Along with the surge in continuous cropping and stubble retention in Western Australia’s northern wheatbelt came the question of how best to handle foliar diseases of wheat, particularly those favoured by the altered cropping system.

With the area typically tipping a third of Western Australia’s annual wheat crop into the state’s bins, albeit often under the burden of yield and quality penalties caused by leaf diseases, the issue simply had to be tackled.

The Grains Research and Development Corporation (GRDC), therefore, with backing from growers and the Federal Government, supported a four year project, now complete, which researched how best to manage these constraints.

Supervised by Department of Agriculture plant pathologist, Robert Loughman, it gave growers the confidence to continue to adopt stubble retention, while enjoying its associated benefits, because it found retained wheat stubble was not a significant source of disease carryover in rotation wheat crops.

A tiny 1-8% of retained stubble remained after germination of the subsequent wheat crop in a typical year in/year out wheat rotation.

Traditionally, fungicides were not commonly applied in the region, but this has recently changed, with growers now facing vexed questions such as "when is it economical for me to spray?"

Economic responses were invariably obtained when leaf rust was the target, either alone or in combination with other diseases.

The research, however, did not answer this complex economic and agronomic question as categorically for yellow spot and septoria nodorum blotch. It recommended fungicides be considered, in this case, when crop yields were potentially three tonnes or more, in those areas where 100mm or more of rainfall was likely in the eight weeks after flag leaf emergence. Best results were generally achieved when applied at full flag leaf emergence.

Selecting which fungicide depended on the disease spectrum, with propiconazole most effective against yellow spot, for example.

According to Dr Loughman’s final report, control of early leaf rust in susceptible wheat varieties was best achieved by foliar fungicide sprayed at early stem elongation (e.g. triadimefon), which could give better results than seed or fertiliser fungicide treatments.