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Ministry of Agriculture, Food and Rural Affairs

Common Smut

Common smut Common smut Common smut
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Beginner

Scientific Name
Ustilago maydis

Identification

  • Greyish smut galls up to 10 cm (4 in.) develop on the stalks, ears and tassels
  • Smaller galls appear on the leaves and develop into a hard, dry growth
  • Spore masses are covered with a white membrane which eventually breaks and releases dark-brown or black powdery spores

Often Confused With
N/A

Period of Activity
High temperatures and dry conditions favour the development of common smut.

Scouting Notes
While conducting regular scouting activities, take note of any smut-infected plants.

Thresholds
None established. There are no fungicides that control common smut.

Advanced

Scientific Name
Ustilago maydis

Two corn smut diseases, common and head smut, occur in Ontario with common smut occurring most frequently. In severe cases, over 25% of the plants in some fields can have smut galls.

Identification
Greyish smut galls up to 10 cm (4 in.) in diameter develop on the stalks, ears and tassels, while smaller galls often appear on the leaves. The galls initially have a white membrane cover that eventually breaks and releases dark-brown or black powdery spores. On the leaves, galls develop into a hard, dry growth. Smut galls can replace kernels.

Often Confused With
N/A

Biology
Spores released from the galls are well adapted for Ontario conditions. They survive in soil and crop residues for many years. In the spring, these spores germinate to produce new spores that will infect the rapidly growing areas or injured areas of the plant. The resulting galls will release spores that infect other plants. Disease development is favoured by rain showers, high humidity and warm temperatures.

Common smut overwinters, not only in the soil but in corn residue as well. The spores are spread by wind and rain through splashing. All above-ground plant tissue is susceptible, but infection occurs most often in areas of actively growing tissue.

Common smut incidence increases in fields where the plants have been wounded by hail, frost, drought, mechanical injury, detasselling, herbicide injury, insects or sandblasting. High levels of nitrogen and manure promote this disease.

Period of Activity
High temperatures and dry conditions favour the development of common smut.

Scouting Notes
While conducting regular scouting activities, take note of any smut-infected plants.

Thresholds
None established. There are no fungicides that control common smut.

Management Notes

  • Most corn hybrids have enough resistance to smut to prevent serious outbreaks; however, some smut is present in most fields.
  • Reduce your risk by minimizing mechanical and herbicide injury while maintaining a balanced fertility program.
  • Rotation and cultivation have little effect on the disease since spores can survive for a long time in the soil.