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Plantwise Technical Factsheet

covered smut of barley (Ustilago hordei)

Host plants / species affected
Agropyron (wheatgrass)
Avena sativa (oats)
Bromus (bromegrasses)
Elymus (wildrye)
Hordeum vulgare (barley)
Secale cereale (rye)
Triticum aestivum (wheat)
List of symptoms/signs
Inflorescence  -  black fungal spores
Leaves  -  fungal growth
Symptoms
The presence of the disease is first noticed at ear emergence when the ears appear dark grey due to the masses of teliospores covered by a thin membrane of tissue. The membrane splits at maturity, or during threshing, releasing the spore mass into the atmosphere. The spores are not readily wind-dispersed if the membrane ruptures before harvest as they stick together due to the presence of an oily coating.

Infected plants may be slightly shorter than their healthy neighbours. Affected ears may emerge later than the surrounding crop and in some cases remain trapped within the sheath of the flag leaf (Sherwood, 1997). Infected ears are readily identified by their dark colour and shrivelled awns (Gair et al., 1987). Sori can occasionally be found in stripes on leaves (Singh et al., 1978) and stem galling has also been reported (Srivastava et al., 1978).
Prevention and control

Host-Plant Resistance

Host resistance occurs but is not generally a major factor in breeding programmes as seed treatments have proved to be highly effective in controlling the disease. There are no completely resistant cultivars (Sperlingsson, 1994).

Chemical Control

Control is by the use of fungicide seed treatments. Ethirimol + flutriafol + thiabendazole, fludioxonil and fuberidazole + triadimenol provide effective control (Anon., 1999).

The bacterium Pseudomonas chlororaphis offers effective control with no residual toxicity (Gerhardson et al., 1998).

Cultural Control

Crop inspection and certification of seed crops reduce disease incidence (Paveley et al., 1996).

Impact
Losses from covered smut average less than 1%, but losses of up to 40% have been recorded. The following formula can be used to calculate losses from covered smut. The percentage of infected ears is directly proportional to grain yield loss.

Loss (kg/ha) = Pr x Pa/100-Pr

Pr = percentage infected heads
Pa = actual yield (kg/ha)

The risk of serious loss of in-crop yield from sowing seed saved from certified and treated seed is considered to be low and of moderate risk where seed is saved repeatedly without treatment. The risk to adjacent crops of barley is negligible unless used for seed (Paveley et al., 1996).

In Canada, losses from barley smuts (U. hordei, U. avenae and U. nuda) were 0.9, 0.6 and 0.5% in 1975, 1976 and 1977, respectively (Thomas, 1978). In the Canadian Prairie Provinces during 1983-88, the three barley smuts were estimated to cause an annual yield loss of 0.7 to 1.6%, representing a monetary loss of $8.8 to $13.2 million. U. hordei caused a 0.7% loss in 1987. The highest level of infection in a single field was 40% in 1988 and 30% in 1987 (Thomas, 1989).

U. hordei-infected plants showed reductions in height, tillers/plant, tiller length, ears/plant and ear length in India (Jain et al., 1997). Trials in Rajasthan in 1980-83 showed that fungicides could control covered smut completely. Untreated plots had a covered smut incidence of 45.9%. The yields of treated plots were superior to those of the control (Mathur and Bhatnagar, 1986). Trials in 1968-69 and 1969-70 revealed that fungicide seed treatment against U. hordei increased yield by 33.9 and 40.4%, respectively (Bedi and Singh, 1974).

In east Azerbaijan and Ardebil, field surveys during 1990-1993 revealed that U. hordei was present in 50% of the fields. Covered smut was estimated to cause 1.37% yield loss (Babadoost, 1995). Under Transural conditions, decreased infection by covered smut was observed when barley was sown at a depth of 5-6 cm in late May to early June. These conditions also resulted in an increased yield (Stepanovskikh, 1976). Seed treatments with fungicides have been shown to decrease the incidence of covered and loose smut (U. avenae). Disease incidence was 0.02-0.3% compared with 3.5-17% in the control. Yields were increased by 0.6-4% (Sabel'nikova, 1977).

In Morocco, a 1974-75 survey revealed that U. hordei was present in 84% of barley seed samples obtained from different parts of the country (Lyamani and Rolli, 1979).

In trials with barley infected with U. hordei, untreated crops yielded 4.51 t/ha and had 1041 infected ears/100 m². Seed treatment increased yields by up to 150 kg/ha (Olofsson, 1972).
Related treatment support
 
External factsheets
Department of Agriculture and Food Western Australia Farmnotes, Government of Western Australia, 2011, English language
Department of Agriculture and Food Western Australia Farmnotes, Government of Western Australia, 2005, English language
Bayer CropScience Crop Compendium, Bayer CropScience, English language
CIMMYT Plant Pest and Disease Factsheets, Centro Internacional de Mejoramiento de Maiz y Trigo (CIMMYT) (International Maize and Wheat Improvement Center), English language
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