March 1990 Circular 99
Sweet Corn Production
Guide for Florida
Edited by W. M. Stall
Commercial Vegetable Guide Series
Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida / John T. Woeste, Dean
1 Sweet Corn Varieties
3 Environmental conditions
5 Pest Management
6 Soil pests
Harvesting & Handling
10 Maturity and quality
12 Suggested reading
W. M. Stall, Professor and Extension Vegetable
Crops Specialist; D. N. Maynard. Professor and
Extension Vegetable Crops Specialist: G. J.
Hochmuth, Associate Professor and Extension
Vegetable Crops Specialist: D. D. Gull, Associate
Professor and Extension Vegetable Crops Spec-
ialist: Vegetable Crops Department. IFAS. F
Johnson, Professor. Entomology and Nematol-
ogy Department. IFAS; T. Kucharek. Professor.
Plant Pathology Department, IFAS: University of
Florida, Gainesville 32611..
Maize, or corn, is thought to have evolved from its
wild ancestors in Mexico and Central America; it
became a staple food for the American Indians in
pre-Columbian times. Ancient sweet corn types have
been found in the Andean zone of Peru. The Iroquois
in upper New York State also grew a sweet corn
whose kernels turned blue as they matured.
Maize was first classified according to the variation
in the carbohydrate stored in the endosperm. In
sweet corn, the sugary (su) or sweet gene on chromo-
some 4 prevents or retards the normal conversion of
sugar into starch during endosperm development,
resulting in a sweet taste. This sweet corn is consi-
dered a high-quality vegetable when used in the milk
stage at 70 to 80%r seed moisture, depending on the
Florida continues as the nation's leading producer,
of fresh market sweet corn. Florida produces 80 per-
cent of the winter (January to June) United States
fresh market sweet corn, but most of the summer/fall
production for fresh market occurs in the Northeast
United States. Florida production by area and aver-
age yields are shown in Table 1.
Table 1. Sweet Corn: Acreage
and Production for
L'i D. N. Maynard
Variety selection, often made several months be-
fore planting, is one of the most important decisions
made by the grower. Failure to select the most suit-
able variety or varieties may lead to loss of yield or
The following characteristics should be considered
in selection of sweet corn varieties for use in Florida:
Yield.The variety selected should produce yields
equivalent to the best varieties available. The state
average yield for sweet corn in the 1987-88 crop year
was 232 crates per acre. Yields per acre varied con-
siderably among various production areas as shown
in Table 1. Potential yields are 400 crates per acre
based on 24,000 plants per acre and 60 ears per crate.
Disease resistance. When available, genetic re-
sistance to disease is the least expensive means of
disease control. Providing that the variety selected
has other desired characteristics, it would be useful
if resistance to northern leaf blight and southern leaf
blight were included.
Horticultural quality. A multitude of plant, husk,
and ear characteristics are included in this category.
Among those to be considered for the plant are ability
to germinate in cool soils, plant vigor, and ability to
withstand lodging. Husk color should be dark green
with good flag leaves and tip cover. Some ear charac-
teristics to be considered are tip fill, silk color, and
kernel tenderness and sweetness.
Adaptability. Sweet corn is well-adapted to pro-
duction in the principal growing areas and typical
production seasons. Certain varieties, however, may
perform better than others in the conditions prevail-
ing in a production area and season. On occasion,
adaptability extends to an individual farm situation.
Market acceptability. Ear size must be appro-
priate to the season and buyers' requirements. Husks
must be free of damage and have good color and flag
leaves. The ear should be free of worms, have good
tip fill, and have well-developed kernels of the proper
stage of maturity. Yellow, white, and bicolor corns
are acceptable for specific markets.
Variety selection is a more complex process than
it was just a few years ago. Plant breeders have
exploited corn genetic resources to develop an array
of genetic types that differ especially in sugar content
and retention. Of the recently developed genetic
types, the supersweets are used most commonly in
Florida at the present time. Sugary enhanced and
improved supersweet types are used to some extent
and their use may increase in the future. A summary
of genetic types that are currently available is given
in Table 2.
Just as white corn must be isolated from fellow
corn, isolation of the new genetic types must occur
in order for them to produce their desired charac-
teristics. Isolation strategies include:
* Separation of genetic types by a distance of at
least 350 feet.
Maturity of different genetic types that differ by
at least 14 days. This can be accomplished by vari-
ety selection or successive plantings.
Currently recommended varieties are listed in
Florida Cooperative Extension Circular 530, Com-
mercial Vegetable Cultirars for Florida.
Table 2. Description of major sweet corn types currently available.
and "EH", "se"
Sweet, or "shrunken"
Genes controlling sweetness
Full complement of sugary (su)
Full complement of sugary (su) and half of full
complement of sugary enhancer (se)
No sugary (su); Full complement of shrunken-2 (sh2)
Full complementof sugary (su); and half
complement of shrunken-2 (sh2)
Half complent of sugary (su); and full
complement of shrunken-2 (sh2)
No sugary (su) or shrunken-2 (sh2) genes; full
complement of ae, du, and wx genes
tortage time wll depend o- var-ies\ cu -ira!
*These values are only rough approximations provided for comparison between types. Actual
practices, postharvest handling methods, and other factors.
by \V. M. Stall and G. J. Hochmuth
Temperature. Optimum growth of sweet corn
occurs when temperatures range from 75 to ,-, F.
High night temperatures are detrimental since they
result in increased respiration rates and loss of
photoassimilates. Growth will not occur when tem-
peratures are below 50 F.
Water. For satisfactory growth and high yields.
sweet corn requires a continuous supply of moisture.
In most cases this is equivalent from 18 to 28 inches
of water to produce a crop. Seed will germinate in
soils with moisture ranging from slightly above the
permanent wilting percentage to field capacity. The
most critical growth periods requiring adequate soil
moisture are during germination and stand estab-
lishment, tasseling and silking, and ear fill. Depend-
ing upon local environmental conditions, 1 to 1.5 in-
ches of water per week may be required to insure
pollination and ear fill.
Light. Sweet corn varieties are affected by day
length. Early maturing varieties grown in the north
are adapted to long, cool summer days and do not
grow well in the winter production months of Florida.
Varieties adapted to the south respond to short days.
Because of day length adaption, cultivars may re-
spond differently when planted during different
months of the year in Florida.
Seeding and seed quality. Precision seeding for
the desired plant spacing can assure uniform stand
establishment and plant growth and reduce the seed
use per acre. Prior to seeding, the field should be
leveled to eliminate low, wet areas that cause poor
stands and plant growth. Treated seed should be
used for protection from soil-borne diseases and in-
sects during germination and seedling development.
This measure is particularly important for seed with
the sh2 gene (and all super sweet types) since they
tend to germinate more slowly and produce weaker
Seed should have a high germination rate (90%)
and vigor, and be separated by size (large and small)
and shape (flat or round). Uniform seeds are espe-
cially useful with precision seeding equipment. Large
seeds frequently produce more vigorous plants and
uniform stands than small seeds. Seeds of the super
sweet types, and particularly those with the sh2 gene,
are very small, fragile (easily damaged in handling
and planting), and germinate poorly in cold soils.
Plant spacing. Highest yields result from rows
28 to 32 inches apart and seeds spaced 6 to 8 inches
in the row to give a stand from about 24,000 to 32,000
plants per acre. For larger ears, wider rows (36 in-
ches with plants spaced 8 to 15 inches (12,000 to
22,000 plants per acre can be used. A minimum row
spacing of 30 inches is recommended for mechanical
Ear uniformity and number per stalk. Uniform
seedling emergence and stalk growth are essential
for ears of uniform maturity at a single harvest. If
there is more than one ear per plant, the range in
maturity and ear size requires extensive sorting be-
fore packing. A much smaller range in maturity and
ear size results from cultivars and plant spacing that
produce only one ear per stalk.
Sweet corn performs well on a wide variety of soil
types. Sandy soils are good for early production in
the spring but require careful attention to water and
fertilizer management. Organic soils in southern
Florida are excellent soils for high yields of sweet
corn. The rockland and marl of south Florida also
can be used to produce acceptable crops of sweet corn
in the winter.
Soil reaction (pH). Sweet corn can be grown suc-
cessfully over a wide range of pH, from about 5.8 to
6.5. Soil with a pH below 5.8 (especially old land that
might contain high levels of micronutrients) should
be limed to reduce the risk ofmicronutrient toxicities.
Soil with a pH above 7.0 can be used to grow sweet
corn, but availability of some micronutrients might
be reduced. Use a well-calibrated lime requirement
test to determine the need for lime.
In situations where the soil has been overlimed,
elemental sulfur can be applied to reduce the pH.
Reducing the pH on naturally alkaline soils, such as
the rockland marl and some mucks, is not economical
Fertilizer. The University of Florida Extension
Soil Testing Lab in Gainesville makes fertilizer re-
commendations based on the Crop Nutrient Require-
ment (CNR) concept. The CNR concept accounts for
all sources of a specific nutrient to the crop. The
major sources are the soil itself and fertilizer. The
sweet corn crop has required levels of the mineral
nutrients for optimum yields. These amounts are
presented in Table 3. These CNR amounts can be
supplied to the crop from soil and/or fertilizer. Soil-
testing is used to determine the amount of the CNR
that can be supplied from the soil. Fertilizer is added
in proper amounts to make up the difference. In
many areas, especially where soils have large re-
sidual amounts of nutrients such as phosphorus and
micronutrients built up, there is little likelihood of
response to added fertilizer.
Nitrogen. Research shows in Florida that nitrogen
(N) should be split-applied. Apply up to 40 lb. N per
acre at planting, usually by banding to the side and
below the seed. The remaining N should be applied
in one to two sidedressings early in the season. Ad-
ditional sidedressings of 30 lb. N and 20 lb. K20 per
acre might be needed after leaching rains (2 to 3
inches of rain in a 3-day period or 4 inches in a 7-day
period). Sources of N can be ammonium nitrate, urea,
and various liquid formulations containing these ma-
Phosphorus. All phosphorus (P) should be
applied at planting using amounts predicted by soil
testing. Where only small amounts of P are needed,
or where the pH is above 7.0, it might be best to
band. Supplemental P is usually not needed except
perhaps in the winter on the alkaline rockland and
marl where P availability is reduced. Phosphorus
can be supplied from triple super (46% P205), normal
super (20% P205), and diammonium or monoam-
Potassium. The management of potassium (K) is
made difficult because K leaches to a certain extent
in sandy soils. The leaching is not as severe as for
N. Apply up to one-half of the K at planting with the
N and apply the remainder in the first sidedressing.
Supplemental applications of K might be needed
after severe leaching rainfall; however, addition of
K with each supplemental sidedressing may not be
needed. Any source of K can be used for sweet corn
(potassium chloride, potassium nitrate, potassium
sulfate, or potassium-magnesium sulfate). If soil-
test-predicted amounts of K are adhered to, then the
source of K and its associated "salt index" are not
important. No concern should be given to any specific
K:N ratio in the fertilizer since the objective of fertili-
zation is to add the correct amount of N and K.
Magnesium and sulfur. Usually these nutrients
are in ample supply in Florida soils. Magnesium (Mg)
can be supplied from dolomitic lime or as magnesium
sulfate or potassium magnesium sulfate. Sulfur (S)
can be supplied from these two materials in addition
to that from potassium sulfate, normal superphos-
Table 3. Crop nutrient requirements for sweet corn on soils testing very low in phosphorus and potassium.
Crop nutrient requirements No.of
N- P205- K20 Supplemental
Soil lb. per acre applications Footnotes
Irrigated mineral 120-120-120 0-4 1
Rockland 70-60-90 0-1 1
Marl 80-70-80 0-1 1
Organic 0-120-180 1,2
1These CNR amounts are applied as fertilizer onlyto soils testing very low in P and K. Use a soil test to determine precisely
how much fertilizer is needed.
2Crops might respond to supplemental applications of 30 to 40 lb. per acre of N during cool winter periods or after a
phate, and other fertilizers. In many situations,
adequate amounts of S can be supplied from the S-
laden irrigation water. In situations where the soil
is found to be deficient in S or Mg, about 30 to 40
lb. of either nutrient can be added as fertilizer.
Micronutrients. Nutrients such as copper (Cu),
manganese (Mn), zinc (Zn), iron (Fe), and boron (B)
are needed in very small quantities and there is a
fine line between adequate and toxic amounts. Most
micronutrients, except B, do not leach from the soil
and can build up in old land. Soil testing is a tool to
predict if a response to added micronutrients will
occur. Small amounts of micronutrients are added
to the foliage through some of the commonly used
fungicides. If the soil alone cannot supply the CNR
for certain micronutrients, then the fertilizer should
supply about 3 lb. Cu per acre, 3 lb. Zn per acre, 6
lb. Mn and Fe per acre and 1 lb. B per acre.
Shotgun foliar applications of multiple micronut-
rients are to be avoided because research has shown
decreases in yield can occur in several vegetables.
Occasionally, foliar application of certain micronut-
rients such as Fe or Zn might be justified to correct
a deficiency where high pH soil ties up these nut-
Plastic mulch. In some areas of the state, sweet
corn is grown on full-bed mulched culture with two
rows of sweet corn on a 30- to 36-inch bed top. In
this system, all P and micronutrients, and about 10
to 20% of the N and K are incorporated into the bed
soil. The remaining N and K fertilizers are banded
in a trench in the center of the bed. Soluble sources
of N and K are used for the main banded N.
In the mulch system, supplemental N and K addi-
tions can be made by a liquid injection wheel. This
implement injects liquid fertilizer into the bed by
piercing the mulch.
Summary. The above information is a general
guideline to fertilization of sweet corn in Florida.
More detail can be obtained from Circular 225C,
Commercial Vegetable Fertilization Guide, and Cir-
cular 805, Commercial Vegetable Crop Nutrient Re-
tbv \\. M. Stall, F. Jo(litlSon, u idt 1. aud lorc'k
Weeds reduce yield and quality of sweet corn by
direct competition for light, water and nutrients in
the soil. Weeds may also harbor insect and disease
pests that attack corn. During 1975-1979, the esti-
mated average annual losses due to weeds in sweet
corn in the United States. were 1,460,000 cwt for
fresh market sweet corn and 185,000 cwt of sweet
corn for processing.
Historically, the major reason for corn being grown
in rows is weed control. Row width was dictated by
the size width of horses needed to pass between the
rows pulling a cultivator.
Mechanical cultivation of sweet corn is still wide-
spread. The initiation of the use of selective her-
bicides some 40 years ago in corn has decreased the
number of cultivations needed per season. This has
substantially lowered the fossil fuel energy used in
sweet corn production. Many sweet corn fields now
receive one or no cultivations at all. Much of the
cultivation used is to reduce surface crusting or to
control weeds resistant to or not controlled by the
herbicide combinations selected. There is at the pre-
sent time a wide selection of herbicides that effec-
tively control most weeds.
Herbicide treatments are primarily categorized on
the basis of the time of application: preplanting,
preemergence, and postemergence. Preplanting
treatments are applied before the corn is planted
either as a surface treatment or incorporated into
the soil. Preemergence application is after the corn
is seeded but before emergence of the corn or weeds.
Preplant and preemergence herbicides, properly
selected and applied, prevent weed competition dur-
ing emergence and early seedling growth. Post-
emergence applications take place after the
emergence of both the corn and weeds. These are
most effective when weeds are small. For currently
recommended herbicides for corn, refer to Weed Con-
trol in Vegetable Crops: Sweet Corn.
Insects can severely damage all portions and ages
of sweet corn plants. More than 50 insect species or
groups of species are known to cause economic losses
to sweet corn in the United States. Soil insects have
been considered the most important pest grouping
which consistently causes damage to all types of corn
in the United States. In Florida, foliar pests and
earworms are also a major concern to sweet corn
Of the soil insects, Florida has different problems
than many corn-growing states. Wireworms can be
a problem and damage is usually noticed as wilted
and dying plants, although the larvae feed on all
underground parts of the plant, including the planted
seed. The adult wireworm is the "click beetle" and
is usually not injurious. There are several types of
cutworms that cause isolated damage each year. Cut-
worms when disturbed will curl into a tight coil and
can be identified easily due to this habit. Cutworms
do not feed voraciously on leaf tissue but will cut off
small plants, usually those less than 4 to 5 inches
in height. A number of plants may be cut off during
the evening hours. The cutworm will hide under soil
clods or in the soil during the daylight hours.
The Southern corn rootworm or cucumber beetle
larvae also attacks the roots of corn. Control of the
worm is difficult and insecticides must be used at
planting time or shortly thereafter if the pest is ex-
pected to be a problem.
Several other soil inhabiting pests may cause dam-
age to corn. Soil grubs, lesser cornstalk borers and
webworms are pests more often when corn follows
pasture or where grassy type weeds were abundant
before the planting of corn. These pests feed on the
roots and lower stems of the corn plants and can
cause stunting and uneven stands.
Corn earworm. The corn earworm is a voracious
feeder in the whorl and in the ear of corn plants. The
adult moth overwinters in the southern United
States and the population will migrate north during
the year. The moth lays eggs on the plants (usually
on the silks) and young caterpillars will feed on the
plants any time during the season. The biggest cause
of loss of grade in fresh market corn is worms in the
ears. Without control, 100% of the corn in a field
may be infested.
Armyworms. Several species of armyworms (fall,
southern and beet) are important, especially in the
southeast. The fall armyworm is by far the most
prevalent and the most serious. On occasion the lar-
vae will migrate in mass, especially across a young
field; hence the name 'armyworm'. These caterpillars
generally feed on the leaves and whorls of the plants,
and are sometimes referred to as budworms. If popu-
lations are severe, complete loss of the bud can occur.
In the southern United States, armyworms can pro-
duce several generations and will also attack the ear.
In the early part of the season they may be the most
prevalent worm found in the ear. They will enter the
ear from not only the silk end but from all sides. In
most cases, the armyworm complex is much more
difficult to control than earworms.
Aphids. Aphids, or plant lice, are frequent pests
of sweet corn. Aphids suck sap from the plants and
heavy infestations may cause plants to wilt and fail
to produce a marketable ear. Aphids also transport
virus diseases, which is probably more damaging
than just their feeding alone.
Besides the above insects, leaf and flea beetles will
attack sweet corn foliage. Also economic damage is
caused by thrips, chinch bugs and the stink bug or
plant bug group. Although not an insect, the spider
mites have been identified as causing serious prob-
lems in several areas of the United States. Of these,
the grass mite, the two spotted spider mite and the
red spider mite are important.
Stem-type borers. Several species of stem borers
can be found attacking sweet corn in the United
States. The European corn borer probably is the most
widely distributed and probably causes the most
damage. However, this pest is found in Florida only
in isolated areas along the Alabama and Georgia
border. The larvae overwinter in field debris. In the
spring, after pupation the adult moth lays eggs on
leaf surfaces. The larvae first feed on the leaf surfaces
and midribs, then bore into the stems. Larger larvae
often tunnel and feed in the stem and the ear, result-
ing in stem and ear breakage.
The lesser corn stalk borer is an important pest
in the southeastern production areas. Dry warm
weather seems to favor the development of this pest.
The lesser cornstalk borer is a pest of many crops in
this area. The feeding activity can produce
"deadheart" condition of young plants. One of the
identifying features of this pest is a silken tube lead-
ing away from the infected plant stem or root. The
larvae will bore into the stem and can kill young
corn plants that are approximately 10 inches or less
in height. Older larger plants respond to attack by
becoming stunted or by heaving tillering resulting
in "bushy" or additional sucker growth.
Pests of the ear. The fall armyworm and the corn
earworm are serious pests of the ear. The corn ear-
worm eggs are generally laid on the silks and the
young larvae consume the silks until they locate gen-
erally in the tip of the ear. The corn earworm will
consume young developing kernels, silk and the ten-
der tip of the cob. Usually only one or perhaps two
corn earworms per ear are found. The fall armyworm
eggs are laid in masses of 100 to 150. Upon egg hatch-
ing, the young larvae will migrate to the protection
of the tight leaf axils or other such niches as behind
the developing ears. The fall armyworm will feed on
foliage but does not hesitate to bore into the ear.
Entries into the ear may be at the silk end but com-
monly are found on the sides of the ear at any loca-
tion. The fall armyworm will also frequently make
entries into the ear from the blind or stalk side. It
is not unusual to find multiple worms in the ear
where they will feed on kernels in close proximity to
where they bored into the ear.
Stink bugs. Stink bugs are frequently found in
large numbers feeding on ears of corn. There are
several species that frequent corn fields (green and
brown colored). The nymphs (immature) as well as
adults pierce the shuck and feed on the developing
kernels. Activity is most concentrated from the time
kernels begin to form and continues during the milk
stage of development. A loss of quality and quantity
can be expected to occur even when populations are
very low, particularly during the early silk through
the milk stage.
Corn-silk fly. The corn-silk fly is a pest that can
cause heavy damage to the developing ears, destroy-
ing the market value of corn. The adult is approxi-
mately 3/16 to 1/4 inch in length. Females lay eggs
on or near the tip of the ear after the silks begin to
show. Hundreds of eggs may be found on a single
tip. The eggs hatch in about 2 to 4 days, resulting
in maggots. The maggots feed down the silk channel,
where they ultimately feed on the kernels. The mag-
gots feeding on the silk also interfere with normal
pollination. Damage is usually more extensive along
the borders of a field.
Sweet corn tends to have fewer diseases than field
corn in most localities because sweet corn is usually
in the field for a shorter period of time and it is
purposely harvested prior to fruit maturation. Those
diseases which have predominated in Florida-
produced sweet corn will be discussed herein. Publi-
cations that are produced in areas outside of Florida,
such as the Compendium Of Corn Diseases (pub-
lished by the American Phytopathological Society),
are excellent resource materials but should not be
used as a sole-source diagnostic aid. As is the case
with all plant diseases, accurate identification is im-
portant when seeking control. Too often, diseases are
misdiagnosed in the field; this situation can lead to
costly misdirected control tactics. Once you have had
a disease diagnosed in your sweet corn, it is possible
that it will occur again in future years.
Seedling blights. Seedling blights, often called
damp off, are commonly caused by fungi that occur
naturally in the soil and sometimes by fungi carried
with the seed. Seedling blights can occur before or
after emergence. For Florida-produced sweet corn,
the following fungi appear to be the primary causes
of seedling blights: Pythium spp., Rhizoctonia spp.,
Fusarium spp., and Penicillium spp. Control of these
organisms is achieved by using a sequence of controls
including: crop rotation with nongrass crops;
adequate preplant tillage of the soil so that prior
organic matter from crops and weeds are totally de-
composed; shallow planting where possible; planting
when soil temperatures are warm to insure rapid
emergence; minimization of postplant tillage that
can injure young plants; and use of a fungicidal seed
treatment. It may be advantageous to use a seed
treatment that also contains an insecticide if you
suspect that soil borne insects may be a problem.
The choice of seed treatment is best attained from
current information available from a county Exten-
Root rots. Root rots of sweet corn are usually
caused by fungi that exist in the soil. The fungi that
are associated with seedling blights (see above) can
cause root rots. Root rots of sweet corn are not known
to be a major problem in Florida-produced sweet corn
except in young plants where seedling blights have
occurred. Root rots commonly occur in field corn
plantings. Plants weakened by seedling infections,
nematode feeding, insect damage, poor fertilization
practices, hardpan formation in the soil or other
stress factors may incur various degrees of root rot.
Control of root rots in sweet corn include those con-
trols listed for control of seedling blights, nematode
control, insect control, proper fertilization, and dis-
ruption of hardpans in the soil.
Stalk rots. Stalk rots of corn, like root rots, are
more likely to be a serious problem in field corn
rather than sweet corn. However, on occasion, stalk
rots do occur in sweet corn in Florida. Probably the
most common stalk rotting organisms in Florida-pro-
duced sweet corn are the fungi Pythium spp. and soft
rotting bacteria. These two groups of organisms are
most likely to become a problem when soils become
saturated with water. On occasion a bacterial stalk
rot occurs on the upper stalk of the plant. This situ-
ation seems to arise after excessive rains or irriga-
tions. Controls include the avoidance of excessive
irrigation and rapid pumping of excess water from
irrigation ditches associated with production fields.
Also, varieties should possess resistance to stalk rot
organisms and lodging. Most field corn varieties are
tested for these characteristics because they require
a longer maturation time. Stalk rots are sometimes
associated with low soil potassium situations.
Leaf rusts. Two species of rust fungi cause rust
diseases in Florida-produced sweet corn. Common
rust is caused by Puccinia sorghi and southern rust
is caused by Puccina polysora. Plant Pathology Fact
Sheet PP-37 has photographs and detailed informa-
tion about these two diseases. Both rust fungi can
cause infections during temperatures suitable for
corn growth. Symptoms will appear between 4 to 14
days after infection depending upon the tempera-
tures. Control of these rust diseases is done by using
resistant varieties, provided they are horticulturally
suitable, and multiple fungicide applications. Fun-
gicide sprays are the primary method of control for
rust diseases in Florida-produced sweet corn because
resistant varieties are not usually available. Sprays
with protectant-type fungicides should be applied as
often as twice each week during warm and wet
weather. Such conditions are highly suitable for rust
fungi development and production of new growth of
the corn plant. Early fall plantings and late spring
plantings in south Florida are often subject to
epidemics of rust diseases. Likewise, late spring
plantings in north Florida are more likely to require
intense spray programs compared to early spring
plantings in this area.
Fungal leaf blights. Two fungal leaf blights pre-
dominate in sweet corn produced in Florida. North-
ern corn leaf blight is caused by Helminthosporium
turcicium and southern corn leaf blight is caused by
Helminthosporium maydis. Other literature may
refer to these fungi by other names (Exerohilum spp.,
Bipolaris spp., or Dreschslera spp.) but fungicide
labels generally refer to them as Helminthosporium
spp. Either disease can appear during weather suit-
able for the growth of the corn plant. Both fungi
require moisture on leaves for spore germination and
infection. Four to 14 days after infection, symptoms
will be present. Usually, leafspots are the primary
symptoms associated with these diseases but plant
parts other than leaves are susceptible. Like rust
diseases, these fungal leaf blights reduce yield and
ear quality. Both the rust diseases and leaf blights
can increase rapidly in south Florida in corn planted
early in the fall and late in the spring when temper-
atures are warmer. For north Florida, earlier plant-
ings will usually escape some effects of these diseases
because of the cooler temperatures. It should be
realized that earlier plantings that minimize leaf
blight and rust diseases are more likely to incur
seedling blights because of the delayed emergence
associated with cool soils. Leaf blights, like rust dis-
eases, are adequately controlled with existing broad
spectrum fungicides if they are applied in a timely
fashion in appropriate amounts. It is important to
make repeat applications so that new emerging tis-
sue, particularly in the whorl, is covered with spray
during warm weather. Fewer sprays (intervals of 7
to 10 days or more) can be used during cool weather
in the winter months.
Bacterial leaf blight. Bacterial leaf blight, caused
by Pseudomonas auenae, has been epidemic in
Florida-produced sweet corn. It causes linear lesions
on the leaves, and blotchy and water ear and husk
rots. It cannot be controlled effectively with currently
available chemicals. Elimination of vaseygrass
around field perimeters and along ditches has re-
duced a major source of inoculum. Varieties vary in
susceptibility but such evaluations have not been
made in recent years.
Common smut. Common smut is caused by the
fungus Ustilago maydis. The disease appears as galls
on any portion of the plant above the ground. Galls
may become several inches across or be as small as
BB shot. At first galls are white and fleshy through-
out, and later massive spore formation inside the
galls causes the inside of the gall to be black. Vari-
eties differ greatly as to their susceptibility to this
disease. Adequate resistance is available for incorpo-
ration into commercial varieties. Any kind of
mechanical injury may contribute to infection by this
fungus. Injuries from blowing soil, hail, insects
(chewing), cultivation, detasseling and other causes
have apparently contributed to increased amounts
of smut. The use of resistant varieties is imperative.
Ear rots. Ear rots from fungi are not common in
Florida-produced sweet corn. However, in field corn,
ear rots are common. Many fungi cause ear rots.
Often ear rots occur because of inadequate natural
husk covering or from prior insect injury. Variety
selection and insect control aid in control of ear rots.
A bacterial ear rot has occurred in Florida. See the
section above about bacterial leaf blight.
Downy mildews. The two downy mildew dis-
eases seen in Florida-produced corn are sorghum
downy mildew, caused by Peronosclerospora sorghi,
and crazy top, caused by Sclerophthora macrospora.
Crazy top has not been a major problem and has
occurred most frequently in field corn in Escambia
County. Crazy top causes extreme plant distortion
and crinkling. Sorghum downy mildew almost be-
came a serious problem in Florida-produced sweet
corn. However, controls were used in time to offset
widespread epidemics. Infections by P. sorghi occur
while the plants are in the seedling or young plant
stage. Another source of inoculum is a condidium
(spore) that forms on the surface of leaves. In Florida,
corn and a sorghum x Johnsongrass weed (Sorghum
alum) have been infected with this fungus and both
have produced these aerial spores. Symptoms in-
clude chlorotic leaf striping, stunting, some plant
deformation, and downy growths of fungus on leaf
surfaces. Control is by use of a seed treatment that
includes metalaxyl Apron and rapid destruction of
infected corn or the above-mentioned weed. Also,
avoid rotations with sorghum and use resistant vari-
eties if they are available.
Viral diseases. Diseases caused by viruses occur
in Florida-produced corn but they have been primar-
ily a problem in field corn in Dade County. The in-
tense spraying of sweet corn with insecticides has
probably reduced viral disease incidence as several
are transmitted by insects in a semi-persistent man-
ner. In the Alachua County area, sweet corn has
been infected by maize dwarf mosaic virus. This virus
is transmitted in a nonpersistent manner by aphids.
They attain the virus from nearby Johnsongrass.
Maize dwarf mosaic virus, maize stripe virus, maize
rayado fino virus, and maize mosaic virus are the
viruses that have been identified in corn in Florida.
Viral diseases in corn are typified by stunting, and
yellow, variable green, and reddish-purple colora-
tions. Absolute identification of virus diseases in the
field can not be done reliably. Johnsongrass should
be eliminated near production fields.
"*, 6- -;' *
Sweet corn can be severely injured by several kinds
of nematodes. Unlike diseases and insects,
nematodes usually do not cause easily recognized
symptoms. Visual observation of a plant and its roots
can often indicate nematode problems, but it is neces-
sary to have soil and root samples examined to be
sure they are present. Nematode injury usually re-
sults in irregularly shaped areas of stunted plants
in a field. Plants may be chlorotic and may wilt dur-
ing hot weather, even when soil moisture is adequate.
Nematodes may cause short, stubby, or galled roots
which may also have brown or colorless lesions. The
sting, stubby-root, awl, rootknot, lesion and lance
nematodes are more common on mineral soils. The
most severe in organic soils include stubby root, spi-
ral, stunt and root-knot nematodes.
by D. D. Gull
Maturity and quality
High quality sweet corn should be of uniform size
and color, contain fresh green husks, have kernels
that are sweet, milky, plump, well-developed, and
be free from insect injury, mechanical damage and
decay; proper harvest maturity occurs when the silks
have just turned brown and dry.
Sweet corn quality is highly perishable. Corn has
a very high respiration rate and heat is a by-product
of the respiratory process; deterioration rate is prop-
ortional to the respiration rate. Sugar content and
flavor volatiles, which largely determine quality in
corn, decrease rapidly at ordinary temperatures.
Loss of sugar in the sugary or sugary enhanced types
is about four times as rapid at 50'F as at 32F. At
85F, 60% of the sugars may be converted to starch
in a single day as compared with only 6% at 32F.
Therefore, storage of these types for more than a few
days results in serious deterioration and loss of ten-
derness and sweetness.
Sugary or sugary enhanced sweet corn cultivars
contain up to 5% sugar at harvest; the newly de-
veloped high-sugar cultivars (shrunken-2) contain
from 5 to 10% sugar. Conversion of sugar to starch
is an enzymatic process and therefore temperature
dependent. The high-sugar cultivars should greatly
benefit the consumer because of the higher initial
level and also the slower conversion to starch during
Once-over harvests, by hand or machine, are prac-
ticed by commercial growers. Harvested ears are
either packed on a harvester aid or hauled to an
assembly area in the field, or packinghouse for grad-
ing and packing. Harvesting methods differ due to
availability of suitable labor. equipment and destina-
tion of the corn.
With hand harvesting, there is more selection for
marketable ears. Self-propelled packinghouses
(mule trains) with conveyers for hand-harvested ears
are used extensively in corn for the fresh market.
Mechanical harvesters cut the portion of stalk con-
taining the ears and then "strippers" remove the ear
from the stalk. Recent improvements in harvesting
machinery allow shank trimming and reduction in
ear damage. Removal of long shanks and flags is
important for fresh market sales to prevent water
loss during transportation.
Kernel denting is an indication of loss of quality.
Long shanks and flag leaves induce denting of the
kernels by drawing moisture from the kernels. A loss
of 2% moisture from sweet corn may result in objec-
tionable kernel denting. Shanks and flag leaves
should be trimmed and the ears maintained in a high
humidity environment to reduce kernel denting.
The major container used in Florida is the
wirebound crate containing 4 1/2 to 5 dozen ears with
a net weight of about 42 pounds. To a lesser extent,
corn is also packed in waxed fiberboard cartons hav-
ing the equivalent volume as crates. Retailers of fresh
market corn dislike a variation in number of ears
per crate, because they purchase by the crate and
sell by ear count. A uniform number of ears per crate
is highly desirable.
Wirebound containers are best adapted to hydro-
cooling. The appearance of fiberboard cartons can be
enhanced by graphics printing and oversized con-
tainers of this type are best adapted to slush-icing.
Commercial fresh market corn is graded United
States Fancy, United States No. 1, and United States
No. 2, that require a minimum cob length of 6, 5,
and 4 inches, respectively. Permissible processing
grades are United States No. 1 and United States
No. 2 with a minimum cob length covered with un-
damaged kernels of 4, and 3 inches, respectively.
Cobs may be clipped for all grades except United
States Fancy. Unclassified consists of ears which
have not been classified in accordance with any of
the foregoing grades; "unclassified" is not a grade
within the meaning of the standards. Wide ranges
in ear length and diameter result from differences
in production areas, season, and cultivar.
Vacuum cooling is the most rapid method to precool
corn; however, the corn must be wetted first to in-
crease the efficiency of the process. Crated corn can
be vacuum cooled from 85 to 40F in about 30 mi-
nutes. Failure to properly wet the corn can result in
a 1 percent moisture loss for each 10-degree drop in
corn temperature; therefore, denting of kernels may
Hydrocooling by showering or immersion in water
is the most common precooling method for sweet
corn. Effectiveness of this cooling method depends
upon low water temperature (32 to 34F), maximum
surface contact of water with corn, and sufficient
time for heat removal. Crated corn may take over
an hour in a hydrocooler to cool to 40F. Many hydro-
coolers are now capable of handling palletized crates,
stacked four or five layers high. Large overhead
spray nozzles must be capable of discharging a large
volume of water over the palletized crates to effi-
ciently remove heat. Corn toward the center of the
pallet is most difficult to adequate cool. Hydrocooling
corn in bulk is more efficient than hydrocooling
crated corn due to improved contact between water
and corn. However, some rewarming of the corn will
occur during the subsequent packing.
Slush-icing is another method to precool corn. A
mixture of ice and water is pumped into each crate
and field heat from the corn is most effectively re-
moved by the water, thus allowing the residual ice
to continue the cooling process. As with hydrocooling,
effectiveness is a function of surface contact with
cold water and sufficient time for heat removal. Over-
size cartons are required for slush-icing to permit
sufficient quantity of ice for residual cooling. Carton
size should be sufficient to hold 60 ears and about
25 pounds of ice.
Rapid removal of field heat from sweet corn (pre-
cooling) is especially critical to retard deterioration.
Maximum quality retention can be obtained by pre-
cooling corn to near 32F within an hour after harvest
and holding ears at that temperature during market-
ing. Corn can be kept in marketable condition (ap-
pearance) for 5 to 8 days at 32F but shelf life is
reduced to 3 to 5 days at 40F and not more than 2
days at a temperature of 50F.
After precooling, top icing ofwirebound crated corn
is desirable during transport or holding to continue
cooling, remove heat of respiration and keep the
husks green and fresh. Corn intended for local mar-
ket benefits from precooling but will remain edible
for a day or two after harvest if kept cool. Keeping
the husks wet will aid by evaporative cooling and
retain the fresh appearance of husks.
Corn may be adversely affected by exposure to
ethylene; therefore, it should not be stored with fruits
and vegetables that are known to produce ethylene,
such as muskmelons and tomatoes.
With proper grading and precooling, postharvest
diseases and disorders of sweet corn are of little con-
sequence during marketing.
Because chemical recommendations and produc-
tion costs change rapidly and are difficult to maintain
current, they are not presented in this publication,
but can be obtained from among the following IFAS
* Plant Disease Control Guide (also available on
* Insect Control Guide Vegetables (also available
* Nematode Control Guide (also available on VAX).
* Weed Control Guide Vegetables (also available
* Chemical Control Guide forFoliarDiseases of Veg-
etables, Plant Pathology Report 6.
* Guidelines for Effective Control of Plant Diseases,
Plant Pathology Report 20.
* Weed Control in Florida Vegetables Sweet Corn.
Vegetable Crops Special Series.
* Commercial Vegetable Crop Nutrient Require-
ments, Circular 806.
* Commercial Vegetable Fertilizer Guide, Circular
* Commercial Vegetable Varieties for Florida, Circu-
* Production Costs for Selected Florida Vegetables,
Economic Information Report.
in this series
Cabbage Production Guide for Florida
Cucumber Production Guide for Florida
Muskmelon Production Guide for Florida
Pepper Production Guide for Florida
Strawberry Production Guide for Florida
Tomato Production Guide for Florida
Graphic design and illustration by Katrina Vitkus.
This publication was produced at a cost of $920.00, or 37.0 cents per copy, to provide updated sweet corn
production and post-harvest information to county agents, growers, and industry. 3-2.5M-90
COOPERATIVE EXTENSION SERVICE, UNIVERSITY OF FLORIDA, INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES. John T Woeste.
director, in cooperation with the United States Department of Agriculture, publishes this information to further the purpose of the May 8 and June
30, 1914 Acts of Congress; and is authorized to provide research, educational information and other services only to individuals and institutions
that function without regard to race, color, sex, age, handicap or national origin Single copies of extension publications (excluding 4-H and youth
publications) are available free to Florida residents from county extension offices. Information on bulk rates or copies for out-of-state purchasers
is available from C.M. Hinton, Publications Distribution Center, IFAS Building 664, University of Florida, Gainesville, Florida 32611. Before publicizing
this publication, editors should contact this address to determine availability.