Smut and bunt diseases of cereal - biology, identification and management

Cereal smut and bunt diseases are caused by fungi which parasitise the host plant and produce masses of soot-like spores in the leaves, grains or ears. These fungi are damaging pathogens of cereal crops, reducing yield and quality of harvested grain. In many cases grain receival points have low or zero tolerance of smut contaminated grain. This page describes how to identify, understand and avoid or manage smut and bunt diseases in wheat, barley and oats. It replaces Farmnote 455.

The major Western Australian cereal crops, wheat, barley and oats, are susceptible to a range of smut and bunt diseases. Generally, smut diseases are host specific, meaning that smut of one cereal crop will not infect others (for example, loose smut of wheat does not infect barley or oats). Smut diseases have one of two distinct life cycles: internally seed-borne or externally seed-borne. It is important to know the type of smut and its life cycle in order to determine effective control options.

Internally seed-borne smut diseases

Loose smut of barley and wheat are internally seed-borne and carried as a small colony of fungus inside the seed embryo rather than as spores on the seed coat. These are the only internally seed-borne smuts that occur in Australian cereal crops. Contaminated machinery and soil do not transmit these diseases.

Loose smut of wheat and barley

Loose smut of barley (Ustilago nuda) and wheat (Ustilago tritici) are caused by different fungal species specific to the crop they infect, however they have similar life cycles. Infected seed shows no symptoms and appears normal. When infected seed germinates, the fungus becomes active and grows slowly in the growing point of the plant. Diseased plants appear to grow normally but may be slightly taller and earlier maturing than surrounding healthy plants. At heading, the fungus forms a compact spore mass to replace all florets within the cereal head (Figure 1).

A close up of barley heads affected with loose smut

Figure 1 Loose smut of barley. Close up view of barley heads affected with loose smut

All tillers on an infected plant can produce smutted heads and infected plants produce little or no grain. The black powdery spores blow away to leave a bare stalk or rachis (Figure 2). The spores are released as the rest of the crop is flowering. They infect the developing grains of healthy plants and remain dormant until sown the next season. Frequent rain showers and high humidity at flowering favour infection. The higher rainfall southern areas of Western Australia are traditionally the worst areas for loose smut of wheat and barley. Further information is available on the my crop pages: Diagnosing loose smut in wheat and Diagnosing loose smut in barley.

loose smut spores have blown away to leave only the rachis remaining

Figure 2 Only the rachis (stalk) remains after the spores of loose smut blow away

A 2014 DAFWA nursery trial reflected field observations that Hindmarsh and its sister line La Trobe are both more likely to be affected by loose smut than the majority of other varieties tested including Bass, Commander, Flinders, Gairdner, Granger, Scope CL, Skipper or Wimmera.

Yield loss is directly related to the level of infection in sown seed. Grain receival points accept small quantities of loose smut contamination in wheat and barley before applying dockages.

How to avoid or manage it

The disease is controlled by pickling seed with a systemic fungicide which penetrates the developing seedling to kill the internal infection. Cereal seed dressing fungicides differ in their efficacy for smut management with trial research demonstrating that some seed dressings can reduce the incidence of loose smut in heavily infected seed to nearly zero. The correct application of seed dressings is critical to ensuring adequate control. In-furrow and foliar fungicide applications are not effective. The factsheet - Controlling loose smut of barley, which compares seed dressings, is available from this page.

Contact information

Geoff.j Thomas
+61 (0)8 9368 3262
Kithsiri Jayasena
+61 (0)8 9892 8477
Ciara Beard
+61 (0)8 9956 8504
Andrea Hills
+61 (0)8 9083 1144
Page last updated: Wednesday, 18 January 2017 - 11:52am