Bunt

Tilletia laevis, Tilletia caries

Bunt is a disease of wheat, rye and other grasses and is known by several names including common bunt, stinking bunt, stinking smut, ball smut and covered smut. Bunt is caused by two fungi species which produce masses of soot-like spores in the grains or ears. Plants may appear stunted and reductions in yield and grain quality are common. There is a zero tolerance for grain contaminated with bunt at receival points across Australia. Karnal bunt is a highly invasive disease which significantly affects grain quality, so the Australian grains industry is working hard to prevent its introduction into Australia.

Refer to links below for more information on other smuts and bunt.

Description

Infected plants are difficult to identify until harvest, as the fungus remains hidden inside the grain as a mass of stinking bunt spores. Infected mature heads can appear darker and glumes are often spread open by the large bunt balls within the glume. Grains look greyish-brown and if the seed coat is broken or crushed, spores are released emitting a stinking fish-like odour.

Bunt is seed and soil-borne and when bunt balls break during harvest, the surrounding seed and soil becomes contaminated. If contaminated grain is sown, or seed is planted into contaminated soil, bunt spores germinate and infect the growing point of wheat seedlings. The fungus grows within the plant, generally without any symptoms until the head develops. In infected plants, the fungus replaces the grain in the head, producing masses of spores.

Control

It is important to source clean seed and thoroughly clean machinery used to harvest or handle contaminated grain. Avoid planting wheat for at least one year back into a paddock where bunt was diagnosed and if possible, plant a tolerant variety of wheat. Cool (5-15 °C) and moist conditions are required for bunt spores to germinate, consequently early sowing into warmer soils may help reduce infection.

Seed treatments are very effective at controlling bunt in wheat and should be applied every year to prevent infection. Good coverage of the grain with an effective seed treatment is essential to maintain disease free crops. EverGol® Prime, EverGol® Energy, Jockey® Stayer® and Raxil® T are registered for the control of bunt (common bunt Tilletia. spp.) in wheat.

Related Pests

Loose smut

Ustilago nuda - (loose smut barley), Ustilago tritici - (loose smut wheat), Ustilago avenae - (loose smut oats)

Affecting wheat, barley and oats, loose smut is rarely seen due to the regular use of effective seed treatments. Each cereal is infected by a particular strain of loose smut, therefore loose smut in wheat cannot infect barley or oats, for example. There is a minimal to zero tolerance of grain contaminated with loose smut at most grain receival points across Australia.

Covered smut

Ustilago hordei (oats and barley), Tilletia laevis (wheat)

Covered smut is caused by the same fungal pathogen in barley and oats, but in wheat it is caused by a different pathogen. Covered smut in wheat has several names including ball smut, stinking smut and common bunt. Like other cereal smuts, covered smut is generally controlled effectively with seed dressings. Covered smut can cause yield losses and there is a nil tolerance of grain contaminated with covered smut at receival points in Australia.

Refer to the link below for more detailed information on bunt.

Flag smut

Urocystis tritici

Flag smut was historically an important disease of wheat in Australia, however through the regular use of seed treatments and planting resistant varieties, it is now effectively controlled. Flag smut differs from other cereal smut diseases as symptoms appear on the leaves rather than the heads. Yield losses of 5 – 20 per cent have been recorded from flag smut.

References

Department of Primary Industries and Regional Development (DPIRD) (2015), ‘Diagnosing common bunt in wheat’, https://www.agric.wa.gov.au/mycrop/diagnosing-common-bunt-wheat

Holloway, G (2012), ‘Bunts and Smuts of Cereals’, Agriculture Victoria, http://agriculture.vic.gov.au/agriculture/pests-diseases-and-weeds/plant-diseases/grains-pulses-and-cereals/bunts-and-smuts-of-cereals

Thomas, G, Jayasena, K, Beard, C and Hills, A (2017), ‘Smut and bunt diseases of cereal – biology identification and management’, Department of Primary Industries and Regional Development (DPIRD), https://www.agric.wa.gov.au/print/node/326