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Fundamentals of Corn Pathology Paul Vincelli University of Kentucky
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Disease triangle What are some factors that favor disease development in KY corn production?
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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
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Almost all disease management in corn is preplant.
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Leaf diseases
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Gray leaf spot
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Hybrid differences Leaf blighting
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Northern leaf blight Image by K. Leonard and E. G. Suggs Courtesy of the American Phytopathological Society
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Large, coalescing lesions of NLB
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Susceptible and resistant reactions to Northern leaf blight Image by K. Leonard and E. G. Suggs Courtesy of the American Phytopathological Society Susceptible hybrid Chlorotic lesion Reaction (Ht resistance)
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NLB: Susceptible vs Ht resistance
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NLB: susceptible (R) vs Ht resistance (L) Henderson County, 2004
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Lodging from Severe NLB Courtesy Bill Meachum, Pioneer
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Rusts Southern rust Common rust Rust spores
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Brown spot
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Purple leaf sheath
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Holcus spot
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Infection of foliage by bacteria Fire blight
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Stalk rots
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Anthracnose lower stalk rot in mature plants
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Anthracnose top dieback G. Munkvold
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Diplodia stalk rot
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Gibberella stalk rot
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Gibberella (left) and Diplodia (right) stalk rots
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Stalk rot = disintegration of pith Charcoal stalk rot
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Factors that Enhance Corn Stalk Rots High plant populations High nitrogen rates High levels of leaf disease
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High-yield production can favor stalk rots
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Seedling diseases
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Pythium damping off Data of Woltz and TeKrony Karen Rane, Purdue U.
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Anthracnose in seedlings
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Other Diseases
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Common Smut
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Maize dwarf mosaic
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Maize chlorotic dwarf virus
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Crazy top
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Ear and kernel rots Mycotoxins
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Diplodia fungus
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Diplodia ear rot
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Fusarium ear rot: Fumonisins
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Gibberella ear rot Produces zearalenone and DON
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Aspergillus ear rot: Aflatoxins
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Extension publications on mycotoxins
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Maximum Fumonisin Levels Recommended by US FDA Intended use Max fumonisins (FB 1 +FB 2 +FB 3 ) Equids and rabbits5 ppm (no more than 20% of diet) Swine and catfish20 ppm (no more than 50% of diet) Human foods2-4 ppm
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Corn with 26 ppm fumonisins
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FDA Aflatoxin Action Levels Action Level (parts per billion) CommoditySpecies 0.5MilkHumans 20Any food except milk Humans 20FeedLivestock* *Exceptions for breeding cattle, breeding swine, mature poultry, finishing swine, & finishing beef cattle
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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
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Crop stress can favor preharvest mycotoxin contamination Fusarium ear rot Aspergillus ear rot
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Harvest management can influence postharvest accumulation of mycotoxins
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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
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Testing corn samples UK Grain Quality Testing Lab Attn: 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
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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
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Overall Yield Response University (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/ac Percent wins: 79% Economically beneficial*: 60% Average net return: $12.63/ac (121 hybrids from 20 companies) PIONEER SUMMARY
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