Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Corn (Zea mays) -- Common Smut
 
Cause: The fungus, Ustilago zeae (syn. = U. maydis), overwinters in soil as teliospores. Spores may survive 2 or 3 years. When cattle feed on corn stalks, spores are carried through into the manure. Spores may be wind-blown long distances. In the Pacific Northwest, the fungus attacks only corn. Younger plants are more susceptible. After ears form, plants are resistant. Any aboveground plant part may become infected. Infection increases with injury from hail, detasseling, earworms, or insect borers. Smut usually is more severe on plants heavily fertilized with nitrogen.

In a warm growing season, the amount of smut coincides closely with soil moisture, especially in June. If temperatures are lower than average, there may be little smut even though soil moisture is high. Below 61°F there is little spore germination. Optimum for spore germination is 79 to 100°F. Higher temperatures and/or higher spore numbers likely contribute to generally increased levels of infection in corn fields planted later in the season (June) compared to those planted prior to May 15th in the Columbia Basin. Moist soil that has been manured generally favors smut infection. 'Golden Jubilee' and 'Super Sweet Jubilee' are very susceptible.

Symptoms: Young, and/or actively growing parts of the plant are susceptible to infection. Infected tissues are transformed into galls by the fungus, sometimes 4 to 5 inches in diameter, containing a mass of black, greasy, or powdery spores. Spores are covered with a greenish white to silvery white membrane. The covering becomes dry and brittle, breaks open, and permits the black powdery contents to spill out. These spores can fall to the ground or become wind borne. There is no stringy mass of vascular tissue as in head smut.

Sweet corn ear infected with common corn smut.

Another sweet corn ear infected with common corn smut, some healthy kernels are visible.

Sometimes common corn smut will infect corn seedlings at the base of plants and such infected plants may die.
 
Cultural control: Controls generally have been unsatisfactory.

  1. 1. Planting tolerant cultivars is the best control. Cultivars that show improved resistance over two years of testing in the Columbia Basin include: 'Elite', 'Chase', 'Conquest', 'Eliminator', 'Diva', and 'Marvel'.
  2. Avoid mechanical injury to plants during cultivation and spraying.
  3. Provide a well-balanced soil fertility.
  4. Cut and ensile green corn before spores mature. In home gardens, remove and throw away or burn galls before they rupture.
  5. Plant before May 15th.
Chemical control: Seed treatment is of no value because spores are not transmitted with the corn seed. Topical applications of fungicides may prove to be effective but none are recommended at this time.
Content edited by: Phil Hamm and Cynthia M. Ocamb on January 1, 2009
 
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