Loose smut (barley)

Loose smut is found in all barley growing areas, but is more common in areas of high humidity and rainfall. Thus, the disease is especially prevalent in Western Australia. Infection levels in susceptible varieties have ranged from 0-25 per cent, resulting in corresponding yield losses.

Masses of spores replace the grain in the head during maturation. When the head emerges the spores are maintained in a thin membrane but this soon ruptures, releasing the spores. All that remains of the head is a bare stalk.

Loose smut of barley, like wheat, is caused by the fungus Ustilago tritici (U. nuda). However, the strain of loose smut that attacks wheat does not attack barley and vice-versa.

Life cycle

The loose smut fungus survives as a dormant fungal thread inside the embryo of barley seed. The pathogen is activated when the infected seed germinates, and it extends toward the growing point of the plant.

Evident from flowering onwards when the plant begins to form the head, the fungus invades all of the young head tissue except for that of the rachis (backbone). Production of plant growth hormones by the fungus results in infected plant heads reaching flowering earlier than healthy heads.

The head produced by the infected plant contains black spore masses in place of the grain. The spores are loosely held and are easily spread by wind onto neighbouring healthy plants. Because flowering of infected heads occurs earlier than healthy heads, production and release of spores occurs when the rest of the crop is flowering. Spores are blown by the wind into the flowers of the healthy plants. The spores enter the ovaries and become part of the developing grain. In this way, seed for the following year becomes infected.

Control

• Treat the seed with a recommended seed treatment (Foliarflo-C, Vitaflo C, Vitavax 200FF, Rancona C, Rancona Dimension)
• Sow disease free seed
• Sow resistant barley varieties