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Sweet Corn Diseases

Fungal. Virus. Sweet Corn Diseases. Common Rust - Puccinia sorghi Smut - Ustilago maydis Northern Corn Leaf Blight - Exserohilum turcicum (Helminthosporium turcicum). Maize Dwarf Mosaic. Maize Dwarf Mosaic Virus. Maize Dwarf Mosaic Virus. Aphid Vectors.

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Sweet Corn Diseases

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  1. Fungal Virus 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

  6. 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

  7. Common Maize Rust

  8. Common Maize Rust

  9. Maize Dwarf Mosaic Virus & Rust

  10. 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

  11. 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

  12. Smut of Sweet Corn

  13. Smut of Sweet Corn

  14. Smut of Sweet Corn

  15. 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 Smut of Sweet Corn - Key Points

  16. 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). Smut of Sweet Corn - Control Strategies

  17. Northern Corn Leaf Blight

  18. Northern Corn Leaf Blight

  19. Northern Corn Leaf Blight

  20. 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 Northern Corn Leaf Blight - Key Points

  21. Some resistant varieties are available Currently registered fungicides are available for commercial production. Northern Corn Leaf Blight - Control Strategies

  22. Hail Injury

  23. Hail Injury

  24. Sweet Corn Disease Resistance* WI= recommended for WI gardens, MD= maize dwarf mosaic, NB= no. corn leaf blight, R=rust, SB= so. corn leaf blight, SM =smut, SW=Stewart’s wilt, BW=bacterial wilt, C=cold * 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, R=rust, SB= so. corn leaf blight, SM =smut, SW=Stewart’s wilt, BW=bacterial wilt, C=cold * 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, R=rust, SB= so. corn leaf blight, SM =smut, SW=Stewart’s wilt, BW=bacterial wilt, C=cold * 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, R=rust, SB= so. corn leaf blight, SM =smut, SW=Stewart’s wilt, BW=bacterial wilt, C=cold * 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, R=rust, SB= so. corn leaf blight, SM =smut, SW=Stewart’s wilt, BW=bacterial wilt, C=cold * 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, R=rust, SB= so. corn leaf blight, SM =smut, SW=Stewart’s wilt, BW=bacterial wilt, C=cold * 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, R=rust, SB= so. corn leaf blight, SM =smut, SW=Stewart’s wilt, BW=bacterial wilt, C=cold * 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, R=rust, SB= so. corn leaf blight, SM =smut, SW=Stewart’s wilt, BW=bacterial wilt, C=cold * See UWEX Publication A3110 for current disease resistant varieties

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