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LEAF DISEASES
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CORN
Disease Name: Southern Corn Leaf Blight
Pathogen: Fungus. Bipolaris maydis
Symptoms: Small (1/8-1/4 in), oblong leaf lesions with
rounded ends and parallel sides. Lesions are commonly tan with
brownish borders, appearing first on lower leaves (Race O).
Conditions: Favored by extended warm, wet, humid weather,
minimum tillage, continuous corn.
Inoculum Survival: Infected crop residue (leaves, leaf sheaths).
Inoculum Dispersal: Airborne spores.
Management: Resistant hybrids. Foliar fungicides may be
useful in seed production fields. Cleanly plow under infected residue. |
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CORN
Disease Name: Stewart's Bacterial Disease
Pathogen: Bacterium. Erwinia stewartii
Symptoms: Leaf blight symptoms consist of long, irregular,
pale green to yellow water-soaked streaks with wavy margins,
becoming grayish brown with age. Lesions are associated with
flea beetle feeding scars on leaves (bacteria are transmitted
from beetles into feeding scars). Systemic infection (wilt phase)
is uncommon on dent corn hybrids. Plants with systemic infections
are stunted, wilted and/or discolored.
Conditions: Favored by high infestation levels of flea beetles
in April through late June.
Inoculum Survival: Insect vector (corn flea beetle), infected
seed (rarely in hybrid dent corn).
Inoculum Dispersal: Insect vector (corn flea beetle), infected
seed (extemely rare in hybrid dent corn).
Management: Apply insecticides early to control corn flea
beetles, resistant hybrids. |
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STALK ROTS
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CORN
Disease Name: Anthracnose Stalk Rot
Pathogen: Fungus. Colletotrichum graminicola
Symptoms: Water-soaked areas on the surface of the
lower internodes, developing brownish linear streaks, turning
black later in the season, larger oval black areas may develop,
disintegrated gray to dark brown pith, severely infected stalks
likely to lodge.
Conditions: Favored by cool to warm, wet, humid weather,
minimum tillage, continuous corn, stresses that result in early
senescence.
Inoculum Survival: Infected crop residue (leaves, leaf sheaths
and stalks), infected seed (rare).
Inoculum Dispersal: Airborne spores. Unlike other stalk
rots, infection occurs aboveground.
Management: Resistant hybrids (full season hybrids tend
to have more resistance than short season), two year crop rotation
with nongrass crops, cleanly plow under infected residue, balanced
soil fertility. |
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CORN
Disease Name: Diplodia Stalk Rot
Pathogen: Fungus. Diplodia maydis
Symptoms: Leaves turn grayish-green and eventually
brown. Dark brown lesions extend in either direction from the
node. Pith is disintegrated and discolored, stalks break easily.
Tiny black bumps (pycnidia) may form just beneath the epidermis
on lower internodes.
Conditions: Warm, moist weather in late summer (2-3 wks
after silking), stresses that result in early senescence.
Inoculum Survival: Infected crop residue (seed, cobs, ear
shanks, stalks),seed, soil.
Inoculum Dispersal: Soilborne hyphal fragments and spores.
Infection occurs through roots.
Management: Resistant hybrids (full season hybrids tend
to have more resistance than short season hybrids), balanced soil
fertility, recommended plant population. |
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CORN
Disease Name: Gibberella Stalk Rot
Pathogen: Fungus. Gibberella zeae
Symptoms: Stalks that are split open have a disintegrated
pith with pink discoloration.
Conditions: Warm, moist weather in late summer (2-3 wks
after silking). More prevalent when plants are subjected to stresses
that result in early senescence and a reduction of sugar to roots
and stalks.
Inoculum Survival: Infected crop residue (seed,stalks),
seed, soil.
Inoculum Dispersal: Soilborne hyphal fragments and spores.
Infection occurs through roots.
Management: Resistant hybrids. Full season hybrids tend
to have more resistance than short season. Balanced soil fertility.
Do not exceed recommended plant populations. |
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CORN
Disease Name: Fusarium Stalk Rot
Pathogen: Fungus. Fusarium moniliforme
Symptoms: Disintegrated pith tissues.
Conditions: Warm, moist weather shortly after pollination.
More prevalent when plants are subjected to stresses (such as
dry weather) that result in early senescence and a reduction
of sugar to roots and stalks.
Inoculum Survival: Infected crop residue (seed, stalks),
soil.
Inoculum Dispersal: Soilborne hyphal fragments and spores.
Infection occurs through roots.
Management: Resistant hybrids. Full season hybrids tend
to have more resistance than short season. Balanced soil fertility.
Do not exceed recommended plant populations. |
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EAR ROTS
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CORN
Disease Name: Diplodia Ear Rot
Pathogen: Fungus. Diplodia maydis
Symptoms: Infection usually starts at the base of
the ear or from the stalk into the shank. White mycelial growth
covers the kernels and pycnidia may be found on rotted kernels,
husks adhere tightly, infected ears remain erect when infection
occurs early in ear development.
Conditions: Dry weather prior to silking, followed by wet
conditions within first 30 days after silking.
Inoculum Survival: Infected crop residue (seed, cobs, ear
shanks, stalks), soil.
Inoculum Dispersal: Airborne spores.
Management: Resistant hybrids, crop rotation, clean plowing,
harvest early to prevent weathering. Dry corn to 15% moisture content
and below to prevent further mold growth in storage. |
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CORN
Disease Name: Gibberella Ear Rot
Pathogen: Fungus. Gibberella zeae
Symptoms: Reddish mold that usually starts at the
tip of the ear. Husks may adhere tightly to the ear (hybrid dependent).
Conditions: Cool wet weather within first 21 days after
silking favors the development of this disease.
Inoculum Survival: Infected crop residue (stalks, seed),
infected seed, soil.
Inoculum Dispersal: Airborne spores.
Management: Resistant hybrids, crop rotation, harvest early
to prevent continued mold growth in the field, clean plowing. Dry
corn to 15% moisture content and below to prevent further mold
growth in storage. |
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