Australia
February 23, 2012

The 2012 winter crop season is shaping up as high risk for yellow leaf spot with grain growers warned to take action before planting rather than relying on fungicide sprays.

Grain Orana Alliance (GOA) trials funded by the Grains Research and Development Corporation (GRDC) have found that managing stubble may be the greatest key to limiting infection and yield impact.

Maurie Street, GOA chief executive will present the research results at GRDC's Dubbo Grain Update at the Dubbo RSL on 1 March.

Mr Street says 2011 was primed for a major epidemic of yellow leaf spot and only the low rainfall from sowing to September and the cooler wet finish saved growers from major yield and quality impacts from the disease.

"Yellow leaf spot hasn't been a major issue since the late 1990s, probably because it can't handle dry seasons very well," Mr Street said.

But with large levels of disease inoculum at the start of 2011 from a major epidemic in 2010, GOA started trials across the Orana region looking at both fungicide timing and management of the inoculum source.

"The results suggest that growers simply can't rely on fungicide the way they can with stripe rust, where even a severe infection can be controlled with one or two sprays," Mr Street says.

"The fungicides commonly used to control leaf diseases in wheat were not as effective as expected. Some treatments involving up to five applications saw only mediocre reductions in disease incidence and although yield responses were seen, they were not commensurate to the effort applied."

In contrast other trials investigating the effect of removing the disease inoculant from the system showed much greater responses. In these trials stubble was slashed, slashed and removed, burned or left alone.

"These trials demonstrated that at early crop emergence there was practically no infection on plots which had the stubble removed or burned, while those which had been left alone or even just slashed had high levels of infection. These effects carried on right up to harvest.

"This work shows the rules learned from stripe rust control may certainly not always apply to yellow leaf spot. Key differences between the two diseases mean they will respond differently to fungicides and the level of response by yellow leaf spot will often be less."

Mr Street says the message to growers is very clear - it all comes down to minimising the disease risk or pressure.

"If we get similar weather conditions to 2010 this year, there's enough inoculum loading around for yellow leaf spot to wreak havoc again.

"So ideally don't plant wheat-on-wheat, particularly if the stubble is infected with yellow leaf spot, as those paddocks are high risk.

"If you can't avoid that, you should manage the inoculum levels first via the stubble and choose varieties most resistant to yellow leaf spot.

"Remember that we cannot control yellow leaf spot as easily or effectively with fungicides and to arrest an epidemic you may need to apply multiple fungicide applications - up to five times - to get an effective response."

Yellow spot trials were also run by the GRDC-funded Northern Grower Alliance (NGA) through 2011, with results also showing minimal value in fungicidal treatment on susceptible barley. Those results will be presented at the GRDC Update at Goondiwindi on 6 and 7 March.

Information about managing yellow spot is available on the GRDC website at www.grdc.co.au/diseaselinks.
 

Website: http://www.grdc.com.au

Published: February 23, 2012