Stripe rust hot spots have been identified across the Wimmera and southern Mallee recently, prompting growers to consider their disease management strategies as harvest draws near.
A fungicide application is advisable for those growing wheat varieties susceptible to the disease such as Mace, Derrimut or Corack, which most growers would have already done.
Keep in mind, however, that in the Mallee at this stage in the season, varieties with adult plant resistance are unlikely to benefit from a fungicide spray, nor will any varieties that are already out in head. Mace, for example, does not have adult plant resistance and will need to be monitored closely, even after head emergence.
This year in particular, it is pertinent to consider yield potential before deciding to spray. Remember, a fungicide will only benefit undamaged leaf area. If a lot of leaf area has been lost to moisture stress, frost or disease, or if you think your yield potential is below 1.5t/ha, it may not be economically beneficial to spray.
Wimmera growers should check all their crops now, make a decision about spraying and act on this decision immediately.
Decisions about how to manage rust diseases, such as stripe rust, are best made quickly. If growers detect rust or believe a fungicide spray is warranted, they should do so without delay as the benefits of a fungicide application will only be realised if timely spraying occurs. Likewise, if it is spraying is not warranted, make the decision and walk away. Deciding to spray two weeks later is likely to be a futile exercise.
Unlike leaf and stem rust, stripe rust spores do not require free water to germinate. They can germinate in as little as six to eight hours at temperatures between five and 15°C. In winter, spores tend to clump together (giving rise to ‘hot spots’) while in spring, spores tend to disperse singly, causing a more uniform infection.
Stripe rust is easiest to detect in the morning and is identifiable by the appearance of yellow stripes of pustules, particularly on the older leaves. These pustules are raised above the leaf surface and can be easily wiped off. If there is a morning dew, detection can be more difficult and growers may need to look at the underside of the leaves, especially the flag minus one.
Hot spots can be one to 10 metres in diameter and are generally well developed just before the disease becomes widespread in the crop.
In conjunction with the Department of Primary Industries and Environment (DEPI) BCG is exploring a range of disease management strategies and looking at how wheat varieties respond to crop diseases at its research site at Quambatook. A crop walk and discussion, featuring DEPI plant pathologists Grant Hollaway and Mark McLean and CSIRO crop scientist James Hunt, will be held at the BCG Quambatook site on October 3. All are welcome.
Growers wanting more information can contact BCG on (03) 5492 2787 or www.bcg.org.au. For more information on stripe rust management and other diseases visit the crop diseases page on the eXtensionAus website: https://www.extensionaus.com.au
