Plenty of leaf and head diseases were seen in the 2007 wheat crops, possibly because of the unusual patterns of rainfall.

Stripe rust

Stripe rust was endemic throughout wheat-producing areas of southern and Central Queensland.

If there was any economic damage, it occurred in wheat varieties that are susceptible - those rated 5 or 4 and less. The late-planted crops seemed to develop more stripe rust, probably because of the build-up of inoculum through the season, coupled with late rains.

High prices for wheat reduce the margin for economic damage, and increase the value of fungicide application.

Controlling stripe rust

Cultural control

Stripe rust cannot survive for any length of time on dead plants. It needs the ´green bridge´ of living wheat plants that survive through the summer to last from one season to the next.

So your first priority should be to destroy all volunteer wheat plants by February or, at latest, March. This eliminates or greatly reduces the inoculum in a region and can prevent or delay the onset of the next stripe rust epidemic. In addition to your paddocks, check road sides, ditches and anywhere else where volunteer wheat plants might be found.

Loose smut

Genetic resistance

Varieties with intermediate levels of resistance to stripe rust may have adult plant resistance (APR). This is genetic resistance where the seedling is more susceptible than the adult plant. Crop vigour, above average moisture, high fertility and early disease onset may affect variety response and APR.

Wheat varieties with high levels (above 7) of resistance to stripe rust are unlikely to be affected by the disease and will restrict the build-up of inoculum in the crop. This will limit any epidemic and subsequent yield lost.

New pathotype not yet in Queensland

A new pathotype of stripe rust (Pugsley Pathotype 134 E16 A+YR17+) has evolved from the Western Australia pathotype 134 E16 A+ which has been present in eastern Australia for the past four wheat growing seasons, but this new pathotype was not found in Queensland in the 2007 season.

The response of varieties carrying the Yr17 resistance may be different to the response of those with the current Western Australia pathotype resistance. Should the new Pugsley Pathotype move into Queensland, current and projected varietal reactions to stripe rust can be found in the 2008 Wheat Variety Guide.

Fungicides - Seed treatment

Yellow spot

Seed dressings and in-furrow treatments can suppress the development of early stripe rust; most are also effective against smut. However, seed dressings and in-furrow treatments can shorten the germinating shoot of the wheat plant, reducing crop establishment, particularly when seed is sown deeply in uneven seedbeds, or when seed is of poor quality, such as shrivelled.

Foliar fungicides

Wheat cultural and chemical trials undertaken by Queensland's Department of Primary Industries (DPI&F) and Fisheries in 2007 validated previous findings. The best returns from applying fungicide applications come when wheat infected with stripe rust is sprayed between 'second node visible' (stage 32) and the emergence of the flag leaf. As the flag leaf is the primary factory for grain production, protecting it is essential for high yield and quality. Damage to the flag leaf by a foliar disease translates directly to yield loss.

However, fungicides will only give a financial return if stripe rust is present.

Crops should be inspected for stripe rust at regular intervals, especially after stage 32 (second node visible) and after cool, wet weather, which favours the disease. Check the crop for stripe rust even if you have sown a resistant variety, in case the new pathotype is present.

Scouting the crop for pests and diseases and applying fungicides at the first sign of rust would seem the best strategy in controlling the disease and minimising losses.

A list of fungicides is in the DPI&F publication, 'Wheat - managing stripe rust' 

Wheat heads affected by various levels of severity of head blight

Other diseases

Loose smut

There were a number of reports of loose smut over the 2007 wheat season.

Loose smut indicates poor seed quality and/or a lack of the use of smut-controlling seed dressings.

Yellow spot

Some wheat-growing regions that received late rains in the 2007 winter witnessed a late infestation of yellow spot.

This infestation was of little economic consequence and was hardly noticed by growers. However, you should be alert to the fact that the yellow spot inoculum has now had a chance to build up and could pose a risk to the 2008 crop if the wetter conditions forecast persist.

Head blight

A head-blight was seen this year. Specimens were collected by DPI&F and we are confirming the identity of the fungal pathogen that caused the disease.

If you see any of these symptoms, please phone the DPI&F Business Information Centre for your local DPI&F development officer.