Originally written February 1, 2006 | Last updated
February 23, 2014
Conditions necessary for disease development:
Host (susceptible)nditions necessary for disease development:
Common disease pathogens in the Midwest:
Fungi (most prevalent)
Managing Diseases (IPM versus ICM)
Integrated Pest Management (IPM): Knowing what pests are present, and taking
appropriate action to minimize economic damage
Integrated Crop Management (ICM): A management approach that recognizes that
all crop production practices have effects on each other, and on the interaction
of crops with pests and diseases. Risks and benefits of each practice need evaluation.
High quality seed
Hybrid or Variety Selection
- Most economical and effective way to control or reduce most diseases
- Genetic concepts relating to disease management:
- Single-gene resistance
- Partial resistance
- Physical attributes
- Brown stem rot in corn/soybean rotations
Tillage and Crop Residue Management
- Tillage increases soybean cyst nematode
- Residue increases survival of pathogens on the soil surface
- Row spacing and white mold
- Corn rust, Gray leaf spot, and common smut and high N levels
- Flea beetle and Stewart's wilt
- Aphids and barley yellow dwarf
Weed and Herbicide Interactions
- White mold and weed hosts
Other Methods for Controlling Diseases
- Seed Protection
- Seed testing and Cleaning
- Seed Treatments
- Foliar and Soil Fungicides and Nematicides
- Biological Control
Common Diseases in Wisconsin
Corn Disease Management National Corn Handbook - 4
SEEDLING DISEASES - Pythium (downy mildew) disease is most common
- Problem in cool, wet springs
LEAF DISEASES - Usually not a major problem
- Leaf rust - Usually not a problem in dent corn
- SCLB - Last major yield-reducing leaf disease; it occurred in 1970
- leafspots and blights (anthracnose leaf blight, eyespot, gray leaf spot, helminthosporium
leaf spot, northern corn leaf blight)
STALK DISEASES usually the main corn disease problem
- Diplodia Stalk Rot- Nodes are infected
- Gibberella Stalk Rot - internodes are infected
- Charcoal Rot
Corn Stalk Rots
Any factors which stress corn during the growing season may contribute to
an increase in stalk rots that season. And this has certainly been a season
of stresses for corn in Missouri with late planting due to wet soil
conditions, flooding, cool temperatures, high temperatures, high night
temperatures, cool night temperatures, overcast days, moisture stress, heavy
rains, hail, some foliage diseases, etc. Therefore, it would be wise to
scout fields for corn stalk rots and to harvest fields with stalk rot
problems as quickly as possible.
A number of different fungi and bacteria cause stalk rots of corn.
Although many of these pathogens cause distinctive symptoms, there are also
general symptoms which are common to all stalk rot diseases. Early symptoms,
which occur a few weeks after pollination, usually start with premature
dying of bottom leaves. Eventually, the entire plant may die and appear
light green to gray. Diseased stalks usually begin losing firmness during
August. The cells in the interior of the stalk are dissolved, resulting in a
loss of stalk firmness and strength. Stalks may then lodge, particularly if
harvest is delayed or wind storms occur.
Fusarium stalk rot and Gibberella stalk rot can be difficult to
distinguish in the field. Both can cause a pink to reddish discoloration of
diseased stalk tissue. Tufts of white mycelium may be evident at the nodes
of diseased stalks. When stalks are split open the pith is usually shredded
Anthracnose stalk rot, caused by the fungus Colletotrichum graminicola,
may be most evident at the nodes. Initially lesions are tan to reddish-brown
but they become shiny black later in the season. These shiny black lesions
may begin at a node and extend out from that node. The lesions may merge to
discolor much of the lower stalk tissue. Internal pith tissues may also be
discolored and may disintegrate as disease progresses.
Diplodia stalk rot may begin as a brown to tan discoloration of the lower
internodes. Stalks become spongy. The pith disintegrates leaving only the
vascular bundles. Mats of white fungal growth of Diplodia maydis may be
evident on affected tissues. Diplodia also produces fruiting bodies which
may be seen as small black specks embedded in the white fungal mat. Diplodia
also causes an ear rot of corn. Diplodia ear rot has been found in scattered
fields across the state so Diplodia stalk rot could also occur this season.
Charcoal rot may begin as a root rot and move into the lower internodes
of the stalks. Pith tissues will be shredded and plants may break at the
crown. The charcoal rot fungus, Macrophomina phaseolina, produces very small
survival structures called microsclerotia which may be visible as very
small, black flecks just beneath the stalk surface or on the vascular
strands remaining in the interior of the shredded stalks. Charcoal rot is
usually more severe under hot, dry conditions, so this corn stalk rot could
be a serious problem in areas of the state which suffered from drought
conditions the latter part of the growing season.
Stalk rots are caused by several different fungi and bacteria which are
part of the complex of microorganisms that decompose dead plant material in
the soil. They survive from one growing season to the next in soil, in
infested corn residues or on seed. Stalk rot pathogens enter the corn plant
in a variety of ways. The spores may be blown into the base of the leaf
sheath where they may germinate and grow into the stalk. Spores may enter
directly into a plant through wounds made by corn borers, hail or mechanical
injury. When fungi are present in soil or infested residue as either spores
or mycelium, they may infect the root system causing root rot early in the
growing season and later grow up into the stalk causing stalk rot.
Stalk rot becomes a problem when plants are stressed during the grain
filling stage of development. Water shortage, extended periods of cloudy
weather, hail damage, corn borer infestation, low potassium in relation to
nitrogen, leaf diseases and other stresses that occur in August and
September may be associated with an increase in stalk rot.
Losses from stalk rots vary from season to season and from region to
region. Yield losses of 10 to 20% may occur on susceptible hybrids. Tolls
greater than 50% have been reported in localized areas. Losses may be direct
losses due to poor filling of the ears or lightweight and poorly finished
ears or indirect through harvest losses because of stalk breakage or
lodging. Harvest losses may be reduced if fields are scouted 40-60 days
after pollination to check for symptoms of stalk rot. Stalk rot can be
detected by either pinching stalks or pushing on stalks. If more than 10-15
percent of the stalks are rotted, the field should be harvested as soon as
Management of stalk rots of corn should include the following:
- Select hybrids with good stalk strength and lodging characteristics.
- Plant at recommended plant populations for that hybrid.
- Follow proper fertility practices.
- Avoid or minimize stress to corn (especially during pollination and
- Harvest in a timely manner.
EAR DISEASES - usually minor in importance
- Smut - may reduce feeding value
- Diplodia and Gibberella Ear Rots
- Fusarium Kernel Rot - present in all corn fields, but rarely causes problems
Ear and Kernel Rots of Corn
Corn harvest is beginning or rapidly approaching in many parts of the
state. So far we have received only a few samples with ear and kernel rots.
Usually Diplodia ear rot, Gibb ear rot, Penicillium ear rot and Aspergillus
species other than Aspergillus flavus are associated with wet conditions,
especially wet falls and harvests that are delayed by wet conditions.
Although much of the state has been unusually dry recently, there have
already been fields in which these ear and kernel rots are present. In some
cases the ears showing molds had been damaged by insects or hail and the
molds had come in around the damaged areas. But in other cases Penicillium
and Fusarium are showing up on the tips of the ears. And then in fields in
which hot, dry conditions occurred at or just after pollination, Aspergillus
flavus and aflatoxin could be problems.
Diplodia ear rot, Penicillium ear rot and Gibb ear rot are common
problems year in and year out but the severity varies with weather
conditions at pollination or close to harvest. The Penicillium ear rot and
Gibb ear rot are particularly evident on the exposed tips of ears, around
insect tunnels and on ears that have remained upright. If there are periods
of wet weather before corn is harvested, some of the corn plants that died
prematurely may show the black discoloration caused by secondary fungi
coming in on the senescing plant tissues. Because of the wet conditions
early in the season, there was a wide range of planting dates for corn.
Unfortunately, there were some fields which were silking and pollinating
during the stretch of hot, dry weather about mid-season. These fields might
be at risk for the occurrence of Aspergillus flavus and aflatoxin.
Diplodia Ear Rot
Both Diplodia maydis and Diplodia macrospora can cause Diplodia ear rot of
corn. The ear leaf and husks on the ear may appear prematurely bleached or
straw-colored. When the husk is peeled back, dense white to grayish-white
mold growth will be matted between the kernels and between the ear and the
husks. Small, black fungal fruiting bodies may be scattered on husks or
embedded in cob tissues and kernels. The entire ear may be grayish-brown,
shrunken, very lightweight and completely rotted. Diplodia ear rot is
favored by wet weather just after silking and is more severe when corn is
planted following corn.
Penicillum and Aspergillus niger ear rots
Penicillium rot is usually evident as discrete tufts or clumps of a
blue-green or gray-green mold erupting through the pericarp of individual
kernels or on broken kernels. Penicillium appears as small, discrete
colonies of mold growth with a dusty or powdery appearance. The fungus may
actually invade the kernel giving the embryo a blue discoloration. Blue-eye
is the term used for this blue discoloration of the embryo.
Gibb ear rot (caused by Gibberella zeae) usually begins as a reddish mold
at the tip of the ear. Early infected ears may rot completely with husks
adhering tightly to the ear and a pinkish to reddish mold growing between
husks and ears. Although mold growth usually has a pinkish to reddish color,
it can appear yellow to yellow-orange or yellow-red. Gibb ear rot typically
begins at the tip of the ear but under favorable conditions it can move down
the ear causing extensive damage. It may also develop around injuries from
hail, birds or insects.
Aspergillus niger is also common on exposed ear tips. This fungus will be
evident as black, powdery masses of spores on the tip of the ear or around
Black corn occurs when any of a number of saprophytic or weakly parasitic
fungi grow on corn plants in the field. Alternaria, Cladosporium,
Aureobasidium and other species are frequently found on these discolored or
black plants. Since the affected plants may have a sooty appearance these
fungi are sometimes called sooty molds. These sooty molds or secondary fungi
tend to develop on plants when wet or humid weather occurs as the crop is
maturing or if harvest is delayed because of wet weather. Typically these
fungi come in on plants that are shaded, undersized, weakened or prematurely
ripened and on senescing foliage. Plants that are lodged or that have been
stressed by nutrient deficiencies, plant diseases or environmental
conditions may be more severely affected. Although many of these fungi
produce dark or black mold growth, the color of the mold growth can range
for dark or black to olive green or even pink to white.
These secondary fungi tend to develop on senescing plant tissues,
primarily leaf, stalk and husk tissue, but under favorable conditions can
cause infection of the kernels. Infected kernels might show a black
It is possible that these sooty molds or secondary fungi could contribute
to stalk deterioration or stalk rot. Lodging could become a problem in these
fields, especially if there are high winds or strong storms before harvest.
Grain from fields with high levels of sooty molds should be treated with
care if it is stored. Grain should be thoroughly cleaned to remove
lightweight, damaged or broken and moldy kernels. Grain should be stored at
the proper moisture content and temperature and checked on a regular basis
Aspergillus flavus is evident as greenish-yellow to mustard yellow,
felt-like growth on or between kernels, especially adjacent to or in insect
damaged kernels. Aspergillus flavus is favored by high temperatures and dry
conditions, so Aspergillus ear rot is typically associated with drought
stress. The fungus survives in plant residues and in the soil and spores are
spread by wind or insects to corn silks where the spores initiate infection.
An additional concern with ear and kernel rots of corn is the possibility
of mycotoxin production. Mycotoxins are naturally produced chemicals that in
small amounts may be deleterious to animal or human health. Aspergillus and
Gibberella are most frequently involved in cases of mycotoxin contamination
in Missouri corn. The presence of molds or their spores does not necessarily
mean that mycotoxins will be produced. Circumstances that favor mold growth
may allow production of mycotoxins in some situations, but frequently mold
growth occurs with little or no mycotoxin production. Once formed,
mycotoxins are stable and may remain in grain long after the fungus has
died. In general, swine and poultry are more susceptible than ruminants to
mycotoxin-induced health problems. In cases where mycotoxin problems are
suspected, a sample should be submitted to a qualified laboratory for
mycotoxin analysis. Table 1 below gives the acceptable levels of aflatoxin
in corn intended for various uses as established by the United States Food
and Drug Administration.
Table 1. Present acceptable levels of aflatoxin in corn used for food and
feed as established by the United States Food and Drug Administration (FDA)
are as follows:
- Corn containing no more than 20 ppb of aflatoxin when destined for
food use by humans, for feed use by immature animals (including immature
poultry) and by dairy animals, or when the intended use is unknown.
- Corn containing no more than 100 ppb aflatoxin when destined for
breeding beef cattle, breeding swine or mature poultry (e.g. laying
- Corn containing no more than 200 ppb aflatoxin when destined for
finishing swine (e.g. 100 lbs. or greater).
- orn containing no more than 300 ppb aflatoxin when destined for
finishing (i.e. feedlot) beef cattle.
Little can be done to prevent or reduce the invasion of corn by fungi in
the field. These ear and kernel rots tend to be more severe on ears with
insect, bird, hail or other physical damage. Ears well covered by husks and
maturing in a downward position usually have less rot than ears with open
husks or ears maturing in an upright position. However, if ear and kernel
rots developed in the field, it is important to harvest the field in a
timely manner and to store the grain under the best possible conditions.
Both Penicillium and Aspergillus can continue to develop on corn in storage
if the grain is not stored at proper moisture content and temperatures.
These two fungi can cause serious storage mold problems.
Adjust harvest equipment for minimum kernel damage and maximum cleaning.
Before storing grain, clean bins thoroughly to remove dirt, dust and any
grain left in or around bins. Thoroughly clean grain going into storage to
remove chaff, other foreign material and cracked or broken kernels. Dry
grain to 15% moisture as quickly as possible and monitor grain on a regular
basis throughout storage life to insure moisture and temperature are
maintained at correct levels. Protect grain from insects.
- rusts (common, southern rusts)
- seed rots and seedling blights (damping off)
- smuts (corn smut)
- stalk and root rots (bacterial stalk rot)
- Stewartâ€™s disease
- virus diseases (corn lethal necrosis, maize dwarf mozaic virus)
NEMATODES (needle, root lesion, sting nematodes)
STORAGE DISEASES - Need to control moisture percentage to minimize storage diseases
Images of common corn diseases
To purchase hard copies of these publications, go to
The UWEX Learning Store
Pest Management in Wisconsin
Field Crops UWEX Bulletin A3646
Scouting Corn--A Guide for Wisconsin Corn Production
UWEX Bulletin A3547
Fungicide Resistance Management in Corn, Soybean, and Wheat
in Wisconsin UWEX Bulletin A3878
Common corn diseases in Wisconsin UWEX Bulletin
Wisconsin Integrated Crop Management Manual: Intro
| Alfalfa |
Corn | Soybean |
Wheat | Nutrients
Pest Management Fast Facts