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.

Description

Plants infected with loose smut may be slighter taller and mature earlier than other plants, however it is generally hard to detect until head emergence. All tillers on infected plants may produce a smutted head and infected heads often emerge before healthy ones. Heads emerge with a mass of dark brown to black spores replacing the grains. A membrane holds the spores loosely which eventually breaks, releasing the spores while rest of the crop is flowering, infecting immature developing seed in barley and wheat. This process is favoured by wet, humid and warm (16 - 22 °C) temperatures. In oats, spores contaminate mature healthy heads of grain, and machinery used to harvest or transport grain can also be contaminated. If untreated, loose smut can cause reductions in both yield and grain quality.

Loose smut in barley and wheat is internally seed-borne. Seed-borne smut survives dormant inside the seed embryo and then starts to grow when the seed germinates. In contrast, spores survive externally on the surface of oat seeds and remain dormant until seed is planted. At sowing, spores germinate infecting the new seedling, this process is favoured by early sowing into warm soil.

Control

Loose smut is effectively controlled through preventative measures. If an outbreak of loose smut is detected, is it advised growers source new clean seed for sowing. Additionally, growers should plant resistant varieties where possible.

Effective control of loose smut can be achieved through the regular use of effective seed treatments. Several seed treatment options are available to control loose smut, including Jockey^® Stayer®, EverGol^® Prime, EverGo^® Energy, Raxil^® T and Hombre^® Ultra.

Jockey Stayer is registered for the control of loose smut in wheat and barley, EverGol Energy for the control of loose smut in wheat, barley, triticale and oats, and EverGol Prime, Raxil T and Hombre Ultra for the control of loose smut in wheat, barley and oats.

Related Pests

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.

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.

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), ‘Loose smut of barley’, http://www.croppro.com.au/crop_disease_manual/ch04s07.php

CropPro (Viewed Nov 2019), ‘Loose smut of wheat’, http://www.croppro.com.au/crop_disease_manual/ch04s04.php

CropPro (Viewed Nov 2019), ‘Smut of oat’, http://www.croppro.com.au/crop_disease_manual/ch04s08.php

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