Vigilance call for barley leaf rust
GroundCover™ Issue: 105 | Author: Tom Dixon
So far, pressure from leaf rust in 2013 has been low in the northern barley-growing region, following low rust levels in 2012, and little inoculum surviving through the summer, according to Greg Platz, a pathologist with the Department of Agriculture, Fisheries and Forestry Queensland (DAFFQ).
However, Mr Platz urges growers to be alert to the risks of a leaf rust outbreak: “The risks may be low this season, but that’s no reason to become complacent,” he says. “Rust can develop very rapidly in susceptible varieties.”
Leaf rust, caused by the fungus Puccinia hordei, can infect barley at any time from tillering to maturity. It thrives at temperatures from 15°C to 22°C when leaves are frequently wet from dew or rain. Early sowing when nights are still warm can increase the risk of infection, as these conditions help the disease to establish.
Barley infected with leaf rust can be identified by the presence of small, brown, circular pustules that produce orange-brown powdery spores. “To survive the off season, leaf rust requires living barley plants,” Mr Platz says. “By removing all volunteer plants growing in the area after harvest, you minimise the risk of disease the following season.”
Mr Platz advises growers to maintain clean fallows and exercise good hygiene around silos, fence lines and in flood debris to help make sure that that any potential host plants are removed.
“Leaf rust cannot survive more than about three weeks without a living host.”
Early detection is crucial to containing the disease. Leaf rust starts to develop near the base of the plant and spreads upwards, so Mr Platz recommends keeping an eye on the lower leaves.
“Sometimes it is easier to detect leaf rust by examining basal leaves that have begun to senesce and turn yellow,” says Mr Platz. “If leaf rust is present it will be seen as tiny green dots in the yellow tissue.”
Growers need to be looking for these symptoms, as well as the brown pustules on green leaves, he says.
Leaf rust is spread by the wind, so growers need to be aware of the disease situation within the district.
“Managing the disease requires a community effort, so if a grower locates leaf rust they should alert their regional departmental pathologist so a general alert can be issued,” Mr Platz says.
“Timely applications of fungicide help provide effective control, but once an epidemic becomes established it is difficult to stop,” he says.
Darling Downs grower and agronomist Tony Anderson has seen first hand how devastating leaf rust can be. In 2010, his community in Brookstead, Queensland, was hit with a major outbreak of the disease.
Conditions in the Darling Downs in 2010 were ideal for leaf rust to establish and spread. High rainfall throughout winter and early spring meant that attempts to control the disease on the susceptible barley variety Grout had limited success in the area. The result was serious yield losses and quality downgrades for many growers.
Varieties with resistance
Planting resistant varieties is one of the easiest ways to help control leaf rust, says Mr Anderson. GRDC-funded research has led to the development of several resistant barley varieties, such as Shepherd, Mackay and Fleet Australia. However, Oxford, Grange and Westminster varieties also have good levels of leaf rust resistance.
Research is being carried out to better understand leaf rust resistance so that breeders can produce more resistant plant lines.
Barley is the third choice behind wheat and chickpeas for winter sowings in the northern grain-growing region, and resistance to leaf rust and other diseases is making barley an increasingly attractive choice.
Grout barley is one of the most susceptible varieties, and although it might produce higher yields, the risk of a leaf rust outbreak makes it a risky choice. “Planting resistant varieties can be the difference between a crop failing or succeeding. Even with the conditions in 2010, I had a paddock of Shepherd barley that was free of leaf rust without any fungicide applied,” Mr Anderson says.
Applying a seed dressing, such as Jockey® or an in-furrow treatment may provide protection from the time of planting through to early-stem elongation, but it is unlikely to remain effective after flowering which is when the disease risk is greatest.
“If you are sowing susceptible varieties, such as Grout, Fitzroy, Gairdner, Commander or Binalong, budget for at least one foliar fungicide application,” Mr Anderson says. “Newer fungicides, such as Amistar Xtra® are effective on very susceptible varieties.”
Growers are advised to closely monitor very susceptible varieties, including Grout, Fitzroy and Binalong from the end of tillering (GS31), as the disease is likely to be detected in these varieties first.
07 4660 3633, 0408 733 055,
07 4693 9299, 0447 399 258,
Variety information for each area can be found in planting guides and at the National Variety Trials website (www.nvtonline.com.au).
GRDC Project Code DAQ00178