True Loose Smut

True Loose Smut

Masses of spores emerge in place of normal heads. Plants show no symptoms. The entire head, except for the rachis, is replaced with dusty, dark brown spores covered with a thin membrane. Spore masses may be easily mistaken for false loose smut but are not quite as dark. Spores are released by wind and rain and don’t cause reduction in grain quality for feed but do affect quality of grain grown for seed. Disease development requires sufficient humidity and temperatures between 16°C and 22°C. As the seed germinates, embedded smut mycelium start to grow and penetrate plant tissues near growing point. The fungus grows inside young plants without causing symptoms. Infected seed does not differ visually from healthy seed – only laboratory analysis can detect infection.

Disease Cycle: True Loose Smut (TLS) has a two-year life cycle and the impact of this disease is determined during the flowering stage in the first year. TLS infection is favoured by cool, moist weather in July, which slows and prolongs the flowering period and allows more time for infection to occur. All other smuts, on the other hand, are favoured by seeding into cold soils during the late fall or early spring. As well, different barley varieties have different levels of susceptibility.

When an infected seed germinates, the fungus is activated and colonizes the growing point of the plant. As the heads develop, disease spores take the place of the normal spikelets. At heading, spores mature and disperse to neighbouring healthy plants. When spores land on open barley flowers, infection occurs and the fungus will establish within the seed embryo, even though the seed appears healthy. Fungi overwinter in the seed embryo and are ready to start the cycle again.

Disease Control:  There are two main ways to control True Loose Smut.  One way is to grow varieties that are resistant. Another way to control the disease is to only plant clean, certified seed. The pathogen does not overwinter in the soil, so using uninfected seed goes a long way to avoiding the problem.