Wheat and barley growers can increase yields by about 15 per cent by applying fungicides to control powdery mildew in spring-infected crops.

Fungicide seed dressings, in-furrow treatments with fertiliser and fungicide spraying are currently the most effective management options for powdery mildew, as other options, including crop rotations, have proved ineffective.

The most popular wheat and barley varieties grown in Western Australia (WA) are either intermediate or susceptible to powdery mildew. Since 1997, due to continuous cropping of these cereals, the fungi have significantly affected WA wheat and barley crops, particularly in high rainfall agricultural areas.

Growers are advised to monitor crops by looking for white powdery spore mass on the upper surface of the lower leaves and stems.

High humidity and temperatures from 15-22C favour their development. Severe infections occur in winter, at early stages of crop growth, and affect yield potential by causing tiller abortion.

The disease generally declines later in the season, except in high production situations with high nitrogen, or in humid coastal areas. Severe infection at later growth stages affects grain filling.

Spraying of the spring-infected crops should be at the late tillering or head emergence stage.

Research by the WA Department of Agriculture, supported by growers and the Federal Government, via the Grains Research and Development Corporation, evaluated the management of powdery mildew using foliar fungicide sprays. Fungicides, including triadimefon (Triad), were tested on barley in 2000 and 2001 and on wheat in 1999 and 2001.

In barley, the level of disease varied from severe (84 per cent affected) to moderate (41 per cent) over the two years and fungicide was applied once, when awns were first visible. Peak profit (over nil treatment) was $82/ha, when using Triad 125EC at 500 mL/ha.

In wheat experiments, a single application of fungicide was sprayed at flag leaf emergence in 1999 and ear emergence in 2001. Although severe frost at the grain-filling stage reduced yield potential in 1999, profit from fungicide application varied from $36 to $48/ha in 2001, with the highest profit coming from using Triad 125EC at 1 L/ha.

Disease onset in these experiments was generally at the mid to later stages of crop development.