Scientists have discovered an exotic strain of a wheat disease in Australia that, when serious enough, can reduce yields by more than 20 per cent.

The disease 'leaf rust' is a well-known foe to Australian grain producers, who have learned the best way to avoid it is to grow resistant wheat varieties.

But the new strain, sourced from overseas, means many varieties will lose their resistant status.

"The rust will have come into the country, probably on people's clothing, walking into a crop overseas and then walking into a crop here," says Dr Hugh Wallwork, of the South Australian Research and Development Institute.

"We suddenly get a completely new strain of the rust in Australia; obviously in this case it differs in its virulence," he said.

"It's more virulent in a number of varieties and sometimes these introductions can be more aggressive."

Testing by the University of Sydney revealed the exotic strain was present throughout the south east of South Australia, on the Eyre Peninsula, Yorke Peninsula and in the Adelaide Plains.

Dr Wallwork says the disease should not have much effect on this year's crops because it's arrived too late in the season.

"The real concern is for future years," he said.

"If this rust survives on volunteer [plants] through the summer, and it usually does, then in subsequent years we'll be finding a number of varieties that we thought had good resistance are now a lot more susceptible.

"We do try and encourage people to remove all green volunteer wheat during the summer period."

The disease will not survive in stubble or soil, it needs green host plants to sustain itself.

Dr Wallwork says treatment for the exotic strain is no different to what farmers have been using for leaf rust.

Seed treatments and foliar fungicides are commonly used and often farmers will use herbicides during autumn and facilitate heavy grazing in a bid to remove any self-sown susceptible wheat.

Scientists are now working on re-classifying the resistance of wheat varieties.

"Mace, which is probably half the area of South Australia if not more - we've always rated that as being moderately resistant," Dr Wallwork said.

"We now have to rate that as being at least moderately susceptible or perhaps a little worse."

"Other varieties, like Emu Rock, had been moderately susceptible; they're now probably susceptible to very susceptible."

Source - http://www.blackseagrain.net/