• TABLE OF CONTENTS
HIDE
 Front Cover
 Credits
 Table of Contents
 Introduction
 Fusarium and gibberella dry...
 Diplodia dry rot
 Brown spot
 Corn smut
 Scutellum rot
 Yellow ear rot
 Green ear mold
 Leaf blight
 Rust
 Ophiobolus leaf spot
 Sheath spot
 Pythium root rot
 Bacterial leaf spots
 Stem rot
 Miscellaneous leaf spots
 Other diseases
 Seed selection
 Seed curing and storing
 Seed testing
 Seed treatment
 Breeding for disease resistanc...














Group Title: Bulletin - University of Florida Agricultural Experiment Station ; 210
Title: Corn diseases in Florida
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Permanent Link: http://ufdc.ufl.edu/UF00027597/00001
 Material Information
Title: Corn diseases in Florida
Series Title: Bulletin - University of Florida Agricultural Experiment Station ; 210
Physical Description: Book
Language: English
Creator: Eddins A. H.
Publisher: University of Florida Agricultural Experiment Station
Publication Date: 1930
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Bibliographic ID: UF00027597
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
    Credits
        Page 2
    Table of Contents
        Page 3
        Page 4
    Introduction
        Page 5
    Fusarium and gibberella dry rot
        Page 5
        Page 6
        Page 7
    Diplodia dry rot
        Page 8
        Page 9
        Page 10
    Brown spot
        Page 11
        Page 12
        Page 13
        Page 14
    Corn smut
        Page 15
        Page 16
        Page 17
        Page 18
    Scutellum rot
        Page 19
    Yellow ear rot
        Page 20
    Green ear mold
        Page 21
    Leaf blight
        Page 22
    Rust
        Page 23
    Ophiobolus leaf spot
        Page 24
    Sheath spot
        Page 25
    Pythium root rot
        Page 26
    Bacterial leaf spots
        Page 26
    Stem rot
        Page 27
    Miscellaneous leaf spots
        Page 28
    Other diseases
        Page 29
    Seed selection
        Page 29
        Page 30
    Seed curing and storing
        Page 31
    Seed testing
        Page 31
        Page 32
    Seed treatment
        Page 33
    Breeding for disease resistance
        Page 34
        Page 35
Full Text





UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
Wilmon Newell, Director




CORN DISEASES IN FLORIDA

By A. H. EDDINS


Fig. 1.-A field of corn, showing method of selecting seed ears.


Bulletins will be sent free upon application to the
Agricultural Experiment Station,
Gainesville, Florida.


January, 1930


Bulletin 210










BOARD OF CONTROL


P. K. YONGE, Chairman, Pensacola
A. H. BLENDING, Leesburg
W. B. DAVIS, Perry
RAYMER F. MAGUIRE, Orlando


FRANK J. WIDEMAN, West Palm Beach
J. T. DIAMOND, Secretary, Tallahassee
J. G. KELLUM, Auditor, Tallahassee


STATION EXECUTIVE STAFF


JOHN J. TIGERT, M.A., LL.D., President
WILMON NEWELL, D. Sc., Director
S. T. FLEMING, A.B., Asst. Director
Y. FRANCIS COOPER, M.S.A., Editor
R. M. FULGHUM, B.S.A., Asst. Editor


IDA KEELING CRESAP, Librarian
RUBY NEWHALL, Secretary**
K. H. GRAHAM, Business Manager
RACHEL McQUARRIE, Accountant


MAIN STATION-DEPARTMENTS AND INVESTIGATORS


AGRONOMY
W. E. STOKES, M.S., Agronomist
W. A. LEUKEL, Ph.D., Associate
G. E. RITCHEY, M.S.A., Assistant*
FRED H. HULL, M.S.A., Assistant
J. D. WARNER, M.S., Assistant
ANIMAL HUSBANDRY
A. L. SHEALY, D.V.M., Veterinarian in
Charge
E. F. THOMAS, D.V.M., Asst. Veterinarian
R. B. BECKER, Ph.D., Associate in Dairy
Husbandry
W. M. NEAL, Ph.D., Assistant in Animal
Nutrition
C. R. DAWSON, B.S.A., Assistant Dairy
Investigations
CHEMISTRY
R. W. RUPRECHT, Ph.D., Chemist
R. M. BARNETTE, Ph.D., Associate
C.' E. BELL, M.S., Assistant
H. L. MARSHALL, M.S., Assistant
J. M. COLEMAN, B.S., Assistant
J. B. HESTER, B.S., Assistant
COTTON INVESTIGATIONS
W. A. CARVER, Ph.D., Assistant
E. F. GROSSMAN, M.A., Assistant**
RAYMOND CROWN, B.S.A., Field Assistant


ECONOMICS, AGRICULTURAL
C. V. NOBLE, Ph.D., Agricultural Economist
BRUCE McKINLEY, A.B., B.S.A., Associate
M. A. BROOKER, M.S.A., Assistant**
JOHN L. WANN, B.S.A., Assistant
ECONOMICS, HOME
OUIDA DAVIS ABBOTT, Ph.D., Head
L. W. GADDUM, Ph.D., Biochemist
C. F. AHMANN, Ph.D., Physiologist

ENTOMOLOGY
J. R. WATSON, A.M., Entomologist
A. N. TISSOT, M.S., Assistant
H. E. BRATLEY, M.S.A., Assistant**
HORTICULTURE
A. F. CAMP, Ph.D., Horticulturist*
M. R. ENSIGN, M.S., Assistant
HAROLD MOWRY, B.S.A., Assistant**
G. H. BLACKMON, M.S.A., Pecan Culturist**
PLANT PATHOLOGY
W. B. TISDALE, Ph.D., Plant Pathologist
G. F. WEBER, Ph.D., Associate
A. H. EDDINS, Ph.D., Assistant
W. B. SHIPPY, Ph.D., Assistant
K. W. LOUCKS, M.S., Assistant
ERDMAN WEST, B.S., Mycologist**


BRANCH STATION AND FIELD WORKERS

R. R. KINCAID, M.S., Assistant Plant Pathologist (Quincy)
JESSE REEVES, Foreman, Tobacco Experiment Station (Quincy)
J. H. JEFFERIES, Superintendent, Citrus Experiment Station (Lake Alfred)
W. A. KUNTZ, A.M., Assistant Plant Pathologist (Lake Alfred)
B. R. FUDGE, Ph.D., Assistant Chemist (Lake Alfred)
GEO. E. TEDDER, Foreman, Everglades Experiment Station (Belle Glade)
R. V. ALLISON, Ph.D., Soils Specialist in charge Everglades Experiment Station (Belle Glade)
L. O. GRATZ, Ph.D., Associate Plant Pathologist (Hastings)
A. N. BROOKS, Ph.D., Associate Plant Pathologist (Plant City)
A. S. RHOADS, Ph.D., Associate Plant Pathologist (Cocoa)
STACY O. HAWKINS, M.A., Field Assistant in Plant Pathology (Homestead)
D. G. A. KELBERT, Field Assistant in Plant Pathology (Bradenton)
R. E. NOLEN, M.S.A., Field Assistant in Plant Pathology (Monticello)
FRED W. WALKER, Assistant Entomologist (Monticello)**
D. A. SANDERS, D.V.M., Associate Veterinarian (West Palm Beach)
M. N. WALKER, Ph.D., Associate Plant Pathologist (Leesburg)
*In cooperation with U. S. Department of Agriculture.
**On leave of absence.












CONTENTS

INTRODUCTION .... ......... ............... ....... ............ 5
FUSARIUM AND GIBBERELLA DRY ROT ................................. 5
DIPLODIA DRY ROT ....................... ........... ............... 8
BROWN SPOT ...................................................... 11
CORN SMUT ............. ...... ................................. 15
SCUTELLUM ROT ............... ................... ............... 19
YELLOW EAR MOLD ................. ............................... 20
GREEN EAR MOLD ................................................. 21
LEAF BLIGHT ........................................................ 22
RUST .............. ............................................... 23
OPHIOBOLUS LEAF SPOT ............... ........... ................ 24
SHEATH SPOT ........ ............................................. 25
PYTHIUM ROOT ROT ................ ............... ............... 26
BACTERIAL LEAF SPOTS ................. ......................... 26
STEM ROT .............. .... ...................................... 27
MISCELLANEOUS LEAF SPOTS .................... .... ................. 28
Phyllosticta sp. ............................................. 28
Macrosporium sp. ........................................... 28
Cercospora sp. ................ ............................... 28
BACTERIAL WILT .... ................... ..................... 28
OTHER DISEASES .................................................... 29
Anthracnose .... ........................................ 29
Helminthosporium Stalk Canker ............... ............ 29
Black Bundle ................ ........................... 29
Downy Mildew ...................... ........................ 29
Head Smut ................... ................................ 29
False Smut ................................................ 29
Mosaic ......................... .. .............. 29
Bacterial Stalk Rot ........................................... 29
Basisporium Dry Rot .............. ......................... 29
Black Ear Mold ............... ........................... 29
Seedling Blights and Root Rots ............................... 29
SEED SELECTION ............... ... ................................. 29
SEED CURING AND STORING ................. ....................... 31
SEED TESTING .................... .............................. .. 31
SEED TREATMENT ................... .............................. 33
BREEDING FOR DISEASE RESISTANCE .................................... 34













CORN DISEASES IN FLORIDA
By A. H. EDDINS'

INTRODUCTION
Diseases of corn are widespread in Florida and cause a con-
siderable reduction in the yield, quality and value of this crop.
Corn growers can reduce their losses by becoming familiar with
the different corn diseases and the known control measures. This
bulletin contains information concerning the occurrence, symp-
toms and known methods of controlling corn diseases.

FUSARIUM AND GIBBERELLA DRY ROT
This disease is caused by Fusarium spp. and Gibberella spp.
It is one of the most common and destructive diseases of corn in
the United States, and the loss varies according to the character
of the weather, the crop being damaged most severely during
wet seasons. The rainy weather and high temperatures which
usually prevail in Florida at the time corn is maturing favor the
development of the disease.
The fungus attacks the stalks, ears and roots of plants, and
lives over the winter in or on the seed and in the soil and crop
refuse. The spores are carried by air currents and upon coming
to rest between the leaf sheaths and stalk at the node and on
the exposed tip of an ear germinate and cause infection. Ears
that are invaded by ear worms are usually diseased, as the fungus
enters the openings in the husks made by the worms.
The disease is severe in fields where velvet beans are grown
with corn, for the vines shade the corn plants and thus create
humid conditions which are favorable for the development of
the disease. Delayed harvesting leads to further loss, as the
fungus will continue to grow and rot the ears as long as they
remain damp.
Symptoms: The disease is indicated on the ear by the white to
pink mold which may be seen on the inner husks, kernels and
cob (Fig. 2). When the husks of a severely rotted ear are re-
moved, the mold may be found as a felt-like mass on the tops and
between the rows of kernels. Only one end of the ear-either
butt or tip-may be diseased, depending on where the fungus

1All photographs appearing .in this bulletin were made under the super-
vision of Mr. David G. A. Kelbert.










CORN DISEASES IN FLORIDA
By A. H. EDDINS'

INTRODUCTION
Diseases of corn are widespread in Florida and cause a con-
siderable reduction in the yield, quality and value of this crop.
Corn growers can reduce their losses by becoming familiar with
the different corn diseases and the known control measures. This
bulletin contains information concerning the occurrence, symp-
toms and known methods of controlling corn diseases.

FUSARIUM AND GIBBERELLA DRY ROT
This disease is caused by Fusarium spp. and Gibberella spp.
It is one of the most common and destructive diseases of corn in
the United States, and the loss varies according to the character
of the weather, the crop being damaged most severely during
wet seasons. The rainy weather and high temperatures which
usually prevail in Florida at the time corn is maturing favor the
development of the disease.
The fungus attacks the stalks, ears and roots of plants, and
lives over the winter in or on the seed and in the soil and crop
refuse. The spores are carried by air currents and upon coming
to rest between the leaf sheaths and stalk at the node and on
the exposed tip of an ear germinate and cause infection. Ears
that are invaded by ear worms are usually diseased, as the fungus
enters the openings in the husks made by the worms.
The disease is severe in fields where velvet beans are grown
with corn, for the vines shade the corn plants and thus create
humid conditions which are favorable for the development of
the disease. Delayed harvesting leads to further loss, as the
fungus will continue to grow and rot the ears as long as they
remain damp.
Symptoms: The disease is indicated on the ear by the white to
pink mold which may be seen on the inner husks, kernels and
cob (Fig. 2). When the husks of a severely rotted ear are re-
moved, the mold may be found as a felt-like mass on the tops and
between the rows of kernels. Only one end of the ear-either
butt or tip-may be diseased, depending on where the fungus

1All photographs appearing .in this bulletin were made under the super-
vision of Mr. David G. A. Kelbert.








Florida Agricultural Experiment Station


has entered and how far it has advanced on the ear. Evidence
of the presence of the mold also may be limited to patches on the
ear bounding the region ravaged by the corn ear worm.
The kernels of a badly molded
ear are usually pink and loose on
the cob. Ears that are not severely
S rotted may show only traces of
mold on the tips of kernels. Ears
also may be so severely infected
that the germs of the kernels are
killed and yet show no external
signs of the disease (Fig. 3). How-
ever, its presence in such cases can
be detected by the use of the rag
doll germinator. Infected kernels,
on the germinator, have white to
pink mycelial masses of the fungus
growing out of them.
The mold appears on the leaf
sheaths and stalks of the plant at
or near maturity of the crop. The
lower part of the plant is most
severely diseased because of more
favorable moisture conditions on
that part. Plants that are severely
molded at the lower nodes are
weakened and may be broken by
the wind.
When diseased seed are planted
the fungus rots the roots of the
young seedlings, causing them to
turn brown and die. This type of
injury is called seedling blight and
Results in the death of the seedling
or a stunting in growth so that the
plant will produce a small ear or
none.
Control: There is no absolute
method of controlling this disease.
Fig. 2.-An ear of corn severely If the seed is carefully selected,
rotted by the Fusarium dry rot
organism. properly cured and stored, tested


I








Bulletin 210, Corn Diseases in Florida


and treated, poor stands and seedling blight resulting from the
use of diseased seed can be avoided.


Fig. 3.-The ear of corn on the left is healthy, and the kernels germinated
100 per cent; the one on the right appears to be healthy but the kernels have
been killed by Fusarium rot.








Florida Agricultural Experiment Station


DIPLODIA DRY ROT

Diplodia dry rot is caused by Diplodia zeae (Schw.) Lev. and
Diplodia macrospora Earle. This disease occurs in all corn
growing regions of the United States, and is worst in the central
and southern portions of the country. In Florida, the disease is
prevalent wherever corn is grown and reduces the yield and
quality of the crop.
The disease attacks the ears, stalks, and roots of corn plants.
It reduces yields because of severely rotted ears and weakened
plants resulting from stalk infections. The planting of infected
seed results in reduced stands, due to the poor germination of the
seed and to the death of plants with diseased roots. Further-
more, infected seedlings that do not die may be reduced in vigor
and develop into plants with low yield.
The fungus causing the disease may be carried over the winter
as dormant mycelium in the seed. It also overwinters in corn
roots, stalks, shanks, husks and rotted ears left in the field. The
Organism produces fruiting bodies on the old plant refuse, and
the spores formed within these bodies serve as agents of infection
the next season. Spores are known to survive at least three years
on old corn stalks left in the field, and are disseminated by the
wind principally, also by rain and running water.
Infection occurs after silking time. The spores lodge in
crevices between the stalk and sheath, at the shank, and on the
tip of the ear and under favorable environmental conditions ger-
minate and cause infection.
Symptoms: The first symptom of infection on the ear is a
fading of the bright green color of the husks to a pale yellowish
green. If the entire ear becomes involved, the husks turn brown
prematurely. In some cases only the tip or the butt end of the
ear becomes diseased. The husks stick closely to a severely rotted
ear and the small black dots or fruiting bodies of the fungus can
be seen on their surfaces (Fig. 4). The white mycelial threads
of the fungus may penetrate and grow between the husks, and in
some instances may be observed on the outside of the ear. If the
husks of a badly molded ear are removed, the ear may be found
covered with a white mold, and the kernels are loose on the cob
and of a dirty gray to brown color (Fig. 5). The black fruiting
bodies of the organism are often found imbedded in the mold on
the kernels and cob. On some ears, the disease is not easily vis-








Bulletin 210, Corn Diseases in Florida


ible and the
mold may be
seen only when
the tips of the
kernels are ex-
amined closely.
Kernels may be
invaded and
killed by the
causal organ-
ism and show
no external
signs of infec-
tion. The pres-
ence of the fun-
gus in such
kernels can be
detected when
the corn is ger-
minated.
Infection on
leaf sheaths by
the fungus re-
sults in yellow
to purple spots
which later
turn brown. A
common symp-
tom is the pres-
ence of the
white mold on
the shank of
the ear. Later,
the develop-
ment of the
small black Fig. 4.-An ear rotted by Diplodia mold, showing
fruiting bodies, the black fruiting bodies or pycnidia of the organism
on the outer hus s.
pycnidia of the
organism, on the diseased ear shanks and stalks (Fig. 6) is the
best evidence of the disease.
The fungus causes seedling blight if infected seed are planted.








Florida Agricultural Experiment Station


The fungus attacks the roots, causing them to turn brown and
die. The plants are killed or stunted in growth so that they are
unproductive.
Control: The most beneficial control measure is to give careful
attention to seed selection, curing and storing, testing and treat-


Fig. 5.-An ear rotted by Diplodia and a normal ear,


w-- .-- -. *: -








Bulletin 210. Corn Diseases in Florida


ment. Crop rotation also will help to hold the disease in check.
The rotation should be such that corn will not be grown more
often than one year in four, for the
causal organism can live at least
three years on old corn stalks in
the field.

BROWN SPOT

This disease is caused by the
fungus Physoderma zeae-maydis
Shaw. It occurs over a large part
of the corn growing regions of the
United States east of the Rocky
Mountains and south of the Great
Lakes. It does little damage to the
corn crop in the north, but the loss
is severe in the lower Atlantic and
Gulf states. In the south, the con-
tinuous high summer temperatures
and abundance of rainfall during
the early growing period of the
crop furnish ideal conditions for
the development of the disease. In
Florida, brown spot is one of the
most common diseases appearing
on corn.
The disease occurs on all types
and varieties of corn and teosinte.
It attacks the leaf, leaf sheath,
stalk, and occasionally the outer
husks of ears. The fungus causing
the disease produces spores in the
invaded cells of the host plant.
These spores can survive at least
two years in the field on old infected
plant refuse and in the soil. The
fungus is disseminated by the wind,
rain, running water, insects and
animals. Spores lodge in the buds
of young corn plants in the early Fig. 6.-Diplodia zeae fruit-
of young corn plants in the early ing on an old corn stalk.








Florida Agricultural Experiment Station


part of the growing period, and in the crevices formed between
the leaf sheaths and stalks of plants at or near flowering time.
They germinate under proper conditions of temperature and
moisture and produce a large number of smaller swimming spores
which swim in the
free water held in
the bud and leaf
sheaths, and final-
ly come to rest on
the tissue of the
plant. The swim-
ming spores then
germinate and
the fungus pene-
trates the cells of
the plant.
The disease can
be found on corn
grown during any
season in Florida.
On the main crop
which is planted
March 15 to April
15, the disease
usually makes its
appearance the
latter part of May
and the first of
June. As the
season advances,
infection becomes
general. Brown
spot is usually
worst on vigorous
plants. Extreme-
ly early corn is
usually freer from
the disease than
the later corn be-
cause the temper-
Fig. 7.-Brown spot on a corn leaf, showing alter- nature and mois-
nate bands of diseased and healthy tissue.








Bulletin 210, Corn Diseases in Florida


Fig. 8.-Leaf sheath on
cornstalk, showing brown
spot infection.


Fig. 9.-Brown spot on a nearly mature
leaf sheath showing rupture of the epidermis
and the fibrous nature of the diseased area
:when the spores are set free.







Florida Agricultural Experiment Station


ture conditions are not so favorable for the development of the
disease early in the season.
Symptoms: The disease first appears on the leaf blades as small
slightly watersoaked to yellowish
spots about 1/25 inch in diameter.
These spots later become reddish
brown with a lighter colored margin
and give the diseased area a brown-
ish appearance. In some cases the
entire leaf blade may have this ap-
pearance, but usually alternate bands
of diseased and healthy tissue occur
on the leaf (Fig. 7). The spots that
appear on the midrib, leaf sheath
and stalk are from 1/10 to 1/4 inch
in diameter and are brown in color.
Sometimes a red color develops in
the spots on the midrib but disap-
pears, leaving the brown color when
the spots become older. As the corn
matures, the spots coalesce and form
chocolate brown patches of diseased
areas (Fig 8). The dry blister-like
epidermis covering the diseased
areas ruptures (Fig. 9) and frees
the spores from the leaf fibers. The
disease occurs on both the nodes and
internodes of the stalks (Fig. 10).
but it is more common on the former.
In severe cases, lodging results from
nodal infections. The disease is
usually worst on the lower part of
the plant.
Control: There is no absolute con-
trol for this disease. However, if
certain practices are followed in re-
ducing the amount of spore material
present in corn fields, the damage to
the crop can be reduced.
Fig. 10.-Brown spot on a The most severe outbreaks of
corn stalk at the nodes and in- brown spot occur on land contin-
ternode.







Bulletin 210, Corn Diseases in Florida


uously cropped to corn. Crop rotation should be practiced and
corn should not be grown on the same land more often than every
third year, for -the spores live at least two years in the soil. As
the spores are disseminated by the wind, the corn field should be
located as far as possible from fields where the disease was prev-
alent the previous season.
The old stalks should be cut fine with a stalk cutter and plowed
under deeply so that they will not be brought to the surface by
cultivation the following season.
The amount of spore material also can be reduced by remov-
ing the infected crop from the land as quickly and completely as
possible. If it is used for silage or fed as stover or fodder, the
barnyard manure should not be used on land which is to be
planted to corn.

CORN SMUT
Corn smut is caused by the fungus Ustilago zeae (Bekm.) Ung.
It is the most common disease appearing on corn in the United
States and causes yearly losses ranging from 1 to 2 percent of
the crop in Florida.
No varieties of corn are known to be immune to smut. Spores
of the fungus, formed in the black masses or smut galls on the
plant, are disseminated by the wind principally, also by rain,
running water, insects and animals. These spores overwinter
in old galls and in the soil where they may remain viable for
several years. The spores germinate under favorable conditions
and form conidia. These conidia are blown by the wind, and,
when they come to rest and germinate on that part of the plant
where there is young growing tissue, they cause the disease. The
plant may become infected at any stage of growth but usually the
disease does not begin to appear until the plant is about three
feet high.
Symptoms: The disease appears on the above ground parts of
the corn plant. Galls which are at first enclosed with a white
membrane become black as they develop. When they are matured
the dry enclosing membrane breaks and the powdery mass of
spores is set free.
The disease on the leaf and tassel usually appears as very small
galls or pustules (Fig. 11), generally less than an inch in diam-
eter. On all other parts the galls are usually several inches in
diameter.








Florida Agricultural Experiment Station


.. .......I.
::1


Fig. 11.-Smut on the tassel of a corn plant.


I -


~i~~i~
,.~ :.







Bulletin 210, Corn Diseases in Florida 17

Ears are most often infected at the tip but they may be invaded
at any other point. The entire ear is sometimes replaced by the
gall which is usually partially or wholly enclosed by the outer


Fig. 12.-Ear of corn entirely replaced by a large smut gall.







Florida Agricultural Experiment Station


husks (Fig. 12) that are not diseased. If plants become severely
diseased before reaching a foot in height (Fig. 13) they are gen-
erally either killed or
stunted in growth.
Large galls that ap-
pear on the plant be-
low the ear at later
stages of growth may
lead to barrenness.
Control: Smut is
not a seed-borne dis-
ease, therefore, seed
disinfection is of no
value as a control
measure. Collecting
and destroying galls
is a good control
practice but is profit-
able only in small
plantings.
Some protection
against the disease is
given when the crop
is used for silage. The
success of this method
of control depends
upon the complete re-
moval of the crop be-
fore the smut galls
are broken and the
spores disseminated.
The manure obtained
from livestock fed
silage can be safely
returned to the corn
field as the spores are
killed in passing
4 through the digestive
tracts of the animals.
A crop rotation in
Fig. 13.-Corn smut on the stalk and leaf of a which corn is not
small corn plant.







Bulletin 210, Corn Diseases in Florida


grown more often than one year in three is a good control prac-
tice. This will prevent the concentration of the disease in the
field. The new corn field should be located as far from the old
field as is practicable, as the spores of the corn smut fungus are
blown considerable distances by the wind.

SCUTELLUM ROT

Scutellum rot may be caused by any one of several different
fungous organisms. The fungi that are known to produce the
disease are Rhizopus spp., Aspergillus spp., Penicillium spp.,
Mucor spp., and Fusarium spp. The disease is found in corn in
all parts of the United States, and is the cause of much poor seed
corn in Florida.
The scutellum is that part of the kernel of corn immediately
surrounding the germ or embryo
and separating it from the endo-
sperm. When the rot invades the
scutellum (Fig. 14) it weakens
the seedling by cutting off its
food supply from the seed, or
enters the tissues of the young
developing plant and rots them.
Usually the rot is not caused by
any parasitic fungus carried
within the kernel, but infection
develops from attacks of organ-
isms on the outside. Kernels
usually become diseased after
they begin to germinate and
when the seed coat has been soft-
ened and ruptured so that the
fungi can enter the sprouting
kernels.
Symptoms: Scutellum rot pro-
duces the same type of symptoms
on plants in the field as is pro-
duced by several other seedling
diseases. The diseased plants
may be killed or so weakened
that they produce nubbins only Fig. 14.-Longitudinal section of
a germinated kernel showing the
or no ears at all. Infected ears blackened and rotted scutellum.







Florida Agricultural Experiment Station


can be detected if the kernels are tested on a seed germinator.
When diseased kernels are cut open the scutellum will appear
brown to almost black
in color. White, pink,
yellow or black molds
also may be found
growing over the sur-
face of scutellum rot-
ted kernels on the ger-
minator.

Control: Good seed
selection, proper cur-
ing and storing, seed
testing, and seed treat-
ment as discussed in
the latter part of this
bulletin will hold this
disease in check.

YELLOW EAR MOLD
Yellow ear mold is
caused by the fungus
Aspergillus flavus
Link. This disease does
some damage to corn
in the southern corn
growing regions of the
United States, and it
ranks as one of the
minor ear rot diseases
in Florida. Yellow
mold does the most
injury during very
wet seasons. Ears are
usually infected during
the early stages of ma-
turity and are never
molded when they are
in a dry matured con-
Fig. 15.-An ear of corn affected with yellow in a dry matured con-
mold at the butt end. edition. The ear is in-







Bulletin 210, Corn Diseases in Florida


fected by the fungus spores which lodge on the exposed tip and
in openings made in the husks by ear worms. The spores also
may lodge in crevices formed by the overlapping of husks at the
butt end of the ear. They germinate if moisture is present, and
the fungus grows through the husks and attacks the kernels.
Symptoms: Diseased ears are recognized when the husks are
removed. Diseased parts of a severely molded ear are covered
with a dusty yellow mold, and the molded kernels are small,
shriveled, and of a brownish color. In some cases the mold may
be seen on the inner husks of an infected ear at the butt end
(Fig. 15) where the entrapped moisture has been favorable for
the growth of the parasite. Kernels may have their germs killed
or weakened and yet show no signs of infection. These kernels
can be detected by the presence of a dusty yellow growth that
appears on them when they are placed on the germinator.
Control: The use of varieties of corn with good husk coverings
will help to hold this ear mold in check. Varieties with drooping
ears prevent the accumulation of moisture in the tip and butt
ends of ears and are not damaged so much by the mold as vari-
eties with upright ears.
If the crop is harvested when mature and placed in well con-
structed cribs, the damage that occurs late in the season in the
field and under poor storage conditions later, will be checked.
The use of good field selected, properly cured, stored and tested
seed will prevent any reduction in stand and seedling injury
resulting from this mold.

GREEN EAR MOLD
This disease, caused by Aspergillus sp., is one of the less im-
portant ear rot diseases in Florida. The disease may enter the
ear through any openings in the husks. Like yellow ear mold,
the green mold does the most damage during wet weather. Ears
that are immature and those that are damp are susceptible to
attack from this disease. Corn that is exposed to the weather
after it has matured or corn that is stored in leaky cribs is often
damaged by the green ear mold.
Symptoms: This mold appears on the kernels of a severely
diseased ear as a dusty green spore mass (Fig. 16). The husks
in direct contact with the ear also may have the green mold on
them. It is only in extreme cases that the entire ear is covered







Florida Agricultural Experiment Station


with the mold. The badly infected kernels have a dull lusterless
appearance. As is the case with other rot diseases, kernels may
be rotted and show no signs of the mold. Such kernels on a ger-
minator have a dusty green
,; v- growth on them.
Control: Same as for yellow
ear mold.

LEAF BLIGHT

This disease is caused by
Helminthosporium turcicum
Pass. It occurs on corn through-
out the United States. In certain
localities during exceptionally
warm, wet seasons, the disease
has done considerable damage.
In Florida, it is very conspicuous
on corn near the end of the grow-
ing season.
The spores of the fungus are
formed on the blighted spots on
the leaves, and overwinter on old
leaves in the field and in the soil.
Spores are disseminated princi-
pally by the wind and upon com-
ing in contact with the leaf, ger-
minate and infect it through the
natural openings or stomata.
Plants may become diseased
when two to three feet high but
usually blighting does not be-
come general until the plants
have flowered. The disease is
usually more severe on the lower
leaves. It weakens the vitality
of the plants and, in severe cases,
may kill them. Therefore, the
growing period is shortened and
the crop matures prematurely,
resulting in a reduced yield of
Fig. 16.-An ear of corn with
green mold growing on it. grain and fodder.







Bulletin 210, Corn Diseases in Florida


Symptoms: The
disease appears
first as small, pale,
yellowish, ellipti-
cal spots on the
leaves. These
spots, usually few
in number, en-
large and form
long, brown, dead
patches (Fig. 17)
sometimes six or
more inches in
length and one or
more inches in 9
width. The dis-
eased leaf tissue
finally becomes
dry and brittle
and the fungus is
visible on the dead
parts of the leaf
as a dark hairy
mold.
Control: No
means of control-
ling this disease
are known.

RUST
Fig. 17.-Helminthosporium blight on a corn leaf.
Rust is caused
by the fungus Puccinia sorghi Schw. It is widely distributed in
the corn growing regions of the United States, but it is of minor
economic importance, as the damage is slight. The disease occurs
on all varieties of corn in Florida but is not considered serious.
The disease may be observed on the crop in the early part of
the season but it does not become abundant until later and reaches
its maximum development just before the corn plant stops grow-
ing. The spores of the fungus are borne in pustules on the leaf,
and, in Florida, overwinter in the old plant refuse and in the soil.







Florida Agricultural Experiment Station


The spores are disseminated by the wind principally and, upon
coming to rest on the leaves of the plant, they germinate and the
fungus enters the host through the natural openings or stomata
on the leaves. Warm, cloudy, moist weather is favorable for the
development of rust. Tha disease is more abundant on the lower
leaves of the plant.
Symptoms: The disease appears on the leaf as small yellowish
spots which turn
reddish brown
when pustules,
containing the red
masses of spores,
are formed. The
spots coalesce
sometimes and
form larger dis-
eased areas, and
the lower leaves
are often covered
thickly with pus-
tules (Fig. 18).
Sometimes a leaf
shows alternate
bands of rusted
and normal tissue.
This condition is
probably due to
alternate favor-
Fig. 18.-A severely rusted leaf of corn. able and unfavor-
able moisture conditions when the leaf was elongating. When
the pustules are broken open, the powdery mass of spores is scat-
tered by the elements.
Control: No control measures have been worked out, as the
disease is considered to be of little importance.

OPHIOBOLUS LEAF SPOT

This leaf spot is a disease caused by the fungus Ophiobolus
heterostrophus Drechs. Although the disease has been reported
only from Florida, it is probable that it also occurs in other
southern states.
The disease does not become general until after tasseling time,







Bulletin 210, Corn Diseases in Florida


although it may appear on the leaves of plants at all stages of
growth. The spores of the fungus are borne on the diseased spots
on the leaves and are disseminated principally by the wind. They
may overwinter on old diseased leaves or in the soil. Under
favorable environmental conditions the spores that come to rest
on a leaf germinate and the fungus enters the host through the
stomata of the leaf. The effect of leaf spot and leaf blight on
corn is similar, al-
though the latter
causes much heav-
ier losses. The
growing period is
shortened, result-
ing in reduced
yields of grain and
forage.
Symptoms: The
disease is first ob-
served as small
watersoaked spots
between the veins
of the leaf. These
spots enlarge and
become irregularly
elongated and cin-
namon-buff color
in the center and a
reddish brown near
the margin. This
gives the spot a zo- Fig. 19.-Leaf spot caused by Ophiobolis
nate appearance heterostrophus.
and the line of demarcation between diseased and green healthy
tissue is very distinct (Fig. 19). The spots never become large
even though they coalesce. A single leaf may have several hun-
dred spots on it.
Control: Like rust, this disease is not serious and no control
measures have been worked out.

SHEATH SPOT

This disease is caused by a number of different bacterial and
fungous organisms, and occurs throughout the United States, but







Florida Agricultural Experiment Station


does little damage to corn in Florida. The disease appears after
the corn has tasseled.

Symptoms: The organisms
which produce the disease start
their growth on the pollen, pollen
Ssacs, and plant and insect secre-
tions which have accumulated
between the leaf and ear sheaths
and the stalk. Later the organ-
isms invade the tissues of the
sheaths and cause purple and
brown spots to appear on them
(Fig. 20). Often these spots
coalesce and produce large irreg-
ularly shaped blotches on the
sheaths.
Control: No control measures
for this disease are known.

PYTHIUM ROOT ROT

This disease is caused byPyth-
ium spp. It is one of the minor
root rots of corn in Florida. The
disease attacks the roots of the
seedling plant and causes the
death or stunted growth of the
young plant. The disease does
the most damage to plants grow-
ing in cold, wet soil. Little injury
results during favorable seasons
when corn is planted in warm soil.

BACTERIAL LEAF SPOTS

Two types of bacterial leaf
spots are common in cornfields in
Florida but the organisms which
cause them have not been deter-
Fig. 20.-Sheath spot on a corn
leaf sheath spot on a orn mined. One type of spot appears
leaf sheath.







Florida Agricultural Experiment Station


does little damage to corn in Florida. The disease appears after
the corn has tasseled.

Symptoms: The organisms
which produce the disease start
their growth on the pollen, pollen
Ssacs, and plant and insect secre-
tions which have accumulated
between the leaf and ear sheaths
and the stalk. Later the organ-
isms invade the tissues of the
sheaths and cause purple and
brown spots to appear on them
(Fig. 20). Often these spots
coalesce and produce large irreg-
ularly shaped blotches on the
sheaths.
Control: No control measures
for this disease are known.

PYTHIUM ROOT ROT

This disease is caused byPyth-
ium spp. It is one of the minor
root rots of corn in Florida. The
disease attacks the roots of the
seedling plant and causes the
death or stunted growth of the
young plant. The disease does
the most damage to plants grow-
ing in cold, wet soil. Little injury
results during favorable seasons
when corn is planted in warm soil.

BACTERIAL LEAF SPOTS

Two types of bacterial leaf
spots are common in cornfields in
Florida but the organisms which
cause them have not been deter-
Fig. 20.-Sheath spot on a corn
leaf sheath spot on a orn mined. One type of spot appears
leaf sheath.







Bulletin 210, Corn Diseases in Florida


on the leaf as small, round to elliptical lesions which closely re-
semble those of Holcus bacterial leaf spot, that occurs in Iowa,
and is caused by Pseudomonas holci Kend. The spots have a light
to dark brown center with a narrow, reddish brown border and
are usually surrounded by a narrow, yellowish halo when viewed
by transmitted
light. The other
type of bacteri-
al spot affects
only the midvein
of the leaf. At
first the disease
appears as round
to elongated,
watersoaked le-
sions which later
enlarge and be-
come dark brown
to black in color
(Fig. 21). Sev-
eral inches of
the midvein may
become involved
when the spots
enlarge and co-
alesce.
These diseases
are of minor
economic impor-
tance in the
state. No con-
trol measures
are known. Fig. 21.--Bacterial leaf spot affecting the mid-vein
of a corn leaf.

STEM ROT

Stem rot caused by Sclerotium rolfsii Sacc. occurs very infre-
quently on corn in Florida, and does little damage. The fungus
attacks the brace roots and stalk at the soil line, and develops
only on plants growing in moist soil. The disease can be recog-
nized by the white thread-like growth of mold, and the small light
to dark brown fruiting bodies or sclerotia of the fungus on the







Florida Agricultural Experiment Station


diseased part of the plant. The fungus causes a rot of the in-
fected roots and stalk. No control measures are recommended.

MISCELLANEOUS LEAF SPOTS

In addition to those already mentioned, the following fungous
organisms cause leaf spots of corn in Florida: Phyllosticta sp.,
Macrosporium sp., and Cercospora sp. The spots produced by
these organisms are similar in appearance and it is necessary to
examine the fungous spores to identify the specific organism
causing the trouble. Usually these leaf spot diseases occur in-
frequently and do little damage in Florida.

BACTERIAL WILT
This disease is caused by the bacterial organism Aplanobacter
stewarti (EFS) McC. and occurs in all of the corn growing
regions of the United States. Sweet corn is very susceptible to
this disease; field corn is only slightly attacked. The disease has
never been observed on field corn in Florida, but it has been
reported as doing some damage to sweet corn.
The causal organism lives from one season to the next in or on
infected seed. Infection occurs in the seedling stage and the
affected plants may be stunted in growth or often killed shortly
after tasseling.
Symptoms: The first symptom of infection is a wilting of the
leaves. As the disease develops the leaves turn yellow and wither.
In some cases all of the leaves on the plant wilt and die simul-
taneously, but generally they wither and die from the base of the
plant upward. The cause of the trouble is a clogging of the water
conducting vessels in the stem of the plant by the rapidly multiply-
ing bacteria. A yellow slime oozes from the ends of infected stalks
that are cut crosswise. This slime, composed of countless num-
bers of bacteria, is of a viscous, stringy consistency and is teem-
ing with bacteria. The bacteria invade the vessels of all parts of
the plant and penetrate the kernels, cob and husks of the ear.
The disease may kill the plant within a period of four days after
its first appearance, or it may develop slowly and require a month
to destroy the plant.
Control: Bacterial wilt is a typical example of a seed-borne
disease. It can be controlled by selecting seed corn from plants
free from the disease. Infected seed can be rendered nearly free








Bulletin 210, Corn Diseases in Florida


from the organism by plunging it for a moment into alcohol and
then allowing it to remain 20 minutes in 1:1,000 solution of cor-
rosive sublimate. It should then be rinsed immediately in water
and spread out to dry, or planted at once.

OTHER DISEASES
There are a number of diseases of corn present in other parts
of the United States that have not been found in Florida. This
list includes anthracnose, Helminthosporium stalk canker, black
bundle, downy mildew, head smut, false smut, mosaic, bacterial
stalk rot, Basisporium dry rot, black ear mold, and seedling
blights and root rots caused by a number of different fungi.
Since these diseases have not been observed in Florida, it is not
necessary to discuss them in this bulletin.

SEED SELECTION
Healthy seed corn, as free from ear rot organisms as it is
possible to get it, should always be used to plant the crop. One
of the first steps to be taken to secure healthy seed is to select the
seed ears from standing stalks in the field as soon as the kernels
are well filled and dented. It is important to select early in Flor-
ida, for the warm, moist weather in late summer and fall is ideal
for the development of ear rot organisms which damage the ears
left in the field after they have matured.
One man with a bag can go through the field and select several
bushels of seed corn in a day (Fig. 1). The seed ears should be
selected from individual stalks on the basis of their freedom from
disease. By selecting early, it is possible to distinguish between
the normally ripened ear and the ear that has prematurely
ripened on account of some disease. The best ears are produced
on good, normal, upright stalks free from smut, brown spot and
rust. Stalks that are leaning, broken and prematurely dead often
bear ears that are in a diseased condition. The ears should be
borne on unbroken, unrotted shanks and show no signs of rotting
of the kernels. About five times as many ears should be selected
from the field as will be needed, so that enough will be left for
seed after the diseased ears are discarded.
After the seed ears have been thoroughly dried, those that
show any symptoms of being diseased should be discarded at this
time. The kernels of good seed ears are firm on the cob and have








Bulletin 210, Corn Diseases in Florida


from the organism by plunging it for a moment into alcohol and
then allowing it to remain 20 minutes in 1:1,000 solution of cor-
rosive sublimate. It should then be rinsed immediately in water
and spread out to dry, or planted at once.

OTHER DISEASES
There are a number of diseases of corn present in other parts
of the United States that have not been found in Florida. This
list includes anthracnose, Helminthosporium stalk canker, black
bundle, downy mildew, head smut, false smut, mosaic, bacterial
stalk rot, Basisporium dry rot, black ear mold, and seedling
blights and root rots caused by a number of different fungi.
Since these diseases have not been observed in Florida, it is not
necessary to discuss them in this bulletin.

SEED SELECTION
Healthy seed corn, as free from ear rot organisms as it is
possible to get it, should always be used to plant the crop. One
of the first steps to be taken to secure healthy seed is to select the
seed ears from standing stalks in the field as soon as the kernels
are well filled and dented. It is important to select early in Flor-
ida, for the warm, moist weather in late summer and fall is ideal
for the development of ear rot organisms which damage the ears
left in the field after they have matured.
One man with a bag can go through the field and select several
bushels of seed corn in a day (Fig. 1). The seed ears should be
selected from individual stalks on the basis of their freedom from
disease. By selecting early, it is possible to distinguish between
the normally ripened ear and the ear that has prematurely
ripened on account of some disease. The best ears are produced
on good, normal, upright stalks free from smut, brown spot and
rust. Stalks that are leaning, broken and prematurely dead often
bear ears that are in a diseased condition. The ears should be
borne on unbroken, unrotted shanks and show no signs of rotting
of the kernels. About five times as many ears should be selected
from the field as will be needed, so that enough will be left for
seed after the diseased ears are discarded.
After the seed ears have been thoroughly dried, those that
show any symptoms of being diseased should be discarded at this
time. The kernels of good seed ears are firm on the cob and have






Florida Agricultural Experiment Station


a bright color. If they are of the dent type, they should be shal-
low dented and smooth, for roughly dented ears with much soft
or white starch are likely to be diseased. Shredded or discolored
shank attachments of the ears indicate that such ears are dis-
eased and they should be discarded. No ears should be kept that
have weathered and molded tips.





AMr



















by placing them on wooden racks.
mImmm


m -i...


~,.,


"-










by placing them on wooden racks.







Bulletin 210, Corn Diseases in Florida


SEED CURING AND STORING
As soon as gathered, the husked ears should be put in a dry
place where there is free circulation of air, such as in an open
shed or loft. If the early, field selected ears are left in a sack
or in a pile during warm weather, with moisture in the cobs and
kernels, fungous organisms will rot the ears. Therefore, prompt
and thorough drying of the seed ears is essential. Drying can
be done best by hanging the ears on strings or placing them on
wire or wooden racks so they will not touch each other (Fig. 22).
To prevent injury by weevils, or grain moths, the dry seed
ears should be fumigated with carbon disulphide at the rate of
one pound per 100 cubic feet of space in air-tight rooms, bins,
boxes or barrels for 24 hours. The disulphide should be placed
in shallow dishes or pans on top of the seed. The disulphide gas
is inflammable, consequently no fire should be present. After
fumigation, the ears should be thoroughly aired and stored in
tight, mouse-proof bins, boxes or barrels. One pound of moth
balls or naphthalene should be inclosed for each bushel of corn to
prevent entrance of grain weevils and moths.
SEED TESTING
Several weeks before planting time, the corn should be given
a germination test in order that the very best seed ears may be
selected. There are several types of germinators in use for test-
ing seed corn. Of the various types, the modified rag-doll ger-
minator is most commonly used by the corn grower. This con-
sists of a strip of good grade muslin cloth, 6 feet long by 12 to
14 inches wide, laid on the same size strip of heavy glazed manila
paper, or heavy butcher's paper. A doll of this size will test 30
ears. If the muslin cloth has been used, it should be boiled an
hour before being used again to kill all of the fungi that may
have collected on it.
Six or eight kernels should be taken from each ear in a spiral
from butt to tip, and placed in a row crosswise of the doll. The
kernels are placed with the germ sides down and all tips pointing
in the same direction. The ears should be numbered corre-
sponding to the order in which they are being tested on the doll.
The rows of kernels should be two inches apart on the doll and
the outside rows should be four inches from their respective ends
of the doll. If the muslin cloth is dampened before the kernels
are placed on it, the doll can be rolled up easily without displacing







Bulletin 210, Corn Diseases in Florida


SEED CURING AND STORING
As soon as gathered, the husked ears should be put in a dry
place where there is free circulation of air, such as in an open
shed or loft. If the early, field selected ears are left in a sack
or in a pile during warm weather, with moisture in the cobs and
kernels, fungous organisms will rot the ears. Therefore, prompt
and thorough drying of the seed ears is essential. Drying can
be done best by hanging the ears on strings or placing them on
wire or wooden racks so they will not touch each other (Fig. 22).
To prevent injury by weevils, or grain moths, the dry seed
ears should be fumigated with carbon disulphide at the rate of
one pound per 100 cubic feet of space in air-tight rooms, bins,
boxes or barrels for 24 hours. The disulphide should be placed
in shallow dishes or pans on top of the seed. The disulphide gas
is inflammable, consequently no fire should be present. After
fumigation, the ears should be thoroughly aired and stored in
tight, mouse-proof bins, boxes or barrels. One pound of moth
balls or naphthalene should be inclosed for each bushel of corn to
prevent entrance of grain weevils and moths.
SEED TESTING
Several weeks before planting time, the corn should be given
a germination test in order that the very best seed ears may be
selected. There are several types of germinators in use for test-
ing seed corn. Of the various types, the modified rag-doll ger-
minator is most commonly used by the corn grower. This con-
sists of a strip of good grade muslin cloth, 6 feet long by 12 to
14 inches wide, laid on the same size strip of heavy glazed manila
paper, or heavy butcher's paper. A doll of this size will test 30
ears. If the muslin cloth has been used, it should be boiled an
hour before being used again to kill all of the fungi that may
have collected on it.
Six or eight kernels should be taken from each ear in a spiral
from butt to tip, and placed in a row crosswise of the doll. The
kernels are placed with the germ sides down and all tips pointing
in the same direction. The ears should be numbered corre-
sponding to the order in which they are being tested on the doll.
The rows of kernels should be two inches apart on the doll and
the outside rows should be four inches from their respective ends
of the doll. If the muslin cloth is dampened before the kernels
are placed on it, the doll can be rolled up easily without displacing







Florida Agricultural Experiment Station


the kernels. After the kernels are placed on the cloth, the doll
can be rolled up and rubber bands placed around each end. The
upper end should be indicated by attaching a tag on which is
written the numbers of the ears used and the date of the test
(Fig. 23). The dolls should be placed in the germinator with
kernel points down.


.MlIW k'lw! i -ia^ Kiedmillailktaki& iiIIll
Fig. 23.-Rag-doll germinator showing paper, cloth and corn kernels in
position and the doll rolled and labeled.


Fig. 24.-Rag-toll germinator box showing outer and inner box with dolls
in position.







Bulletin 210, Corn Diseases in Florida


The germinator box consists of an outer and inner box with
2 to 3 inches of sawdust between them. The inside box should
be at least 18 inches deep. Wire cross rods placed 3 inches apart
in the upper part of the inner box will provide a separate space
for placing each doll (Fig. 24). The sawdust must be kept thor-
oughly wet and the rag dolls should be sprinkled twice daily with
warm water. Clean, wet, fertilizer bags serve as a good cover
for the top of the germinator box. The temperature of the box
should be kept at 750 to 850 F. while the kernels are germinating.
At the end of seven days the rag dolls are ready to be removed
from the germinator box, unrolled and carefully read (Fig. 25).


Fig. 25.-Rag-doll germinator unrolled for reading the results.

Ears whose kernels all germinate and show clean, vigorous seed-
lings without rotting should be selected for seed. All ears that
are represented by rotted and weak seedlings and dead kernels
should be thrown out.
SEED TREATMENT
Chemical dust treatment of seed to control seedling blights of
corn has been used with good results in the corn growing regions
in the central part of the United States, and is being tested at the







Florida Agricultural Experiment Station


present time in Florida. The dust fungicides consist of organic
mercury compounds of a slowly soluble nature. Among those
that have been used successfully are Merko, Semesan, Jr., Bayer
and Sterocide dusts. These are manufactured by commercial
concerns and can be purchased from seed companies and local
druggists.
The mercury dusts do not injure healthy seed and will kill dry
rot organisms on diseased seed. The efficiency of the dust treat-
ment in increasing yields depends upon the amount of infection
on the seed, the time of planting, and growing conditions. The
treatment is beneficial in protecting the seed in cold wet soil by
preventing it from rotting. The dust fungicides will not bring
dead seed to life and they offer no protection against birds and
rodents in the field. They are used only to reduce the damage
from dry rot organisms. Seed treatment cannot take the place
of good seed selection, proper seed curing, storage, and seed
testing.
The dust fungicide should be applied to dry shelled seed accord-
ing to directions given on the package. Care should be taken to
see that the dust is mixed thoroughly with the seed so that each
kernel is coated with a thin layer. This can be done by placing
the dust and seed in a closed container such as an old barrel
churn or milk can and revolving the container slowly for 5 to
10 minutes.
The dust fungicides are very poisonous and for this reason
proper precautions should be taken when using them. The seed
and dust should be mixed in a tightly closed container and a wet
cloth should be tied over the nose and mouth while making the
treatments, unless the work is done in the open and the operator
can stand on the windward side of the dusting machine. Treated
seed should be labelled "poison" and should not be used as feed
for poultry, livestock, and human beings.

BREEDING FOR DISEASE RESISTANCE
No varieties of corn are immune to the diseases discussed in
this bulletin. However, it has been demonstrated that strains of
corn resistant to such diseases as smut and rust can be created by
intensive inbreeding. Corn is a naturally cross fertilized crop
and inbreeding results in reduced vigor. Hence, inbred strains
yield much less than the parent variety. In order to secure high
yields and disease resistance, it then becomes necessary to cross







Bulletin 210, Corn Diseases in Florida 35

selected inbred strains. The method of combatting disease
through inbreeding and crossing of corn is still in its experi-
mental stages. The development of disease resistant varieties is
a problem for the future and the results so far indicate that
progress can be made in this phase of disease control.




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