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Floral smut of green couch

By | February 4, 2013 at 8:15 am | No comments | Provisioning

General information

Most Queenslanders have heard of the smut disease affecting sugar cane in the Bundaberg area. A much smaller grass, green couch (Cynodon dactylon), is susceptible to its own flower smut. Couch smut (Ustilago cynodontis) was first recorded in New South Wales in 1907 and is prevalent throughout the mainland states of Australia. In most circumstances, it is no more than an annoyance to home gardeners. However, the disease can become a more severe problem and, like the related sugar cane smut, it is difficult to control once established.

Couch smut has been found to exclusively affect grasses in the genus Cynodon and is most commonly seen in green couch (also known as Bermuda grass). Although blue couch is similar in some ways to green couch, it is a completely different species from a different genus (Digitaria) and is not susceptible to couch smut. So if you think you might have couch smut, you should first take a close look at the grass species present in your lawn.

Scientific name Ustilago cynodontis
Symptoms
  • Symptoms are seen when the grass forms flower heads. Instead of a healthy, open arrangement of two to six spikes, the spikes fail to open and the seeds are replaced by a mass of black, powdery spores which can cause allergies in some people.
  • Shoots with infected seed heads also show a more upright habit of growth, which is particularly unsightly in the more prostrate green couch cultivars.
  • The root system of infected plants is weakened, making them more susceptible to environmental stresses such as drought.
  • Infected couch has reduced growth and survival in crowded conditions.
  • Seed production is prevented in affected flower heads. However, the presence of the organism will not prevent healthy seed from germinating and seedlings emerging.
Management
  • Be aware of the potential for a problem and check your lawn regularly for any early symptoms.
  • Mowing the lawn regularly, as flower heads appear, will significantly reduce the number of infected seed heads. However, the fungus will still be present within infected plants, waiting for a future opportunity to show itself.
  • There is no effective chemical control for this disease.
  • In severe cases, the only permanent solution is to replace the lawn with something other than green couch.
Further information Learn about the visual differences between blue and green couch.

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