Foliar spray strategies
Reducing early epidemic development, particularly in VS-MS varieties, is most important. Economic responses have been achieved in susceptible varieties from registered foliar fungicide sprays from pre-head emergence to grain filling. Responses in less susceptible varieties will be less with later sprays.
Crops infected with stem rust before flowering are considered at high risk as yield losses of 50% or more are possible. If infection starts or re-starts after flowering, losses of around 25% are possible.
When and what rate to spray
If any stem rust is detected spray susceptible or moderately susceptible crops as soon as possible with an appropriate fungicide at a high rate. For crops with intermediate resistance continue to monitor and spray if infection exceeds an average of 5% of random stems infected.
If stem rust is detected after head emergence, short term control can be achieved with standard application rates provided infection is not severe. However, high fungicide rates have been found to be more profitable in experiments.
If stem rust is detected after grains are at the dough stage, apply fungicide if the crop has at least four more weeks of grain filling to go before hard dough stage. It is important to consider withholding periods when choosing an appropriate fungicide.
Biosecurity measures
Because there are different strains of stem rust, care must be taken when travelling interstate/overseas or receiving interstate/overseas visitors, since spores carried on clothing could introduce new strains of rusts. Implement biosecurity measures to minimise rust becoming established or spreading on your farm. Rust spores are small, light and may survive for several days without a host. Rust spores can spread long distances by wind, on machinery/vehicles, on tools, clothing and footwear. Remember that if you walk through an infected crop, follow biosecurity protocols and thoroughly clean your boots, hands and trousers before entering another paddock or travelling, as rust spores can be unknowingly transferred via people locally and also from overseas. Also check biosecurity measures taken by your visitors and agronomists.
Be particularly vigilant when returning from eastern Australia or internationally, as rust pathotypes with different virulences exist outside WA. The Australian Cereal Rust Control Program conducts rust pathotype testing and produces reports each year detailing new rust incursions that are a threat to Australian cereal varieties.
If entering a paddock suspected to be infected with rust, biosecurity suggestions include:
- Wear protective overalls and rubber boots;
- After crop insprection clean any material off boots with a brush. Prepare footbath of bleach (10% household bleach, 90% water) and spray bottles of methylated spirits brew (95% metho, 5% water) for use to disinfect footwear, pants and hands,
- Decontaminate vehicles, tools and machinery,
- Walk instead of driving through crops,
- Ask visitors/agronomists to leave their vehicle at the gate and only travel on your property in your vehicle.
Research
Department of Agriculture and Food, Western Australia has published findings of wheat stem rust research and these can be accessed via the external links on the right hand side. This research was funded by Grains Reasearch and Development Corporation.