STRIPE rust lurking in the green bridge and taking aim for an early strike could cause torrid times for some WA wheat crops.
The speed with which stripe rust emerges has been shown to have a major bearing on its overall management and yield impact.
Supported by the Grains Research and Development Corporation (GRDC), Agriculture Department pathologist Manisha Shankar last year found that when stripe rust landed on susceptible varieties just seven weeks after sowing, they shed about 75pc of yield.
When stripe rust arrival was delayed two to four weeks, the speed of disease development was halved, but about 40pc of yield was still lost.
The trial, at the Agriculture Department's Medina Research Station, compared highly susceptible varieties such as EGA Bonnie Rock and H45 with the moderately susceptible Carnamah and the partially resistant Wyalkatchem and EGA Castle Rock.
Dr Shankar monitored leaf disease throughout the crops' lives and measured yield at the end to determine reaction to different times of infection.
When stripe rust infection occurred nine weeks after seeding, partially resistant varieties performed significantly better than when infected after seven weeks, producing 15pc more yield.
When infection was delayed to 11 weeks, yields improved another 10pc.
When plants had only to deal with infection for a short time, as when disease inoculum arrived late, partially resistant varieties performed almost as strongly as resistant varieties.
However, without a long summer drought to burn off inoculum, growers will need to take their own action to delay infection in 2006.
One way is to destroy nearby volunteer wheat, particularly self-sown paddocks of highly susceptible varieties that provide favourable green bridges for stripe rust.
Growers can also consider seed dressing and in-furrow fungicides, which delay infection by 12-16 weeks in varieties lacking full stripe rust resistance.