Loose Smut of Wheat | Pioneer Seeds

Loose Smut of Wheat

Pathogen Facts

  • Loose smut of wheat is caused by the seedborne fungal pathogen Ustilago tritici.
  • Loose smut infections are favored by cool and humid conditions during flowering (60-72 °F).
  • Grain is completely replaced by spores, rendering yield loss equivalent to the number of infected heads. Losses are usually below 1%, but losses up to 27% have been reported.

Photo - cloesup - wheat leaf rust pathogen spores.

Ustilago tritici teliospores. Photo courtesy of Bruce Watt, U. of Maine, Bugwood.org.

Photo - closeup - wheat leaf rust pathogen spores.

Seeds are entirely replaced by masses of brown teliospores. Photo courtesy of Bruce Watt, U. of Maine, Bugwood.org.

Symptoms and Signs

  • Early symptoms are minor and can range from yellow leaf streaks to stiff, dark green leaves.
  • Spikelets of wheat are replaced with the fungus, appearing as sooty black teliospores.
  • Infected plants head out early and are visibly darker than a normal wheat head.
  • Spores quickly blow away in the wind or are disturbed by raindrops because they are not enclosed in a seed coat.

Photo - Wheat leaf with leaf rust pustules.

Close up of teliospores on what would have been a wheat head. Photo courtesy of Bruce Watt, U. of Maine, Bugwood.org.

Life Cycle

  • The pathogen overwinters within infected wheat seeds and becomes active when the seed germinates.
  • After germination, the fungus colonizes the meristem tissue, growing systemically within the plant.
  • Ustilago tritici matures in the growing point and the developing grain of the infected plant.
  • Dark colored teliospores completely replace the rachis, and can be blown to uninfected plants during flowering or kernel development.

Management Considerations

  • Because this disease is seedborne, seed should not be saved from infected fields for future planting.
  • Certified seed is required to have a low amount of disease, planting certified seed ensures that Ustilago tritici will not be present in fields.
  • If planting certified seed is not preferable, systemic fungicide seed treatments are readily available, and effective against this pathogen.

Photo - Wheat plot with different levels of resistance to leaf rust.

Loose smut of wheat with darker coloration. Photo courtesy of Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org.

References



Author: Madeline Henrickson
May 2020

The foregoing is provided for informational use only. Please contact your Pioneer sales professional for information and suggestions specific to your operation. Product performance is variable and depends on many factors such as moisture and heat stress, soil type, management practices and environmental stress as well as disease and pest pressures. Individual results may vary..