Transcript Unit 1: Corn Diseases

Unit 1: Corn Diseases
Unit 1: Corn Diseases
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Corn Smut
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Caused by fungus: Ustilago maydis
Most widely recognized corn disease
Symptoms:
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Complete barrenness in most plants
Result:
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Reduced grain development
~30% yield loss
Unit 1: Corn Diseases
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Appears as galls on both the ear and stalk
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White at first, but develop into dark lesions w/ dark
spores inside whitish membrane
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Found on:
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Galls break and scatter spores
Ears
Near midrib of the leaf
Nodal buds on the stem
More likely to attack vigorous growing plants
Not poisonous to livestock
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Smut organism lives in the soil
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Seed disinfection or treatment is ineffective, except to
prevent spread to new fields
Treatment:
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Crop rotation
Don’t spread manure smut infested manure on fields
Many resistant hybrids
Unit 1: Corn Diseases
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Head Smut
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Galls on ear and tassels
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Entire destruction of these structures
Mostly affects Southwestern & Pacific Coast
states
Also caused by fungus living in the soil, or on
seed
Galls dispense spores just as corn smut
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Control:
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Rotate field out of corn for 2 years
Used treated seed to prevent infestation into other
fields
Most field corn hybrids resistant, sweet corn
varieties are susceptible
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Root, Stalk, & Ear Rot
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Effects:
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Reductions in field stand
Reductions in plant vigor
Chlorosis
Barrenness
General blighting of the plant
Rotting of the ear
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Caused by fungal infestations:
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Ear rot:
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Root rot:
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Pythium, Gibberella, Diplodia spcs.
Stalk rot:
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Gibberella, Fusarium, Aspergillus, & Pythium spcs.
Fusarium, Gibberella, Diplodia
Stalk Rot
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Genetic resistance not available
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Problems tend to occur under certain conditions
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Symptoms prevalent when plant is stressed
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Stresses:
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High N w/ low K
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High moisture mid to late season after dry early season
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High moisture stress early in season & during grain fill
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High leaf disease pressure
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Insect damage
Select hybrids resistant to the above stresses & have
good soil fertility
Unit 1: Corn Diseases
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Ear rot
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Can continue growth and damage after corn is
harvested
Mold damage to corn when moisture of grain in
storage is >14%
Rot and darkening of the corn embryo (called
Blue Eye)
Nearly all organisms are carried on decaying corn
residues or in the soil
Unit 1: Corn Diseases
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Some also carried on the seed
Molds are typically evident on the ear
Can also observe dark bodies on outside or inside
of old stalks
Root rot
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Develops on infested kernels
Crown roots rot, weak plants die
Subcrown roots appear dry, brown instead of
healthy white
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Little evidence that root rot fungi advance up the
stalk
Most serious under dryland conditions
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Stalks will die and fall
Prevention:
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Use disease-free treated seed
Plant at proper soil temperature
Balance soil nutrients
Plant resistant hybrids
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Chemical seed disinfectants are effective
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Captan, metalaxyl, fludioxonil
Increase yield, stand, vigor
Leaf Diseases
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Northern Corn Leaf Blight
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Infection of the lower leaves
Boat-shaped, grayish lesions
Spread to other leaves in cool, damp weather
Can cause leaf death
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Treatment:
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Has caused losses mostly in the East & South
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Use resistant hybrids
Significant damage as far West as NE
Southern Corn Leaf Blight
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Usually not considered a problem
Major infestation in 1970 w/ major losses throughout
corn belt
Needs warm, moist weather to flourish
Lesions form on leaf, ear shanks, husks
Can infect the ear
Unit 1: Corn Diseases
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Gray Leaf Spot
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Problem since 1925 from Atlantic states to eastern
corn belt
Cool temps w/ prolonged overcast days
Lesions can be confused w/ other blight diseases
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Mature lesions are rectangular restricted by leaf veins
Signified by yellow halo
Lesions can join causing blight of large portion of the leaf
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Stewart’s Wilt
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Found throughout the Corn Belt
Carried by the corn flea beetle
Symptoms:
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Long, water-soaked lesions that can extend the length of the
leaf
Leaves turn necrotic
Goss’s Wilt
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Water-soaked lesions forming next to leaf veins
Stalks can be discolored
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Affected plants can be stunted and die at any stage
Bacterium overwinters in corn debris near soil surface
and in the seed
Next time—
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Quiz!