A new strain of stem rust, with the ability to attack Wyalkatchem wheat, has been identified in Western Australia.

Recent tests on behalf of the Department of Agriculture revealed three samples of stem rust collected in the southern regions were a mutated variant of an existing strain and was now able to attack Wyalkatchem wheat. 

Department principal plant pathologist Robert Loughman said Wyalkatchem had become a popular variety because of its excellent yields and rust resistance.

"Wyalkatchem is the only variety affected by the new stem rust strain, which has not occurred in other parts of Australia," Dr Loughman said.

"The significance of the new strain lay in its potential to impact on Wyalkatchem crops in 2004 or beyond. 

"Wyalkatchem is now rated as susceptible to stem rust in WA. The resistance of Wyalkatchem to leaf and stripe rusts has not been affected by this mutation."

The tests were conducted by the Sydney University Australian Cereal Rust Control Program, as part of its annual national rust survey. The survey is funded by the Grains Research and Development Corporation to provide early warnings of rust changes to industry.

Dr Loughman said the experience with Wyalkatchem is likely to be similar to the experience of stem rust on Camm.

"Camm became susceptible to a strain of stem rust, which increased in 2002 and became prominent on the variety in 2003, requiring extensive control," he said.

"Reduced reliance for stem rust resistance must be placed on Wyalkatchem in future and it should no longer be grown in areas where stem rust pressure is traditionally high, such as the Esperance region.

"Carnamah, EGA Castle Rock, GBA Ruby and Perenjori represent competitive wheats combining stem rust resistance with other rust resistance combinations in relevant sowing window classes and wheat grades."

Dr Loughman said the overall impact would not be clear for several seasons. He said because stem rust was a late season phenomenon, seed treatments did not offer protection, but effective fungicide sprays exist.

"Growers are likely to find spraying a necessity to control stem rust in Wyalkatchem in the future.

"Growers now need to manage stem rust as a production risk in Wyalkatchem wheat, by considering planting intentions and alternative varieties for rust prone areas and by budgeting for fungicide in other regions in green-bridge seasons predisposed to stem rust outbreaks," he said.