Leaf rust pathotypes detected in WA since 1990
In the past 25 years, since 1990, nine leaf rust pathotypes have been identified in Western Australia (WA) (Table 1). The dominant pathotypes over the last ten years have been stable and wheat variety leaf rust rankings have not changed significantly in that time. Over that period, statewide leaf rust epidemics occurred in WA in 1992 and in 1999. Smaller regional outbreaks of leaf rust have developed regularly over that period.
Pathotype detected in 2013
In 2013, a new leaf rust pathotype to WA was detected which was the first occurrence of virulence for the resistance genes Lr13, Lr17a, Lr17b, and Lr26 in WA. As a result wheat varieties dependent on these resistance genes are now more vulnerable to leaf rust infection by this strain. The new pathotype was first detected in wheat crops in eastern Australia in 2011 and is presumed to have entered WA on prevailing winds or someone’s clothing. In the spring of 2013, this new pathotype was identified in crops from Northampton to Esperance on a range of varieties showing unusually high levels of leaf rust, including Mace and Wyalkatchem. Until 2013, Mace and Wyalkatchem had demonstrated effective resistance to leaf rust in WA.
Since that time, this pathotype has established across the WA wheatbelt.
Pathotype detected in 2015
In 2015, another new leaf rust pathotype to WA was detected in the northern wheatbelt and it is expected to become the dominant pathotype across the wheatbelt. The new pathotype differs from those detected previously in WA in being fully virulent on the complementary resistance genes Lr27+Lr31, the adult plant resistance gene Lr12, and in combining virulence for Lr1 with Lr13, Lr17a, and Lr26. As a result wheat varieties dependent on these resistance genes are now more vulnerable to leaf rust infection by this strain. A radio interview with Professor Robert Park from ACRCP about the detection of this new leaf rust pathotype can be heard online through the ABC site.
This pathotype was first detected in South Australia in August 2014, and has since spread throughout much of the eastern Australian wheat belt. It is presumed to have entered WA on prevailing winds or someone’s clothing. It is expected that this pathotype will quickly spread to be the dominant wheat leaf rust pathotype in WA.
This is only the third example of a wheat rust isolate migrating from eastern Australia to WA in the past 25 years, all being wheat leaf rust: an isolate of pathotype 104-1,2,3,(6),(7),11 was first found at Salmon Gums in 1990; in 2013, an isolate of pathotype 76-1,3,5,7,9,10,12 +Lr37 was found at Esperance.
|Was common, less so now|
|Was common, less so now|
|Common (less since 2013 incursion)|
|Introduced dominant pathotype currently|
104-1, 3, 4, 6, 7, 8, 10, 12 +Lr37
|New, introduced, likely to become dominant eventually|
What changes are there in wheat variety ratings to leaf rust?
Wheat varieties dependent on the resistance genes which are no longer effective are now expected to be more vulnerable to leaf rust infection by these strains.
- After the 2013 pathotype incursion Several variety rankings changed, these included Mace, Wyalkatchem and Corack, Bonnie Rock, Emu Rock, Tammarin Rock, Halberd, Binnu,Yitpi, Arrino and to a lesser degree Fortune, Zippy and King Rock.
- After the 2015 pathotype incursion there were further changes: Arrino, Binnu, Emu Rock, Envoy, Estoc, Grenade CL Plus, Mace, Tammarin Rock, and Zippy became rated more vulnerable to leaf rust, if infected by this pathotype.
The changes to wheat variety ratings since both incursions are reflected in the current wheat variety guide. See wheat variety resistance ratings.
At any time, variety disease rankings reflect the dominant pathotype. The Australian Cereal Rust Control Program (ACRCP) continuing to conduct testing in order to keep us up to date with the potential impact of these new pathotypes on WA wheat varieties.
Is it known where the recent new pathotypes have come from?
Not exactly, but it is presumed that they entered WA on prevailing winds or someone’s clothing as both pathotypes were previously detected in crops in the eastern states of Australia. Remember that if you walk through an infected crop, please follow biosecurity protocols and thoroughly clean your boots and trousers before entering another paddock or travelling as rust spores can be unknowingly transferred via people. For more information see Biosecurity section and GRDC article Rust pathogens and the east-west route.
What should grain growers do now?
The new pathotypes have rendered much of the WA wheat crop more susceptible to leaf rust. This serves as a warning for growers to consider the following management options :
Be vigilant and destroy green bridge
Wheat growers are encouraged to be vigilant in destroying any volunteer wheat regrowth at least four weeks before the commencement of each new season, earlier to benefit from soil moisture conservation. Also growers need to carefully consider management of those varieties that may have higher susceptibility to leaf rust infection.
In high risk areas, where varieties rated S to MS haven't been replaced with more resistant options budgeting for foliar fungicide application is advisable.
Be aware of variety disease rating changes
Keep informed by looking out for variety disease rating updates each year. Current wheat variety resistance ratings to leaf rust are available in the wheat variety guide.
Report rust finds and take samples
Monitoring crops, early detection and reporting of rust will improve disease management outcomes for the grains industry. Any occurrences of rust in crops or regrowth should be reported to the Department by emailing PestFax or completing an online report here which will benefit industry as a whole.
Growers and agronomists who find any leaf rust on volunteers or crops this season are encouraged to collect samples and submit to the Australian Cereal Rust Control Program directly. The analysis which is done in Sydney will help us understand the distribution of this new pathotype in WA or may even lead to the detection of a new pathotype.
Leaf rust samples should be mailed in paper envelopes, not plastic wrapping or plastic lined packages, to: University of Sydney, Australian Rust Survey, Reply Paid 88076, Narellan NSW 2567, noting the location, variety, date and contact details of the sender. You can obtain the sampling instructions, posting details and further information on the new pathotype finds from Australian Cereal Rust Control Program website. Alternatively, growers can deliver samples to their nearest Department of Agriculture and Food office to be forwarded for testing.
In case of high early disease risk consider seed dressing or in-furrow fungicides
Seed dressing or in-furrow fungicides can provide early protection against leaf rusts of wheat in susceptible or partially resistant varieties and other diseases such as powdery mildew. An effective strategy is to delay general seed dressing or in-furrow treatment of susceptible varieties until autumn. Where ‘green bridge’ cereals survive through autumn in local districts there is an increased likelihood that stripe or leaf rust could establish early in young susceptible crops.
A seed dressing or in-furrow fungicide will control rust for four to six weeks and provide suppression on seedlings depending on the product and rate. A list of registered seed dressing and in-furrow fungicides is available to assist decision making.
Apply fungicide if leaf rust found
The application of a registered foliar fungicide when the disease first becomes apparent and before it fully establishes in a crop could help successfully manage leaf rust in susceptible wheat varieties. Leaf rust can cause up to 30% yield loss on susceptible varieties if not controlled promptly. For further information see the Managing stripe rust and leaf rust in wheat page.
Growers should budget for a fungicide spray at flag leaf emergence if growing MS or lower rated varieties. If spraying is likely to be carried out for the control of Yellow Spot or Stagonospora Nodorum Blotch (Glume Blotch) then that spray is also likely to help control the leaf rust.
Biosecurity measures - avoid spreading rust around
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, interstate 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.
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.
Funding and materials for research to support some of the findings and options presented in this factsheet was provided by the Department of Agriculture and Food (DAFWA), the Grains Research and Development Corporation (GRDC), and the Australian Cereal Rust Control Program (ACRCP). We particularly thank Professor Robert Park and Associate Professor Harbans Bariana for providing much of the information.
The State of Western Australia, the Minister for Agriculture, the Chief Executive Officer of the Department of Agriculture and Food and their respective officers, employees and agents:
- do not endorse or recommend any individual specified product or any manufacturer of a specified product. Brand, trade and proprietary names have been used solely for the purpose of assisting users of this publication to identify products. Alternative manufacturers’ products may perform as well or better than those specifically referred to.
- do not endorse the use of fungicides above the registered rate, off-label use of herbicides or off-label tank mixes. Always adhere to label recommendations.
- accept no liability whatsoever by reason of negligence or otherwise from use or release of this information or any part of it.