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Gail Ruhl
Department of Botany and Plant Pathology
Purdue University
West Lafayette, IN 47907
Email: ruhlg@purdue.edu
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This web page address is:
http://www.btny.purdue.edu/Extension/Pathology/CropDiseases/Corn/
Search for a Disease Name
SEED and SEEDLING DISEASES
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CORN
Disease Name: Seed Rot
Pathogen: Fungi and bacteria. Pythium, Fusarium, Diplodia, Rhizoctonia,
Penicillium spp., various soilborne bacteria
Symptoms: The seed rots (embryo is killed) before germination.
Conditions: Favored by prolonged wet and cold soil conditions in
the spring. Soil temperatures 50 F or lower favor seed rots.
Inoculum Survival: Soil, infected plant residue (leaves,stems, roots),
occasionally infected seed.
Inoculum Dispersal: Soilborne hyphal fragments and spores, sometimes
seedborne hyphal fragments and spores.
Management: Fungicide seed treatment. Plant when soil conditions
are warmer and drier, use the proper planting depth.
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LEAF DISEASES
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CORN
Disease Name: Gray Leaf Spot
Pathogen: Fungus. Cercospora zeae-maydis
Symptoms: Initial lesions appear as greenish black water soaked
circular areas with chlorotic halos, expanding into oval and then the diagnostic
parallel sided rectangular brownish gray lesions.
Conditions: Infection is favored by extended warm, wet, humid weather.
Inoculum Survival: Infected crop residue (leaves and leaf sheaths).
Inoculum Dispersal: Airborne spores.
Management: Select hybrids with resistance (tolerance based on risk),
two year crop rotation, cleanly plow under infected residue. |
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CORN
Disease Name: Anthracnose Leaf Blight
Pathogen: Fungus. Colletotrichum graminicola
Symptoms: Small, oval to elongated water-soaked lesions enlarge
to become brown, spindle shaped spots with yellow to reddish-brown borders.
Lesions may coalesce and blight entire leaves. Older lesions will turn gray
in the center with small black specks (acervuli with sterile black hairs).
Leaf blight may be followed by top kill and stalk rot. Leaf blight rarely
causes large yield losses. Stalk rot phase is most important (see Anthracnose
Stalk Rot).
Conditions: Favored by cool to warm, wet, humid weather, continuous
corn with reduced tillage.
Inoculum Survival: Infected crop residue (leaves, leaf sheaths and
stalks), seed (endosperm).
Inoculum Dispersal: Airborne spores.
Management: Resistant hybrids, rotate corn with nongrass crops. Cleanly
plow under infected residue.
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CORN
Disease Name: Common Corn Rust
Pathogen: Fungus. Puccinia sorghi
Symptoms: Initial symptoms are chlorotic flecks on leaf surfaces.
Flecks develop into oval to elongate reddish brown powdery pustules on upper
and lower leaf surfaces. Reddish brown spores break through the leaf epidermis.
Pustules become brownish-black as they mature. Usually not a serious disease
in hybrids.
Conditions: Disease favored by cool (66 F optimum) humid weather.
Inoculum Survival: Spores blown into the Midwest from the South.
Does not survive winter in Indiana, except possibly in rare years along
the Ohio River.
Inoculum Dispersal: Airborne spores.
Management: Resistant hybrids. Foliar fungicides may be useful in
seed production fields.
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CORN
Disease Name: Southern Corn Rust
Pathogen: Fungus. Puccinia polysora
Symptoms: Similar to common rust except pustules occur almost
exclusively on the upper leaf surface, rarely on lower. Pustules are more
orange than brick-red and slower to break through epidermis of leaf than
common rust pustules.
Conditions: Favored by high humidity and temperatures around 80 F.
Inoculum Survival: Spores blown into the Midwest from the South.
Does not survive winter in Indiana, except possibly in rare years along
the Ohio River.
Inoculum Dispersal: Airborne spores.
Management: Resistant hybrids. Foliar fungicides may be useful in
seed production fields.
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CORN
Disease Name: Northern Corn Leaf Blight
Pathogen: Fungus. Exserohilum turcicum
Symptoms: Long cigar-shaped gray-green or tan lesions.
Conditions: Favored by extended wet, cool, humid weather, minimum
tillage, continuous corn. Usually occurs during or after pollination.
Inoculum Survival: Infected crop residue (leaves, husks, stalks).
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: Northern Leaf Spot
Pathogen: Fungus. Helminthosporium carbonum (Race 3)
Symptoms: Narrow, small, linear to oval shaped leaf lesions. Lesion
type may vary with the genotype of host and isolate. Lesions are grayish
tan and surrounded by a light to darkly pigmented (usually purple) border.
Chain-like leaf lesions are often produced.
Conditions: Favored by moderate temperatures and high relative humidity,
minimum tillage, continuous corn.
Inoculum Survival: Infected crop residue (leaves, husks, stalks,
seed).
Inoculum Dispersal: Airborne spores.
Management: Resistant hybrids. Disease is primarily a problem in
seed production fields with certain highly susceptible inbreds. Foliar fungicides
may be useful in seed production fields. Cleanly plow under infected residue.
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