Remember the lessons learned by William Farrer
During the late 1800s and early 1900s, William Farrer and the Reverend Dr Nathan Cobb were among the first in the world to work on solving the problem of wheat rusts. They started as collaborators, but the two men disagreed about which rust to target. Cobb was firmly convinced that wheat leaf rust was more urgent because it occurred almost every year, while Farrer believed the more sporadic but devastating wheat stem rust was the more important target. The two men went separate ways, with Farrer going on to be considered the father of Australian wheat breeding.
Farrer’s success in dealing with stem rust was not directly through incorporating resistance genes. He selected earlier-maturing varieties that spent less time growing under conditions that favoured stem rust, and in this way escaped rust infection.
Now there are signs that some growers have forgotten this lesson, such as:
- the high volunteer numbers left unchecked over summer in southern states and parts of Western Australia in early 2016;
- an interest in earlier sowing windows in the southern region; and
- some growers flirting with sowing winter wheat from late spring in the high-rainfall zone.
Table 1 shows the temperature ranges that can result in rust infections. There are very few times of year when a susceptible wheat crop could not fall prey to one of the three wheat-attacking rusts.
Because fungicide insensitivity has now been reported for all three wheat rusts in Europe, fungicides cannot be relied upon as the foundation of a rust management strategy. That is why, building on Farrer’s work, Australia has focused on breeding rust-resistant varieties and on maintaining green bridge control by destroying volunteers and not growing crops over summer.
Resistant varieties not only limit the spread of rust during the cropping season, they also prevent rust survival over summer because any volunteers that do occur are also rust resistant.
Years of in-paddock trials have shown that choosing a more resistant variety, even switching from a susceptible (S) to a moderately susceptible (MS) variety, significantly reduces the rate of rust epidemic development and radically alters the final yield penalty.
The Consultative Committee of the Australian Cereal Rust Control Program has devised a rating system of minimum disease-resistance standards for wheat varieties grown in Australia (Table 2).
The standards vary depending on the likely threat of rusts in different locations. These are the minimum recommended resistance levels. So if growing varieties that satisfy only the minimum resistance standard, a fungicide management plan is likely to be required as a back-up for protection, depending on when and if rust infects a particular paddock.
Growers who choose to plant early need to select varieties with the maximum rust resistance, ideally varieties rated moderately resistant (MR) or resistant (R).
In reality, there are only a few varieties that satisfy this requirement for the three wheat rusts. The rapid spread of wheat leaf rust pathotype 104-1, 3, 4, 6, 7, 8, 10, 12 +Lr37 since its introduction into South Australia in 2014, and its introduction and spread in WA, has cut the list of varieties that satisfy the minimum disease-resistance standards for leaf rust significantly.
Where growers want to plant early, some of the triticale varieties should be assessed for whether they can provide decent yields with good resistance to wheat leaf and stem rusts.
|Rust||Temperature range for
infection of leaf (ºC)
|Temperature range for
incubation in leaf (ºC)
Note: the infection temperature ranges indicate when rust spores can infect the plant. The incubation temperature ranges indicate the conditions required for disease development after infection has occurred.
|Queensland and northern NSW
|Southern NSW, Victoria, South Australia and Tasmania
|Long-season and early-sown wheats
More information:Dr Will Cuddy,
02 9351 8871,
Professor Robert Park,
02 9351 8806,
GRDC Project Code US00067, US00053, CSP00164