the diseases, such as
common scab and black scurf, because they are present almost
everywhere in the country tho in some places they are only
slightly developed. As the parasites causing these two diseases
are carried on the very surface of the tubers, they can easily be
rendered harmless by disinfection.
Of the diseases of Irish potatoes in Florida, late blight is the
most important. Next in order are bacterial wilt, Fusarial wilt,
and the scab. Others mentioned here are also of more or less im-
This disease attacks the leaves, stems and tubers of the po-
tato plant. On the leaves, it produces spots usually near the
margin or tip, or at the midrib, probably because rain or dew re-
mains longest on these parts. The spots (fig. 92) are at first
water-soaked in appearance, later, if the weather is dry, they
shrivel somewhat and turn brown, or, if the weather is moist,
turn black and become soft. Just outside of the affected part
one can usually see a lighter green band. If the weather is moist,
the fungus Phytophthora infestans (Mont.) DeBy, which causes
this disease, will produce on the lower side of the leaves and just
inside the margin of the spots a downy growth composed of the
spore stalks and numerous spores borne on the tips of the stalk
branches. If the weather continues moist, the spots will rapidly
increase in size and rot the entire leaf, sometimes in a day's time.
An entire field may be thus ruined in a few days.
Affected stems turn black and in time are killed. Here again
the downy growth of the fungus is produced. A field with the
blight has a characteristically offensive odor. On the tubers, the
disease produces a reddish-brown rot. When the tubers are dry
the rot will be dry, and will appear on the surface in the form of
Some Important Diseases of Truck Crops in Florida 55
FIG. 92.-Potato leaf affected with late blight.
Florida Cooperative Extension
slightly depressed areas. (Fig. 93.) But, if infected tubers are
left in a wet soil or in a damp storeroom, they often become af-
fected with a soft rot.
DISSEMINATION.-The disease is introduced into a locality
with diseased seed. Such seed will usually produce a slow growth
resulting in inferior tops, often only sprouts barely above the
ground, and these will be affected with the disease. If the
weather is moist the diseased plants will produce some spores of
,'1G. 93.-Potato tuber affected with late-blight dry rot. (After H. H.
the fungus which causes the disease. The spores fall and are
readily carried by the wind and with drops of water to other
leaves of the same plant and to neighboring plants and fields.
When the spores fall on potato leaves or stems, if there is suffi-
cient moisture, they soon germinate and grow into the plant
tissues rapidly killing the plants and producing new masses of
About five days are required from the time a potato leaf is
infected for the appearance of blight spots bearing a new crop of
spores. These are again scattered and thus the process is re-
peated until an entire field becomes thoroly infected. Yet, to the
grower, the field may appear comparatively healthy at this period
Some Important Diseases of Truck Crops in Florida 57
with only now and then some of the lower leaves showing any
effect of the blight, because the greatest part of the young infec-
tions has not developed. If the weather continues moist, in five-
days' or a week's time the whole field may suddenly become
blighted as if swept by fire.
The disease is called late blight because its noticeable out-
breaks occur only late in the growing season. As a rule, the
blight does not occur before the plants bloom and, on account of
the very early digging time in Florida, it begins to show up short-
ly before harvest time. But the disease is present in the field
some time before it can be generally observed by the grower. In
fact, it takes about a month's time for the disease to establish
itself in the field after its first appearance. Keeping this fact in
mind, we may conclude that knowledge of the weather conditions
during the month prior to harvest is essential to forecast success-
fully an epidemic of late blight1. In other words, if the weather
is continually moist during the month preceding the usual time
for a late-blight outbreak, we should reasonably expect a severe
outbreak of the disease. This must be kept in mind when plan-
ning to control the disease. Records at the Florida Experiment
Station show that during the last twelve years the disease has
often been serious, reducing the yield by 20 to 50 percent.
VARIETAL RESISTANCE.-Experimental data show that dif-
ferent varieties of potatoes show a marked difference with regard
to susceptibility to late blight. It was shown (Vt. Exp. Sta. Bul.
168, pp. 69-94) that in general, American varieties are very
susceptible to the disease but a number of English and German
varieties are resistant to it. Unfortunately, the varieties that so
far have been found resistant are not acceptable to American
markets. The work may yet lead to the desired end-the pro-
duction of a variety resistant to the disease and also acceptable to
CoNTRoL.-Use only seed from potato fields that were not
affected by late blight. The seed should be certified to that effect.
In any case, the seed should be perfectly free from any kind of
rot. Every tuber which on cutting shows any discoloration
must be discarded.
If an entire potato-growing district would follow this sug-
gestion strictly, we have every reason to believe there would be
no late blight in that district, and no other measures would need
1The idea was clearly presented by G. H. Coons, at a meeting of the
American Phytopathological Society, New York, Dec., 1916.
Florida Cooperative Extension
be taken against this trouble no matter how favorable the weather
conditions for the development of the disease might be. This
would be an ideal way to control the disease. At present, on ac-
count of a lack of community cooperation for plant disease con-
trol, this method cannot be considered for immediate application,
and potato growers must resort to individual effort to control
the trouble. In any case, the matter of planting clean, healthy
seed must be observed. Under the present conditions, the chief
method of fighting late blight is by spraying.
Spray the plants with 4-4-50 bordeaux mixture. The first
spraying should be made when the plants are from four to six
inches high, and it should be repeated every week if the weather
is favorable to the disease-continuously rainy and cloudy; but if
the weather is comparatively dry and clear, spraying once every
other week will be sufficient. Spray thoroly and with a pump that
maintains high pressure so that the spray mixture will be applied
in the form of a fine mist.
Besides the fact that spraying the potato crop year after
year insures safety to the crop against late blight there is no
question but that the spraying pays, even if there would be no
general occurrence of the disease otherwise. This is due mainly
to two reasons; first, there are some other diseases of potatoes,
such as the early blight, that will be kept in check by it, and sec-
ond, the effect of the bordeaux mixture on the plants will be di-
If for some reason a grower is unwilling to spray his po-
tatoes regularly each year, he should remember that an outbreak
of the disease is likely to occur if the weather is generally cloudy
and wet during the month preceding harvest time, and spray his
crop at least during such seasons.
Plants affected with this disease usually begin to show the
first symptoms about the time of blooming. The disease causes a
wilting, or rather a drooping, of tender parts of the plants. Such
wilt may affect only a single leaf or branch or it may affect an
entire plant; it may or may not be preceded by a yellowing of the
diseased plants. Plants affected with the blight die in a short
time; brown rot of the tubers and stems accompanies later stages
of the disease. If the disease attacks comparatively young plants
they will die before any full-size tubers are produced; if more
nearly mature plants are attacked, they will produce a more or
Some Important Diseases of Truck Crops in Florida 59
less normal yield of tubers which will, as a rule, be affected with
an internal brown rot.
The disease can be easily recognized on examination of the
affected stems, leaf petioles and tubers; if cut thru, they will show
a distinct browning of the water-conducting vessels which in a
healthy plant remain white. A few minutes after the cut is
made dirty white drops of moisture will ooze from the discolored
vessels (fig. 94). This oozing substance is composed entirely of
FIG. 94.-Cross-sections of young potato tubers affected
with bacterial blight, showing oozing of bacteria.
the bacteria Bacillus solanacearum E. F. Sm. which causes the
These bacteria produce a similar disease of tomatoes and
other important truck crops and information relative to it can
be found under tomato bacterial blight.
CONTROL.-Destroy every affected plant as soon as the dis-
ease is detected.
Spray the field with a contact insecticide, such as "Black
Leaf 40" 1:1000, and with a stomach poison, such as arsenate of
lead (1 pound of dry arsenate or 2 pounds of the paste to 50
gallons of water), to keep in check as much as possible all insects
working on the plants.
Practice a crop rotation in which plants of the family to
which potatoes belong will not be grown more than once in at
least four years.
This disease which causes considerable damage to the potato
crop in some parts of the State, is similar to bacterial blight es-
pecially in its effect on the plant. The parasite causing this dis-
ease, the fungus Fusarium oxysporum Schlecht., invades the
water-conducting vessels, cutting off the water supply and there-
by causing the plants to wilt. A gradual wilting of the plant with
Florida Cooperative Extension
a more or less noticeable yellowing of the lower leaves and dis-
coloration of the fibrouascular bundles (water-conducting vessels)
is characteristic of the disease. No brown rot of the stems and
tubers is present.
Potato plants slightly affected with the disease may produce
some tubers which as a rule will also be invaded by the fungus
causing the wilt. If a tuber is cut thru near the stem end one
can see a ring of the vessels. In a healthy tuber these vessels
will be nearly white, while the vessels in a tuber invaded either
by the wilt fungus or by the blight bacteria will be darkened. No
exudation of bacterial masses results from the cut vessels when
they are invaded by the wilt fungus. A microscopic examination
shows whether the vessels are affected with bacterial blight or
with fungus wilt.
The fungus causing the wilt is disseminated mainly with in-
fected seed and contaminated soil. It evidently remains active in
the soil for awhile and therefore the trouble grows worse from
year to year if proper crop rotation is not practiced. Apparently,
it does not attack any other important truck crop, tho tomatoes
are seriously damaged by a fungus which is closely related to it
and which produces a disease of tomatoes nearly the same as the
wilt of potatoes. (See Fusarial wilt under tomato diseases.)
CONTROL.-Use only healthy seed. It is a good practice to
cut off a small piece of each seed tuber at the stem end to see if
there is any discoloration of the fibrous ring. No tuber showing
discoloration should be used for seed purposes. A field showing
any of the wilt should not be planted to potatoes again for at least
This disease produces more or less roundish, brown spots on
the leaves, somewhat marked with concentric rings. The spots
(fig. 95) gradually increase in size and, if the weather is favor-
able, in number until the entire leaf becomes involved. A badly
affected leaf shrivels and dies. A field severely affected appears
as if scorched by intense heat or as if the plants were badly in-
jured by dry weather.
The disease is caused by the fungus Macrosporium solani
E. & M. Spores of this fungus are scattered by the wind, rain or
overhead irrigation from one leaf to another. The disease is not
a new one and occurs practically everywhere potatoes are grown.
It also affects tomatoes on which it produces a disease having the
same appearance and effect as the early blight of potatoes.
Some Important Diseases of Truck Crops in Florida 61
Altho the effect of this disease is commonly not striking and
usually appears as a mere spotting of the leaves, it is, neverthe-
less, quite an important disease. It reduces the healthy foliage
FIG. 95.-Potato leaf spotted with early blight.
and thereby reduces the yield and it shortens the plant life, which
leads to the same end. Rarely can a field be found entirely free
from this disease which almost invariably causes some damage to
the crop. The amount of damage varies with the season but not
infrequently it amounts to twenty percent of the total yield.
CONTROL.-Spraying with a good fungicide, such as bor-
Florida Cooperative Extension
deaux mixture, is so far the only method known for controlling
this trouble. Spraying should be done in the same way as recom-
mended for the late blight.
This disease which is common thruout all potato-growing
regions, is known mainly by its effect on the tubers where scabby
spots are produced on the surface. These spots (fig. 96) vary
from small roughened areas to deep pits and irregular channels
with a rough, corky lining. There may be only a few spots or
there may be so many that the
whole tuber surface is covered
With them. Badly scabbed tubers
are rendered unmarketable but
their cooking qualities do not
seem to be affected.
The scab also affects beets and
some other plants. It is caused
by certain bacteria, Actinomyces
chromogenus Gasp., which live
in the soil for an indefinitely
long time with no apparent need
for the presence of any living
S^ plants to sustain it. This means
that once the bacteria are intro-
FIG. 96.-Common scab of potato, duced into the soil they will stay
there for a long time and be
ready to affect a new crop of potatoes or beets. It also means
that no crop rotation will help rid the soil of the disease.
The disease is disseminated chiefly with diseased seed and
with particles of contaminated soil adhering to seed tubers.
EFFECT OF SOIL AND FERTILIZERS.-The severity of attacks
varies with the soil and its treatment, all evidence pointing to the
reaction of the soil as the chief factor influencing the development
of the disease. An acid soil seems to check it, while an alkaline
soil aids development of the trouble. Therefore, fertilizers such
as lime which increase the alkalinity of the soil greatly favor scab
development, while sulphate of ammonia, acid phosphate and
the like have a more or less checking effect on it.
Some Important Diseases of Truck Crops in Florida 6Z
seed treated against the
scab. A field badly af-
fected with the scab
should not be replanted
to potatoes, beets and
other root crops sus-
ceptible to the disease.
When a field is slightly
affected, work the soil and
FIG. 97.-Black scab of potato. (U. S. fertilize it in such way as
Dept. of Agr., Farmers' Bulletin 544.)
to increase its acidity.
Alkaline fertilizers, such as lime and ashes, should not be used.
BLACK SCAB (LITTLE POTATO, SPROUT BLIGHT)
This disease, which is of general occurrence wherever pota-
toes are grown, affects
parts of the plant near
the ground or below its
surface. When the fun-
gus Rhizoctonida solani
Kuhn, which causes this
trouble, produces dark
brown to black specks
on the tubers (fig. 97)
it is commonly known
as black scab. When by
its injury to the plant
stem it stimulates the
production of small tu-
bers above the ground '
(fig. 98), it is called lit-
tle potato. If the fun-
gus injures or kills
young potato plants
pushing thru the soil,
we then have the sprout
or stem blight (fig. 99).
It is here that the dis-
ease is of greatest im-
portance because it re-
FIG. 98.-Little potato, caused by Rhizoctonia.
duces the stand and con- (U. S. Dept. of Agr., Bulletin 64.)
Florida Cooperative Extension
sequently the yield from the field. This same fungus is the one
most commonly responsible for damping off in seed beds in
Florida and is also the common cause of the bean hollow stem.
CONTROL.-Treat the seed with corrosive sublimate solution.
When a field has been badly affected by the disease, it should not
be replanted to potatoes or any other crop readily susceptible to
attack by the fungus
/causing this trouble.
with this disease
first appear un-
thrifty and under-
sized, with a some-
S what compact in-
d stead of spreading
top and often with
the young leaves
curled up; in time the
Slaves turn yellow
and the plant grad-
ually dies. Under
favorable for a rap-
id development of
the disease, the plant
may collapse in a
short time without
signs of attack.
When an affected
FIG. o.-rotato stem blight, due to the Rhizoc-
tonia. (U. S. Dept. of Agr., Bulletin 64.) plant is pulled up it
will show an inky-
black discoloration of the stem from its base up (fig. 100), some-
times one to three inches above the ground. Under conditions of
moist and cloudy weather, the disease may rapidly move up the
stem and quickly destroy it. Almost without exception the diseased
plants occur in the field singly rather than in patches and thus the
disease presents no appearance of a rapid spread from one plant to
another. Seed pieces from which the affected plants have grown
This discussion is based on Dr. W. J. Morse's studies upon the blackleg
disease of the potato; Jour. Agr. Res. 8:79-126, 1917.
Some Important Diseases of Truck Crops in Florida 65
either show a soft rot,
or have been entirely
This disease is caused
by certain bacteria the
name of which is yet
which is probably Ba-
cillus athrosepticus "
Van Hall. Its first ap-
pearance in Florida is
not definitely known
but the writer observed
it in 1916 and 1917 in
districts of the State.
The bacteria are car-
ried with the seed; any
injured or decaying
seed is likely to be con- 1
taminated with viru-
lent bacteria of black-
nated seed when plant-
ed will produce plants
affected with the dis-
ease. In the North, the
bacteria evidently do
not remain virulent in
the soil or in tubers
left in the ground, from
one season to another.
Whether the same is
true in the South is as
yet an open question.
CONTROL.-Seed tu- k 1G. 100.-Blackleg of potato.
bers should be sorted
out before and while cutting and all tubers showing wounds,
cracks or discolorations and decay of any kind be rejected.
The seed should be disinfected.
It is very desirable that seed be purchased from a field cer-
tified to be free from the disease or in which all diseased plants
Florida Cooperative Extension
and tubers produced by them were destroyed as soon as the
symptoms of the disease were observed.
Plants affected with this disease, the cause of which is not
known, have spotted or mottled leaves portions of which are light
I'IG. 101.-Potato plant, Eureka variety, affected with
mosaic. ( U. S. Dept. of Agr., Bulletin 64.)
green in color; the light areas varying from comparatively large
plainly marked spots to very small spots with indefinite margins.
In later stages of the disease (fig. 101) brown, dead areas may
appear in the center of the diseased parts, the foliage be irregular
or wrinkled, and the plants as a rule may be smaller than healthy
The disease is evidently carried with the seed. It may affect
any number of plants in the field, some Florida fields showing
The discussion of this disease is presented here on the basis of W. A.
Orton's description of it; U. S. Dept. Agr. Bul. 64:42-43, 1914.
Some Important Diseases of Truck Crops in Florida 67
nearly sixty percent of the plants affected. The tuber yield of
such plants is about twenty percent less when compared with
The Green Mountain variety of potatoes seems to be highly
susceptible to the disease; some other varieties are also suscep-
FIG. 102.-Healthy potato plant, Eureka variety. Compare
with figure 101. (U. S. Dept. of Agr., Bulletin 64.)
tible to it, while the Irish Cobbler seems to be free from the
CONTROL.-Plant, if practicable, varieties not susceptible to
the disease. Use seed certified to be from plants that were free
from the trouble.
This disease which sometimes affects potatoes (fig. 103) is
discussed under tomato diseases.
Florida Cooperative Extension
FIG 103.-Irish potato plant stems affected with
For a discussion of the root-knot disease see under bean dis-
eases. Its effect on potatoes is shown in figure 104.
SWEET POTATO DISEASES
There are several important diseases of sweet potatoes in
Florida. Of these the stem rot, also known as blue stem, wilt and
yellow blight and certain rots of the roots in the field and in
Some Important Diseases of Truck Crops in Florida 63
storage cause considerable damage to the crop every year. Dis-
eases of this crop have been studied extensively and some publi-
cations made. Reference may be had to U. S. Department of
Agriculture, Farmers' Bulletin 714, Sweet Potato Diseases. The
writer will give only the principal methods of preventing the most
important diseases of the crop. These measures should be em-
ployed whether the diseases are recognized by the grower or not
because the diseases are already common in his field or soon will
be if the precautionary measures are not taken.
GENERAL METHODS FOR CONTROL.-Use only healthy seed
selected at digging time. Split the stems of each hill desired for
FIG. 104.-Irish potato tubers affected with root-knot.
seed and examine them for black streaks. Only roots of plants
free from such streaks should be stored for seed.
In the spring, just before bedding time, the seed potatoes
selected in the fall should be sorted over and all roots showing
any rot or discoloration be discarded.
The healthy seed roots should be soaked in 1:1000 solution
of corrosive sublimate for 10 minutes. Immediately after the
treatment, rinse them freely in clean water and lay them in a thin
layer in the sun for quick drying.
The seed beds should be located preferably in a new soil; that
is, in a soil where sweet potatoes have not been grown before or
at least not for several years.
Rotate the crops in such way that sweet potatoes will not be
planted in the same field more than once every four years.
After digging the potatoes they should be left on the ground
for several days to dry thoroly in the sun.
In digging and handling the potatoes avoid any injury to or
bruising of the roots.
After the potatoes are well dried in the field, it is best to put
70 Florida Cooperative Extension
them in open crates for storage. In this way much injury to them
by handling will be avoided, the potatoes will have better venti-
lation, and can be removed for marketing much more conveniently.
During the first two or three weeks of storage the potatoes
should be kept at a comparatively high temperature, 806 to 850 F.,
and be constantly and thoroly ventilated. Then the temperature
should be gradually lowered to about 500 to 550 F. and this tem-
perature be maintained to the end of the storage period. The
safest place to store the potatoes is in a specially constructed
storage house, as described in Farmers' Bulletin 548, U. S. De-
partment of Agriculture.
Tomatoes in Florida are subject to several important dis-
eases. Of these the early blight is of most common occurrence
and causes probably the greatest damage to the crop. The black
spot is also common and during the rainy season causes even
greater damage than does the early blight. Leaf mold is of gen-
eral occurrence but is
not as important as
the other two named.
These three diseases
are controlled by
spraying with a good
Of the other dis-
eases, Fusarial wilt
and bacterial blight
are the most import-
ant and, in general,
are probably the most
serious diseases of to-
matoes. So far, they
are not as common as
the early blight, but
they are much harder
to control and when
they have a good start
are more destructive.
Spraying with a fun-
gicide is not effective
against these two
FIG. 105.--Tomato plant stems spotted with
early blight. diseases. Crop ro-
Some Important Diseases of Truck Crops in Florida 71
station, seed dis-
in the case of
blight, control of
insects, are the
that can be sug-
gested for con-
Buckeye rot of
tomato fruit is
of some import-
ance in growing
tomatoes on low
lands in South
the plants in the
field and holding FIG. 106.-Tomato fruit affected with early blight,
the fruit for a
few days before packing are methods for controlling this disease.
Blossom-end rot of tomato fruit often causes considerable
damage to the crop. This disease is caused by adverse conditions
of the plant's growth, chief of which is irregular water supply.
Irrigation is usually the chief remedy for this trouble.
EARLY BLIGHT (RUST, LEAF SPOT, BIRDSEYE, BLACK ROT)
This disease is commonly known among growers as rust.
Sometimes it is called brown rust, blight, and leaf spot. When
affecting the fruit it is often known as French rust, nailhead rust,
birdseye or black rot.
Early blight affects the leaves of tomatoes in a way similar
to those of potatoes (fig. 95), also the stems (fig. 105), and the
fruit (fig. 106) where it produces light brown to dark brown and
black spots of various sizes. These spots often have a target-like
appearance and with age become covered with a thin, velvet-like
layer of brown spores of the fungus Macresporium solani E. & M.,
which causes this disease and the early blight of Irish potatoes.
Spores of the fungus are easily carried by the wind, and
when there is enough moisture they will soon germinate and in-
vade the plant tissues. After awhile spots will result on which
Florida Cooperative Extension
new crops of spores are produced, and again these spores will
be scattered from plant to plant. If the weather is favorable this
process will go on until all the plants in the field are thoroly
infected. If the weather following this dissemination is com-
paratively dry, the plants will remain green tho much spotted.
If the weather is continuously wet and cloudy, the disease will
soon destroy the entire field of plants. The disease is not a new
one and it occurs practically everywhere tomatoes are grown
This disease is of special importance because, besides in-
juring the foliage of the plants, it also spots and rots the fruit.
An accurate estimate of the damage caused by it is not available
but it is safe to say that wherever the disease is present a loss
up to one-half the crop is sustained even during a comparatively
dry season. A much heavier loss is not rare.
CONTROL.-Spray with 4-4-50 bordeaux mixture once a week
or once every two weeks, depending on weather conditions and
the amount of the disease in the field. If the weather is rainy
and there is much of the disease, spray more often.
The spraying is to prevent the disease, therefore it pays
best to begin before the disease appears. Begin spraying in the
seed bed and continue it in the field until about a week before the
last picking. It will be found advantageous to change to the use
of ammoniacal solution of copper carbonate or soda bordeaux a
short time before the first picking because common (lime) bor-
deaux mixture stains the fruit.
BLACK SPOT (RUST, BLIGHT, ROT, SCAB)
This disease is also known among the growers as rust, black
rust, spot, blight, black rot, scab, and stem-end rot. The last three
names refer to the disease on the fruit. Tomato plants are
affected at all stages of growth. Leaves, stems, and fruits (fig.
107) are subject to it. The spots produced by this disease differ
from those caused by the early blight by being of a darker color,
but chiefly by the production on the affected parts of a number
of small, pimple-like pustules which are fruiting bodies (pynci-
dia) of the fungus Phoma destructive Plowr., causing the disease.
The fungus produces great numbers of minute spores which
are carried with drops of water to other leaves and plants. In-
sects working on wet, infected plants probably help scatter the
spores. It is also probable that the disease is spread by working
in the field when the plants are wet with dew or rain.
Some Important Diseases of Truck Crops in Florida 73
The disease is frequently observed on young plants in the
seed beds, and because of the fact that it affects the fruit on plants
in the field it seems reasonable to believe that the trouble is also
spread with contaminated seed. Infected seedlings are surely one
of the important means of introducing the trouble into the field.
Old plant rubbish contaminated with the fungus probably is an-
other source of infection of plants in the field and in the seed bed.
By spotting the leaves the veins are injured and by spotting
and rotting the fruit the disease renders it unmarketable and
FIG. 107.-Tomato fruit affected with black spot.
often unfit for any use. The disease during the rainy season may
cause the destruction of an entire field of plants.
CONTROL.-Spray as recommended for the early blight.
Spraying in the seed bed should be specially emphasized. The
transplanting of spotted plants should be avoided.
This disease affects tomato leaves on which it produces pale
yellow spots without definite margins. The spots on the under
side of the leaves are covered with an olive green to cinnamon
brown, powdery layer of spores of the fungus Cladosporium ful-
vum Cke., which causes the disease. The disease injures the
Florida Cooperative Extension
leaves and under favorable circumstances causes considerable
damage to the crop.
CONTROL.-Spray as for early blight of tomatoes.
FUSARIAL WILT (BLIGHT)
This disease is also known as sleepy disease, blight and wilt.
It attacks tomato stems and roots. The affected plants show a
gradual wilting beginning with the lower leaves and the wilting
is usually accompanied by a yellowing and finally a dying of the
lower leaves. Affected stems and leaves show a distinct discolora-
tion of the water-conducting vessels, which can be easily ob-
served by cutting thru the stems and petioles.
The disease is caused by the fungus Fusarium lycopersici
Sacc., which grows in the water-conducting vessels of the plants'
stems and roots thus cutting off the water supply to the tops. The
diseased roots and stems finally decay and then the fungus comes
to the surface of the affected parts and produces abundant
masses of spores. The spores, and also the contaminated soil and
particles of plant rubbish, can be scattered from one plant to
another by the wind, water, cultivation implements and by other
The most common way of spreading the disease is probably
by means of young plants grown in an infected seed bed. The dis-
ease often attacks young plants but the effect is usually not no-
ticeable until they approach maturity. Thus the affected plants
may appear healthy and be transferred into the field. It is also
possible that the disease is carried with contaminated seed.
In some localities this disease is often responsible for an en-
tire crop failure. The fungus which causes it, once introduced
into the field, will remain there in the soil for some time in a
virulent state ready to attack new plants. Such soil is often
entirely unfit for the cultivation of common varieties of tomatoes.
Some varieties and selected strains of tomatoes show more or less
resistance to the disease but unfortunately no resistant variety of
high commercial value has been found.
CoNTROL.-Plant the seed bed on a new soil or a soil ster-
ilized by steam.
Rotate crops so that tomatoes will not be planted in the same
field more often than once in three years.
Every plant that shows symptoms of the disease should be
immediately pulled out and destroyed.
Disinfecting the seed by soaking it in 1:1000 solution of
Some Important Diseases of Truck Crops in Florida 75
corrosive sublimate for three minutes, with a subsequent washing
in clean water may also be of service in preventing the disease.
Spraying of any kind seems to be entirely useless for con-
trolling the disease.
BACTERIAL BLIGHT (BLIGHT, WILT)
This disease is also sometimes known as southern blight,
blight, or wilt. It usually shows itself first by the wilting of a
single branch or leaf; soon other leaves and branches begin to
wilt and in time the wilt affects the whole plant. The wilting
may or may not be preceded or accompanied by a yellowing of
the affected plants. The disease usually becomes pronounced
about blossoming time or somewhat later. First symptoms of the
wilting become evident by a bending down of the diseased leaves
and by a drooping and shriveling of the young stems and growing
shoots. On the latter, numerous knob-like incipient roots can
usually be observed.
After the first symptoms appear the disease progresses
rapidly and, to an inexperienced observer, the final result of its
attack, the entire plant wilting and dying, appears to be sudden.
Stems of affected plants and petioles of affected leaves in cross
and longitudinal sections show a more or less pronounced brown-
ing of the woody elements from which, when cut thru, sometimes
ooze dirty white masses of the bacteria causing the disease.
Later, patches of brown rot may be observed, the stems soon
shrivel and decay and the whole plant dies.
The disease is caused by bacteria, Bacillus solanacearum E.
F. Sm. The bacteria may invade the plant either from the soil
thru a root injured by nematodes or in some other way, or they
may be introduced into the plant by insects working on the stems
and leaves. Seed contaminated with the bacteria, young plants
grown in a seed bed contaminated with them, and various insects
working from infected plants to healthy ones, are probably the
chief agents which spread the disease. When once introduced
into a field, the bacteria will remain in the soil in a virulent state
for a number of years.
Bacterial blight also attacks tobacco, potato, eggplant, pep-
per, peanut, and several other cultivated and wild plants. At
present no variety of tomatoes resistant to the disease is known.
The disease often ruins whole fields of tomatoes and once
infected a field is unfit for the cultivation of tomatoes or other
crops susceptible to it for a number of years.
Florida Cooperative Extension
CONTROL.-Obtain seed from localities free from the disease.
Disinfect the seed as recommended for the wilt of tomatoes.
The seed bed should be either on a new land or the soil be
It is best not to plant tomatoes in a field where the disease
was previously present. In case it is desirable to plant tomatoes,
practice a crop rotation in which no susceptible crop will be
grown more often than once in four years. In planting suscepti-
ble plants on previously infected soil, see that the soil is free from
root-knot nematodes and that the roots of the plants are not in-
jured in transplanting. It would be better, if practicable, not to
transplant at all but to grow the plants from the seed in the field.
Destroy all insects working on the plants. Use both a con-
tact insecticide such as Black Leaf "40," 1/2 pint to 50 gallons of
water, and a stomach poison such as arsenate of lead, 11/2 pounds
of the powder or 3 pounds of the paste to 50 gallons of water.
Watch the fields for the first signs of the disease and destroy
immediately all plants affected with it. The drooping of leaves
and tender growing shoots and tips of leaf veins are good symp-
toms to watch for providing the soil is not too dry and no other
disease is present, such as Sclerotial blight which produces a sim-
ilar effect on the plants.
SCLEROTIAL BLIGHT (BLIGHT, WILT, FOOT ROT)
This disease is also known as blight, wilt or foot rot. The
trouble manifests itself by a rotting of the plant stem just at,
below or above, the surface of the ground. The ground around
the affected stem and the stem itself become covered with a white
moldy growth of the fungus Sclerotium rolfsii Sacc., which causes
the disease. This moldy growth often produces numerous hard,
round bodies, sclerotia, of the size of a mustard seed. These are
white at first but later become yellowish, then brown, and nearly
black when old.
The blight is first evident by a wilting of the tips, then by
the wilting and dying of the whole plant. The white moldy
growth at and near the affected base with the sclerotia on it can
often be observed sometime before the plant begins to wilt.
Scattering of plant rubbish containing diseased plants and
sclerotia are probably the chief means of disseminating the dis-
ease. The disease also affects potatoes, peppers and a number of
other cultivated and wild plants.
The disease was reported and described for the first time by
P. H. Rolfs in 1893 (Fla. Agr. Exp. Sta. Bul. 21, pp. 25-36).
Some Important Diseases of Truck Crops in Florida 77
Since then it has been reported from nearly all Southern States
and from some places in the North. It has been reported serious
during some seasons but usually it is destructive only locally altho
it can be commonly found at any season on isolated plants or
groups of plants. During the last three seasons it has been found
most common on potatoes, while it was not uncommon on to-
mato and pepper plants and on velvet bean pods.
CONTROL.-Because the fungus causing this disease lives in
the soil and from there attacks the plants, spraying is of no value.
Nevertheless, experiments show that a thoro spraying of the
ground around the stems with a good fungicide helps considerably
FIG. 108.-Buckeye rot of tomato fruit.
in reducing the damage caused by the disease. For this spraying
use either ammoniacal solution of copper carbonate or 4-4-50
bordeaux mixture at the rate of from 1 to 2 pints per plant.
BUCKEYE ROT (BROWN ROT, WATER-LOGGED FRUIT)
This disease is sometimes known as water-logged fruit or
brown rot. It attacks the fruit only, on which it appears as a
grayish or pale to dark brown, often distinctly zonate, hard rot.
(Fig. 108.) This zonation is sometimes indistinct or even en-
tirely lacking. The affected parts of the fruit usually remain
of the same shape as that of normal fruit with a smooth, clean
surface. But, if the fruit is kept in a moist atmosphere the af-
fected parts will often be covered with a white moldy growth of
the fungus causing the disease.
The rot occurs on the fruit at any stage of growth and, in
all cases observed, only when the fruit touches or is very close to
Florida Cooperative Extension
the ground. Because the fruit usually touches the ground with
the blossom end, the disease often starts there and appears as a
peculiar form of blossom-end rot, for which it is sometimes
The disease is caused by the fungus Phytophthora terrestria,
and occurs on low soils rich in humus, along the east and west
coasts of South Florida. So far it has not been observed on any
other truck crop. The fungus lives in infected tomato fruit and
evidently in the soil and can be readily and gradually spread by
means of infected
soil g nd diseased
Fruit. The disease
is evidently not a
new one in the
State and was
as early as 1911.
It has been studied
Sby the writer since
January, 1915, and
the results pub-
129, Figs. 5,1917).
much of the fruit
FIG. 109.-Blossom-end rot of tomato fruit. in the field and in
transit and thus
causes considerable loss to the crop grown on land infected with
CONTROL.-Staking plants in the field so as to prevent the
fruit from touching the ground, and holding the picked fruit for
a few days before packing, seem to be practical methods for con-
trolling the disease and preventing excessive losses.
This disease, as its name implies, attacks tomato fruit at the
blossom end. It first appears in the form of a bruised, water-
soaked, dark green spot near or at the base of the style; in a
short time the spot increases in size and turns black, shrinks,
and becomes hard and leathery. (Fig. 109.)
Some Important Diseases of Truck Crops in Florida 79
The disease is not infectious and is due to some abnormal
condition of the plant's growth of which irregular water supply
is probably the chief factor. It appears to be worse on light
soils; the amount of it evidently depending greatly on the kind
and probably the amount of fertilizer used. The disease under
favorable conditions often affects a large percent of the fruit and
for that reason is of much importance.
CONDITIONS AFFECTING THE DISEASE.-Here are some con-
clusions of Charles Brooks of the New Hampshire Experiment
Station in his recent extensive work on the disease (Phytopath.
4:345-374, pls. 3, 1914) which will be of interest to growers:
The blossom-end rot of the tomato is not due primarily to
bacteria or fungi. Plants are most susceptible when in a con-
dition of great activity. Either continued excessive watering
or a sudden check in the water supply may produce the disease.
With liberally watered greenhouse plants, potassium chloride
increases the disease and lime and sodium nitrate decrease it,-
these facts have not been found to hold true under field conditions.
Ammonium sulphate, dried blood, and cottonseed meal have in-
creased the disease out of proportion to the increase in vigor of
CONTROL.-The plants should be irrigated regularly, or at
least be cultivated in such way as to conserve the soil water supply
and thus protect them against the injurious effect of sudden dry
Ammonia (nitrogen) should be supplied in the form of ni-
trate of soda in preference to either ammonium sulphate, dried
blood, or cottonseed meal. Heavy applications of stable manure
should be avoided. Under certain conditions an application of
lime may be beneficial, and of potassium chloride may be harmful.
OTHER TOMATO DISEASES
Other diseases affecting tomatoes are: Root-knot (see under
bean diseases) and damping off (see under care of the seed bed).
Several diseases of watermelons have been more or less
commonly observed in Florida, but on the whole it seems that
none of them regularly play an important part in watermelon
culture. Nevertheless, some of the diseases in some isolated cases
cause large losses, and the growers should be on the lookout for
them. Only a brief mention of the most common diseases of
Florida Cooperative Extension
watermelons is made here and therefore it is necessary to em-
phasize these important and general methods for their prevention
1. Some of the diseases are undoubtedly introduced into the
field with the seed and the growers should demand from their
seed dealers that seed be obtained from healthy plants and fruits
under such sanitary conditions as to make contamination with the
disease-producing organisms at least improbable. In any case,
the seed should be disinfected before planting them.
2. Because some disease-producing organisms remain in
the soil in a virulent state for a few years or more, it is necessary
to practice a crop rotation in which watermelons and other closely
related crops, such as cantaloupes, will not be planted in the
same field more often than once every ten years, if the field was
once infected with the wilt. No volunteer plants should be per-
mitted to grow.
3. All diseased plants and fruits, when detected, should be
immediately pulled out and burned.
4. When the plants are observed to be subject to attack by
some of the diseases, such as downy mildew and anthracnose
which can be controlled by spraying, this should be done thoroly
and at the right time. In general, spraying will pay when the
crop is an early one and will command a high price.
This disease causes plants to wilt, and the stems of affected
plants show a yellow discoloration of the water-conducting ves-
sels. It is caused by the fungus Fusarium vasinfectum Atk. var.
niveum Sm., which can remain in the soil in a virulent state for
probably ten years or more.
The wilt is not a new disease and is of general occurrence in
this State and others. Commonly, in a field planted on new land,
only a few plants affected with the trouble can be found, but
in some cases even on a new soil a great many of the plants may
be killed by it. Watermelons planted again in such a field are
often nearly ruined by the disease.
CONTROL.-Do not plant watermelons more often than once
in ten years on the same land if the disease has been present, and
during that time do not let volunteer watermelons grow. Disin-
fect the seed, and do not fertilize with a manure containing
refuse from old watermelon plants.
Some Important Diseases of Truck Crops in Florida 81
This disease affects all parts of the grown plants (figs. 110,
111, 112); sometimes it severely injures young plants also. Its
effect is specially noticeable on the fruit on which it produces
dark, sunken spots covered in the center with numerous pustules
bearing masses of pinkish spores of the fungus Colletotrichum
lagenarium (Pass.) Ell. and Halst., which causes this disease.
A young fruit attacked by the disease commonly decays before
reaching maturity. All diseased young parts of the plant turn
black. Affected leaves turn dark and become brittle.
FIG. 110.-Anthracnose on young watermelon.
In 1905, the disease caused considerable damage in the State.
During the last few seasons, excepting 1917, it has not been.of
CONTROL.-Spray as recommended for Mycosphaerella wilt.
This disease affects the stems of young watermelon plants
at the base of the leaf petioles. The diseased parts appear las
water-soaked, green to dark green and brown, gummy, then dry,
and gray rot. Old diseased spots are covered with numerous mi-
nute, brown, pimple-like fruiting bodies (pycnidia) of the fungus
Mycosphaerella citrulina (Sm.) Gr., which causes this disease.
In one instance it was observed to kill a great many of the
young plants. In that case the disease to all appearances came
with the seed. The disease also attacks full-grown watermelon
and cantaloupe plants.
CONTROL.-Disinfect the seed, and spray with 4-4-50 bor-
deaux mixture. Spray for the first time when the plants have
Florida Cooperative Extension
two fully developed leaves. Repeat the spraying in about two
weeks. Spray again when the fruit begins to form and from that
time on spray every other week until the first picking of the
fruit. The later sprayings, especially of the fruit, are also useful
to prevent stem-end rot and anthracnose. In general, spraying
I . .... . .
FIG. 111.-Anthracnose on watermelon leaf.
Stem-end rot has been reported from several Southern States as se-
verely damaging watermelons in transit. It is supposed to be caused by the
fungus Diplodia sp. So far, the trouble has not been observed in this State,
tho its occurrence here is not improbable. (See Journ. Agr. Res. 6:149-152,
Some Important Diseases of Truck Crops in Florida 83
will often be beneficial on account of
the downy mildew (rust) which is
controlled by this treatment and
commonly attacks watermelons.
This disease starts as a shrink-
ing, then a paling, and then a black-
ening and dry decay of the blossom
end of the fruit. The rot gradually
spreads until a considerable portion
or nearly the whole fruit becomes in-
volved. In many instances the trou-
ble has been observed to attack a
considerable percent of the fruit.
The disease seems to be due to
some unfavorable conditions of
growth, perhaps chiefly to a sudden
check in the water supply. It is
probably of the same nature as other
similar diseases, such as blossom-
end rot of peppers and tomatoes.
CONTRoL.-Cultivation of the
crop in such way as to conserve the
water supply in the soil undoubtedly
is an important factor. Fertiliza-
tion is also probably of importance
and the findings in the case of blos-
som-end rot of tomatoes suggest
that when any form of nitrogen is
applied, nitrate of soda will be per-
haps the safest one to use. Liming
may also prove beneficial. Very lit-
tle is actually known in this connec-
tion and therefore one must proceed
carefully with the fertilization, try-
FIG. 112. Anthracnose on ing it first on a small scale. Every
watermelon stems. fruit affected with the rot should be
destroyed to prevent a useless strain on the plant's vitality.
OTHER WATERMELON DISEASES
Other diseases affecting watermelons are: Downy mildew
(see under cantaloupe diseases) and root-knot (see under bean
Actinomyces chromogenus, 62
Ammoniacal solution copper carbon-
Anthracnose, bean, 21
Bacillus athrosepticus, 65
carotovorus, 41, 52
solanacearum, 59, 75
Bacterial blight, eggplant, 47
Bean, diseases, 20
hollow stem, 27
powdery mildew, 27
white mold, 32
Birdseye, tomato, 71
Black heart, celery, 40
Black mold, cabbage, 35
Black rot, cabbage, 33
tomato, 71, 72
Black scab, potato, 63
Black spot, tomato, 72
Blackleg, potato, 64
Blight, bean, 21, 24
celery, 38, 40
potato, 54, 58, 60, 63, 67
sweet potato, 68
tomato, 71, 72, 74, 75, 76
Blossom-end rot, tomato, 78
Blue stem, sweet potato, 68
Blue stone, 4
Bordeaux mixture, 4
composition of, 4
objections to, 7
Brooks, Charles, 79
Brown, Nellie A., 48
Brown rot, tomato, 77
Brown rust, tomato, 71
Buckeye rot, tomato, 77
Burger, 0. F., 49
Cabbage diseases, 33
black mold, 35
black rot, 33
downy mildew, 35
Cantaloupe diseases, 36
downy mildew, 36
Carbonate, copper, 8
Care of the seed bed, 15
Cauliflower diseases, 37
Celery diseases, 38
black heart, 40
early blight, 38
foot rot, 42
late blight, 40
Cercospora apii, 39
Cercospora leaf spot, pepper, 51
Cladosporium fulvum, 73
Collar rot, eggplant, 43
Colletotrichum lagenarium, 81
Common scab, potato, 62
Control of diseases, general meas-
materials used, 4
on specific crops, 20
Copper carbonate ammoniacal, 8
Copper sulphate, 4
Corrosive sublimate, 9, 13
Crop rotation, 14
Cucumber diseases, 36
see cantaloupe diseases
Cultural methods to control diseases,
Cyanamid for soil sterilization, 31
Damping off, 15
control of, 16
Disease control, general measures,
materials used in, 4
Disease resistance, 19
Disinfection, seed, 12
Some Important Diseases of Truck Crops in Florida
Downy mildew, cabbage, 35
Drop, lettuce, 48
Drop, leaf, pepper, 51
Dry collar, eggplant, 43
Early blight, celery, 38
Eggplant diseases, 42
bacterial blight, 47
Phomopsis diseases, 43
Erysiphe polygoni, 28
Fawcett, H. S., 49
Fire-blight, cantaloupe, 36
Foot rot, celery, 42
Formaldehyde, 9, 13
Formalin, 9, 13
sterilization with, 17
Formulae, ammoniacal solution of
copper carbonate, 8
bordeaux mixture, 4
corrosive sublimate, 9
rosin-salsoda sticker, 8
soda bordeaux mixture, 8
French rust, tomato, 71
Fruit rot, eggplant, 43
Fruit spot, eggplant, 43
Fumigation, beans, 24
Fusarial wilt, potato, 59
Fusarium oxysporum, 59
General measures for disease con-
Heterodera radicicola, 29
Hollow stem, bean, 27
Late blight, celery, 40
Leaf drop, pepper, 51
Leaf mold, tomato, 73
Leaf spot, eggplant, 43
Lettuce diseases, 48
black rot, 49
Little potato, 63
Macrosporium solani, 60, 71
Materials used to control diseases,
Mildew, downy, cabbage, 35
downy, cantaloupe, 36
downy, cucumber, 36
powdery, bean, 27
Mold, black, cabbage, 35
leaf, tomato, 73
white, bean, 32
Mosaic, potato, 66
Mycosphaerella citrulina, 81
Mycosphaerella wilt, watermelon, 81
Nailhead rust, tomato, 71
Pea diseases, 50
Pepper diseases, 51
Cercospora leaf spot, 51
fruit soft rot, 52
Peronoplasmopora cubensis, 36
Peronospora parasitica, 36
Phoma destructive, 72
Phomopsis leaf spot, eggplant, 43
Phomopsis vexans, 15, 45
Phytophthora infestans, 54
Potato diseases, Irish, 53
bacterial blight, 58
black scab, 63
common scab, 62
early blight, 60
Fusarial wilt, 59
late blight, 54
Sclerotial blight, 67
Florida Cooperative Extension
Potato diseases,.sweet, 68
see sweet potato
Powdery mildew, bean, 27
Pseudomonas campestris, 34
Pseudomonas sp.,.. 49
Pythium debaryanum, 15, 27
Rhizoctonia solani, 15, 27, 63
Rolfs, P. H., 76
Root-knot, bean, 29
Root rot, bean, 27
sweet potato, 68
Rosin-salsoda sticker, 8
Rot, black, cabbage, 33
black, lettuce, 49
black, tomato, 71, 72
blossom-end, tomato, 78
blossom-end, watermelon, 83
buckeye, tomato, 77
foot, celery, 42
foot, tomato, 76
fruit, eggplant, 43
fruit, pepper, 52
root, bean, 27
root, sweet potato, 68
stem, bean, 27
stem, sweet potato, 68
stem-end, tomato, 72
Rotation of Crops, 14
Rust, bean, 21; 27
cucumber,, 36 ,
tomato, 71, 72
Scab, potato, 62, 63
Sclerotial blight, potato, 67
Sclerotinia libertiana, 15, 32
Sclerotium rolfsii, 76
Seed bed, care of, 15
Seed, disinfection of, 12
healthy, importance of, 12
Septoria petroselini, 40
Sleepy disease, tomato, 74
Soda bordeaux mixture, 8
Soil sterilization, 17
with cyanamid, 31
with formalin, 17
with steam, 18
Southern blight, tomato, 75
Spot, bean, 21
Sprout blight, potato, 63
Steam, sterilization, 18
Stem blight, potato, 63
Stem canker, eggplant, 43
Stem-end rot, tomato, 72
Stem rot, bean, 27
sweet potato, 68
Sterilization, soil, 17, 31
Stevens, H. E., 53
Sticker, rosin-salsoda, 8
Sublimate, corrosive, 9, 13
Sulphate, copper, 4
Sweet potato diseases, 68
Tipover, eggplant, 43
Tomato diseases, 70
bacterial blight, 75
black spot, 72
blossom-end rot, 78
buckeye rot, 77
early blight, 71
Fusarial wilt, 74
leaf mold, 73
Sclerotial blight, 76
Truck diseases, materials used to
Varietal resistance, 19, 23
Water-logged fruit, tomato, 77
Watermelon diseases, 79
blossom-end rot, 83
Fusarial wilt, 80
Mycosphaerella wilt, 81
Some Important Diseases of Truck Crops in Florida 87
Watson, J. R., 31
White mold, bean, 32
Wilt, potato, 59
sweet potato, 68
tomato, 74, 75, 76
watermelon, 80, 81
Winters, R. Y., 41
Yellow blight, sweet potato, 68