Plant Pathology: Extension: Plant Disease Library

Loose Smut - Ustilago nuda (barley); Ustilago tritici (wheat)

Barley - Hordeum vulgare
Wheat - Triticum aestivum

Symptoms are seen when the grain head emerges. All of the flower tissues are replaced by masses of black powdery smut spores (teliospores). Masses of smut spores in the head can be seen macroscopically and with a hand lens.

Disease Symptoms:
Symptoms are seen when the grain head emerges. All of the flower tissues are replaced by masses of black powdery smut spores (teliospores). At first the mass of spores is covered by a thin gray membrane which disintegrates quickly. The smut spores are dispersed rapidly by wind and within a few days only the remnants of the rachis, the central structure of the head to which florets are attached, remains. Heads on smut-infected tillers often emerge earlier than those on healthy plants. Most or all heads on an infected plant are smutted.

Signs:
Teliospores develop in loose masses. The spores are nearly spherical, yellow-brown to olive-brown, and appear small at 200X magnification. The embryo of the seed is infected but there is no visual sign of infection.

Masses of smut spores in the head can be seen macroscopically and with a hand lens. Mount smut spores in water and observe at 200-400X. Specialized techniques are available to remove and stain seed embryos to see fungal growth.

Disease Management:
Certified seed which is field-inspected should be planted to prevent loose smut. Seed treatment with systemic fungicides effectively controls loose smut (see GA Pest Control Handbook or Wheat Production Guide). Loose smut can increase rapidly from one year to the next if untreated seed from the same farm or seed source is used. Therefore, seed saved from the same farm should be treated at least every other year. Most cultivars are very susceptible.

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Compiled by: Barry M. Cunfer, UGA Plant Pathologist, Griffin, GA