Smut diseases commonly occur at low levels, but without seed dressings they may increase rapidly and cause significant economic losses to growers. Fungicide seed dressings can control but not always eradicate the smut. When choosing a seed dressing, consider the type of smut that is present. Walk through the crop at heading, looking for diseased plants. Once the smut is identified, choose the right seed dressing and ensure seeds are evenly covered with fungicide. Some smuts can only be controlled by specific registered dressings applied at the correct rate.
Covered smut (common bunt) of wheat
Covered smut of wheat (also known as common bunt or stinking bunt) is potentially the most important smut disease of wheat because there is zero tolerance for it in wheat delivered to Cooperative Bulk Handling Ltd (CBH). It can be both seed- and soil-borne. It is extremely difficult to detect in the field and low levels can remain undetected in harvested grain. Regular pickling is recommended and effectively manages this disease.
If bunt infection does occur, infected seed should not be used; contaminated machinery should be thoroughly cleaned and contaminated paddocks rotated out of wheat for at least one year. Barley, oats and broad leaf crops are not hosts of this disease. In the break crop year, any wheat regrowth should be destroyed before it reaches maturity to prevent carryover of infection. Subsequent wheat crops in the affected paddocks and adjoining paddocks should be sown with fungicide protected seed. Some variety resistance is available.
Flag smut of wheat
Flag smut can be both seed- and soil-borne. Sowing clean seed into a contaminated paddock will not control the disease. It is also important to use a correct seed dressing. Wheat varieties vary in susceptibility to this disease (see current wheat variety guide). Seed dressings are always recommended for susceptible varieties. Where soil-borne infection is known to occur, sow resistant (R) or moderately resistant (MR) varieties with seed dressing. Barley, oats and broad leaf crops are not affected by flag smut.
Loose smut of barley and wheat
Loose smut of barley and wheat is prevalent in areas receiving more than 450mm average annual rainfall. The smut fungus destroys the heads of infected plants, reducing yield by about the same percentage as number of heads infected. This disease is seed borne but the level of seed infection cannot be predicted, however a heavy smut infection in one year will probably produce heavy smut infection in harvested seed. All registered seed dressings reduce incidence of loose smut but the effectiveness varies.Recent work has shown that some products can reduce the infection level of heavily infected seed to nearly zero. Using a highly effective seed dressing will avoid the need to replace heavily infected seed, which was previously recommended.
Other head smuts
Covered smut of barley and loose and covered smut of oats occur generally at low levels. These smuts can be detected in the crop and controlled by regular use of registered seed dressings.