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Whilst they are not seen as commonly as their close relatives the rusts, smut fungi can affect a range of garden plants, including some widely-grown vegetables and ornamentals. Some smuts cause conspicuous growth distortions, whilst others cause leaf spotting. All can contaminate the soil for extended periods of time.
Smuts are fungal diseases that can affect leaves, stems, flowers and sometimes storage organs such as bulbs and corms. Some produce huge quantities of black spores which, when they are shed from the plant, resemble soot (or smut, hence the common name).
Smuts are relatively specialised pathogens with narrow host ranges. For example, the smut that affects sweet corn is caused by a different species of fungus from the one attacking carnations.
Many grasses are also affected by smut diseases, although they are rarely a problem on the species and cultivars grown in the garden. However, on members of the grass family grown as valuable cereal crops, such as wheat and barley, smuts (or bunts, as some of them are called) can be a significant problem.
You may see the following symptoms:
There are no fungicides available for the control of smut diseases.
The smuts producing masses of dark spores on the hosts listed are species of Urocystis and Ustilago. Those producing leaf spots without obvious spore masses are species of Entyloma (often referred to as white smuts). Entyloma smuts produce spores that are embedded within the affected leaf tissue.
Spores of all of the smut species can contaminate the soil for long periods of time (15-20 years in the case of onion smut). They eventually germinate to produce a second spore type that infects the plant. In some cases (e.g. Entyloma smuts) the spores can also germinate in situ on the plant, and the disease may then spread rapidly during the growing season.
Some smuts are able to colonise the entire plant internally in what is known as a systemic infection (even though symptoms and spore production may be confined to isolated parts of the plant). Others remain localised in the parts of the plant where symptoms are produced.
In 2012, Entyloma smut of Eschscholzia californica (California poppy) was recorded by the RHS for the first time in the UK.
Antirrhinum rustChrysanthemum white rustDahliaDisposing of diseased materialFuchsia rustHollyhock rustOnionPelargonium rustSweetcorn
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