Title Page
 Bacterial stalk rot
 Fungal spots and blights
 Downy mildews
 Brown spot
 Fungal ear and kernel rots of field...
 Diseases caused by viruses and...

Title: Some diseases of corn in Florida
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00066837/00001
 Material Information
Title: Some diseases of corn in Florida
Series Title: Plant Pathology Circular 1130
Physical Description: Book
Language: English
Creator: Kucharek, Tom
Raid, Richard
Affiliation: University of Florida -- Florida Cooperative Extension Service -- Department of Plant Pathology -- Institute of Food and Agricultural Sciences
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Publication Date: 1994
Spatial Coverage: North America -- United States of America -- Florida
 Record Information
Bibliographic ID: UF00066837
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved by the source institution and holding location.

Table of Contents
    Title Page
        Page 1
        Page 2
    Bacterial stalk rot
        Page 3
    Fungal spots and blights
        Page 4
        Page 5
    Downy mildews
        Page 6
    Brown spot
        Page 7
    Fungal ear and kernel rots of field corn
        Page 8
    Diseases caused by viruses and mycoplasma
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
Full Text


Some Diseases of Corn in Florida

Tom Kucharek and Richard Raid, Respectively Professor of Plant Pathology,
Gainesville; Professor, Everglades Research and Education Center, Belle
Glade. 1994. Copied February 2000.
Florida Cooperative Extension Service/ Institute of Food and Agricultural Sciences/ University of Florida/ Christine Waddill, Dean


^l r





Design and Illustration: Katrina Vitkus

tb:,. -

A .f


Sweet corn and field corn are the principal
types of corn grown in Florida. Field corn is
grown for animal feed and hybrid seed; sweet
corn is grown primarily for the fresh market.
Numerous diseases of corn occur in Florida and
frequently have caused severe yield losses.
Tentative field diagnoses should be confirmed
with laboratory tests.


Seedling blights are caused by fungi such as
Fusarium spp., Rhizoctonia spp., Pythium spp.,
and Penicillium spp. It is not uncommon for two
or more of these fungi to be present in a seed-
ling at the same time. These fungi infect many
plant species including grasses and broadleaf
plants. These fungi survive in the soil, some
weeds, and old crop debris. Seedling blights
tend to be most severe when the seedling is
being stressed during emergence from factors
such as cool soils or extremes in soil moisture.
Seedlings may die before or after emergence.

Symptoms of seedling blights include dis-
colorations of the roots and stems, stunting, and
browning or yellowing of emerged seedlings.
Infection from Pythium spp. typically results in
a slightly greasy to watery rot of tissues, par-
ticularly of the root tips, outer root tissues, and
lower stems. Infection from Rhizoctonia spp.
typically causes reddish brown-orange lesions
in stems and roots. Penicillium spp. secrete a
toxin which translocates up the stalk and causes
yellow streaks in, or a dull green appearance
of, the leaves.

Seedling blights are reduced by the treat-
ment of seed with a labeled fungicide, crop ro-
tation with non-grass crops, planting in warm
soils, and the avoidance of deep seeding. Also,
debris from previous crops and weeds should
be allowed to decompose as long as possible

before planting. Every possible control measure
should be used with super-sweet types of sweet
corn because they are highly susceptible to
seedling blights.


Root rots occur in sweet and field corn.
Stalk rots that are caused by fungi are com-
mon in field corn after tasseling but are typi-
cally uncommon in sweet corn. The fungi that
cause root and stalk rots in Florida include
those that cause seedling blights, Exerohilum
rostratum Helminthosporium rostratum), Diplodia
maydis, Macrophomina phaseolina, and others. It
is not unusual for more than one fungus to
cause disease in stalks at the same time. Root
and stalk rots tend to be most severe when
crop rotation is not used (Fig. 1).

Root- and stalk-rotting fungi can survive in
the soil, particularly if old crop debris is
present. In susceptible varieties, some stalk rots
progress from infections that originated in the
roots. However, stalk rots caused by E. rostratum
and D. maydis begin in the stalks. Root and stalk
rots are enhanced by injuries caused by culti-
vation, excess fertilizer in the root zone, hail,
nematodes, soil insects, dense stands, and ex-
cessive damage to the foliage from leaf diseases
and foliar feeding insects.

Symptoms of root and stalk rots include
stunting, off-colored plants, lodging (Fig. 1),
discolored and abbreviated root systems (Fig.
2), and internal stalk discoloration (Fig. 3). Dark,
internal, stalk tissues are typical for infections
from E. rostratum, D. maydis, and M. phaseolina.
Stalk rots caused by Fusarium spp. typically
have reddish to pink, inner-stalk tissues.

Stalk rot can be reduced significantly by use
of resistant varieties; crop rotation; control of
nematodes, insects, and foliar diseases; proper
use of fertilizers; and avoidance of extremes in

soil moisture. Excessive rates of nitrogen and
insufficient rates of potassium are conducive
for development of root and stalk rots. The crop
should be harvested as early as possible.


Bacterial stalk rot (BSR) is caused by the
bacterium Erwinia carotovora; it has occurred on
occasion on the muck soils in the Belle Glade
area. Warm soils that are excessively wet are
conducive for BSR. Symptoms include lodging,
shrunken or ropey stems (Fig. 4), watery or hol-
low inner stalk tissues (Fig. 5), and foul odors.
The main control is to avoid excessively wet
sites and to be able to pump water out of the
production area should excessive rains occur.


Common smut, caused by the fungus Ustilago
maydis, is the only known smut of corn reported
to exist in Florida. Teosinte (an ancestor of corn)
is also susceptible. Smut is more likely to oc-
cur in field corn than in sweet corn. Some vari-
eties of field corn are highly susceptible. The
black spores (teliospores) produced in smut
galls can survive in the soil and serve as inocu-
lum. Infection occurs when the teliospore ger-
minates and forms a germ tube-like structure
(promycelium) which can penetrate the tissue
or by the formation of a similar structure formed
by the mating of sporedia (spores formed on
promycelia) of two opposite mating types.
Temperatures from 79 to 930 F are conducive
for the infection process. The wounding of corn
tissue from insects, hail, pesticides, fertilizers,
cultivation, blowing sand, or other causes can
increase the severity of smut. Young and mer-
istematic tissues are most susceptible to infec-

Galls that are pea-sized to several inches
across can be formed on any part of the plant
above the soil. Commonly, galls occur on stems
near nodal tissues (Fig. 6), ears (Fig. 7), and tas-
sels. Sometimes, galls form on leaves (Fig. 8),

leaf axils, and brace roots above the ground.
Initially a gall is a compact mass of white, fun-
gal hyphae that gradually becomes transformed
into a mass of dark teliospores which is envel-
oped by a whitish-colored covering peridiumm)
of hyphae. Smut galls that have not yet formed
the teliospores have been eaten by humans.
Recently, a limited fresh market has developed
in the United States for these white, immature,
smut galls.

Control of smut is best achieved by the use
of resistant varieties. Ample resistance is avail-
able for corn breeders to incorporate into their
varieties. Physical damage to corn plants
should be minimized to the extent possible.

The three rust diseases that have occurred
in corn in Florida are common rust (CR), caused
by Puccinia sorghi; southern corn rust (SCR),
caused by Puccinia polysora; and tropical corn
rust (TCR), caused byPhysopella zeae. The former
two rusts continue to occur but the one time
occurrence of TCR at Fairchild Gardens was
quickly followed by its eradication in 1974.
Teosinte, a relative of corn, is also susceptible
to CR.

Both CR and SCR produce similar symptoms
with the formation of spore-bearing, orange-
reddish brown pustules (uredia) in leaves or
husks. However, CR typically produces its
pustules without the peridium (covering over
pustule) persisting (Fig. 9). The pustule of SCR
may also exist without a persistent peridium,
but typically, it is persistent (Fig. 10). The color
of the spore mass of CR tends to be chocolate
brown and that of SCR tends to be orange.

The shape of the pustule varies for the two
rusts, but CR tends to have elongated pustules
and SCR tends to have somewhat rounded pus-
tules. Also, formation of the pustules on the
lower surface of the leaf is delayed and com-
monly absent with SCR. Identification of which
rust is present can be done quickly with a mi-

croscope. The somewhat round urediospores
of CR are nearly isodiametric whereas those of
SCR are oblong. Another spore stage, the
teliospore, occurs in black telia after uredia
have formed. Teliospores of CR and SCR can
be distinguished with microscopic examina-
tion. The effects from rusts include lodging,
reduced ear fill, and lower market grades.

Common rust is a cool weather disease. In
south Florida, CR occurs routinely in the spring.
Urediospores of CR germinate from 39-86 F
with the optimum for spore germination and
infection being from 59-63 F. After infection,
pustules form most rapidly from 59-68 F. As
temperatures deviate from the optimum, the
time for formation of pustules takes longer at
temperatures such as 860 F or 500 F.

Oxalis spp. serve as alternate hosts for two
other spore stages (pycniospores and ae-
ciospores) of CR. Infection of this alternate host
occurs when teliospores germinate and form
basidiospores which infect Oxalis spp. Appar-
ently, this alternate host is of importance in

Southern corn rust tends to occur more
frequently during the fall in south Florida and
summer months in north Florida, particularly
with late-planted or double-cropped corn. The
optimum temperatures for SCR are higher than
for CR. Near 820 F, germination of urediospores
and penetration of stomates of leaves is abun-
dant for the fungus that causes SCR. New rust
pustules will appear in nine days at 820 F but
require about 14 days at 750F. Development of
pustules ceases at 900F. Leaf-wetness periods
of eight hours will support infection near opti-
mal temperatures. As temperatures deviate
from the optimum, leaf-wetness periods up to
16 hours may be required for infection.

Control of corn rusts is done best with resis-
tant varieties. Resistance to CR is available, but
resistance to SCR has not generally been incor-
porated into varieties. Any available resistance

is likely to be partial and subject to infection
by "new" or different races of the rust fungi.
When sequential plantings are used, earlier
plantings should be downwind in relation to
predominant winds. For example, in south
Florida, east winds predominate during the
sweet corn seasons, hence the corn should be
planted from west to east.

Spraying with fungicides is a major measure
to control foliar diseases in sweet corn, particu-
larly in peninsular Florida. Spray programs
should be initiated at the first sign of rust. Sev-
eral sprays may be required. Super-sweet
(shrunken-two types) are particularly suscep-
tible. Spraying field corn for rust control may
not be economical. However, if a major epi-
demic occurs and control is mandated, some
fungicides may be labeled for field corn. How-
ever, strict adherence to cessation of sprays in
relation to the days-to-harvest must be used to
avoid residues in milk and meat products if the
corn is used for animal feed.


Northern corn leaf blight (NCLB), is caused
by the fungus Exerohilum turcicum
(Helminthosporium turcicum). NCLB is a problem
primarily in sweet corn in Florida, particularly
in peninsular Florida, but it can be a serious
problem in field corn if susceptible varieties are

Symptoms of NCLB vary depending on the
genes for resistance and races of the fungus
present. Individual leaf spots are typically 1 to
6 inches long and 1/2 to 1 inch wide (Figs. 11
& 12). Resistance is expressed as smaller le-
sions, fewer lesions, or delayed appearance of
lesions. Usually the lesions are widest in the
center and tapered or serrated at the ends. Le-
sions are typically tan to dark brown in color.
When spores are produced in mass, the inner
zones, sometimes concentric, have a greenish-
black tinge. Sometimes the outer part of the le-

sion, particularly expanding lesions, will have
water-soaked tissue. Lesions tend to form first
in lower leaves and progress to higher leaves
over time (Fig. 11). However, mid- or upper-
stalk leaves may display lesions first, often in a
band of lesions (Fig 12). This latter situation is
the result of spores germinating in the mois-
ture within the leaf whorl during a specific pe-
riod of time that was favorable for infection or
from large "spore showers" from nearby fields.
When the leaves unroll and expand, a line of
lesions is evident.

Sources of spores are from lesions in old crop
debris, volunteer corn, and existing production
fields nearby, particularly if they are upwind
from your field. Spores of E. turcicum are dis-
seminated naturally by wind. However, spores
can be dislodged in mass by mechanical move-
ment in nearby fields during cultivation, har-
vesting, or other processes.

Tezrperatures betw een 59 F and 860F are suit-
able for production of spores and infection pro-
vided leaf wetness periods of at least 7 to 8
hours occur. With favorable weather, the time
from infection to occurrence of symptoms can
be as short as 5 to 7 days. As temperatures de-
viate from the optimum, fewer lesions form and
the time for lesions to form is increased.

Sorghum, Sudangrass, Johnsongrass,
gamagrass, and teosinte are also susceptible to
E. turcicum. Pathogenic races that infect sor-
ghum and Sudangrass apparently do not infect
corn. However, some races that infect corn can
infect Sudangrass.

Control of NCLB for field corn is accom-
plished primarily by the use of resistant variet-
ies. When alternate rows of different varieties
are planted to enhance pollination, higher lev-
els of NCLB have resulted if one of the variet-
ies is susceptible. For sweet corn, resistance
may be available but sprays of fungicides are
commonly necessary in peninsular Florida.
Crop rotation should be used and sequential

plantings should be made into the predominant
wind patterns for your area as described ear-
lier for the control of rusts.

Southern corn leaf blight (SCLB) is caused
by the fungus Bipolaris maydis (Helminthosporium
maydis). In 1970, SCLB became epidemic on
those Fl hybrid varieties produced with Texas
male-sterile, cytoplasm (Tcms) primarily in the
southeastern but also in other corn producing
areas in the United States (Fig. 13). In Florida,
the average statewide yield of field corn was
reduced by 50%.

Seedling blight can be caused by B. maydis.
However, symptoms of SCLB occur typically
in leaves (blades & sheaths). Mature foliar le-
sions can be rounded on the sides but they tend
to be parallel-sided, often restricted by the
veins. Lesions are light tan in the center with a
darker reddish- brown border (Fig. 14). A green-
ish growth near the center of the lesion may be
evident if abundant spores are present (Fig. 14).
Mature lesions range from 1/4 to 1 1/2 inches
in length and may be tapered, flat or somewhat
serrated on the ends. Typically, lower leaves
are infected first (Fig. 15) with the epidemic
progressing upward to higher leaves over time.
Occasionally, infections of the ear husk, silks,
kernels, cob, and floral bracts in tassels occur.

Sources of spores for infection include vol-
unteer corn (Fig. 16), old corn debris on the soil
from previous crops, stored corn seed, fodder,
and nearby corn plantings. Teosinte and a wild
grass (Rottboellia exaltata) are also susceptible.
Other crop species are not susceptible to B.
maydis in natural field situations.

With optimal weather conditions, the time
from infection by germinating spores to lesion
formation with new spores may be as short as 3
to 5 days. Temperatures near 730 F are optimum
for production of spores, formation of germ
tubes, infection, and formation of lesions. As
temperatures deviate to 590 F and 860 F, the
fungus is still active but progress of the dis-

ease will be delayed. Six hours of leaf wetness
is all that is needed for spore germination and
infection. Leaf wetness is not required for le-
sion expansion.

Control of SCLB is best achieved with resis-
tant varieties. However, where resistance is
lacking, spraying with fungicides may be nec-
essary, particularly with sweet corn produced
in peninsular Florida. Spray programs should
begin at the first sign of disease if favorable
weather is likely in the future. Also, the use of
crop rotation and deep plowing of old crop
debris will reduce inoculum for the next crop.
Two other leaf spots caused by
Helminthosporium spp. occur occasionally in
Florida but have been minor problems.
Helminthosporium leaf spot (HLS) is
caused by the fungus Bipolaris zeicola
(Helminthosporium carbonum). It can cause a leaf
spot that is intermediate in size to NCLB and
SCLB and may be linear or slightly oval (Fig.
17). Also, it causes an ear rot that usually ap-
pears near the tip of the ear on the kernels. In
Florida, HLS has occurred in inbred lines within
seed production fields. Leaf spots associated
with Helminthosporium setariae have been found
occasionally in sweet corn in the Zellwood and
Everglades areas.


Two downy mildew fungi occur in corn in
Florida. Sclerophthora macrospora causes crazy
top and Peronosclerospora sorghi causes sorghum
downy mildew.

Crazy top (CT) has been diagnosed only in
Escambia and Santa Rosa Counties. The fun-
gus grows systemically in the plant. It has oc-
curred in spring planted corn when the soil
became saturated or flooded for 1 to 2 days af-
ter planting but before the plants had 4 or 5
leaves. Stunting, excessive tillering, excessive
twisting, and rolling of leaves, are common
symptoms of plants prior to flowering. Exces-
sive leafyness of ear husks and tassels (Fig. 18)

occur on older plants.

The fungus that causes CT produces resting
spores oosporess) that can persist in the soil for
many years. With water-saturated soils and cool
temperatures, the oospores germinate and pro-
duce sporangia which, in turn, produce motile
spores with tails zoosporess) that migrate in free
water. Zoospores produce germ tubes that
penetrate corn tissue in contact with the moist
soil. Optimum temperatures for formation of
zoospores is between 53 and 610 F but the fun-
gus is active beyond these temperatures. Some-
times, sporangia produce germ tubes directly.
Corn plants are susceptible until the fourth or
fifth leaf stage. This fungus has been identified
in more than 140 species of grasses including
oats, wheat, sorghum, rice, crabgrass, witch-
grass, and foxtails.

The best controls for CT are to provide for
adequate water drainage in fields and to break
soil hard pans. Planting in areas that are prone
to flooding should be avoided.

Sorghum downy mildew (SDM) was found
in the Zellwood and Leesburg areas in the early
1980s in sweet corn, forage grasses in the sor-
ghum group used as summer cover crops, and
Sorghum alum. Teosinte and Panicum spp. are
also susceptible. The fungus grows systemi-
cally within the plant if infection occurs before
the plants are about 4 weeks old. Symptoms
include stunting, yellowing of leaves, light yel-
low-white leaf striping, leafy proliferation of
tassels, and the presence of a greyish-blue
downy, mold growth on the leaves (Fig. 19).

The downy growth is composed of sporan-
gia (spore-like structures) and sporangiophores
(stalks on which sporangia form). Sporangia are
transported by wind or water. Sporangia are
formed, germinate, and infect leaf tissue be-
tween 630 F and 840 F. Optimum temperatures
are near 70 to 770 F if high humidity or free
moisture is present. Some isolates have consid-
erably lower optimal temperatures for germi-

nation (e.g., 590 F). Sporangia germinate by
forming germ tubes that penetrate the leaves
directly or through stomates (breathing pores).
The fungus then grows systemically in the
plant. After the plant becomes about four weeks
old, infection of leaves results in the formation
of distinct lesions.

Within the infected leaf, thick-walled, rest-
ing spores oosporess) can be formed which al-
low the fungus to survive in the soil for long
periods of time. Also, infected corn or sorghum
debris among seed or fodder could allow the
fungus to be transported to new locations. The
oospores produce a germ tubes which penetrate
roots of seedling or plant tissue in contact with
the soil and the fungus then grows systemically.

Control of SDM includes use of resistant va-
rieties, if available; crop rotation, and plowing
of land deep enough to place the oospores be-
low the level of seed at planting. Susceptible
grass weeds from the field area should be elimi-
nated. Also, the use of select, systemic, fungi-
cidal, seed treatments (e.g., those with
mefenoxam) has effectively controlled SDM in
sweet corn in Florida. Cover crops of sorghum-
type grasses should be avoided.


(Chocolate Brown Spot or Physoderma Brown

Brown spot (BS) is caused by the fungus
Physoderma maydis. Teosinte is also susceptible.
More than 50 years ago, this disease was re-
ported to be a major problem in Florida. Over
the past 30 years, BS has been seen on occasion
in field corn but has not been a major problem.
Symptoms include clusters (blotches) or bands
of round to oblong yellow spots, each spot usu-
ally being less than 1/2 inch across, in leaf
blades, leaf sheaths, ear husks, or tassels (Fig.
20). Symptoms tend to be more abundant near
the base of the leaf blades or other areas where
free water accumulates. Later these symptom-

atic spots turn brown to red (Fig. 20) and may
form blister-like pustules. These pustules dis-
integrate which then expose a mass of dusty
brown, powdery resting spores. Lodging can
occur if severe infections are present.

The resting spores (sporangia) are the pri-
mary means by which this fungus survives be-
tween crops. Each sporangium can germinate
by producing up to 50 spores zoosporess) with
tails so they are motile in water. Zoospores ger-
minate by producing small threads hyphaee)
which penetrate corn tissue, particularly young
tissue. New sporangia can be produced within
16 to 20 days after infection. Free water accom-
panied by temperatures from 73 to 900 F are
most suitable for germination of spores and
infection. Thus BS is most likely to be a prob-
lem in young field corn during warm and wet
spring weather.

Control of BS includes crop rotation, tillage
programs that allow for decomposition of corn
tissue, and resistant varieties, if available.


Bacterial leaf blight (BLB) is caused by the
bacterium Pseudomonas avenue (P. alboprecipitans).
This disease has been an occasional problem
on sweet corn in the central Florida area. Vasey
grass (foliage and seed), Johnsongrass, Setaria
lutescens (foxtail), Sudangrass, and goosegrass
are also susceptible.

Symptoms of BLB include aggregations of
elongated lesions of more than several inches
in leaves (Fig. 21). When moist conditions ex-
ist, the lesions will have a greasy, water-soaked
dark appearance, particularly on the margins
(Fig. 21). Older lesions will tend to be light
brown or tan in the center and may be shred-
ded. Other symptoms include a basal rot of the
ear, stalk rot, lodging, and a tassel rot.

Infections of leaves often occur when the

bacteria are in the moisture within the leaf
whorl. The bacteria enter leaves through
stomates (breathing pores) or wounds in leaves.
New lesions appear three to four days after in-
fection. As leaves age, they become progres-
sively more resistant to infection. Although
temperatures between 65 and 700 F are suitable
for development of BLB, temperatures from 85
to 950 F are more conducive for development
of this disease especially during wet weather.

Rain and overhead irrigation can spread this
bacterium. Tractors and other mechanical
movement within fields also spread this bacte-
rium along the rows.

Because this bacterium does not survive well
in soil, it is important to suppress the amount
of vasey grass and other susceptible grasses
around plantings of sweet corn. Some varieties
are more resistant than others. Also, the move-
ment of equipment should be minimized
within fields when plants are wet if BLB is


An extensive discussion of this disease is avail-
able in Plant Pathology Fact Sheet No. 12.


Numerous fungi can cause ear and kernel
rots of field corn. Infection can occur before or
after harvest. Of significant concern are Fusarium
spp., Aspergillus spp., and Penicillium spp. be-
cause many of these are capable of producing
mycotoxins that are toxic to livestock and man.
Some of the disorders in animals related to
these toxins are cancer, reduced growth, hem-
orrhagic enteritis, abortion, tremors, staggering,
convulsions, edema, toxicity to kidneys and liv-
ers, vomiting, feed refusal, decreased egg pro-
duction, diarrhea, infertility, reduced immune

responses, gastrointestinal inflammation, de-
generation of bone marrow, hormonal imbal-
ances, and death. Because other factors can
cause these symptoms in animals, consultations
with veterinarians are advised.

Mold growth of Fusarium spp. tends to be
white-pink-red. A brief treatise on Fusarium-
infected corn and its relationship to toxic ani-
mal feed is presented in Plant Pathology Cir-
cular 1025.

Aspergillus flavus and A. parasiticus produce
aflatoxins and grow rapidly above 750 F. The
presence of greenish-yellow molds that fluo-
resce when exposed to a "black light" on ker-
nels and silks are suggestive (but not conclu-
sive evidence) of A. flavus. Many biological
materials fluoresce and not all strains of A.flavus
produce aflatoxins. It is imperative to have feed
samples analyzed in a laboratory for the pres-
ence of any kind of mycotoxin. Mold growth of
Penicillium spp. is blue-green-grey.

Ear and kernel rots are often associated with
corn that is or was stressed from drought or
poor production practices or damaged from
insects (weevils, worms, thrips, or others). Some
varieties are more susceptible, particularly
those that do not have an adequate husk cover
over the kernels. Harvesting time (22-30% mois-
ture content of grain) and equipment (slower
cylinder speeds) should be adjusted to mini-
mize damage to grain. Corn grain should al-
ways be clean and dried to moisture content
below 14% as soon as possible before storage.
Storage facilities should be cleaned before use.
Fans should be used routinely during dry
weather to displace moisture that builds up on
the storage structure or the grain. Sources of
moisture during storage are condensation
(warm grain with cool ambient temperatures),
grain, and storage molds. Moldy grains gener-
ate more moisture than healthy grain. Consult
Agricultural Engineering Circular 1104 for de-
tails on maintaining storage facilities. Certain
chemical treatments (e.g., ammoniation, propi-

onic acid) are labeled to prolong storage by re-
ducing damage from fungi. Some of them are
corrosive to equipment, explosive, and harm-
ful to humans. Some modern conveying equip-
ment is coated with protective materials. Sup-
pression of ear- and kernel-rotting fungi by non-
chemical methods is best. Chemically pre-
served grain is not accepted in the grain trade.


Viral diseases of corn have been erratically
occurring problems in Florida. Maize dwarf
mosaic virus (MDMV) has occurred in sweet
and field corn in Alachua County near dense
stands of Johnsongrass. Aphids transmit the
submicroscopic viral particles from infected
corn or Johnsongrass on their mouth parts when
feeding. Symptoms from nutrient imbalances
can appear similar to those caused by viruses
and mycoplasma. Symptoms of MDMV in corn

include stunting and somewhat linear, diffuse
shades of greens, yellows, reds, and purples
(Fig. 22). The elimination of Johnsongrass in and
around corn fields is an effective control for

In south Florida, particularly Dade County,
several viral diseases have occurred in seed
production fields for field corn. Maize stripe
virus (MSV), maize rayado fino virus (MRFV),
and maize mosaic virus (MMV) have been iden-
tified. In addition, maize bushy stunt myco-
plasma and corn stunt spiroplasma (CSS) have
been identified. Symptoms of these diseases can
be similar to those of MDMV and display chlo-
rotic spots or stripes (Fig. 23). Stunting and leaf
twisting may be present (Fig. 23). While MSV
and MMV are spread by planthoppers, MRFV
and CSS are spread by leafhoppers. Resistant
inbreds and varieties should be used. Also,
weed grasses (e.g., itch grass) in the vicinity
should be minimized as they may serve as hosts
for these organisms. Little is known about vi-
rus-corn interactions in Florida at this time.

Figure 1. Most severe lodging where corn Figure 2. Most severe root rot where corn
followed corn vs. corn followed by soy- followed corn.


Figure 3. Internal stalk discoloration from
fungal stalk rot.


Figure 4. Bacterial stalk rot.

Figure 5. Bacterial stalk rot in corn.

j 1*.~



Figure 6. Corn smut on stalk.

Figure 7. Corn smut on ears. Figure 8. Corn smut on leaf.



Figure 10. Southern corn rust.


Figure 9. Common corn rust.

Figure 11. Northern corn leaf blight. Figure 12. Northern corn leaf blight in


Figure 13. Susceptible vs resistant varieties to Figure 14. Southern corn leaf blight.
southern corn leaf blight.

.!. ~;

Figure 15. Southern corn leaf blight. Figure 16. Southern corn leaf blight on
volunteer corn.

Figure 17. Leaf spot caused by Bipolaris

Figure 18. Crazy top (downy mildew) in


Figure 19. Sorghum downy mildew in corn.

Figure 21. Bacterial leaf blight in corn.

Figure 22. Maize dwarf mosaic virus infec-
tions in corn.

Figure 20. Brown spot in corn


Figure 23. Complex of mixed viral infections in corn.

University of Florida Home Page
© 2004 - 2010 University of Florida George A. Smathers Libraries.
All rights reserved.

Acceptable Use, Copyright, and Disclaimer Statement
Last updated October 10, 2010 - - mvs