Fundamentals of Corn Pathology

Paul Vincelli

University of Kentucky

Disease triangle

What are some factors that favor disease development in KY corn production?

Corn residue can favor certain diseases

What is the most practical way to kill out pathogens surviving in corn residue?

Spores of gray leaf spot fungus

Almost all disease management in corn is

preplant.

Leaf diseases

Gray leaf spot

Gray leaf spot

Hybrid differencesLeaf blighting

Northern leaf blight

Image by K. Leonard and E. G. SuggsCourtesy of the American Phytopathological Society

Large, coalescing lesions of NLB

Susceptible and resistant reactions to Northern leaf blight

Image by K. Leonard and E. G. SuggsCourtesy of the American Phytopathological Society

Susceptiblehybrid

Chlorotic lesionReaction (Ht resistance)

NLB: Susceptible vs Ht resistance

NLB: susceptible (R) vs Ht resistance (L)

Henderson County, 2004

Lodging from Severe NLB

Courtesy Bill Meachum, Pioneer

Rusts

Southern rust

Common rust

Common rust

Rust spores

Brown spot

Purple leaf sheath

Holcus spot

Infection of foliage by bacteria

Fire blight

Stalk rots

Anthracnose lower stalk rot

in mature plants

Anthracnose top dieback

G. Munkvold

Diplodia stalk rot

Gibberella stalk rot

Gibberella (left) and Diplodia (right) stalk rots

Stalk rot = disintegration of pith

Charcoal stalk rot

Factors that EnhanceCorn Stalk Rots

•High plant populations

•High nitrogen rates

•High levels of leaf disease

High-yield production can favor stalk rots

Seedling diseases

Pythium damping off

Data of Woltz and TeKrony

Karen Rane, Purdue U.

Anthracnose in seedlings

Other Diseases

Common Smut

Maize dwarf mosaic

Maize chlorotic dwarf virus

Crazy top

Ear and kernel rotsMycotoxins

Diplodia fungus

Diplodia ear rot

Fusarium ear rot: Fumonisins

Gibberella ear rot

Produces zearalenone and DON

Aspergillus ear rot: Aflatoxins

Extension publications on mycotoxins

Maximum Fumonisin Levels Recommended by US FDA

Intended use

Max fumonisins (FB1+FB2+FB3)

Equids and rabbits 5 ppm(no more than 20% of diet)

Swine and catfish 20 ppm(no more than 50% of diet)

Human foods 2-4 ppm

Corn with 26 ppm fumonisins

FDA Aflatoxin Action Levels

Action Level (parts per billion)

Commodity Species

0.5 Milk Humans

20 Any food except milk

Humans

20 Feed Livestock*

*Exceptions for breeding cattle, breeding swine, mature poultry, finishing swine, & finishing beef cattle

Factors That Enhance Corn Ear and Kernel Rots and Preharvest Mycotoxin

Accumulation

• Hot, dry weather during silking or grain fill

• Delayed harvest

• Injury to kernels (insects, birds)

• Hybrids with ears at maturity that are:

- upright

- incomplete husk coverage

Crop stress can favor preharvest mycotoxin contamination

• Fusarium ear rot• Aspergillus ear rot

Harvest management can influence postharvest accumulation

of mycotoxins

Reducing risks of mycotoxins in storage

• Adjust combine for minimum kernel damage• Dry below 15.5% within 24-48 hours of shelling• Clean storage facilities and control insects• Aerate and check for heating and crusting

Testing corn samples

UK Grain Quality Testing LabAttn: Michael D. Montross 

Biosystems & Agricultural Engineering

128 Barnhart Bldg. 

University of Kentucky

Lexington, KY  40546-0276

Voice: (859) 257-3000 X106

Fax: (859) 257-5671

Email: montross@baeuky.edu

Headline 6 fl oz, Quilt 14 fl oz, Stratego 10 oz

63 out of 168 = 38% of the time had a yield increase of 6 bu/A or greater.

Mean = 3 bu/A increase over the untreated

-35-30-25-20-15-10

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1015202530

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Overall Yield ResponseUniversity (68) and On-Farm (121) Trials

*Assumes $3.75/bu corn and $20/ac for fungicide. Break-even response = 5.3 bu/ac

Overall yield advantage: 8.7 bu/acPercent wins: 79%Economically beneficial*: 60%Average net return: $12.63/ac

(121 hybrids from 20 companies)

PIONEER SUMMARY