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.

Description

Covered smut is a disease affecting seed heads and generally remains undetected until head emergence. Infected heads may emerge later than healthy ones and the ears often break through the sheath below the flag leaf. Infected heads are filled with dark brown to black sooty spores instead of grains. Covered smut spores are held tightly compared to loose smut spores. Infection is encouraged by wet conditions and warm temperatures (15 - 20 °C) during flowering.

Spores from covered smut are seed and soil-borne. During harvest, spores from infected heads contaminate healthy clean seed, soil and machinery, where they remain dormant. Spores on contaminated seed used for planting germinate at the same time as seedlings, infecting the plant. Conditions favouring infection are early sowing into dry soil and warm (15 - 21 °C) temperatures. Following infection, the fungus grows within the plant, appearing later in the heads as masses of spores, replacing grains.

Control

There are no control options in-crop for covered smut, therefore preventative control measures should be employed. Following an outbreak of covered smut, growers should source clean seed and grow resistant varieties where possible.

Regular use of seed dressings, particularly after an outbreak, is important. Ensure good coverage of grains to ensure seed dressings provide effective control of covered smut. Jockey^® Stayer^®, EverGol^®Prime, EverGol^® Energy, Raxil^® T and Hombre^®Ultra can be used to control covered smut (common bunt) in wheat. Jockey Stayer and EverGol Energy are registered for the control of covered smut in barley and EverGol Prime, Raxil T and Hombre Ultra are all registered for the control of covered smut in barley and oats.

Related Pest

Smut

Ustilago nuda - (loose smut barley), Ustilago tritici - (loose smut wheat), Ustilago avenae - (loose smut oats), Ustilago hordei - (covered smut oats and barley), Urocystis tritici - (flag smut wheat), Tilletia spp. – (covered smut or bunt of wheat)

Smut is a fungal disease affecting cereals crops in Australia. Commonly known as loose, flag or covered smut; hosts include wheat, barley and oats. The pathogens causing smut produce masses of soot-like spores in the leaves, grains and ears, causing significant reductions in both grain quality and yield. Each pathogen is specific to each type of cereal and therefore cannot be transferred between them. In Australia, there is a minimum to zero tolerance for grains contaminated with smut at grain receival points.

Refer to the links below for more detailed information on smut in each crop.

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.

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.

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.

References

CropPro (Viewed Nov 2019), ‘Covered smut of barley’, http://www.croppro.com.au/crop_disease_manual/ch04s06.php

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

Department of Primary Industries and Regional Development (DPIRD) (2017), ‘Diagnosing smut in oats’, https://www.agric.wa.gov.au/mycrop/diagnosing-smut-oats

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