Paddock Practices: Barley diseases to be wary of this season
Author: Quinton McCallum | Date: 17 Jul 2018
Barley growers across the southern region should remain vigilant when it comes to monitoring their crops for foliar diseases this season, especially new varieties.
The variety of barley grown has a significant influence on the disease risk factors.
With large areas planted in 2018 to the new variety RGT Planet,there may be a high risk of net form net blotch (NFNB) this season, according to South Australian Research and Development Institute (SARDI*) crop pathology’s Dr Hugh Wallwork.
Spot form of net blotch (SFNB) and scald are likely to be an issue in medium and high rainfall areas in Victoria, while leaf rust is a lesser risk than usual owing to the lack of volunteers through summer.
NFNB is generally more of a problem in higher rainfall areas, while SFNB can be an issue in marginal areas where there is often barley in cropping rotations.
“If you’re out in the Mallee, SFNB is likely a common issue, while if you’re in the Lower North, Mid North or South East of South Australia then NFNB is likely to be a bigger problem,” Dr Wallwork says.
Growers should look out for blotches on the leaves early in the season and Dr Wallwork recommends monitoring any new varieties closely.
Agriculture Victoria research scientist Dr Mark McLean says barley foliar diseases have the potential to become severe and cause grain yield and quality losses in Victoria.
“SFNB, NFNB and scald are favoured by sowing barley into infected barley stubble from a previous season as well as wet seasonal conditions and early sowing,” he says.
According to Dr McLean, SFNB and scald were common in southern Victoria last season, while NFNB was found in susceptible varieties including RGT Planet, Fairview and Oxford.
“Most commercial barley varieties are susceptible to the spot form including La Trobe, Spartacus CL, Rosalind, Westminster and RGT Planet. Fathom on the other hand has good resistance,” he said.
“Most varieties are moderately resistant to the net form including La Trobe, Spartacus CL, Rosalind, while RGT Planet is susceptible. However, variety resistance can change due to variation in the pathogen.”
Once these foliar diseases become established, they can be quite hard to rein in, according to Dr Wallwork.
Growers need to be vigilant in monitoring barley crops when conditions are conducive to disease infection.
“Growers have to start monitoring from the time they start doing herbicide sprays,” Dr Wallwork says.
“If a disease is established then it is important to consider applying a fungicide early in the epidemic’s development. Once it gets into that lower canopy of the crop it’s hard for chemicals to then get control on those older tissues.”
Dr Wallwork believes an early spray is best to get on top of disease and says trials have also shown seed treatment with Systiva® (fluxapyroxad) is highly effective.
This was confirmed by several years of trials in Victoria by Dr Mclean.
In one field experiment at Curyo in the Mallee, during the favourable 2017 season, the benefits of Systiva® and different timings of foliar applied Prosaro® (prothioconazole and tebuconazole) for control of SFNB, in susceptible barley variety Rosalind, were evaluated.
Seven treatments were tested and compared to a minimum disease treatment (Systiva® + Prosaro® at growth stage 31 and 39) and nil treatment (no fungicide) (Table 1).
Moderate SFNB developed, reducing grain yield by 0.6 tonnes per hectare (10 per cent) (Figure 1). Fungicides provided significant grain yield improvements when applied proactively.
Systiva® alone or Systiva® and Prosaro® at growth stage 39 provided the greatest yield benefits of 0.4t/ha (six per cent) compared to the nil treatment.
Foliar fungicide application of Prosaro® at growth stages 25, 31 or both 31 and 39 were effective in reducing SFNB during grain development stages and provided a 0.3t/ha (five per cent) yield improvement. Prosaro® at GS39 was less effective due to dry conditions after flag leaf emergence.
Prosaro® application at GS15 did not provide significant yield improvement compared to the nil treatment as SFNB was able to re-establish during the winter and spring months, showing that foliar fungicide application at the seedling stages was too early to provide benefit.
Another experiment was conducted near Horsham to evaluate 10 different fungicide treatments for the control of SFNB on the very susceptible barley variety Dash. Systiva® was applied to seed, Uniform® to fertiliser and all other treatments as foliar sprays at early stem elongation (GS 31). These treatments were compared to a no fungicide approach.
All fungicide treatments provided reductions in SFNB severity and improved grain yield compared to the nil treatment (Figure 2), while Systiva® provided the greatest yield improvements.
The Victorian trials showed fungicide treatments at early stem elongation reduced the severity of SFNB and provided yield improvements.
The grain yield and quality loss of four varieties of barley with differing susceptibility to NFNB were revealed during other experiments near Horsham.
A low disease treatment was applied to determine grain yield and quality potential, and a high disease treatment (no fungicide) to determine loss.
Severe NFNB developed in the susceptible variety RGT Planet and breeding line VB9613, resulting in yield losses of about 2t/ha (Figure 3) and quality losses in relation to grain plumpness (retention and screenings) and weight (Figure 4).
The severity of NFNB on grain yield and quality losses were significantly less for Fathom and Commander showing that growing resistant varieties is important. However, these varieties can show much greater susceptibility and yield loss to NFNB in areas of SA where there are different strains.
Dr McLean’s work also showed timing and the number of fungicide applications are important when managing NFNB.
“Systiva® has been shown to be very effective during the seedling stages. Foliar application of a registered foliar fungicide is most effective when applied at stem elongation and flag emergence,” Dr McLean says.
“A combination of seed applied Systiva and foliar fungicide at flag emergence has been shown to be most effective as NFNB can move quickly later in the season as well.
“The economics of these approaches needs to be considered in light of seasonal conditions, as economic returns are only gained during seasons with good yields.”
While the decision on Systiva® seed treatment has already been made by growers, Dr Wallwork says the focus is now on preventing fungicide resistance.
“If growers do apply fungicide sprays then it is important to alternate between different fungicide groups,” he says.
“We need to use different chemicals. We’ve got strobilurins, azoles, and succinate dehydrogenase inhibitors (SDHIs) all available. We need to mix them up within label guidelines and have different combinations or rotate them — not just rely on one.
Dr Wallwork says the potential yield losses caused by SFNB in susceptible varieties like the Spartacus and Hindmarsh families could reach 20 per cent in a worst-case scenario.
An outbreak of NFNB could be much worse if left uncontrolled, according to Dr Wallwork, with damage to an untreated crop potentially reaching 70 per cent in yield loss.
Disease resistant barley genes discovered
Plant breeders will find it easier to develop barley varieties that can withstand common foliar diseases after the discovery of six barley genes which carry resistance to disease.
Agriculture Victoria’s cereal pathology team made the significant breakthrough during pre-breeding research.
Currently, diseases such as scald, powdery mildew, net form of net blotch (NFNB), spot form of net blotch (SFNB) and leaf rust cost barley growers and the wider industry $252 million a year due to reduced grain yield and quality, and costs associated with applying fungicides.
Agriculture Victoria research scientist Dr Mark McLean says the best way of reducing that cost is by developing resistant varieties.
Japanese barley variety Yangsimai 3 was the focus of Dr McLean’s research and was found to have durable host plant resistance, which is likely to be effective for decades.
Yangsimai 3 was screened across Australia and internationally from 2008-10, with findings showing resistance to SFNB everywhere it was tested plus novel resistance to scald.
Dr McLean says the Japanese variety’s SFNB and scald resistance is initially what caught researcher’s attention, but they also found the foreign variety was agronomically and phenotypically well adapted to local environments.
During research, Yangsimai 3 was crossed to commercially available varieties, producing high-yielding, disease-resistant lines for breeders.
As part of this process, resistance genes were genetically characterised by the University of Adelaide’s Australian Wheat and Barley Molecular Marker Program, resulting in the detection of four resistance genes to SFNB, two to scald and molecular markers for breeders to track the resistance traits in their breeding programs.
“In total we identified six novel resistance genes for breeders from one variety, with more likely to come in the next year or two,” Dr McLean says.
There was also resistance found to barley stripe rust, with genes to be genetically characterised in the future.
SFNB, scald and stripe rust resistant lines have been forwarded to breeding programs, with Dr McLean hopeful the outcome will be commercial barley varieties with improved disease resistance.
*SARDI is a division of Primary Industries and Regions SA
GRDC research codes: DAS00139, DAV00129, DAV00136
More information
Dr Hugh Wallwork, 08 8303 9382, hugh.wallwork@sa.gov.au
Dr Mark McLean, 03 5362 2111, mark.mclean@ecodev.vic.gov.au
Useful resources
GRDC Update paper – Cereal disease update (Victoria)
GRDC Update paper – Cereal disease update (SA)
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