1. Unit 1: Corn Diseases

2. Unit 1: Corn Diseases Corn Smut Caused by fungus: Ustilago maydis
Most widely recognized corn disease
Symptoms:
Complete barrenness in most plants
Result:
Reduced grain development
~30% yield loss

3. Unit 1: Corn Diseases Appears as galls on both the ear and stalk
White at first, but develop into dark lesions w/ dark spores inside whitish membrane
Galls break and scatter spores
Found on:
Ears
Near midrib of the leaf
Nodal buds on the stem
More likely to attack vigorous growing plants
Not poisonous to livestock

4. Unit 1: Corn Diseases Smut organism lives in the soil Treatment:
Seed disinfection or treatment is ineffective, except to prevent spread to new fields
Treatment:
Crop rotation
Don’t spread manure smut infested manure on fields
Many resistant hybrids

5. Unit 1: Corn Diseases Head Smut Galls on ear and tassels
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

6. Unit 1: Corn Diseases Control:
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

7. Unit 1: Corn Diseases Root, Stalk, & Ear Rot Effects:
Reductions in field stand
Reductions in plant vigor
Chlorosis
Barrenness
General blighting of the plant
Rotting of the ear

8. Unit 1: Corn Diseases Stalk Rot Caused by fungal infestations:
Ear rot:
Gibberella, Fusarium, Aspergillus, & Pythium spcs.
Root rot:
Pythium, Gibberella, Diplodia spcs.
Stalk rot:
Fusarium, Gibberella, Diplodia
Stalk Rot
Genetic resistance not available

9. Unit 1: Corn Diseases Problems tend to occur under certain conditions
Symptoms prevalent when plant is stressed
Stresses:
High N w/ low K
High moisture mid to late season after dry early season
High moisture stress early in season & during grain fill
High leaf disease pressure
Insect damage
Select hybrids resistant to the above stresses & have good soil fertility

10. Unit 1: Corn Diseases Ear rot
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

11. Unit 1: Corn Diseases Root rot 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
Develops on infested kernels
Crown roots rot, weak plants die
Subcrown roots appear dry, brown instead of healthy white

12. Unit 1: Corn Diseases
Little evidence that root rot fungi advance up the stalk
Most serious under dryland conditions
Stalks will die and fall
Prevention:
Use disease-free treated seed
Plant at proper soil temperature
Balance soil nutrients
Plant resistant hybrids

13. Unit 1: Corn Diseases Leaf Diseases
Chemical seed disinfectants are effective
Captan, metalaxyl, fludioxonil
Increase yield, stand, vigor
Leaf Diseases
Northern Corn Leaf Blight
Infection of the lower leaves
Boat-shaped, grayish lesions
Spread to other leaves in cool, damp weather
Can cause leaf death

14. Unit 1: Corn Diseases Southern Corn Leaf Blight Treatment:
Use resistant hybrids
Has caused losses mostly in the East & South
Significant damage as far West as NE
Southern Corn Leaf Blight
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

15. Unit 1: Corn Diseases Gray Leaf Spot
Problem since 1925 from Atlantic states to eastern corn belt
Cool temps w/ prolonged overcast days
Lesions can be confused w/ other blight diseases
Mature lesions are rectangular restricted by leaf veins
Signified by yellow halo
Lesions can join causing blight of large portion of the leaf

16. Unit 1: Corn Diseases Stewart’s Wilt Goss’s Wilt
Found throughout the Corn Belt
Carried by the corn flea beetle
Symptoms:
Long, water-soaked lesions that can extend the length of the leaf
Leaves turn necrotic
Goss’s Wilt
Water-soaked lesions forming next to leaf veins
Stalks can be discolored

17. Unit 1: Corn Diseases Next time— Quiz!
Affected plants can be stunted and die at any stage
Bacterium overwinters in corn debris near soil surface and in the seed
Next time—
Quiz!