Corn Diseases in Corn Following Corn
By Laura Sweets
The escalating interest in ethanol production has led to
speculation that 2007 may see an increase in corn acres through
much of the Midwest including Missouri. This could lead to
an increase in acres of corn following corn. Certainly there are
many factors to take into consideration as decisions are made
on how many acres of corn and/or soybean to plant and which
fields are to be planted to which crop. Certainly it would be
wise to put some thought into how corn on corn could affect
the diseases that occur in the second year corn crop.
Corn diseases can and do occur each year in Missouri.
Problems with germination and stand establishment that are
related to seed decay, damping-off and seedling blights are often
encountered in the field. These losses can be costly, especially
if replanting is necessary. Diseases may cause leaf spots or leaf
blights, wilts or premature death of plants. Corn diseases also
can cause harvest losses, affect the quality of the harvested
crop and cause storage losses. The extent of the damage due
to corn diseases in a given season depends on a number of
factors, including the susceptibility of the corn hybrid to the
specific disease, the level of pathogen inoculum present and the
environmental conditions during the growing season.
Since many of the common corn diseases in Missouri
are caused by pathogens that can survive on infested residues
left on the soil surface, corn following corn in fields in which
residues are left on the soil surface may mean that the level
of inoculum present in the field is higher for the second year
corn crop. This can mean an increased risk or potential for
disease development from the higher level of inoculum in the
field and the fact that the inoculum is in close proximity to the
developing corn. Weather during the growing season will still
have a significant impact on disease severity. Even if inoculum
levels are high in a given field, if the weather conditions are
not conducive to disease development, the disease may not
occur or may not occur at damaging levels. However, if weather
conditions are favorable for disease development, a disease may
occur earlier in the season or at more damaging levels because
inoculum was present in close proximity to the developing
corn.
The principle diseases of corn in Missouri can be divided
into seed rots and seedling diseases, foliage diseases, stalk and
root rots and ear and kernel rots. Management strategies for
each of these categories of corn diseases along with suggestions
if corn is following corn are given below. In general if corn
is being followed by corn, hybrid selection (especially the
selection of hybrids with resistance to diseases likely to occur in
that field) and agronomic practices such as planting under best
possible conditions, planting at proper populations for specific
hybrid, following appropriate fertility practices, and managing
weed and insect problems become more important.
Seed Rots and Seedling Blights
Seed rots and seedling blights are caused by a number
of different fungal species. Some of these, such as Pythium
species, Fusarium species and Rhizoctonia solani are common
soil fungi found wherever corn is grown. Some, such as
Fusarium moniliforme and Penicillium oxalicum, may be
either soilborne or seedborne. Most of these pathogens can
survive as saprophytes colonizing crop residues, but many
also produce survival structures that enable them to survive
adverse environmental conditions such as low or alternating
temperatures and low soil moisture until conditions are again
favorable for their growth.
Most of the seed rots and seedling blights on corn are
more severe in wet soils, in low-lying areas in a field and in
soils that have been compacted or remain wet for an extended
period of time. Low soil temperatures (below 50-55 degrees
F) favor seed rot and seedling blights. Disease severity is also
affected by planting depth, soil type, seed quality, mechanical
injury to seed, crusting, herbicide injury and other factors
which delay germination and emergence of corn. Residues left
on the soil surface may influence the incidence and severity of
seedling blight through their effect on soil moisture and soil
temperature.
ManageMent options for seed rots and seedling blights:
- Plant good quality seed of hybrids adapted for your area.
- Plant under good seedbed conditions, especially at soil temperatures above 50 to 55 degrees F.
- Use fungicide treated seed. Most commercial corn
hybrid seed comes treated. Be certain that the seed treatment
is one that will control both water mold fungi such
as Pythium and other fungi such as Rhizoctonia, Penicillium
and Fusarium. This may mean that a combination
of active ingredients is needed or that an additional at
planting seed treatment is needed.
Foliage Diseases
There are a number of fungi and a few bacteria that cause
foliage diseases of corn. These various foliar pathogens cause
leaf spots, leaf blights and similar symptoms on corn. The fungi
that cause most of these corn foliage diseases (gray leaf spot,
northern corn leaf blight, anthracnose leaf blight, yellow leaf
blight, eyespot, etc.) survive in infested corn residues left on the
soil surface. The following season spores are produced during
moist periods and are carried by wind currents to susceptible
corn leaves where infection may begin.
Common rust and southern rust are two exceptions to this
simplified explanation of disease development. The rust fungi
do not survive in infested residues left in a field and , in fact,
do not survive the winter months in this area. Rather, the rust
fungi are reintroduced into this area each season when spores
are carried up on air currents from the southern United States.
are carried up on air currents from the southern United States.
Most of the corn foliage diseases are favored by warm
temperatures and wet or humid weather or heavy dews. They
tend to start in the lower canopy and, if weather conditions are
favorable, move up through the plant.
ManageMent options for corn foliage diseases:
Select disease-resistant corn hybrids. Keeping records of
which diseases have been problems in individual fields
and then choosing hybrids with resistance to those
diseases is important and will be even more important if
corn is planted in fields with infested residues present.
Rotate crops with at least one year out of corn. If crop
rotation is limited, then hybrid selection and other agronomic
practices become even more important.
Manage corn residues. In reduced tillage systems, hybrid
selection and crop rotation are especially important. If
crop rotation is limited, then hybrid selection and other
agronomic practices become even more important.
Follow appropriate fertility practices.
Manage insect and weed problems.
Plant at the proper population for the hybrid.
Apply foliar fungicides if warranted. Traditionally foliar
fungicides have tended to give the best economic return
on speciality corns such as seed corn, white corn or
popcorn rather than field corn. This may change in corn
on corn situations. To achieve the maximum benefit from
foliar fungicides it is critical to scout corn on a regular
basis and begin fungicide applications at the onset of
disease development. If a foliar disease is already well
established in field, the benefits of a fungicide application
may be minimal.
Stalk Rots
Stalk rots are important worldwide and are among the
most destructive diseases of corn. A number of different fungi
and bacteria cause stalk rots. Stalk rots are caused by a variety of
fungi and bacteria that survive one growing season to the next
in soil, in infested corn residues or on seed. Stalk rot pathogens
enter the corn plant through one of several avenues. The spores
may be blown into the base of the leaf sheath, where they may
germinate and grow into the stalk. Spores may enter into a
plant through wounds made by corn borers, hail or mechanical
injury. When fungi are present in the soil or infested residue
as either spores or mycelium, they may infect the root system
causing root rot early in the season and later grow up into the
stalk causing stalk rot.
Stalk rot becomes a problem when plants are stressed
during the grain filling stages of development. Water shortage,
extended periods of cloudy weather, temperature stresses, 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.
ManageMent options for corn stalk rots:
Select hybrids with good stalk strength and lodging characteristics.
Plant at recommended populations for that hybrid.
Follow proper fertility practices.
Maintain good insect and weed control.
If irrigating, try to deliver optimum water from silking
through late dough stage.
Avoid or minimize stress to corn (especially during pollination
and grain fill).
Harvest in a timely manner.
Ear and Kernel Rots
There are a number of fungi that can invade and cause
damage to corn ears and kernels. Field fungi invade the ears or
kernels before harvest while the corn is still in the field. These
fungi may affect the appearance and quality of kernels. Some of
the field fungi on corn in Missouri include species of Alternaria,
Cladosporium, Aspergillus, Penicillium, Diplodia, Fusarium
and Gibberella. Most of these fungi are more prevalent when
rainfall is above normal from silking to harvest. One exception
is Aspergillus flavus, which is favored by drought stress to corn
during pollination and warm temperatures as kernels mature.
These ear and kernel rot fungi may survive in residues left on
the soil surface or as survival structures in the soil.
ManageMent options for ear and kernel rots:
Select locally adapted hybrids with husks that close over ear
tips.
Plant at recommended plant populations for that hybrid.
Maintain good plant vigor over the growing season.
Use a balanced fertility program.
Select planting dates appropriate for your area.
Follow recommended management practices to limit damage
by ear-feeding insects.
If irrigating, try to deliver optimum water from silking
through late dough stage.
Harvest in a timely fashion.
Laura Sweets
Ag Ext.-Plant Sciences
573-884-7307
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