Queensland's Department of Primary Industries and Fisheries (DPI&F) specialists have suggested how wheat farmers can reduce the impact of stripe rust, which has been found in some southern Queensland wheat crops.

DPI&F extension agronomist Michael McDonald said stripe rust (Puccini striiformis) was widespread across Australia and had become endemic in northern New South Wales (NSW) late in the 2004 season.

Mr McDonald said the rust had now been detected in Queensland wheat around Goondiwindi, Bungunya, Westmar and at the Gatton Research Station.

"It appears to have over-seasoned in the Bellata area of northern NSW, become well established in early-sown crops and then spread north from there," he said.

"It's likely to over-summer in the region and while it might pose a threat in 2005 it's relatively easily controlled with fungicides."

DPI&F plant pathologist Emma Colson said there were several ways farmers could manage the disease to minimise yield losses next season.

Pathotyping of early season isolates by Col Wellings of the Australian Winter Cereals Rust Control Program indicated the rust was the Western Australian pathotype and appeared more aggressive on several popular wheat varieties.

Dr Colson said she and DPI&F plant pathologist Greg Platz evaluated infected sites in northern NSW in early October for the effectiveness of control measures and to validate wheat variety resistance rankings.

"We found infection responses of the main commercial varieties in current planting guides were reasonably accurate, but the effect of resistance in reducing crop damage mainly depended on crop growth and stage and the timing of infection.

"Even though varieties may have reasonable levels of resistance as adult plants, some can be quite susceptible in the vegetative stage," Dr Colson said.

She said where varietal resistance was inadequate, chemical control should be considered.

Vegetative stage infection could be delayed with seed treatments and foliar-applied fungicides, such as propiconazole, tebuconazole and triadamefon.

"These appear to have provided very useful control for up to eight weeks where heavier rates are used."

She said highly susceptible varieties should be avoided, but growers saving their own seed for sowing next season should keep the stripe rust threat in perspective.

"It may be unwise to discard high performing varieties that have only moderate levels of resistance to stripe rust," Dr Colson said.

Management strategies to control stripe rust included using clean summer fallows to eliminate the green bridge.

Stripe rust survived on living wheat plants and volunteer wheat growing in summer fallows, providing the bridge that allowed the disease to persist from season to season.

Other approaches included:

• Sowing resistant varieties where possible. If other agronomic attributes such as crown rot resistance favour the planting of moderately susceptible varieties, ensure the seed is treated with a fungicide, and avoid highly susceptible varieties.
   

• Treating seed of varieties with a score of 5 or less for stripe rust resistance with a systemic seed treatment for protection to the six to eight leaf stage or even up to flag leaf emergence, depending on the fungicide preparation used. These seed dressings reduce coleoptile length and may affect emergence under unfavourable sowing conditions.
   

• Monitoring crops in 2005 to detect disease early so appropriate management can minimise economic losses.
   

• Use foliar applications of fungicides to protect the flag leaf, the source of around 40 per cent of the carbohydrates that contribute to wheat yield. Earlier application of fungicides might be appropriate if significant stripe rust is found in varieties with resistance scores of 5 or less.

Dr Colson said when considering growing "at risk" varieties with rust ratings of less than 5, a rust management package that included a systemic seed treatment, early monitoring and budgeting for the application of a foliar spray after flag leaf emergence should be considered.

All control measures were aimed at keeping inoculum levels low because large amounts encouraged the development of genetic diversity within stripe rust and increased the chance of more pathogenic forms of the disease rust developing.

"Keeping inoculum levels low is critical for sustaining the stripe rust resistances that are currently effective," she said.

Information on the stripe rust will be published before the 2005 winter crop season.