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Western Australian grain growers are warned that stem rust has been observed in a 700 hectare Yitpi wheat crop at Warralakin in WA’s eastern wheatbelt and are asked to be vigilant checking their own crops.

David Keamy of Merredin Rural Supplies found the rust in less than 10 per cent of the crop, with the infection averaging 5-10 pustules on leaves and stems of scattered plants at early flag leaf emergence.

Dr Colin Wellings, plant pathologist at the Grains Research and Development Corporation (GRDC) supported Cereal Rust Laboratory (CRL), University of Sydney, described stem rust as “a disease to be nervous about”.

“It could represent the beginnings of an epidemic if temperature and moisture conditions are favourable,” he said.

“Optimal average daily temperatures are 18-30 degrees Celsius and the latent period, which is the time between infection and production of new spores, is eight to 12 days.

“If moisture conditions become favourable, we could have a problem,” Dr Wellings indicated.

Samples are now being typed at CRL, but the process takes three weeks.

Dr Wellings said Yitpi, a wheat variety grown in WA and widespread in the Mallee region of SA, is vulnerable to stem rust.

Under favourable conditions, stem rust outbreaks could destroy up to 70 per cent of a susceptible wheat crop, according to Dr Rohan Rainbow, GRDC Manager, Crop Protection.

“The Warralakin outbreak is a classic example of green bridge proximity, where small patches of self sown Yitpi, with advanced heading plants, spread the disease to the sown crop.

“After this season’s harvest, growers should be careful with variety selection for next year and make informed choices based on several factors, including degree of rust resistance,” he said.

Local plant pathologist, Geoff Thomas of the Department of Agriculture and Food WA (DAFWA), advised growers to send rust samples to AGWEST Plant Laboratories for free identification and subsequent forwarding to CRL for pathotype testing.

He indicated growers should also report the finding to PestFax, Email PestFax@agric.wa.gov.au or Tel 9368 3753, so local industry can be informed.

Advice on identification and management of rust diseases is available through DAFWA and other sources such as www.grdc.com.au/rustlinks

“Management will vary depending on the variety, disease level and growth stage of the crop,” Mr Thomas said.

“When stem rust is detected, particularly in susceptible varieties, economic control can be achieved with fungicide applications.

“Early identification of the problem is important because control is likely to be more effective if applied applied early in the disease’s development ,” he said.

Mr Thomas indicated stem rust was caused by the fungus Puccinia graminis f. sp. tritici which produces large, oval to elongated pustules containing reddish-brown spore masses on both sides of the leaf, on leaf sheaths on stems, and occasionally on outsides of heads.

Stem rust pustules have conspicuously tattered edges.

Rust is likely to be evident first in early sown susceptible crops or in advanced regrowth of susceptible varieties and should not be left unchecked, as it could cause significant yield loss and quality downgrades.

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