Sweet Corn Diseases

1
Sweet Corn Diseases

• Common Rust - Puccinia sorghi
• Smut - Ustilago maydis
• Northern Corn Leaf Blight - Exserohilum turcicum
  (Helminthosporium turcicum)

• Maize Dwarf Mosaic

2
Maize Dwarf Mosaic Virus
3
Maize Dwarf Mosaic Virus
4
Aphid Vectors
5
Maize Dwarf Mosaic Virus - Key Points

• Symptoms
• Mosaic pattern of light and dark green streaks
  along and between veins
• Most striking in whorl stage
• Evident on flag and husk leaves
• Poor cob fill, stunted plants, reduced yield
• Increased rust problems
• Many strains of MDMV identified
• Strain A Source Johnsongrass
• Strain B Johnsongrass is not host
• Infects all types of corn and many grass species
• Transmission Aphid species
• Corn leaf aphid is primary vector
• Nonpersistent transmission

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Maize Dwarf Mosaic Virus - Control Strategies

• Resistant cultivars
• Planting to avoid peak aphid flights
• Eliminate perennial grass hosts
• Insecticide sprays may control aphids but not
  transmission

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Common Maize Rust
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Common Maize Rust
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Maize Dwarf Mosaic Virus Rust
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Sweet Corn Rust - Key Points

• Pathogen Puccinia sorghi
• Symptoms
• circular to oval, orange-brown pustules
• on leaves husks, necks, tassels
• Can overwinter in southern US as urediospores,
  these spores are wind-borne to new areas as corn
  is planted progressively northward
• Infection favored by
• temperatures 59-68 F
• about 24 hours of very high humidity or dew for
  germination and infection
• Multiple secondary cycles can occur on corn
• Heavy rain may wash spores away and destroy them

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Sweet Corn Rust - Control Strategies

• Resistant cultivars
• Cultural practices
• Rotation
• Field preparation
• Fungicides
• Bravo - fresh market only
• maneb
• mancozeb
• Tilt
• 4 fl. oz/A when rust first appears
• 7-14 day schedule, 14 day PHI
• 4 spray maximum

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Smut of Sweet Corn
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Smut of Sweet Corn
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Smut of Sweet Corn
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Smut of Sweet Corn - Key Points

• Pathogen Ustilago maydis
• Affects both field corn and sweet corn but more
  severe on sweet corn
• All above ground parts of the corn plant are
  susceptible
• Fungus can invade directly through cell walls, or
  through wounds
• Fungal galls are edible in early stages of
  formation
• When the fungus breaks through the membrane
  cover, spores are disseminated to new sites by
  wind and splashing rain
• Overwinters as resistant spores in galls and
  plant debris on soil surface

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Smut of Sweet Corn - Control Strategies

• Resistant varieties
• Avoid mechanical injury to the corn plant
  especially following a rain.
• Maintain good fertility
• Cut off and burn galls before they burst (for the
  home gardener).

17
Northern Corn Leaf Blight
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Northern Corn Leaf Blight
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Northern Corn Leaf Blight
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Northern Corn Leaf Blight - Key Points

• Pathogen Exserohilum turcicum (Helminthosporium
  turcicum)
• Symptoms
• Lesions are long (1-8 inches), elliptical in
  shape, grayish-green or tan
• Severe infection can lead to death of the leaf
• Ear infection does not occur, but lesions can be
  found on the husks.
• Affects at least 22 plants in the grass family
  including corn, sorghum, Johnsongrass, Sudangrass
• Disease favored by frequent rain, high RH, heavy
  dew and relatively low temperature
• Disease is limited by warm, dry periods
• Overwinters as soil-borne debris from infected
  plants or in dried leaves on standing plants

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Northern Corn Leaf Blight - Control Strategies

• Some resistant varieties are available
• Currently registered fungicides are available for
  commercial production.

22
Hail Injury
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Hail Injury
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Sweet Corn Disease Resistance
WI recommended for WI gardens, MD maize dwarf
mosaic, NB no. corn leaf blight, Rrust, SB so.
corn leaf blight, SM smut, SWStewarts wilt,
BWbacterial wilt, Ccold See UWEX Publication
A3110 for current disease resistant varieties
25
Sweet Corn Disease Resistance
WI recommended for WI gardens, MD maize dwarf
mosaic, NB no. corn leaf blight, Rrust, SB so.
corn leaf blight, SM smut, SWStewarts wilt,
BWbacterial wilt, Ccold See UWEX Publication
A3110 for current disease resistant varieties
26
Sweet Corn Disease Resistance
WI recommended for WI gardens, MD maize dwarf
mosaic, NB no. corn leaf blight, Rrust, SB so.
corn leaf blight, SM smut, SWStewarts wilt,
BWbacterial wilt, Ccold See UWEX Publication
A3110 for current disease resistant varieties
27
Sweet Corn Disease Resistance
WI recommended for WI gardens, MD maize dwarf
mosaic, NB no. corn leaf blight, Rrust, SB so.
corn leaf blight, SM smut, SWStewarts wilt,
BWbacterial wilt, Ccold See UWEX Publication
A3110 for current disease resistant varieties
28
Sweet Corn Disease Resistance
WI recommended for WI gardens, MD maize dwarf
mosaic, NB no. corn leaf blight, Rrust, SB so.
corn leaf blight, SM smut, SWStewarts wilt,
BWbacterial wilt, Ccold See UWEX Publication
A3110 for current disease resistant varieties
29
Sweet Corn Disease Resistance
WI recommended for WI gardens, MD maize dwarf
mosaic, NB no. corn leaf blight, Rrust, SB so.
corn leaf blight, SM smut, SWStewarts wilt,
BWbacterial wilt, Ccold See UWEX Publication
A3110 for current disease resistant varieties
30
Sweet Corn Disease Resistance
WI recommended for WI gardens, MD maize dwarf
mosaic, NB no. corn leaf blight, Rrust, SB so.
corn leaf blight, SM smut, SWStewarts wilt,
BWbacterial wilt, Ccold See UWEX Publication
A3110 for current disease resistant varieties
31
Sweet Corn Disease Resistance
WI recommended for WI gardens, MD maize dwarf
mosaic, NB no. corn leaf blight, Rrust, SB so.
corn leaf blight, SM smut, SWStewarts wilt,
BWbacterial wilt, Ccold See UWEX Publication
A3110 for current disease resistant varieties