Front Cover
 Table of Contents
 Diseases incited by bacteria and...
 Diseases incited by viruses
 Diseases incited by nematodes
 Diseases of physiological or uncertain...
 Principles of disease control

Group Title: Bulletin - Florida Agricultural Experiment Station ; 731
Title: Tomato diseases in Florida
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00027582/00001
 Material Information
Title: Tomato diseases in Florida
Series Title: Bulletin - Florida Agricultural Experiment Station ; 731
Physical Description: Book
Language: English
Creator: Jones, J. P.
Weber, G. F.
Kelbert, D. G. A.
Publisher: Agricultural Experiment Stations, Institute of Food and Agricultural Sciences, University of Florida,
Publication Date: 1969
 Record Information
Bibliographic ID: UF00027582
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.

Table of Contents
    Front Cover
        Page 1
    Table of Contents
        Page 2
        Page 3
    Diseases incited by bacteria and fungi
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
        Page 40
        Page 41
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        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
    Diseases incited by viruses
        Page 53
        Page 54
        Page 55
        Page 56
        Page 57
        Page 58
        Page 59
        Page 60
        Page 61
        Page 62
    Diseases incited by nematodes
        Page 63
        Page 64
        Page 65
    Diseases of physiological or uncertain origin
        Page 66
        Page 67
        Page 68
        Page 69
        Page 70
        Page 71
        Page 72
        Page 73
        Page 74
        Page 75
        Page 76
        Page 77
        Page 78
        Page 79
        Page 80
        Page 81
    Principles of disease control
        Page 82
        Page 83
        Page 84
        Page 85
        Page 86
        Page 87
        Page 88
Full Text
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Diseases incited by Bacteria
and Fungi
Gray Leafspot
Bacterial Spot
Verticillium Wilt
Fusarium Wilt
Southern Bacterial Wilt
Phoma Rot
Late Blight
Early Blight
Soil Rot
Botrytis Gray Mold
Southern Blight
Stem Rot
Leaf Mold
Buckeye Rot
Septoria Leafspot
Nailhead Spot
Minor Fruit Rots
Fusarium Rot
Oospora Rot
Rhizopus Rot
Bacterial Rot
Myrotheecium Rot
Nematospora Rot
Diseases Incited by Viruses
Tobacco Mosaic (Tomato
Pseudocurly Top

Veinbanding Mosaic
(Potato-Y Virus) 58
Cucumber Mosaic 59
Double Virus Streak 62

Diseases Incited by Nematodes 63
Root Knot ........ 63

Diseases of Physiological or
Uncertain Origin 66
Blossom-End Rot 66
Blotchy Ripening (Graywall) 69
Puffy Tomato 71
Sunscald .......... 72
Growth Cracks 74
Catface 75
Leaf Roll 76
Blossom-Drop 78
Crease Stem 79
Black Shoulder 81

Principles of Disease Control 81
Sanitation and Rotation 81
Seedbed Sterilization 83
Soil Sterilization with Methyl
Bromide 83
Soil Sterilization with Other
Fumigants 84
Soil Sterilization with Steam 84
Seed Treatment 85
Bichloride of Mercury ...... 85
Dry Seed Treatments 86
Fungicide Application 86
Fungicides for Disease
Control 88

Since the initial preparation of this bulletin, "Walter", a
race 2-resistant variety has been released.
Page 13 & 15

J. P. Jones, G. F. Weber, and D. G. A. Kelbert'

Tomatoes have been grown in Florida for a considerable
number of years, and in each successive season the acreage and
production have been advanced, until at present the value of
the crop exceeds that of any other vegetable in the state.
The tomato growing acreage might be divided into six dis-
tinct areas: (1) the Lower East Coast area (Dade County,
Pompano, Martin County, Palm Beach County), (2) the Fort
Myers-Immokalee area, (3) the Fort Pierce area, (4) the
Wauchula area, (5) the Manatee-Ruskin area, and (6) the
Oxford-Belleview-Lowell (Figure 1). The culture of tomatoes
is intensive within these six areas, and it is here that plant
diseases appear most frequently in destructive form. The crop
in Florida can be expected to be troubled with nearly every
disease known to be destructive to tomatoes in this country,
because a great number of the most damaging pathogens are
well distributed throughout these areas, the weather is mild
and humid, and tomatoes are either being seeded, planted, or
harvested the year around.
The purpose of this bulletin is to bring together for the
benefit of the grower the latest information concerning tomato
diseases that may appear in the state. This bulletin supplements
the information found in previous publications and includes
considerable additional information. Since control recommen-
dations change as superior products and better information
become available the reader is urged to consult with his county
agent to obtain the latest recommendations.


Gray Leafspot
Gray leafspot is caused by the fungus Stemphylium solani
Weber. The disease was first noticed in the Gainesville vicinity
and in Manatee County in 1924, and by 1928 it had spread

1 J. P. Jones, Associate Plant Pathologist, Gulf Coast Experimental Station,
Bradenton; G. F. Weber, Professor of Plant Pathology (Retired), Uni-
versity of Florida, Gainesville; D. G. A. Kelbert, Associate Horticulturist
(Retired), Gulf Coast Experiment Station, Bradenton.

J. P. Jones, G. F. Weber, and D. G. A. Kelbert'

Tomatoes have been grown in Florida for a considerable
number of years, and in each successive season the acreage and
production have been advanced, until at present the value of
the crop exceeds that of any other vegetable in the state.
The tomato growing acreage might be divided into six dis-
tinct areas: (1) the Lower East Coast area (Dade County,
Pompano, Martin County, Palm Beach County), (2) the Fort
Myers-Immokalee area, (3) the Fort Pierce area, (4) the
Wauchula area, (5) the Manatee-Ruskin area, and (6) the
Oxford-Belleview-Lowell (Figure 1). The culture of tomatoes
is intensive within these six areas, and it is here that plant
diseases appear most frequently in destructive form. The crop
in Florida can be expected to be troubled with nearly every
disease known to be destructive to tomatoes in this country,
because a great number of the most damaging pathogens are
well distributed throughout these areas, the weather is mild
and humid, and tomatoes are either being seeded, planted, or
harvested the year around.
The purpose of this bulletin is to bring together for the
benefit of the grower the latest information concerning tomato
diseases that may appear in the state. This bulletin supplements
the information found in previous publications and includes
considerable additional information. Since control recommen-
dations change as superior products and better information
become available the reader is urged to consult with his county
agent to obtain the latest recommendations.


Gray Leafspot
Gray leafspot is caused by the fungus Stemphylium solani
Weber. The disease was first noticed in the Gainesville vicinity
and in Manatee County in 1924, and by 1928 it had spread

1 J. P. Jones, Associate Plant Pathologist, Gulf Coast Experimental Station,
Bradenton; G. F. Weber, Professor of Plant Pathology (Retired), Uni-
versity of Florida, Gainesville; D. G. A. Kelbert, Associate Horticulturist
(Retired), Gulf Coast Experiment Station, Bradenton.

Figure 1. Tomato producing areas.
1. Lower East Coast
2. Ft. Myers Immokalee
3. Ft. Pierce
4. Wauchula
5. Manatee Ruskin
6. Oxford Bellview Lowell

throughout the state, causing widespread loss. Currently, gray
leafspot is one of the most destructive diseases of tomato in
Florida and annually causes extensive damage to susceptible
varieties. Although it is common and destructive throughout
southeastern United States, it causes only sporadic damage to
tomato in the Central and Eastern states.


Gray leafspot begins in the seedbeds and on field-seeded
seedlings, often when the plants are in the first true-leaf stage.
Cotyledons are frequently but not severely infected. The tomato
plant is subject to infection anytime during its development.
However, several varieties, such as Floradel, Immokalee, Indian
River, Manapal, Manalucie, Marion, and Supermarket, are re-
sistant to the disease.
In Florida S. solani remains viable on tomato plants which
grow in some area of the state throughout the year. The
fungus also survives from season to season on diseased plant
debris in the soil. Abandoned fields and seedbeds, volunteer
plants, and wild solanaceous plants also act as sources of in-
Much pathogen spread occurs by the transplanting of dis-
eased seedlings from infected seedbeds to the fields. The spores
of S. solani are spread over extensive areas by the wind. The
spores germinate quickly in the presence of water and warm
temperatures (75o-79 F) and produce extensive growth during
a single night. The fungus develops rapidly within the host,
and in 2 to 3 days symptoms can be distinguished.

Gray leafspot lesions are limited almost entirely to the
leaf blades. Under very favorable conditions, occasional lesions
develop on the petioles and the more tender parts of the grow-
ing stems. In these instances the spots are linear and parallel
with the stem. No lesions have been found on the fruit.
Gray leafspot first appears as minute, barely visible, brown-
ish-black specks on the lower leaves. The spots are circular
to oblong and variously scattered over the leaf surface without
any apparent restriction by the veins. Occasionally the spots
are marginal and in such cases are somewhat elongated or
irregular in outline. The spots enlarge to about 1/12 inch in
diameter, turn in color from a brownish-black to a grayish-
brown, and become somewhat shiny and glazed (Figure 2).
By this time there is in most cases a definite yellow area ap-
parent around the spots. Lesions rarely exceed 1/12 inch in
diameter, although on the very oldest leaves near the base of
the plant individual spots may obtain the diameter of 1/6 inch
or more. Occasionally on the older leaves the spots coalesce,
involving and killing large areas of the leaf blade (Figure 3).
As the centers of the spots dry out, they often crack in various

Figure 2. Tomato leaflets affected with gray leafspot: (Left) upper surface
and (Right) lower surface.

patterns. It is often in this stage that yellowing of the entire
leaf becomes most conspicuous, especially if the infection is
severe. The leaves then die rapidly, become brown, and drop.
Serious infections in the seedbeds result in marked defolia-
tion without conspicuous yellowing.
In contrast with other leaf spots of tomato caused by Alter-
naria solrni (early blight), Phoma destructive (Phoma rot),
and Xanthomonas vesticatoria (bacterial spot), the gray leaf-
spot lesions generally are smaller, more regular and more
evenly distributed, and do not enlarge as rapidly. They are
circular to oblong, uniform grayish-brown over the killed area,
and show no concentric zonation as is characteristic of spots
caused by A. solani and P. destructive. Leaf mold spots, caused
by Cladosporium fulvum, differ from gray leafspot in that they
appear as large, yellow blotches on the upper surfaces of the
leaves, immediately above the infection on the lower surfaces.
The spots caused by Septoria lycopersici differ in that they
usually have a light colored central area, or "frogeye" spot,


Figure 3. Gray leafspot diseased leaf, showing coalesced lesions and yellowed

that is more or less speckled with black pycnidia (the fruiting
bodies). Bacterial spot lesions are darker in color than gray
leafspot lesions and are not as evenly distributed over the leaf

Use resistant varieties. Recommended fungicides are effec-
tive if applications are made before the disease occurs and if
the foliage and stems are thoroughly covered.

Bacterial Spot
This disease is caused by the bacterium Xanthomonas vesi-
catoria (Doidge) Dows., and is an adverse factor in tomato
production in the Central, Eastern, and Southern states.
Bacterial spot was first detected in Florida in about 1925 and
since that time has become one of the major diseases of tomato
in the state.
The disease symptoms are most conspicuous on the fruit,
but severe damage occurs to the foliage and fruit spurs. Bac-
terial spot is very destructive to seedlings and spreads very
rapidly. Pepper is the only other host of economic importance.
X. vesicatoria is carried on the surface of the seed and lives
on old leaves of field plants and volunteer tomato plants. There
is some evidence that the bacterium can survive for short
periods in debris in the soil. The pathogen is spread from
primary infections in the seedbed and by wind and rain in the
field. Progress of the disease is favored by abundant rainfall
and moderate temperatures of about 750 to 850 F. Consequently,
bacterial spot is most severe during the months of August,
September, and October. Infection of the leaves and fruit takes
place through stomata and wounds caused by wind-driven sand,
insect punctures, or mechanical means such as high spray-
pressures. Often fruit are severely spotted on the windward
side following a wind-driven rain.

Bacterial spot on the leaves and fruit spurs is characterized
by the development of brown, water-soaked, circular spots.
They rarely assume large proportions usually being about 1/,
inch in diameter. They can be confused with young early blight
and gray leafspot lesions on the leaves. However, the bacterial
spot lesions usually lack the concentric zones which characterize
early blight, and generally they are darker in color and less
uniformly distributed on a leaflet than gray leafspot lesions
(Figure 4). Often the lesions tend to be elongated on the leaf
margins; and occasionally, after a heavy rain during which


4. Leaflets showing bacterial

spot lesions.

the leaves have become saturated with water, entire inter-
veinal areas will become infected.
On the fruit the early symptom is a very minute black
speck surrounded by a slightly lighter area. As the spot en-
larges it becomes brownish in color, scab-like, slightly raised
on the edges, and sunken in the center (Figure 5). The epi-
dermis of the fruit finally ruptures and curls back from the
center of the spot. This is the most characteristic symptom
of the disease on the fruit. Often a spot, which is brown to
black, will have a faintly distinguishable halo which soon dis-
appears. The bacterial spots are very seldom deeper than half
way through the outer fleshy layer of the tomato fruit. Severely
infected fruit often become malformed because of the retarda-
tion of growth in these areas.

Figure 5. Green tomatoes showing bacterial spot lesions.

Bacterial spot can be seed transmitted. Consequently, to
avoid infection from this source treat the seed with bicholoride
of mercury or Ceresan M. Because bacterial spot is quite
difficult to control once established in the field, use disease-free
transplants and remove all volunteer tomato plants from the
area. If the weather is rainy and bacterial spot is prevalent,
protect plants in the seedbed or field-seeded seedlings by spray-
ing the plants 4 to 5 days after emergence with recommended
materials. Continue spraying with a recommended material
on field plants on a 5- to 7-day schedule depending upon the
amount of rain and disease prevalence. Spray applications
applied before rains give much more effective control than
applications made after rain; however, no spray schedule gives
adequate control of the disease during periods highly favorable
for disease development. Do not place seedbeds in the area
of an abandoned field where bacterial spot was present the
previous season.

Verticillium Wilt
This wilt disease is caused by the fungus Verticillium albo-
atrum Reinke & Berthold. The pathogen is widely distributed
and causes severe losses in some areas in the United States.
The disease was first reported in Florida in 1931 but not
described until 1959 and is of importance only in Dade County.

V. albo-atrum lives in the soil from one season to the next
and can survive in soil which has not been planted to a sus-
ceptible crop for several years. Infection almost invariably
originates from inoculum in the soil, although tomato leaves
are sometimes infected by aerial spores of the fungus. When
this occurs, the fungus moves through the petiole into the
stem and invades the vascular elements. Seed may be infected
but has little to do with the spread of the fungus.
Although soil reaction has very little effect on disease devel-
opment or persistence of the fungus in the soil, V. albo-atrum
grows most rapidly in soils near alkalinity and becomes less

Figure 6. Tomato plant showing typical Verticillium wilt symptoms.

injurious as the soil pH approaches 5.0. The temperature range
most favorable for disease development is from 700 to 750 F.
V. albo-atrum attacks a wide range of plants including
weeds. The most commonly affected vegetables are tomato,
potato, eggplant, okra, and southern pea.

In Florida the first apparent symptoms generally do not
occur until the beginning of fruit set, and consist of the diurnal
wilting and recovery of the lower leaves. Initially the leaves
are green, but yellow areas develop along the margins or
between veins of the leaflets. Fan-shaped necrotic lesions de-
velop as the yellowing progresses, and the affected leaves grad-
ually wither. The wilting and yellowing may involve only a
few terminal leaflets, or it may occur on most of the bottom
leaves, sometimes causing a 50% loss of foliage. Diseased
plants, although not killed by the fungus, are stunted, do not
respond to fertilizer, and produce only small fruit (Figure 6).
The foliage loss and stunting expose the fruit to the sun and
considerable sun scald may occur. Fruit yield may be reduced
30% to 40%, and the quality is poor. However, yield reductions
may be negligible when weather and soil conditions are favor-
able for the crop.
A lengthwise cut of an infected plant near the base reveals
a light tan discoloration of the vascular tissue. The discolora-
tion, in Florida, is typically lighter than that of Fusarium wilt
and usually does not extend far up the stem before fruit are
mature. There is no decay of the pith typical of southern
bacterial wilt, nor dark colored vascular bundles at the base of
the petiole typical of Fusarium wilt.

Locate seedbeds on soil free of the Verticillium fungus.
Use resistant varieties when they become available. Practice
sanitation and crop rotation.

Fusarium Wilt
This common wilt disease is caused by the fungus Fusarium
oxysporum (Schlecht.) f. lycopersici (Sacc.) Snyder & Hans.
The disease occurs throughout the United States wherever
tomatoes have been grown. The section east of the Mississippi

River and south of the Ohio River incurs the greatest losses.
Two races of the tomato wilt fungus have been found in
Florida. The common race 1 of the fungus is distributed
throughout the entire tomato-growing area but causes little
damage because of the general use of resistant varieties. In
1960, race 2, which infects race 1-resistant varieties, was dis-
covered in the Delray Beach area. This infested area was
delineated by the Division of Plant Industry as being bounded
to the North by Juniper, to the south by Fort Lauderdale, to the
west by Loxahatchee, and to the east by the Alantic Ocean.
In 1965, race 2 was also found to be widely distributed through-
out the Ruskin-Manatee County tomato growing area. Both
races of the Fusarium wilt fungus are identical in form and
structure and are known to differ only in their pathogenicity.
Nearly all commercial varieties commonly used are resistant
to race 1, but no race 2-resistant commercial varieties are yet
F. oxysporum f. lycopersici lives in the soil from one season
to the next and has been known to survive in soil which has
not been planted to tomatoes for a number of years. Although
the fungus itself is not much influenced by soil moisture, disease
development is inhibited by wet soils. Factors which favorably
predispose plants to disease development are low soil moisture,
high potassium, low nitrogen, and low light intensity. This
fungus tolerates considerable acid in the soil in- which it lives,
and its development is inhibited in soils showing an alkaline
reaction. The optimum temperature for disease development
is about 800-90o F.
F. oxysporum f. lycopersici is disseminated over the tomato-
growing area by the transplanting of infected seedlings from
the seedbed to the field, by infested soil adhering to' the seed-
lings at transplanting time, by infested soil clinging to old
stakes, trellising gear, and crates, and by water movement of
infested soil. It is distributed locally by tools and machinery
used in the cultivation of the seedbed and the field. Seed trans-
mission of the wilt fungus is rare. Occasionally the fungus may
penetrate into the fruit and into the seed. If diseased fruit
are harvested, the infected seed are so light that they are
floated off and eliminated during the extraction process. Spores
may cling to the surface of some seed, but-a-seed disinfectant
will eliminate this source of infection. Conently, th ap-
pearance of Fusarium wilt in a new area is nearly always
traceable to infested soil.

Infected seedling plants are stunted, the older leaves droop
and curve downward, and the plants frequently wilt and die.
Symptoms on older plants generally become apparent during
the interval from blossoming to fruit maturation. The earliest
symptom is the yellowing of the older, lower leaves. These
yellow leaves often develop on only one side of the plant, and
the leaflets on one side of the petiole frequently turn yellow
before those on the other side. This one-sided effect is caused
by the invasion by the fungus of the vascular system on one
side of the plant, while the remaining vascular system is
functioning normally. The yellowing process gradually includes
more and more of the foliage and is accompanied by wilting
of the plant during the hottest part of the day (Figure 7).
The wilting becomes more extensive from day to day until the
plant collapses and dries up. The vascular tissues of a diseased
plant is often dark brown in color (Figure 8). This browning
often extends far up the stem and is especially noticeable in a
petiole scar. The browning of the vascular system is character-
istic of the disease and generally can be used for its identifi-
cation. Fruit infection occasionally occurs and can be detected
by the vascular tissue discoloration within the fruit.

Figure 7. Tomato plants with Fusarium wilt.

Figure 8. Tomato stems affected with Fusarium wilt, showing the darkened
vascular tissues.

Use resistant tomato varieties for the control of the common
race 1.
Sanitation must be practiced for control of race 2, since
no resistant commercial varieties are yet available. Prevent
movement of race 2-infected plants and infested soil clinging
to machinery, hand-tools, vehicles, trellising and staking im-
plements, and field crates into areas free of race 2. Do not


flood land, since this will spread the fungus. Do not overhead
irrigate with ditch water which may be contaminated with the
tomato wilt Fusarium. Do not use infested land for seedbeds.
A 5- to 7-year crop rotation, while it does not eliminate the
Fusarium fungus, will greatly reduce losses.

Southern Bacterial Wilt
Southern bacterial wilt is caused by the bacterium Pseudo-
monas solanacearum E. F. Smith which attacks numerous plants
such as tomato, tobacco, potato, eggplant, and many weeds.
The disease is most prevalent in southern United States. The
bacterium is distributed throughout most Florida soils, but it
is not present in the calcareous soils of Dade County, possibly
because of the high soil pH. On old, light, sandy soils of central,
southern, and northern Florida the bacterium may cause ex-
tensive damage in late spring during warm, wet weather.
Considerable seedling loss is also encountered in early fall
during the warm, wet months of August, September, and
The bacterium (P. solanacearum) causing southern bacterial
wilt is soil borne, and infection usually occurs through the root
system. Spread of the baterium can occur from unwounded
diseased roots to unwounded healthy roots, but root wounding
by nematodes and cultivation greatly enhances disease spread.
Infection of stems through insect and pruning wounds occa-
sionally can occur. The bacterium is spread by drainage water
and by transplanting symptomless infected plants from the
seedbed to the field. The organism is also commonly spread
in ditch spoil when drainage ditches are cleaned. This often
results in the disease being most prevalent along ditches where
spoil has been spread. The bacterium is most destructive during
periods of warm (86-90 F), wet weather, and its damage is
worse where drainage is poorest, since the bacterium needs
abundant moisture for optimum development.

A diseased plant is characterized by its wilted condition
and lack of yellowing of the foliage. Affected plants rapidly
wilt and die without yellowing of the leaves (Figure 9). Plants
that are attacked by this pathogen frequently appear stunted
before wilting occurs. The pith near ground level is dark colored
and has a water-soaked appearance. If the stem is cut near

Figure 9. Bacterial wilt of tomato: (Top) healthy and wilted tomato plants
and (Bottom) split stems showing discoloration and decay of pith. (Courtesy of
the United States Department ofoAgriculture.)

the base, a slimy, gray material may exude from the cut.
In later stages the pith decays and the stem becomes hollow
(Figure 9). The vascular tissue becomes brown, and adven-
titious root formation may be enhanced. The rapidity of wilt-
ing and death, the lack of foliage yellowing, and the pith decay
and hollowness distinguish this wilt disease from the Fusarium
and Verticillium wilts.

Control is obtained by sanitation, sterilization, and crop
rotation. Avoid rotation with solanaceous crops. Do not spread
ditch spoils onto areas to be cropped. To prevent spread by
drainage water do not plant near land where the disease was
present the preceding year. Do not flood infested land for
nematode or disease control, since spread of the bacterium will
result. Do not plant seedbeds on land where the disease has
ever been present. If such land must be used, treat with methyl

Phoma Rot
This disease is caused by the organism Phoma destructive
Plowr. It is not common in the United States except in the
southern tomato-growing areas where it is often destructive.
In Florida this disease occurs throughout the entire tomato-
growing area and appears more or less sporadically from season
to season. Occasionally P. destructive causes considerable
damage to the foliage and stems of tomatoes. Fruit decay is
more prevalent in transit than in the field.
P. destructive is able to live from one season to the next
in decaying plant material. It is spread in the field by infected
seed, by spores which form on stem and foliage lesions, by
diseased seedlings that are transplanted from the seedbeds to
the field, and by spores on fruit lesions. The infected fruit
may be transported to the packing house, and there through
the packing process the spores may be distributed over a large
number of fruit which may become infected through superficial
injuries. Experimental test shipments have shown that mature-
green tomatoes showing no evidence of Phoma rot at time of
packing may develop visible decayed spots by the time the
tomatoes reach the northern markets. The amount of infection,
however, depends directly upon the number of growth cracks,
shoulder bruises, or other wounds present, and upon surface

moisture. The spores cannot germinate and penetrate the tomato
fruit unless they are moistened by irrigation, rain, dew, wash
water, or by the tomato juice coming from wounds. The fungus
can grow at temperatures as low as 42 F and as high as
920 F, but it is most favored by a temperature of about 80 F.

On the foliage, small black spots first appear on either
surface of the leaf. These spots are round or irregular in shape,
slightly sunken, and as they rapidly enlarge, become typically
zonate as in early blight (Figure 10). In fact, it is necessary
to examine these spots very critically with a hand lens to
ascertain whether they are Phonma rot or early blight lesions.
They enlarge and often coalesce, causing the leaves to become
yellow, curl up, and adhere to the main stem of the plant in
much the same manner as with early blight. The pycnidia or
fruiting bodies, which are produced in these spots on the
foliage, are imbedded or sunken in the leaf tissue with only a
small opening to the outside. Thus they are very difficult to
observe, and without a hand lens it is almost impossible to
make a definite diagnosis. On the stems the lesions are black,
elongate, and zoned. The damage to young seedlings may be
extremely severe, since they are often completely girdled by

/ ,.

Figure 10. Phoma spotting of tomato leaflets.

Figure 11. Phoma rot of tomato fruit.

the stem lesions. Plants are attacked from the seedling stage
to maturity.
On the fruit the spotting takes place only where the fruit
have been injured, and in most cases the fungus enters through
growth cracks, the stem scar, and other mechanical injuries
around the stem end, although in some cases it enters through
punctures made by insects. When it enters any skin rupture
it produces a distinctly sunken spot almost black in color which
enlarges rapidly and involves large portions of the fruit (Figure
11). The disease is readily distinguished from other rots by
the black color of this spot which is speckled with small, black,
pimple-like eruptions. These specks are the pycnidia or fruiting
bodies of the fungus.
The spotting of packed fruit in transit is very important.
The typical injury inflicted on fruit in the packing and transit
period is a scarring that takes place around the stem end. In
packing the fruit, the general practice is to overload the crate.
The top layer of fruit of this crate is not completely protected,
and if it becomes injured is subject to the attack of this fungus.

Disinfest seedbeds (p. 82) and disinfect seed (p. 83) before

planting. Do not set diseased plants in the field. Spray seedbed
and field plants with recommended fungicides. If these practices
are followed, excellent field control will be obtained and little
loss in transit will be experienced.
Pack only smooth fruit, discarding any that may show spot-
ting or lesions. Bulging, overfilled crates cause fruit injury
and should be avoided.

The wilting and falling over of young seedlings encountered
every year in the seedbed or field is spoken of as damping-off.
This disease is not confined to tomato but is found on seedlings
of numerous vegetable crops. It is often difficult to name the
organism causing the trouble, and in a large number of cases
several organisms are involved. Some of these commonly found
in the seedbeds in Florida are Rhizoctoni( soloni, Pythiun spp.,
Phytophora parasitica, Sclerotihn rolfsii, Sclerotilnia scle'rotio-
rnm, and Fusarium spp. Other fungi have been found associated
with diseased seedlings, but usually they have been found secon-
dary to those previously mentioned. Some of these damping-off
fungi cause diseases of older plants and are discussed further
under the appropriate section.
There are two kinds of damping-off: pre-emergence and
post-emergence. Pre-emergence damping-off consists of a decay
of the seed or seedling before emergence from the soil. Post-
emergence damping-off occurs after the seedlings have emerged
from the soil. Seedlings are extremely susceptible to this disease
for about two weeks after emergence. As the seedling stems
harden and enlarge, damping-off generally ceases to be a prob-
lem. Often seedlings do not die but are severely damaged and
have limited root systems. Such plants remain stunted and often
do not produce well.
In Florida damping-off generally is most serious in wet
soils during the warm months of August and September when
the fall crop is planted.

The symptoms of damping-off, resulting from invasion of
the plant tissue by any of the above organisms, are in most
cases quite similar. The first indication of the disease is a
slight drooping of the cotyledons at the tips and a general lack
of turgidness of the seedlings. This drooping of the tips of

Figure 12. Damping-off of tomato seedlings.
Figure 12. Damping-off of tomato seedlings.

the cotyledons rapidly develops into a marked wilting, and
very shortly, often within 12 to 24 hours, the stems appear
water-soaked at the soil line (Figure 12). Soon the plants fall
over, with the stems bending at the surface of the soil. The
affected plants then quickly wither and die. During the next
24 hours, the mycelium of the fungus may overgrow the diseased
seedlings. At times the spidery web-like threads of the fungus
can be readily detected in the early morning over the surface
of the soil and of the diseased seedlings. Attacked seedlings
often are not killed. They merely are stunted and abnormally
green, and have cotyledons that roll downward. This type of
attack is destructive because such diseased plants, unnoticed
by the grower, are left in the field or transplanted in the field
and die later.
Damping-off may be found in spots in the seedbed where
it is developing from a primary infection, killing the seedlings
in more or less circular patches. It may also be found generally
infecting rows of plants in seedbeds, killing large numbers of

Soil sterilization is the only sure way of controlling damping-
off in seedbeds. This can be accomplished either by the appli-
cation of methyl bromide or other seedbed fumigants, or by

treating the soil with live steam. Another important consider-
ation is the selection of the seedbed in reference to the type
of soil, moisture relationships, and ventilation. A general prac-
tice that has been found of considerable benefit in the field
is the stirring of the soil between the rows of seedlings by
use of small tools to allow drying of the top soil.

Late Blight

The disease known as late blight of tomato is caused by
Phytophthora infestans (Mont.) dBy., the same fungus that
causes late blight of potato. In the United States the disease
on tomato was virtually unknown outside New England and
some areas of West Virginia and Pennsylvania until 1946,.-
when an epidemic destroyed much of the crop. In Florida the
disease occurs sporadically, and occasionally it is very destruc-
tive. Late blight in Florida must always be considered danger-
ous during the cool months of November, December, January,
and February if rains, fogs, or heavy dews occur.
The late blight fungus causes considerable damage to the
stems and leaves and also produces a distinctive rot of both
the mature and immature fruit. Affected fruit decay very
rapidly in transit and are a menace to the load because the
fungus is able to pass from one fruit to another.
In Florida the late blight fungus remains alive during the
hot summer months on Soloanum hosts. In the Northern states
the fungus survives between crop seasons in potato tubers, and
the disease may develop on volunteer plants from tubers inad-
vertently left in the soil, from tubers in cull piles, or from
tubers used as seed pieces.
During periods of high humidity (91%-1007%) and mild
temperatures (64-73' F), fruiting bodies (sporangia) are
formed on the surface of lesions. These sporangia are dis-
seminated by wind and splashing rain, and insects. The fungus
is also spread on diseased transplants.
The sporangia germinate in two different manners depending
upon the temperature. At approximately 530 F the sporangia
germinate by forming zoospores (usually 8 zoospores per spor-
angium) which in turn form germ tubes that penetrate into
susceptible tissue. At about 77' F the sporangia germinate
directly by means of a germ tube. Therefore at low tempera-
tures the inoculum level is increased tremendously because of
the formation of zoospores. The germ tubes from both zoo-

spores and sporangia grow and develop best at 700-76 F.
Consequently, the importance of late blight is almost entirely
determined by weather conditions. Cool (500-70' F), moist
nights favor spore germination, and warm (70o-80' F) days
favor development of the fungus within the plant. Under such
weather conditions the disease will cause extreme damage to
tomato plants. Hot, dry seasons are so unfavorable for the
growth and dissemination of the fungus that it is unable to
cause damage.

One of the first symptoms is the bending of the leaf petiole.
This bending can occur before leaf symptoms are evident, and
the angle may increase from an acute angle to 90 or more
degrees. The lesions produced on the leaves are rather large,
irregular, greenish, water-soaked areas (Figure 13). These
areas enlarge rapidly and become brown and paper like. During
moist weather or periods of heavy dew, a fine, white mold may
develop near the margin of the diseased tissue on the lower
surface of the leaf. The spores are borne in great profusion
in this ring of white mildew. In severe epidemics this leaf
blight may destroy a majority of the plants in a field.
Stem lesions may occur anywhere on the stem, and appear
as water-soaked brown areas that may girdle and kill the plant.
Severely diseased plants often appear to have been frozen.
Fruit lesions appear as large, green to mahogany colored,
irregular, water-soaked blotches (Figure 14). These lesions
most commonly appear on the upper half of the fruit, are firm
in texture, and may occasionally become zonate. Often soft rot
organisms invade blighted fruit and cause rapid disintegration
of the fruit.

Excellent control of late blight can be obtained by spraying
on a 4 to 5-day schedule with recommended fungicides. Tomato
fruit that show water-soaked blotches should never be packed
for shipment.

Early Blight
This destructive disease is caused by the fungus Alternaria
solani (Ell. & G. Martin) Jones & Grout and has been found

Figure 13. Tothato leaflets showing late blight lesions. (Courtesy of the
United States Department of Agriculture.)

in most of the tomato-growing regions of the United States.
Early blight is damaging in the New England, Southeastern,
Middle Atlantic, and Central states but is of minor importance
in the Pacific Coastal states. The disease is common throughout
Florida and is destructive in all parts of the state.
A. solani attacks the foliage, stem, and fruit of the tomato
plant and can cause severe damage during all stages of develop-
ment of the plant. The fungus survives from season to season
on decaying plant debris in the soil and on volunteer tomato
plants. Primary infection generally is caused by the fungus
in the soil and occurs during periods of mild (75' F), rainy
weather. The thick-walled spores which are formed on the stems

Figure 14. Tomato fruit and foliage affected with late blight. (Courtesy
of the West Virginia Agricultural Experiment Station.)

and leaves are able to survive unfavorable conditions. They
are disseminated by wind and rain.

Early blight is first observed in the field as small brownish-
black lesions on the older foliage. The spots enlarge rapidly,
and by the time they are 1/4 inch in diameter or larger, con-
centric rings may be distinguished on the dark brownish portion
of the spot (Figure 15). The tissue surrounding the spot may
become yellow in color, and when spotting is abundant the
entire leaf may become yellow. In some instances when the
spot is located on one of the primary leaf veins the area beyond
the spot soon dies and becomes brown. In the latter part of
the season the lesions become very numerous, and under favor-
able conditions for disease development an affected plant be-
comes defoliated, which exposes the fruit to sunscald.
Stem lesions on seedlings are small, dark, and slightly
sunken (Figure 16). These lesions enlarge, forming circular
or elongated lesions with concentric rings and light centers.
If stem-infected seedlings are set in the field, the lesions con-
tinue to enlarge at the ground line and partially girdle the

5 7

Figure 15. Symptoms of early blight on a tomato leaflet.


4C 4

stem attachment, either in the green or ripe stage. The fruit



lesions attain considerable size, often involving nearly the entire
fruit, and usually show concentric ringing (Figure 17). The
diseased areas appear leathery and may be covered by a velvety
mass of black spores. Infected fruit frequently drop, and losses
of 50% of the immature fruit may occur.

Figure 17. Symptoms of early blight on tomato fruit.

Spray with recommended fungicides. Do not use old tomato
land for seedbeds. If old land must be used, or if permanent
beds are used, disinfest the soil with steam or a chemical.
Provide adequate ventilation of seedbeds. Destroy seedbeds
where the disease has become prevalent. Do not set diseased
plants in the field.

Soil Rot
Soil rot is caused by the fungus Rhizoctonic solani Kuhn
which has been found damaging tomatoes in most sections of the

United States. In Florida, R. solani is distributed over the
entire tomato-growing area.
Soil rot has been exceedingly important to the grower be-
cause of the extensive damage to immature fruit prior to pick-
ing. Instances during the past have been noted in which large
portions of "old" fields have been total losses because of soil rot.
Such instances are exceptional, but R. solani must be consid-
ered present in all "old" soils and under favorable conditions
potentially destructive. The disease is most prevalent during
periods of wet weather and moderate temperatures on crops
where the fruit come into contact with the soil.
R. solani lives in the soil from one season to the next and
is spread by wind, rain, flowing water, and by the distribution
of dieseased plants at transplanting time.
R. solani attacks tomato plants at all stages of development
and is damaging to seedlings both in the seedbed and in the
field. The seedling disease caused by this fungus is discussed
under the section entitled "Damping-Off".
Transplants occasionally are attacked at the soil-line or an
inch or two above, soon after being set into the field. This
disease phase is prevalent in "old" tomato fields where seasonal
conditions are favorable for development of the fungus and the
plants in the field are yet small.
Under optimum conditions R. solani forms sexual basidio-
spores which cause aerial infections. However, most infection
occurs where the larger branches and leaves of the tomato plants
come in contact with the soil. The fungus also attacks the fruit
wherever they contact the soil, and in some instances it causes
a rot of fruit that are as much as 14 to 18 inches above the
soil. The fruit seem to be more susceptible to invasion by this
fungus than the older plant stems. Most of the fruit lesions
are large enough at packing time so that infected tomatoes
can be easily graded out, but if any are overlooked and get
into the crate they will be decayed by the time they reach the
market. Wounds are not necessary for infection, and for this
reason the fungus often infects neighboring tomatoes in a crate
merely by contact.


R. solani on seedlings causes a typical damping-off. The
tender seedling stems become water-soaked and weakened to
such an extent that the plants wilt at first, then fall over and

die. In older plants that have formed woody tissue the fungus
invades the cortical tissue of the stems, causing them to become
brown and roughened. The epidermis, cortex, and cambium
are killed, become soft, and slough off, leaving large cankers
which often completely girdle the stems and kill the plants.
In the development of these cankers the plants appear to be
dwarfed and in an unhealthy condition. Finally a slight wilt-
ing is observed, and eventually the plants wither and die.
Examination in most instances will reveal a few brownish,
shiny, hair-like threads of the mycelium of the fungus growing
over the invaded tissue.
R. solani causes the fruit to decay in all stages of develop-
ment. It penetrates the fruit through wounds or the unbroken
epidermis and invades the tissue, causing numerous small,
brown, sunken spots on the side of the fruit that is in contact

Figure 18. Soil rot of tomato fruit.

with the soil. Usually there is a single point of invasion by the
fungus, and as this spot enlarges it becomes zonate with
concentric brown rings, somewhat typical of buckeye rot
(Figure 18). This marking may be distinguished from buck-
eye rot in most instances by the narrowness of the concentric
zones. With this disease the zoning is extremely definite and
more pronounced than in buckeye rot. In transit these mark-
ings gradually disappear as the spot enlarges, so that by the
time an infected fruit reaches the market the zonation is en-
tirely obliterated. In most cases the epidermis is ruptured at
the center of the spot in soil rot, whereas in buckeye rot the
epidermis is very seldom broken. Soil rot develops much more
slowly than buckeye rot and does not produce a watery, soft
decay. In the early stages of the disease the fungus mycelium
seldom can be detected on the outside of invaded fruit, but in
the more advanced stages it may be seen if the tomatoes are

The most important methods of control for this disease are
the disinfestation of the seedbed to prevent damping-off and
the careful regulation of moisture. The disease is seldom of
importance in fields where the plants have been staked and
Fruit losses in transit may be controlled by careful grading.

Botrytis Gray Mold
This disease is caused by the fungus Botrytis cinerea Pers.
ex. Fr. and should not be confused with leaf mold or with gray
leafspot, which are distinct diseases caused by different fungi.
Prior to 1949, gray mold was considered primarily to be a
disease of greenhouse tomatoes. However, as Florida growers
in search for virgin land moved from the naturally calcareous
coastal soils to the palmetto-pine acid soils, the disease became
prevalent and destructive in Florida. Because gray mold de-
velops primarily on plants grown in calcium-deficient soil, very
little damage occurs to plants grown on soils limed to a pH of
6.5 or on naturally calcareous soil. With the exception of some
areas in California and North Carolina, gray mold causes little
damage to field tomatoes outside Florida.
B. cinerea generally attacks large plants with heavy foliage
during cool, wet, and humid weather. The fungus gains entrance

through leaf scars, insect wounds, freeze-damaged tissue, other
disease lesions, or other dead or dying tissue, and from there
grows into the living parts of the plants. Under favorable
conditions B. cinerea may cause stem lesions severe enough to
cause wilting or even death of the plant. Fruit become infected
through wounds, growth cracks, insect injuries, or directly
through the cuticle. Grayish-brown conidiophores and conidia
form on the diseased plant tissue in great profusion. The
conidia are easily detached by wind currents and spread through
considerable distance. Occasionally these spores germinate and
penetrate young green fruit during nights when heavy dews
or rains occur and temperatures range between 600 and 750 F.
If bright sunlight and high temperatures occur the following
morning, the fungus is killed. These abortive infections result
in the development of small whitish rings called "ghost spots".
For many years ghost spots were considered to be symptoms
of a disease distinct from gray mold, but evidence presented
during the past decade prove that ghost spot is merely another
aspect of Botrytis gray mold.

On the stems gray mold is characterized by large, elliptically
shaped, water-soaked lesions which during cool, wet weather
soon become covered with the grayish-brown mycelium and
spores of the fungus (Figure 19).
The lesion produced on the fruit is a watery area with a
light brown or tan colored central region (Figure 19). The
decay develops rapidly, and the fruit is converted into a soft,
watery mass within a few days. If the skin is broken the
grayish mycelium and spore clusters develop within a few

Figure 19. Symptoms of gray mold: (1) tomato fruit rot, (2) "ghost spot"
symptom, and (3) stem lesions showing the sporulating fungus. (Courtesy
of R. E. Stall.)

Occasionally following abortive infections, small whitish
rings approximately 1/6 inch in diameter develop on young
green fruit (Figure 19). These "ghost spots" are usually single
rings but may be solid white spots; in the center of a spot
there generally is a dark-brown speck. The spots are super-
ficial on the pericarp of the fruit, do not increase in size, and
do not affect fruit quality.
Infected leaves, which develop gray lesions that are often
wedge shaped, soon wither and die. During cool, wet weather
the diseased leaves become covered with the gray mycelium
and spores of the fungus.

To avoid gray mold, crop tomatoes on soil limed to pH
value of 6.5 or on naturally calcareous soil. Spray with recom-
mended fungicides.

Southern Blight
Southern blight is caused by the fungus Sclerotium rolfsii
Sacc. This disease is typically southern in its range, although
it has been found in scattered places in some of the North
Central states. The disease is common and widespread in Flor-
ida, being serious in all sections of the state except Dade County.
It has been collected in Florida on more than 100 different
host plants, both cultivated and wild, including woody peren-
S. rolfsii is favored in its growth by high temperatures
and abundant moisture; consequently it is most prevalent in
light, poorly drained soils of the South. The fungus usually
does not form spores but the fungal threads during hot rainy
weather grow luxuriantly and extensively through the soil.
The fungus also is distributed by spherical, tan-to-brown, hard,
mustard-seed-size sclerotia which survives in the soil and are
spread by surface water and by movement of infested soil.
In the past, because of the growing of tomatoes during
the winter and early spring, S. rolfsii was seldom found attack-
ing seedlings or small plants. But in recent years as tomato
growers have moved inland and the fall season has become
initiated during the warm and wet months of August and
September, considerable seedling loss has been caused by the
southern blight fungus.





Figure 20. Tomato stems affected with southern blight, showing sclerotic
and mycelial growth.


Mature plants are attacked just below the soil surface and
are completely girdled. The tops wilt and die in a manner
similar to those attacked by the Fusarium wilt or southern
bacterial wilt organisms. The mycelium often grows over the
diseased tissue and surrounding soil forming a white mat of
mycelial threads with the typical tan-to-brown, mustard-seed
size sclerotia (Figure 20). The fungus moves more readily down-
ward than upward in the plant, and often the entire root system
is destroyed. The fungus is exceedingly destructive on ground
crops and attacks the fruit where they contact the soil. Slightly
sunken, yellow spots develop on invaded fruit, which rapidly
decay, collapse, and become covered by a white fungal mass
with numerous sclerotia (Figure 21).
Seedling invasion occurs rapidly, and the seedlings die
quickly. As the plants grow older they become more woody
and more resistant to attack.

The best protection against southern blight is sanitation.
Whenever diseased fruit or plants are found in a field they
should be collected and disposed of, preferably by burying
2 or 3 feet deep or by burning. In this way the distribution
of the sclerotia throughout the field will be prevented, and to
a large extent the disease will be controlled. Since these sclero-

Figure 21. Tomato fruit affected with southern blight, showing type of rot
and numerous sclerotia.

tia are so large that they are not carried by the wind and
since their numbers are comparatively small, sanitation is an
effective control measure. The careful regulation of water by
means of a well-designed irrigation-drainage system to prevent
excessive soil moisture will help prevent the occurrence of the
disease. Plants in fields where the disease has been prevalent
should be staked. This will keep the fruit from touching the
ground and thus prevent infection.

Stem Rot
The disease caused by the fungus Sclerotinia sclerotiorum
(Lib.) dBy. is not a common disease of tomatoes in Florida.
Stem rot occasionally is serious, but in general comparison with
other diseases it is of minor importance. The disease is most
commonly found in fields where it has been prevalent on other
prior crops. The disease also is found on tomatoes in other
South Atlantic and South Central states, but only occasionally
is it destructive.
S. sclerotiorum attacks lettuce, celery, cabbage, potato, egg-
plant, pepper, beet, and numerous other crops. It survives
from season to season principally as hard, black, shiny sclerotia
which are 1/- inch in size. These sclerotia are hard growths
of the fungus capable of surviving considerable periods of un-
favorable weather conditions. When the soil becomes cool (66-
72' F) and moist the sclerotia develop delicate apothecia which
produce sexual spores of the fungus in large numbers. These
spores are scattered by the wind and rain and are capable of
causing the disease whenever they find a favorable environment.
S. sclerotiorum requires abundant moisture and is found
most often attacking mature plants with sufficient foliage to
retain moisture about the stems following rains, fogs, or heavy
dews. Air temperatures of 60-70 F are most favorable for
disease development.

The seedling disease occasionally caused by S. sclerotiorumn
is a typical damping-off, resulting in quick wilting and finally
death of the seedlings. The fungus usually attacks older plants
at or slightly above the soil line. The grayish-white mycelium
covers the surface of infected tissues and invades the epidermal
and cortial layers of the main stem, penetrating the vascular
system and cutting off the food supply. The plant shows a

:+ -**.
.' c *
r-. ,1

Figure 22. Stem of tomato plant killed by stem rot, showing large sclerotia
formed by the fungus. (Courtesy of the United States Department of Agri-

marked wilting condition and eventually withers and dies. An
examination at this time will show a large canker at the base
of the plant, which girdles the stem and causes the softer
tissue to disintegrate. Spliting of the stem will reveal cavities
filled with the black, large, hard sclerotia and the grayish-white
fungal growth characteristic of the fungus (Figure 22). In-
fected fruit may develop a watery soft rot. Occasionally the
leaves are affected; however, if petioles become affected the
fungus generally grows into the stem.

Adequate drainage, sanitation, and crop rotation are im-
portant in the control of this disease. Plant tomatoes in well-
drained fields. Do not plant tomatoes immediately following
Sclerotinia-diseased crops of beans, cabbage, celery, lettuce,
potato, or any other susceptible crop. Flooding fields for 5 or
6 weeks in the summer greatly reduces the sclerotial population
and gives excellent control of the disease. However, flooding
will further spread other soil-borne pathogens and possibly
make diseases such as Fusarium and southern bacterial wilt of
more general distribution within the flooded area. Apply
cyanamid to marl soils at the rate of 500 to 700 pounds per
acre and wait 30 days before setting plants. On sand land
apply 900 pounds per acre of cyanamid and wait 3 months
before planting.

Leaf Mold
Leaf mold is caused by the fungus Cladosporium fulvum
Cke. This disease is more or less common on tomatoes in the
United States. In the northern section of the country leaf
mold is considered to be more serious on greenhouse tomatoes
than on field tomatoes. It is occasionally important in the
fields of the eastern tomato sections and in the South. The
disease once was common and widespread in Florida, but with
the introduction of the modern carbamate fungicides and re-
sistant varieties it now is of little consequence.
The importance and destructiveness of leaf mold on un-
protected susceptible varieties depend on seasonal conditions,
since development of the disease is especially dependent upon
moisture and temperature. A relative humidity between 95%
and 100%o is needed for spore germination and growth. Very
few spores germinate between 90% and 95% relative humidity,

and no spore germination occurs below 90%. Infection can
occur in temperatures from 390 to 900 F but rarely occurs
below 51 F. The optimum range is from 70 to 77' F.
C. fulvum survives from season to season as mycelium and
conidia in diseased plant debris in the soil. The conidia are
readily disseminated by wind and splashing rain.
Floralou, Floradel, Indian River, Manalucie, and Manapal
have been resistant to four races of the causal fungus in Florida
to date, although there are areas in North America where this
type of resistance is not effective.

Leaf mold is usually first observed on the oldest leaves
closest to the ground where ventilation is poorest and the period
of excessive moisture is most uniform. It is detected on a
leaf by the appearance of small, light-colored spots which turn
to a distinct light yellow color followed by the browning, drying,
and death of the cells in this area. Often when the infection
is severe these spots coalesce, and the foliage is rapidly killed.
The causal fungus sporulates on the lower surface of the leaf
but very rarely is found producing spores on the upper surface.
Careful examination of a yellow-spotted leaf will reveal an
olive-green mold on the lower surface almost exactly coinciding
with the yellow area (Figure 23), the only discrepancy being
that the yellow area may be a trifle larger than the patch of
mold. This patch of mold is more dense and of a slightly deeper
color in the center than at the edges. The dense mass is com-
posed of spores of the fungus that are readily disseminated
by air currents. When the spores settle on another tomato
plant they are capable of causing a similar spot. The fungus
primarily attacks leaf blades, but it has been found on petioles,
peduncles, blossoms, stems, and, rarely, on fruit.

Leaf mold is controlled by the application of recommended
fungicides. Use resistant varieties. Staking, pruning, and ven-
tilation help to control the disease.

Buckeye Rot
Buckeye rot is a disease caused by the fungus Phytophthora
parasitic Dastur. The range of this disease over the United


Figure 23. Leaf mold of tomato leaflets.

States is limited, and it is rarely found to be of serious eco-
nomic importance outside of the Southeastern and Gulf states.
In Florida the disease occurs throughout the entire tomato
area, although usually it is not exceedingly destructive. How-
ever, it may become destructive during periods of warm, wet

'IIIl~i~ 1

P. parasiticm-may -cause damping-off-of seedlings, girdling
of the stems, blight of the leaves, and rot of the fruit in any
stage of development. The rot is usually confined to fruit in
contact with the soil. This is not always the case, however,
since half-mature fruit a foot or more above the soil may
occasionally rot. These fruit probably are infected by the
pathogen in infested soil splashed onto them during heavy
rains. In instances where the fungus attacks fruit that are
not touching the soil, weather conditions must be exceptionally
favorable for disease development. Since the fungus is soil-
borne and needs abundant moisture for optimum development,
its damage is worse where drainage is poorest. During warm
(75-85 F) periods of extended rainfall the disease can de-
velop in epidemic proportions, causing complete losses. Wounds
in fruit are not necessary for infection as the fungus is able
to penetrate directly. It can also spread from one fruit to
another in the pack during transit.

Damping-off caused by P. parasitic is similar to that caused
by other damping-off organisms. Girdling of the stem may



Figure 24. Buckeye rot of tomato fruit.

cause the plant to wilt and eventually to die. The lesion, which
is brown and generally sunken, develops primarily at the soil
surface but may extend 4 to 6 inches upward. Leaf symptoms
are identical with late blight except no sporulation of the
fungus can be seen on the undersides of the leaf.
On fruit that are touching soil P. parasitica enters at the
point of contact, causing a slight brownish spot. As the fungus
develops and the spot enlarges, a series of irregular brownish
and light colored concentric bands are produced, forming a
typical buckeye effect (Figure 24). Fruit very rapidly decay
and break down in a semi-rot. All stages in the growth of the
tomato fruit are attacked by the fungus. In some instances
when the fruit remain damp and moist for a day or two, the
concentric zoning effect may be quite feeble and invasion of
the fruit by the fungus exceedingly rapid. Under these con-
ditions the invaded areas become dull brown, and the fruit
collapse without the production of .the marked concentric zones.
In some cases where the epidermis is ruptured, the mycelium
of the fungus can be distinguished.

Drainage is an important factor in the control of this
disease. Where the excessive moisture can be withdrawn from
the fields, the disease seldom is of serious economic importance.
Staking plants is of considerable benefit, making possible ade-
quate ventilation and preventing fruit from coming in contact
with the soil. Recommended fungicide sprays give excellent
control of the disease. To prevent loss from buckeye rot in
transit, it is important to grade and pack the fruit carefully.

Anthracnose is a common disease caused by the fungus
Colletotrichum phomoides (Sacc.) Chester and has been found
widespread on tomatoes in the United States. In Florida the
disease is widely distributed but seldom is serious in the field
or of any consequence during transit.
C. phomoidcs can enter healthy fruit, but it is mostly a
wound parasite and primarily enters fruit through insect stings
or mechanical injuries or through skin and growth cracks that
may develop on the fruit in the field. The fungus invades green
fruit, but the symptoms do not appear until the fruit begin

to ripen. Then disease symptoms develop rapidly and a charac-
teristic soft-rot ensues. Consequently the greatest losses occur
in fruit that have been matured on the vine for local markets.
C. phomoides is spread in the field by spores which are
easily detached and scattered by wind and rain. The fungus
lives from year to year in diseased tomato tissue that remains
in the soil.

The first sign of infection is a sunken, water-soaked spot
on the fruit. It enlarges, forming a circular spot which is
distinctly sunken, and soon involves large portions of the fruit
(Figure 25). If the causal fungus enters through a growth-
crack, the tissue on each side of the crack collapses and in a
very short time involves the entire fruit. The epidermis rarely
becomes ruptured in case of infection at a single spot. The

f| HN1-

Figure 25. Anthracnose of tomato fruit.

fruiting bodies of the fungus develop on the epidermis. They
are irregular in shape and vary in color from pink to brownish-
black. These fruiting bodies, or acervuli, are often arranged
in concentric circles, but this is not always the case. Incon-
spicuous, small, dark spots of dead tissue develop on the tomato
foliage and stems. Sporulation on these spots is sparse but
sufficient to maintain the fungus until fruit are formed.

Spray with recommended fungicides.

Septoria Leafspot
This leaf spot disease of tomatoes is caused by the fungus
Septoria lycopersici Speg. It is common and destructive in the
Central and Northern states east of the Mississippi River, and
less troublesome in the states bordering on the west of the
Mississippi River. In the central portion of the United States,
east of the Mississippi River, it is considered the worst disease
on tomatoes and probably is as destructive as all other diseases
combined. In Florida its occurrence is exceptionally rare.
The fungus spreads rapidly from the primary infection
by means of spores which are scattered by wind, rain, running
water, and cultivation. The disease flourishes and is most
serious during the warm parts of the growing season. It de-
velops rapidly even during periods of little rainfall, since abun-
dant dews are all that is necessary for germination of the
spores and infection of the plants. The fungus lives over un-
favorable periods on dead plant material such as stems and
leaves and is scattered in this way over considerable areas in
the field. When conditions are favorable for development, the
spores germinate and penetrate the plants.
Following infection of a plant by the Septoria fungus, small
water-soaked spots develop on either surface of the leaf. The
spots rapidly enlarge until they are about 1/4 inch in diameter;
very few become larger unless a number of them coalesce.
The spots are brownish-black to a dull slate-white in color
and usually when light colored are surrounded by a dark
margin. The fruiting bodies or pycnidia usually develop and
can be observed as little black specks in the spots. These
pycnidia vary in number from about 3 to 15 per spot. When
the disease is severe the leaves are killed rapidly, turn brown,
and hang on the plant.

Seed treatment and seedbed sterilization are suggested.
Recommended fungicides should be applied at regular intervals.

Nailhead Spot
Before 1926, nailhead spot caused by the fungus Alternaria
tomato (Cke.) Weber was of considerable importance in the
lower Atlantic and Gulf states. At that time, nailhead spot
was the most destructive disease of tomato in Florida. The
introduction and the general use of resistant varieties now
keep the disease under excellent control.
Nailhead spot affects the foliage, stems, and fruit of the
tomato plant and is severe anytime during the development of
the plant. A. tomato lives from one season to the next on old
vines and volunteer tomato plants. The spores are thick walled
and are able to survive long periods of unfavorable weather
conditions. They are disseminated primarily by wind and rain.
Under the favorable conditions of warm, rainy weather the
spores germinate in-approximately 4 hours and penetrate into
the tomat leaf within another 4 hours. Consequently infection
occurs rapidly, symptoms appear within a few days, and new
spores are produced within a week.

Lesions occur on the foliage, stems, and immature and
mature fruit. Foliage and stem symptoms of nailhead spot (Fig-
gure 26A), although similar to those of early blight, are charac-
teristically different in that (1) the concentric rings of the
lesions are much closer together and more delicate in appearance
and (2) the stem and leaf lesions, being usually about 1/ inch
in diameter, are smaller than early blight lesions. However,
unless there is fruit infection it is difficult, without micro-
scopical examination of spores, to definitely distinguish nailhead
leaf spots from those caused by several other pathogens.
Fruit lesions constitute the most conspicuous and diagnostic
symptom of the disease (Figure 26B). A fruit lesion first ap-
pears as a minute, light brownish discoloration on the epidermis.
As the spot enlarges, the outline becomes more definite and turns
dark brown. The epidermal cells are killed, and the inner area of
the spot fades until it is a dull grayish-white in color surrounded
by a narrow brownish band. This whitish inner area of the


F- m
r ;m
c 9^


Figure 26A. Nailhead spot on tomato stem.

Figure 26B. Nailhead spot on tomato fruit.

spot is gradually overgrown with fruiting structures of the
fungus which are black in color and cause the interior of the
spot to become smoky in appearance. The spots are slightly
sunken and continue to enlarge and deepen. At this stage of
development, the dry epidermal layer of cells ruptures, pro-
ducing a roughened center. The spots scattered over the fruit
enlarge considerably and in some cases coalesce, causing the
fruit to develop irregularly. Single spots on green fruit may
become 1/2 inch in diameter. In ripening, the area immediately
surrounding the infection spot frequently retains its green color.

Use resistant varieties. Spray with recommended fungicides.
Do not use old tomato land for seedbeds. If old land must be
used, or if permanent beds are used, disinfest the soil with



steam or a chemical. Provide adequate ventilation of seedbeds.
Destroy seedbeds where the disease has become prevalent. Do
not set diseased plants in the field.

Minor Fruit Rots
Fustrium rot, caused by Fusarium spp., is distributed over
the entire tomato-producing area of Florida. The disease is
most common on mature fruit following warm, wet weather
and in fields where blossom-end rot is prevalent. The causal
organism is a typical wound parasite attacking fruit through
natural openings at the blossom-end, punctures caused by in-
sects, and growth cracks. The fungus develops rapidly in the
fruit, causing a dry rot which may envelop the entire fruit
(Figure 27). The invaded fruit mummify and persist on the
vines except during rainy weather when the rot becomes soft
and watery. Fusarium rot is characterized by the development
of a pinkish mass of mycelial threads and conidia on the surface
of the invaded area.

Figure 27. Fusorium rot of a tomato fruit.

Oospora rot is caused by the fungus Oospora lactis (Fres.)
Sacc. f. parasitica Pritchard, which is one of the secondary
organisms. The disease in Florida is most common and destruc-
tive during rainy periods. These periods are not only favorable
for the development of Oospora but are also conductive to the
development of growth cracks wherein it gains entrance to the
fruit. Oospora is weakly pathogenic and invades through growth
cracks, insect punctures, or bruises. The moisture held in
growth cracks is ideal for development of the fungus. The
organism invades the tissue on either side of the point of
entrance and rapidly breaks down the cells, causing a watery,
soft decay (Figure 28). The disease develops rapidly and under
favorable conditions involves the entire fruit within 48 hours.
Rhizopus rot is caused by the fungus Rhizopus stolonifer
(Ehr. ex Fr.) Lind. The disease principally is a problem of
ripe fruit in transit and rarely occurs on green fruit. In the
field this fungus usually invades injuries produced by insects,
although it can invade natural cracks in the epidermis. Under
favorable conditions of high humidity and temperature (86'-
90 F) considerable growth of the fungus mycelium occurs
the first 12 to 18 hours after infection of growth cracks. Spor-
angiophores then develop, turn black after 6 to 8 hours, and
appear as small brown-black knobs on the end of the fungal
threads (Figure 29). The entire fruit may be broken down
and mushy within 36 to 48 hours.

Figure 28. Oospora rot of tomato fruit.

Figure 29. Rhizopus rot of tomato fruit.

Bacterial rot, caused by bacteria of the Ercinia carotorora
(L. R. Jones) Holland type, has been occasionally destructive
during past seasons in the tomato fields in Florida. The bacteria
gain entrance to the fruit through the stem scar after picking,
insect punctures, growth cracks, and wounds caused by culti-
vation, pruning, harvesting, or by other disease producing or-
ganisms. The bacteria cause a watery, soft rot. This soft decay
develops very rapidly and in a day or two will involve the
entire tomato fruit. The contents of the fruit become soft and
watery, and the fruit resembles a thin rubber bag one-half to
three-fourths full of water (Figure 30). A fruit in this con-
dition persists on the vine for several days or, if ruptured,
the ill-smelling contents leak out. Often the contents may evap-
orate, and the epidermis drys up and persists on the vine long
after the field has been abandoned.
Myrothecium rot is caused by Myrothecium species which
also attack onion, potato, southern pea, squash, and other vege-
tables. Development of this rot is favored by high tempera-
tures and abundant moisture. Consequently, the disease is most
common in the Southern states or in greenhouses. Fruit lesions,
caused apparently by direct penetration of the fungus, are
brown to black and are usually small, being 1]/ to 1 inch in
diameter. When the fungus invades through wounds, the lesions
are larger and may involve half the fruit. Spore masses form
on the fruit surface in concentric rings, giving the lesion a
zonate appearance. The rot may penetrate into the seed cavities

Figure 30. Bacterial rot of tomato fruit.

* 'fl
.- 4fv*-'

_- ,r .

Figure 31. Nematospora yeast rot of tomato fruit.

and there form spore masses. The rot is generally firm, but,
as other organisms invade, the fruit become soft and watery.
Nematospora yeast rot, caused by Nematospora coryli Peg-
lion, is principally a sub-tropical disease although it has been
reported in some Northern states. The fruit appear normal
except for small reddish-brown depressed areas (Figure 31).
The infected tissue is hardened and shriveled. So far as is
known, the yeast invades through feeding punctures caused by
the southern green stink bug, Nezara virid2la (L.). Warm,
sunny days encourage stink bug movement, and favor spread
of the yeast.

Use of crack-resistant varieties, avoidance of mechanical
damage during harvesting and packing, care in sorting and
packing to prevent the inclusion of infected fruit, staking or
trellising, crop rotation, and sanitation are major factors that
will reduce losses caused by the tomato fruit-rot organisms.
An insect and disease control program as normally practiced
in Florida should be followed.

Tobacco Mosaic (Tomato Mosaic)
The tobacco mosaic disease of tomato is caused by the virus
that also causes the common mosaic of tobacco. The disease
is found throughout Florida and the United States. The in-
citing virus not only causes mosaic diseases of tomato and
tobacco but also of eggplant, jimson weed, pepper, petunia,
nightshade, and many other solanaceous plants as well as plants
of other families.
The tobacco mosaic virus is readily transmitted by any
means which brings juice from a diseased plant into contact
with a slight abrasion or wound on a healthy plant. The virus
is commonly spread by machinery or workers who set trans-
plants, cultivate, stake, tie, prune, and harvest the crop. Al-
though aphid transmission of the tobacco mosaic virus was
reported as early as 1931, it is now generally accepted that
the virus is not transmitted by sucking insects. The virus
may occasionally be mechanically transmitted by chewing in-
sects such as beetles, grasshoppers, and caterpillars, as well as
by leaf mining flies (on the ovipositor of female flies) but

insect transmission of the virus must be considered to be far
less important than human transmission.
Infection after fruit setting causes loss reduction up to 5%,
but if infection occurs at the time of planting, yields may be
reduced 10% to 15%. Most of this loss occurs on the early
set fruit which usually command the higher market prices.
The infected plants tend to recover and produce normally after
this early fruit loss.
If plants infected with tobacco mosaic virus also become
infected with potato-X virus, a most serious disease ensues,
called double virus streak. The combined infection of the two
viruses causes affected plants to be nearly worthless. The com-
bination of tobacco mosaic virus and potato-Y virus also causes
a more pronounced effect than either virus alone. For these
reasons it is important to prevent or delay infection of young
plants as long as possible.
Tobacco mosaic virus can remain viable in plant debris in
the field, and thus infection occasionally occurs in Florida from
the remains of a previous tobacco mosaic virus-infected crop.
The virus moves to the roots of diseased plants, and it is of little
value to rogue infected plants and then set healthy plants in
the same area, for the healthy transplants will soon become
infected by the virus remaining in the roots of the diseased
plant. Seed transmission is rare, because the commercial prac-
tices used in extracting seed inactivate the virus. Tobacco
mosaic virus is present in cigarette, pipe, and cigar tobacco.
Possibly it also is present in chewing tobacco and snuff despite
the high temperatures used in their manufacture. Consequently,
workmen who use tobacco in any form are apt to spread the

The ordinary green strains of tobacco mosaic virus cause
mottled areas of light and dark green on the leaves (Figure 32).
The dark green areas are usually raised and crinkled. Plants
may be somewhat stunted and yields reduced if infected while
small, but little harm is incurred if the plants are not infected
until after one or two clusters of fruit have set. There may be
no fruit symptoms, or fruit may be deformed or marked with
spots or streaks. Certain strains of tobacco mosaic virus cause
a yellow mottling of the leaves and occasionally a mottling of
the stems and fruit (Figure 33). The yellow mosaic is more

severe than the green and may cause pronounced stunting of
the plants and large yield reductions.

Before handling plants and during staking, pruning, or tying
operations wash hands thoroughly in soap and running water

Figure 32. Tobacco mosaic of a tomato leaf. (Courtesy of the Ohio
Agricultural Research and Development Center.)


Figure 33. Fruit affected with the yellow strain of the tobacco mosaic virus.

or in 70% alcohol. This will wash off or inactivate the virus.
Do not use tobacco when working with tomato plants. If seed-
beds are used, periodically remove diseased plants. Do not
carry diseased plants to the field. Eliminate all volunteer
tomato plants. Direct seed where possible to avoid contact
with transplants. Sterilize equipment before each growing

Pseudocurly Top \
Pseudocurly top is a virus disease with symptoms identical
to those of true curly top of tomato, which is also virus incited.
Because pseudocurly top is transmitted only by the treehopper,
Micrutalis sp., and curly top only by the beet leafhopper, dif-
ferent viruses apparently are involved. Pseudocurly top ap-
parently is limited geographically to the state of Florida. Within
the state the disease occurs in all the major tomato-producing
areas during the fall crop season. Pseudocurly top was first
found in the Bradenton area in the early 1940's and at the
time affected only a few plants. By 1957 the disease had
become one of the most common and destructive of the virus
diseases occurring in Florida. Losses in individual plantings
have amounted to 20% or 30%.
The virus as far as known, is transmitted only by the tree-
hopper, which is a warm weather insect. Consequently, the
disease occurs generally during the warm months of the fall
planting. The virus is not known to be transmitted by contact
or through the soil or seed. Tomato is the only suscept crop
planted in Florida. The virus is found in the common weeds,
ragweed, Ambrosia artemisifolia; nightshade, Solanum gracile;


Figure 34. Pseudocurly top
Figure 34. Pseudocurly top

on right, healthy plant on left.



and ground-cherry, Physalis heterophylla, which apparently
serve as innoculum sources.

Pseudocurly top is primarily a disease of young plants;
however, plants of fruiting size have been known to become
infected. The first evidence of pseudocurly top is an extreme
rolling upward and twisting of the leaflets which exposes the
undersides (Figure 34). The plant becomes brittle and yellow.
Often there is purpling of the veins of the leaflets, and the
branches and stems become erect. The plant is severely stunted,
and little to no fruit are set after infection. Diseased plants
never recover.

Remove all ragweed, nightshade, ground-cherry, and diseased
tomato plants from the field and vicinity of the field. This will
reduce the inoculum sources.

Veinbanding Mosaic (Potato Y-Virus)
The potato-Y virus is of little or no concern in the United
States except in Florida where it causes considerable damage
to tomato and pepper. The virus is widespread on pepper in
the Everglades. On tomatoes it occurs principally on the East
Coast trellis area and in Dade County. The virus is found in
tomato, eggplant, pepper, potato, several species of the solan-
aceae (nightshade) family, zinnia, and purslane. The principal
source of inoculum is the weed, nightshade. The virus is trans-
mitted by the green peach aphid, Myzus percicae (Sulz.), and
the cotton aphid, Aphis gossypii Glover.

The young leaflets cup inward slightly and curl downward.
The petioles also curl downward and give the plant a drooping
appearance. The veinal areas of the leaflets are banded with
yellow. Dark-brown necrotic areas develop on the younger
leaves, especially on the terminal leaflets (Figure 35). The stem
tips and petioles are usually streaked with purple. Entire shoots
may be killed. Infected plants are stunted, unthrifty, and yield
poorly, but the fruit do not show symptoms. Frequently potato-
Y diseased plants also become infected with tobacco mosaic

Figure 35. Necrosis of tomato leaflets caused by potato virus Y. (Courtesy
of R. A. Conover.)

virus (Figure 36). This combination of viruses produces a
disease more severe than that produced by either virus alone.
Such diseased plants are severely stunted, the leaves become
mottled with yellow, and a necrosis of the terminal leaflets
develops. Yields are greatly reduced.

Eradicate known host plants from the field, the ditches, and
from around the field before planting.

Cucumber Mosaic
Cucumber mosaic is caused by the virus that causes mosaic
on cucumber and melons. Although the disease is distributed
throughout Florida and the entire United States, it is relatively
rare on tomato, because the cucumber mosaic virus is not easily
transmitted to tomatoes by handling of the plants, and because
tomatoes are relatively resistant to the virus.
The virus is rapidly inactivated by drying and does not
remain viable for any time on the hands or clothing; it is not
seed transmitted and does not persist in the soil. Therefore
most infection on tomato occurs through the agency of the
cotton and green peach aphids.


Figure 36. Mottling and distortion of a tomato leaf caused by the com-
bination of tobacco mosiac virus and potato virus Y. (Courtesy of R. A.

Figure 37. Cucumber mosaic of seeding tomato, showing filiform (shoe-
string) foliage.

A number of cultivated and wild plants are susceptible
to cucumber mosaic virus and can serve as sources of infection.
Some of these alternate hosts are cucumber, celery, cantaloupe,
watermelon, pepper, potato, eggplant, corn, spinach, petunia,
gladiolus, periwinkle, wandering jew, wild balsam-apple, and
ground-cherry. The most important weed hosts in Florida are
wandering jew, Commelina nudiflora, and wild balsam-apple,
Momordica charantis.
Several strains of cucumber mosaic virus are known to
affect tomato. These strains not only vary in prevalence but
in the type and severity of symptoms they produce.

Affected plants are considerably stunted, the internodes of
the stems are shortened, and the plants appear bushy. The
leaves exhibit a green mosaic pattern similar to that produced
by the tobacco mosaic virus. But unlike tobacco mosaic virus,
which does not deform the leaf, cucumber mosaic virus causes
the leaves to be extremely malformed and distorted (Figure
37). The most characteristic symptom is the shoestring appear-
ance of the leaves caused by the reduction of the leaf to a central
rib. Fruit production is reduced, and the few fruit formed
are small.

Eradicate wandering jew and wild balsam-apple from the
field, the ditch banks, and the periphery of the field. Do not
grow tomatoes adjacent to pepper, potato, gladiolus, tobacco,
or any plant that is likely to carry the cucumber mosaic virus.
Spray at weekly intervals for aphid control.

Double Virus Streak
Double virus streak is caused by the combined action of the
tobacco mosaic virus and potato-X virus. This disease has long
been troublesome throughout the central and eastern areas of
the United States. Principally it is a problem of greenhouse
tomatoes. In Florida the disease occurs only sporadically and
causes relatively little damage. However, where potatoes and
tomatoes are grown together, considerable damage from double
virus streak can be expected.
Tobacco mosaic virus and potato-X virus separately incite
relatively mild symptoms, but together they produce a syner-
gistic effect resulting in severe stem streaking, leaf necrosis,
fruit malformation, and plant stunting.
Potato-X virus occurs without symptoms in nearly all estab-
lished standard potato varieties. In tomato it causes only a
slight mottling of the foliage without stem or fruit symptoms.
There are several strains of potato-X virus which vary in the
intensity of symptoms they produce. The severity of double
virus streak depends primarily on the potato-X virus strain
present. Regardless of which strain is present, some leaf spot-
ting and stem necrosis occurs.
Both tobacco mosaic virus and potato-X virus are, trans-

mitted readily through contact and remain active for long
periods in vitro. Staking, pruning, and tying operations in
stake and trellis tomato cultures are ideal means for trans-
mission of both viruses. Once workers' hands are contaminated,
the viruses will be spread throughout the field whenever plants
are handled.

Double virus streak is first characterized by a light-green
mottling of the leaves together with the development of small
grayish-brown necrotic spots. These leaves often wither and
die during the early part of the disease development. Later
the foliage is mottled green and yellow, and curled, and the
leaflets are covered with brown necrotic lesions. Infected plants
are stunted, and numerous narrow, dark brown streaks develop
on the stems and petioles. Fruit-set is extremely reduced, and
the few fruit produced are malformed with irregular small
greasy-brown areas roughly 1/8 to 3/8 inch in diameter.

Do not grow tomatoes after potatoes, and do not grow
tomatoes near potatoes. Follow practices already given for the
prevention or spread of the tobacco mosaic virus. Guard against
the mechanical transmission of the potato-X virus by washing
hands thoroughly with soap and running water or with 70%
alcohol before handling tomato plants. This is extremely criti-
cal if potato tubers or plants have recently been handled.
During the staking, tying, or pruning operations, hands should
be washed frequently with soap and running water or with
70% alcohol. Eliminate all volunteer tomato plants. However,
if the disease is well distributed throughout the field, roguing
will be of little value.


This common disease is caused by the nematode Meloidogyne
spp. Rootknot nematodes are worldwide in distribution and
are most damaging in areas with long summers and short mild
winters. They are widely distributed in Florida especially in

the well-drained sandy soils that have been cleared for several
years. Although nearly every vegetable known is affected to
some extent, the most susceptible vegetable crops are cucumber,
tomato, eggplant, potato, spinach, parsley, carrot, parsnip, and
The young, newly hatched, male and female larvae are
threadlike in shape and are barely visible to the naked eye.
The young, motile nematodes work through the soil until they
contact tomato roots. They then burrow into the roots at or
near the tips, settle down, and while feeding upon the cellular
contents eject through their stylets a secretion which causes
the plant to form knot-like galls. Some larvae remain 2 or 3
weeks within the roots and then emerge as adult males. Females
become pear shaped and remain embedded in the root tissue.
During warm weather the females begin to lay eggs 20 to 30
days after penetrating the roots as larvae. In small roots the
posterior ends of the egg-laying females protrude from the
root tissue. The eggs accumulate in a prior extruded gelatinous
substance which holds them in masses and forms a protective
cover. These egg masses become weathered and tanned and
develop into black masses easily dislodged from the root surface.
Under the proper warmth, moisture, and oxygen conditions the
eggs hatch and initiate another cycle.

Figure 38. Rootknot on tomato.

Delayed hatching for long periods may occur with rootknot
nematode eggs. During periods of cool, dry weather the cell
walls of the eggs may dry, and the eggs remain some time in a
stage of arrested development.
Since rootknot nematodes survive as eggs, larvae, or adults
in the soil or in diseased roots of the soil, they are spread by
surface water, by irrigation water, in diseased tubers, bulbs,
corms, rhizomes of other host plants, and diseased tomato trans-
plants, and in infested soil on tillage implements.

Generally only the roots of tomatoes are attacked by the
rootknot nematode, but occasionally stems may be invaded before
emerging from the ground. Larvae cause only very slight me-
chanical injury when entering roots. Most of the rootknot nema-
tode effect is the proliferation and hyperthrophy of the cortical
cells resulting in the formation of galls (Figure 38). The galls
usually are large, are on the main roots, and are swellings
of the roots themselves. Infected plants have fewer small feeder
roots than uninfected plants. Because of the galling and the lack
of small rootlets, the root system of an infected plant may be
extremely limited. Often rootknot-infected plants become yel-
lowed and stunted; this is not a direct effect of the nematode
but is a nutritional deficiency brought about by the restricted
root system.
Although rootknot can be a very destructive disease, the
fact that the roots are galled and partially devoid of rootlets
does not necessarily mean that plant growth will be retarded
or that fruit production will be greatly decreased. When sup-
plied with abundant fertilizer and moisture an infected plant
can grow well and produce a large crop of fruit. However,
when put under conditions of stress such as drought, low fer-
tility, or attack by other disease organisms, infected plants are
less able to grow and produce than non-infected plants.

In-the-row fumigation with recommended nematocides may
be used effectively and inexpensively for the control of rootknot
nematodes. The summer fallow method is a most efficient
method to depress populations of nematodes in the soil for a
single season. The land is plowed immediately after the crop

is off and kept bare of vegetation all summer. It must be
harrowed at least once weekly and after heavy rains. It is
essential that a crust does not form over the soil, because it
excludes air and prevents the eggs of the nematodes from
hatching. By continued cultivation the eggs are hatched and the
young larvae, finding no food plants, starve to death.
When tomato plants became diseased, they should be ferti-
lized liberally and a high level of available moisture maintained.


Blossom-End Rot
Blossom-end rot is a disease caused by a deficiency of cal-
cium. The disease is of general occurrence throughout the United
States and is especially common in the Mississippi Valley and
the Southern States. In Florida it is present every year and
takes an annual toll of the tomato crop, varying with the
season. It is of no concern on the naturally calcarious marl
soils, but on unlimed, sandy soils fruit loss may be serious in
some fields.
Blossom-end rot commonly occurs on luxuriantly growing
plants which are subjected to prolonged dry weather at the
time when the young fruit are developing. However, it can
develop after periods of abundant or excessive rain. Heavy
applications of nitrogenous fertilizers and extreme variations
in the water supply are conducive to blossom-end rot develop-
A deficiency of calcium is the fundamental cause of the
disease. An excess of soluble ammonium, magnesium, potassium,
or sodium salts causes decreased calcium uptake. Additions
of fertilizers containing these soluble salts therefore tend to
lower the calcium-total soluble salts ratio. Addition of soluble
calcium salts increases the ratio. Excessive total salts also bring
about a calcium deficiency even when the measurable calcium
ratio is considered high or adequate. As salt concentrations
increase, the solubility of calcium salts decreases at a more
rapid rate than other soluble salts, thus bringing about a physio-
logical calcium deficiency. During dry weather soluble salts
accumulate in the surface soil. When rain moves these salts
downward into the root zone the total salt concentration in-
creases and the calcium ratio is decreased. If rainfall is
excessive and causes leaching, the soluble calcium salts are


Figure 39. Blossom-end rot of tomato fruit.

removed from the root zone. If the soil remains excessively
wet the ammonium form of nitrogen accumulates, which de-
creases calcium uptake resulting in blossom-end rot development.
Rapid growth increases the calcium requirement and accent-
uates the calcium deficiency. Because calcium is not trans-
located from older to younger tissue even a temporary calcium
deficiency may quickly cause damage to actively developing

First symptoms of this disease on tomato fruit develop at
the blossom end where small, pale green to brown patches
begin to appear. The patches enlarge into definite spots which
become sunken and enlarge in circular outlines (Figure 39).
The part of the fruit which is involved shrinks, and a distinctive
dry-rot develops unless the affected area becomes overgrown
with secondary organisms such as Alternaria fasciculata. The
fruit become flat on the blossom end, and the color of these
fruit on the upper surface is a lighter green than that of
healthy fruit. As the rot advances, the whole fruit becomes
involved and in many instances is mummified and persists on
the vine. Internal browning or blackening also can occur and
may be present without the characteristic external symptoms
(Figure 40).

Figure 40. Interior decay resulting from blossom-end rot.

On calcium-deficient soils apply liming materials such as
dolomite or high calcium limestone 2 to 4 months before plant-
ing. Use gypsum or superphosphate to supplement these liming
materials. Avoid excessive ammonium, potassium, magnesium,
or sodium salts, and excessive soluble salt accumulation. Soil
additions of lime are not generally recommended after the
tomato crop is planted. Such additions generally are of little
value in blossom-end rot control during that crop season.
If during the growing season the calcium level becomes
inadequate, soil additions of the more soluble calcium-bearing
materials should be made. Foliage sprays of anhydrous calcium
chloride also can be used for blossom-end rot control. For good
control, the calcium sprays should be applied within 24 to 48
hours after rain. When excessive salts are causing blossom-end
rot, periodic sprays should be continued as long as the salts
remain excessive. Calcium sprays should also be used during
periods of rapid growth. Use of these calcium sprays should
be considered as supplementary to the calcium supplied from
the soil. Prolonged periodic use of calcium chloride may cause
leaf burn.

Blotchy Ripening (Graywall)
This disease of tomato fruit has caused serious losses
throughout the entire central and eastern tomato producing
areas of the United States. Blotchy ripening is common in
Florida and frequently occurs in epidemic proportions.
The cause of the disease has not definitely been determined,
although there is evidence that non-soft rotting bacteria may
incite the disease. Many factors such as temperature, soil
moisture, tobacco mosaic virus infection, light intensity, and
mineral nutrition have been shown to influence disease develop-
Several excellent tomato varieties have been developed in
Florida, which are resistant to the disease. Some of these are
Floradel, Floralou, Immokalee, Indian River, Manalucie, and

The most characteristic symptom of blotchy ripening is
the dark brown tissue which develops around the vascular

Figure 41. Blotchy ripening (graywall) : (Top) internal symptoms, and
(Bottom) external symptoms. (Courtesy of the Ohio Agricultural Research and
Development Center.)

bundles within the outer fruit wall and occasionally in the
septa and middle column. Cross-sectioning of diseased fruit
near the stem end readily exposes this diseased tissue (Figure
Often external symptoms are difficult to detect on green,
immature fruit, but upon close examination the dark wall tissue
can usually be seen through the translucent skin. The blotchy
areas, where the dark colored tissue shows, appear gray, are

without distinct margins, and sometimes are slightly flattened.
As the fruit mature and ripen the blotchy areas generally re-
main gray but occasionally they become yellow. In severe cases
the wall tissue shrinks and sunken spots develop on the fruit
(Figure 41).

Use resistant varieties.

Puffy Tomato
Puffy tomato is a non-parasitic disease which is widely
distributed in the South. This disease is common over the
entire tomato area in Florida, and in all sections the disease
is destructive year after year. It appears at the beginning of

Figure 42. Sections of puffy tomato, showing interior cavities.

the harvest season and in many instances affects the fruit
throughout the season. This disease apparently is caused by
weather and fertility conditions which prevent normal polli-
nation or affect later development of the seed-producing tissue
of the fruit.

The fruit are the only part of the plant affected, although
the plants that show puffy fruit generally are of an exceedingly
succulent growth. The fruit may vary in shape from perfectly
normal to scalloped. The fruit partitions protude and the fleshy
portions between them are sunken. Puffy fruit are usually
detected because of their angular shape, light weight, and, by
one familiar with the condition, by their slightly lighter color.
In cutting such fruit in half it will be observed that there are
large, unfilled spaces in the interior of the fruit between the
solid seed mass and the fleshy part of the skin. The outer layer
of flesh next to the epidermis in most cases is of normal thick-
ness and of good texture, whereas the central portion of the
fruit appears to be hard, compact, and undeveloped. The dif-
ferent stages of puffiness are shown in Figure 42. This con-
dition prevails from the time the young fruit are two-thirds
developed in size until they are completely ripened on the vine.

No definite methods of control are recommended.

Sunscalded fruit may be attributed to the combined action
of light and heat resulting from direct exposure to the sun.
It is most serious on fruit that have been grown under cover
and then are suddenly exposed. Fruit that develop in full sun-
light are seldom scalded. Sunscald is very common throughout
the United States and Florida on both staked and unstaked
crops. On unstaked crops it becomes most prevalent after one
or two pickings because the pickers, in turning the vines in
search of mature fruit, expose previously shaded fruit to direct
sunlight. On staked plants sunscald is usually found following
a severe pruning of the plants in which the protecting foliage
is cut away. Sunscald is conducive to invasion by secondary
organisms which cause fruit rots.

The injury is usually located on the sides and top half of
the tomato fruit and appears in the form of a whitish, shiny,
blistered area (Figure 43). The chlorophyll which gives the
plant the green color is completely destroyed, leaving the tissue
white. In some cases cells break down, leaving the surface
shiny, soft, and often shrunken. The injury is always on the
outside of the cluster of fruit. In instances where no secondary
infection takes place, the injured area often remains light
colored when the remaining part of the fruit ripens.


Figure 43. Sunscald of tomato fruit.


Sunscald can be greatly alleviated if in picking the fruit
the harvesters are careful to leave the vines in the same
position they found them, thus preventing the exposure of the
unpicked fruit to the direct rays of the sun. Staked and trel-
lised tomatoes should be placed close enough in the rows so
that when pruning takes place the fruit will not be fully exposed.


Growth Cracks
This disease of tomato fruit is found more or less where-
ever tomatoes are grown. In Florida it is found over the entire
state and is most common during periods of abundant rain and
high temperatures, which tend to produce quick growth. Al-
though it is widespread, losses from growth cracks generally
are not large; occasionally, however, losses are great.
Cracking is not common on small green fruit, but it is found
shortly before the fruit mature. It is less frequent when fruit
are picked mature-green than when picked vine-ripe. Although
certain varieties such as Floralou, Floradel, Immokalee, Mana-
pal, and Indian River have some resistance to cracking, no
variety has been developed with sufficient resistance.

The first sign of growth cracks appears around the stem
end where the fruit are attached to the vine (Figure 44). The
cracks at this time are exceedingly small and radiate from
the stem attachment. As the fruit develop, these cracks become

Figure 44. Radial and concentric growth cracks. (Courtesy of the United
States Department of Agriculture.)




deeper and develop through the fleshy part of the tomato ex-
posing the seed. In some cases a circular, concentric cracking
develops around the stem end, often 3 or 4 distinct circular
cracks appearing in the upper half of the tomato. These cracks
cross at right angles to the cracks radiating from the stem end.
Another type of cracking is characterized by the splitting of
the epidermis of the fruit that have began to show the pink
ripening condition. This is particularly common and destructive
following heavy rains.

Fruit that are picked green-mature or vine-ripe for ship-
ment should be carefully graded because of the possibility of
loss in transit. Use varieties that have some resistance to

This name has been applied to fruit that show a distinct
marking and distorted shape at the blossom-end. Catface is
common in tomatoes over the United States wherever they are
grown and has been observed in all the tomato sections of
The exact conditions causing catface are not known; how-
ever, factors such as (1) prolonged cold weather during flower-
ing and (2) faulty fertilization which affect the development
of the flower parts may be involved.

Fruit typified by the name catface are malformed and show
ridges, furrows, protuberances, ribs, creases, indentations, and
blotches beginning at the blossom-end and often involving the
entire fruit (Figure 45). The fruit are usually unbalanced
in contour, unevenly developed, and unfit for market.

No definite recommendation for control can be given, since
the cause of catface is not known. It is suggested that varieties
not subject to catface be grown. Most standard market varieties
are resistant to this disease. Care should be exercised in pack-
ing. All fruit that show catface should be discarded, since

Figure 45. Catface of tomato fruit.

they bring a very low price on the market and are liable to be
bruised and injured in the packing process because of their
uneveness of contour. In transit secondary organisms will cause
loss to these fruit and those adjoining them.

Leaf Roll

Leaf roll of tomato is very similar to a virus-incited disease
of potato. However, leaf roll of tomato is not caused by a
virus infection. The disease is common in Florida and can
be found in almost any field during the latter half of the tomato
Leaf roll appears to be more common on staked tomatoes
that have been severely pruned than on those that are not
staked. Leaf roll does not develop markedly on an individual
plant until about the time of fruit setting of the first and
second clusters. At this time the leaves begin to roll and the
disease develops rather suddenly. It involves practically all
the leaves on the lower half of the plant. Plants with leaf
roll are not stunted and produce a normal fruit crop.

When leaf roll is first observed, the margins and tips of the
older leaves begin to roll inward, thus tending to form curled

Figure 46. Tomato leaf roll.

leaves shaped like the hollow of a spoon. As the rolling pro-
gresses, these leaves become more cylindrical, the margins
touching or overlapping the midrib and the ends of the cylinder
remaining open (Figure 46). In severe cases three-fourths of
the leaves on a single tomato plant may be involved in this
rolled condition. The leaves affected are stiff to the touch,
brittle, and at times almost leathery. They are much thicker
than normal leaves, become stiffened, and are shiny on both
upper and lower surfaces. Leaves that have been long affected
are so brittle that they will break rather than bend to the touch.
Other parts of the plant do not appear to be materially affected.

No method of control can be recommended.

Blossom-drop is a disease characterized by shedding of the
blossoms at the beginning of the blooming period and continuing
for some time thereafter. This disease is general and has been
experienced by growers all over the United States. In Florida
blossom-drop at times causes considerable worry among growers.
Several environmental factors have been advanced as
causing blossom-drop, although the exact cause is not known.
Hot, dry winds are considered in the Southwest United States
to favor abnormal styler elongation and subsequent nonfertili-
zation and drop of such flowers. Elsewhere, cool temperatures
and driving rains are considered to influence blossom-drop.
An unbalanced fertilizer relationship is considered by some as
being a more important cause than any other factor.


The blossoms separate from the plant at the first joint in
the blossom peduncle. The shedding flowers include the buds
that are not yet open as well as blossoms that are declining.
The plant is not injured by the shedding process.

Maintain an adequate but not excessive soil moisture, and
do not over-fertilize with nitrogen, especially during the early
plant growth.

Crease Stem

The cause of this disease is not known, but it occurs during
periods of rapid growth and seems to be associated with a
temporary mineral deficiency at the growing point. The disease
apparently is limited to Florida, where it appears each season
in scattered locations.

During early stages of the disease, the stem begins to
pinch together longitudinally so that a crease forms on the
opposite side. A lengthwise cut of such a creased stem shows
internal necrosis and stem hollowing where the internal cells
have disintegrated (Figure 47A). At times the creasing is so
severe as to form a hole through the stem. Plants showing the
crease stem condition may become severely stunted and have
a huddled appearance (Figure 47B). Fruit may be late in set-
ting and maturing. However, affected plants usually recover
and continue normal growth and fruit production.

Avoid over fertilization, especially during early stages of
growth. Use resistant varieties, such as Manapal, Immokalee,
Indian River, or Floralou.



Figure 47A. Crease stem of tomato: internal necrosis.


Figure 47B.

Crease stem of tomato: stunted plant.

Black Shoulder
Black shoulder has been observed in Florida and Georgia
for several years. The cause of the disease is not known, al-
though cool, rainy weather is usually associated with disease


development. The disease occurs sporadially throughout Florida
and may result in severe fruit loss in individual fields. Fruit
approaching maturity appear to be most susceptible to black

Black shoulder is characterized by the development of dark-
gray to blue-black areas on the shoulders of the fruit (Figure
48). These areas are irregular in shape and indefinite in size.
Often the diseased tissue collapses and definite sunken lesions
are formed. As the lesions age, the affected tissue appears to
harden and to shrivel, but further lesion enlargement does not
usually occur.

No control measures are known.

Figure 48. Black shoulder of a tomato fruit.


Sanitation And Rotation
It is absolutely necessary to practice sanitary methods in
both the seedbed and the field to insure a good crop of tomatoes
with the least amount of disease. Under Florida conditions
many of the pathogens of tomato live from one season to the
next in old refuse, on wild plants, and on volunteer tomato
plants. When harvesting tomatoes, all fruit not suitable for
shipping are normally left in the field. It is usually these fruit
that are afflicted with numerous diseases such as late blight,
early blight, and phoma rot. This culled fruit should be de-
stroyed. Abandoned fields should be disked immediately to
prevent the multiplying of the pathogenic fungi and bacteria
that are present on the diseased plants. After tomato fields
are well established, seedbeds should be disked and planted to
cover crops. This will prevent this area from being overgrown
with obnoxious weeds and straggling tomato plants which serve
as inoculum sources.
Diseases tend to become numerous and severe on tomatoes
as the industry becomes concentrated, because one crop tends to
closely follow the preceding crop. This practice is extremely
favorable for the rapid increase of soil-borne pathogens which
survive on the decaying refuse in the soil. Frequent cropping
tends to increase and perpetuate these pathogens. Consequently a
definite rotation program is strongly recommended. Such a pro-
gram necessitates a growing of other crops on the land planted
to tomatoes during the period of the year when tomatoes are
not growing; it also calls for rotation from year to year. If
possible, a minimum of 3 to 4 years should intervene between
tomato crops. If bacterial wilt has been prevalent, a 4- to 5-year
lapse between crops is suggested. Although the organisms
causing Fusarium and Verticillium wilts persist indefinitely in
the soil, a 5- to 7-year rotation will greatly reduce losses caused
by them. Without such a rotation the organisms increase to
such a point that tomato production is nearly impossible.
Rotation crops should be limited to legumes, cucurbits, pasture
grasses, hay, corn, or root crops. Care should be exercised in
planning the rotation schedule so that tomatoes do not follow
sweet potato, cabbage, white potato, eggplant, pepper, celery,
or lettuce, because some of the destructive diseases of these
plants are also important on tomato. Do not plant tomatoes

following any crop damaged with Sclerotinia stem rot, southern
blight, or southern bacterial wilt.

Seedbed Sterilization
It is necessary to combat certain diseases of tomatoes in
the seedbed, because that is where they may first appear and
cause considerable loss. Even when the conditions are such
that little loss occurs in the seedbeds, there is still the danger
of carrying the disease-causing organism to the field where it
might cause damage when conditions are favorable for its
development. For example, if the rootknot nematode is estab-
lished in the seedbed, there is a grave danger the entire field
planting will be severely infected. Similarly other soil-borne
pathogens can be introduced into the field from contaminated
seedbeds. In sterilizing the seedbed a thorough job should be
done. Three efficient methods of sterilizing soil to be used as
a seedbed are given in the following discussion.

Soil Sterilization with Methyl Bromide
Methyl bromide is a gas heavier than air that controls
weeds, bacteria, fungi, and nematodes. It is available in 1-pound
cans or in larger capacity cylinders. Most formulations con-
sist of 98% methyl bromide and 2% chloropicrin. The chloro-
picrin is included as a warning agent, since methyl bromide
is odorless and extremely poisonous. The seedbed area to be
treated should be prepared for planting with the soil being
loose and of good moisture content. Place plastic over the area,
bury the edges, and support the film a few inches above the soil
surface. If 1-pound cans are used, place them in the tent,
release the gas, and secure the tent. If a large cylinder is used,
bury glass jars diagonally in the bed and deliver the methyl
bromide into the jars. Three pounds of methyl bromide per
100 square feet of soil are recommended. Remove the cover
24 to 48 hours after application. Allow 3 to 7 days after treat-
ment to permit the gas to escape from the soil before seeding.

Soil Sterilization with Other Fumigants
For seedbeds located on sand Brozone, methyl bromide
(previously discussed), Mylone (85W), Nemex, Trizone, Vapam
(VPM), Vorlex, and Vorlex-201 are recommended at the fol-

lowing rates per 1,200 square feet:

Fumigant Application Rate
Brozone 12 pounds
Mylone (85W) 8 pounds
Nemex 1 gallon
Trizone 5 pounds
Vapam (VPM) 3 gallons
Vorlex 1 gallon
Vorlex-201 1 gallon

These fumigants give control of weeds, fungi, and nematodes.
Prepare the seedbed for seeding and keep it moist for two
weeks before application. Apply the selected fumigant at the
proper rate, and cover immediately with a tarpaulin. For good
results keep the tarpaulin in place for at least 48 hours, then
remove. Sow seed two weeks later. Manufacturer's recom-
mendations should be followed.

Soil Sterilization with Steam
This process necessitates the use of a steam boiler of con-
siderable capacity and a rectangular galvanized iron pan (5 to
7 feet wide and 8 to 12 feet long) large enough to cover a con-
siderable area but small enough to be moved by four men. The
pan should have sides 6 to 10 inches high with sharp edges
so that it can be inverted and pushed down into the soil. In
this position it is connected to the boiler by a rubber hose so
that steam from the boiler is discharged into the inverted pan.
Steam should be released into this pan until a potato of medium
size buried 6 inches into the soil under the pan is cooked. Then
move the pan to another portion of the bed and repeat the
process. For good penetration of the steam the soil should be
loose and of moderate moisture. The soil should never be wet,
or inadequate sterilization may occur. Extreme care must be
exercised to prevent recontamination of sterilized seedbeds, be-
cause certain pathogens increase rapidly when introduced into
freshly sterilized soil.

Seed Treatment
It is a well established principle in modern agriculture that
seed treatment is good business. Fortunately, practically all

seed from seed companies is of high quality and has been
properly treated. However, on occasion an individual may need
to treat a batch of seed. This process takes only a short time,
and the results usually are profitable. All pathogenic organisms
adhering to the seed, such as bacteria and fungi, are killed if
the proper materials are used. Moreover, the seed treatment
protects the seed and seedlings from damping-off organisms
in the soil. The seed themselves generally are either uninjured
or are not severely harmed by the chemicals when used properly
and will germinate almost as quickly and produce as strong
plants as untreated seed. After treatment extreme care must
be exercised to prevent recontamination of the clean seed.
Several disinfectants and seed treatments are available for
use, but bichloride of mercury is stressed because of its ex-
cellent record against fungi and bacteria on the surface of the
seed. The material is especially good against the bacterial spot
organism, but it does not protect seed against damping-off
organisms in the soil.

Bichloride of Mercury
This disinfectant can be purchased from your local druggist
and can be obtained in the form of dry crystals or made up
in the form of tablets. An ounce of the crystals dissolved in
15 gallons of water makes a solution the designated strength
of 1:2,000. When smaller quantities of the disinfectant are
desired, it is advisable to use tablets. One tablet dissolved in
one quart of water gives a solution of the strength of 1:2,000.
If a gallon of the disinfectant is desired, dissolve four tablets in
a gallon of water.
The container should not be of metal, because some of the
mercury in the bichloride of mercury unites with the metal, thus
weakening the solution. Instead use plastic or wooden con-
tainers such as pails, half barrels, or earthenware crocks.
Place the seed in a cloth bag and tie the top securely,
leaving plenty of space in the bag for the seed. Submerge the
bag of seed in a 1:2,000 solution of bichloride of mercury
for 5 minutes. During the time move the bag around in the
solution with a short stick. This will insure the removal of air
bubbles so that all seed will come into contact with the disin-
fectant. After 5 minutes remove the bag of seed from the dis-
infectant and rinse 15 minutes in several changes of clear water.
After the seed are thoroughly rinsed, spread them in the shade
to dry. When dry, the seed are ready to plant.

Bichloride of mercury is a deadly poison when taken inter-
nally; consequently it should be kept away from children. When
the solution is prepared it looks like water, is tasteless and
odorless yet deadly poisonous. Precautions should be taken in
disposing of the liquid after it has been used to prevent
accidental poisoning.
Although mercury compounds such as bichloride of mercury,
Semesan, and Ceresan M are suggested as seed treatments,
they are difficult to use. At slightly higher than average tem-
peratures for good growth, mercury affects the growth hor-
mones of seeds and many inhibit germination.

Dry Seed Treatments
Seed may be treated without soaking by the use of one of
the many seed treatment materials, such as thiram, captain,
Ceresan M, or Semesan, prepared in the form of dust. The
seed are disinfected by thoroughly mixing certain amounts of
them with a specific amount of the dust. These dusts can be
purchased from most seed and pesticide dealers. Manufacturers'
recommendations should be followed. Semesan and Ceresan M
are mercury compounds and at slightly higher than .average
temperatures for good growth may inhibit seed germination.

Fungicide Application
The effectiveness of fungicides and the subsequent disease
control is largely dependent on (1) selection of the proper
material, (2) complete coverage of the plants including the
underside of the leaves, and (3) proper timing. Spraying is
generally much more effective than good dusting; consequently
dusting should never be considered if spraying is possible.
The best protection is obtained when plants are sprayed before
rather than after rain. Applications must be thorough to be
effective. Tank pressure should be between 150 and 200 pounds
per square inch. The spray should be applied often enough to
keep the growing plant well protected during inclement weather
conditions that favor disease development. This generally calls
for a 5-day schedule. For routine control weekly applications
are generally sufficient. Approximately 200 gallons per acre
of spray are needed for adequate coverage of mature tomato
plants singly planted in 5-foot rows. The control of plant
diseases with fungicides is a protective measure rather than
a cure. Spraying should begin as soon as the plants emerge and

should be continued methodically until the crop is gathered.
Careful attention should be given to the proper nozzle height,
the number and arrangement of nozzles, and the proper tractor
speed to ensure complete coverage. During the spray operation
the tractor driver should periodically check for plugged nozzles.
In order to spray tomato plants thoroughly and frequently
enough where large acreages are involved, it is necessary to
select an adequate power sprayer. It is important to select a
machine that will maintain the desired pressure when several
nozzles are in operation (Figure 49).
Spray machines should be thoroughly cleaned immediately
after use. If the spray material is allowed to remain in the
machine, it will dry and form flakes or cakes that will not pass
through the nozzles. At least 25 gallons of clear water should
be run through the sprayer to clean out the tank, pump, and
all nozzles. If this precaution is taken, considerable time will
be saved as it will not be necessary to clean out the nozzles
when the machine is used again. It is never advisable to spray
herbicides through sprayers used to apply fungicides.
For the large number of gardeners who plant only a small
number of plants, the use of power sprayers may be out of
the question. In such cases it is necessary to do the spraying
with smaller hand sprayers such as a knapsack sprayer. The
spray rod is easily handled, and with care the plants can be
thoroughly sprayed.

Figure 49. Spraying staked and trellised tomatoes in Florida.

Fungicides for Disease Control
Many chemicals used for disease control are poisonous to
man and animals when taken internally, and many cause skin
irritation. Handle them with care, and prevent their contact
with eyes, skin, mouth, and nostrils. Wear respirator masks
when using dusts for seed treatments, when spraying or dust-
ing plants in the field, or when mixing fungicides in spray
tanks. Thoroughly wash hands and clothing after using fungi-
cides. Do not smoke or handle tobacco or food while working
with fungicides. Always read and follow instructions and fol-
low precautions on the package labels. Be certain not to exceed
the dosages recommended and the minimum number of days
that should be allowed between harvesting and the last appli-
cation. Properly dispose of the empty containers so that children
and animals will not be poisoned.

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