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Loose smut in Hindmarsh barley

Barley Loose Smut AvondalIncreasing incidences of loose smut infections in Hindmarsh barley crops in South Australia and Western Australia has prompted investigation into the effectiveness of seed treatments in controlling the disease, particularly in susceptible varieties.

Observations made by the South Australian Research and Development Institute (SARDI) pathology team over the past three years suggest that the efficacy of some seed treatments may not be sufficient to control loose smut in the susceptible variety Hindmarsh (Cereal Seed Treatments factsheet).

Further testing is currently underway with results due to be released this month. However, it has been suggested that it is likely that more than one fungicide will be required for Hindmarsh. The same situation is expected for LaTrobe.

Similar observations in Western Australia have prompted the Department of Agriculture and Food (DAFWA) to establish trials comparing the levels of loose smut resistance in 12 barley varieties, including Hindmarsh.

However, as researchers and farmers await the results of this research, DAFWA is continuing to advocate the use of seed treatments for the control of loose smut as part of any best practice farming system.

DAFWA trials carried out at Wongan Hills and Gibson in 2013 showed that seed dressings, including EverGol® Prime and Jockey® Stayer™ and Jockey® + Raxil ®, were able to reduce loose smut to near zero levels in Hindmarsh that was heavily infected.

The latest information and trial results from DAFWA can be found in the Controlling loose smut in 2015 factsheet.

Loose smut facts

AHills loose smut hds

Loose smut is an internally seed-borne disease, caused by the fungus Ustilago tritici (U. nuda) that can reduce barley yields.

The disease is not noticeable until ear emergence. At this time, the head of infected plants will emerge earlier, be darker in colour and slightly taller than healthy plants. Infected ears will contain the ‘smut’ (masses of black/brown spores), initially held by a thin membrane that soon ruptures releasing the spores.

Effectively, loose smut replaces the grain with smut which infect the open flowers of healthy plants and grow into the seed. Eventually all that remains of the head is a bare stalk.

Loose smut spores spread in the wind at flowering time and infect developing embryos. Infection during flowering is favoured by frequent rain showers, high humidity and temperatures of 16-22°C.

The infection remains hidden inside the seed; the fungus survives as dormant hyphae in the embryo until germination. When infected seed germinates the fungus grows within the plant.

Control

Loose smut requires control because infected plants produce no grain on their tillers, so grain yield is lost. Although it generally occurs at low levels, in the absence of seed treatments, it has the potential to increase rapidly, causing significant economic losses.

Loose smut spores blown away

Rachis or stem from smutted heads when smut spores have blown away.

Systemic seed fungicides are the control method for loose smut. However correct application of seed dressings, which ensures every seed is treated, is critical to ensuring effective control.

Growers should select a seed dressing that is registered for loose smut control as well as other diseases that may pose a risk to the crop such as scald or powdery mildew. This may mean growers need to apply two different treatments to their barley.

In-furrow fungicides are not registered for the management of smut and bunt diseases and have been shown to be ineffective for the control of loose smut in WA trials.

Following a loose smut outbreak, purchasing clean seed and using the full rate of registered seed treatments will ensure the disease is not spread to the following year’s crop. However, growers should be aware that as well as being costly, replacing seed can pose a biosecurity risk (i.e. introduction of new weeds or weeds with a different herbicide resistance profile).

DAFWA research has shown that applying appropriate treatments to heavily infected seed can result in close to 100 per cent control of loose smut so that properly treated seed will be acceptable for sowing the next season.

Receival standards

Grain Trade Australia’s commodity standards allow a maximum of three pieces of loose smut infected ear per half litre for all grades. Some countries have zero tolerance to the importation of loose smut contaminated grain.

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