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Australian Wheat Growers to Scout for Leaf Spot

26 August 2011

AUSTRALIA - The Department of Agriculture and Food is encouraging wheat growers to inspect their crops for leaf spot diseases, which are a common problem across the WA wheatbelt this season.

Department plant pathologist Ciara Beard said wet weather had produced excellent crops in many parts of the region but was also driving infection and spread of septoria nodorum blotch and yellow spot in wheat as reported by Seed Quest.

Department research on leaf spot diseases, investigating early fungicide applications and the importance of nitrogen for disease control, will be on show at a field walk today at the DAFWA Research Annex on Valentine Road, Eradu.

"Leaf spot diseases in wheat appear as irregular or oval-shaped spots that initially are small and yellow, but enlarge to form brown dead centres, with yellow edges," Ms Beard said.

Wheat heads infected with septoria nodorum blotch, also known as glume blotch.

"Typically, a badly affected leaf will die back from the tip as lesions merge, reducing the photosynthetic area and causing premature leaf death. These diseases are particularly a problem in continuous wheat crops in stubble retention farming systems."

Ms Beard said leaf spot diseases had the capacity to significantly reduce yield and grain quality in medium-high rainfall areas or other areas receiving above average rainfall this growing season.

"Septoria nodorum blotch is a concern this year. It can spread by rain splash and is becoming quite widespread in susceptible varieties," Ms Beard said. "It is particularly a problem in Mace this year, even in rotation crops."

"When the disease is severe late in the season, it can spread from the leaves to attack wheat heads during grain-fill causing dark patches on the glumes. This is known as glume blotch and can result in shrivelled grain and even complete loss of seed."

Ms Beard said she had already seen one case of glume blotch this season and expected it could be more widespread unless growers inspected their crops and applied fungicide where necessary.

"It is important to control septoria nodorum on upper leaves by applying fungicide before crop heading is complete to reduce risk of head infection. Later spraying is sub-optimal and spraying after crop flowering finished is generally not economic," she said.

Department research has shown that yield responses to fungicide application are more likely in well grown crops in situations where disease is moving rapidly from lower leaves to upper canopy leaves, and in areas where there is a good chance of August-September rainfall of around 100 mm.

Local research into leaf spot diseases will be the focus of a field walk on 26 August at the DAFWA Research Annex on Valentine Road, Eradu. Commencing at 9am, the field walk will also include new wheat varieties that compete with weeds, and fungicide application to manage sclerotinia stem rot in Canola.

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