Cereal foliar and root disease update 2019
Take home messages
- Proactive disease management can minimise losses associated with root and foliar diseases.
- Avoiding highly susceptible varieties where possible provides effective disease control.
- Identifying paddocks at risk of root disease prior to sowing using PREDICTA® B testing enables strategies to minimise yield loss to be implemented.
Dry conditions during 2018 meant cereal diseases were generally of limited concern. However, Agriculture Victoria (AgVic) field trials still measured yield losses of 12% due to foliar diseases and more than 50% due to crown rot, highlighting the importance of effective disease management strategies.
Cereal disease management in 2019
Cereal diseases will require proactive management prior to and during the 2019 season. Often, following dry seasons where diseases had limited impact, there is a temptation to be complacent about preventative disease management strategies, especially when cash flows are constrained. However, 2016 should serve as a reminder of how challenging disease management can be in a wet season following the dry season of 2015.
The widespread early summer rain across Victoria (December 2018) will likely support a green bridge (volunteer cereals growing over summer/autumn) that will carry over rust and viral diseases to provide early infection of crops in 2019. Likewise, dry conditions during 2018 will have limited the breakdown of stubble. This is likely to increase the carryover of stubble borne pathogens (e.g. crown rot, yellow leaf spot (YLS) and net blotch fungi) into 2019, even from cereal crops grown in 2017.
For 2019, a disease management plan that considers variety rating (consult a current disease guide) and inoculum loads within a paddock (consider stubble and soilborne diseases and cropping history) and the district (consider the green bridge) should be adopted. A fungicide strategy should then be developed for each crop based on the identified risks. Diseases can be cost effectively controlled when a proactive management approach is used.
Wheat foliar diseases
In general, wheat foliar diseases had minimal impact on wheat production during 2018. Septoria tritici blotch (STB) required management in the Western District, but did not progress under drier conditions in the Wimmera. Stripe rust and leaf rust appeared late in the 2018 season, but did not affect crop yield. There were no reports of stem rust in Victoria during 2018.
Rust in wheat
Widespread rain across Victoria in the early summer (December 2018) will support the growth of volunteer cereals that will act as a green bridge to carry rust inoculum over into the 2019 season. Rust is most severe in seasons following wet summers where there are large areas of uncontrolled cereal volunteers (green bridge).
Rust carryover can be reduced by removing volunteer cereals in paddocks by the end of February, thus providing a break in the life cycle of rusts from one season to the next. Removing volunteers also provides benefits for water storage, general management of weeds and other pests and diseases such as aphids and viruses.
Following a wet summer, it is important that increased attention is given to the management of cereal rusts. Where possible, avoid susceptible varieties to the three rusts (consult a current Cereal Disease Guide) and develop plans for rust management during 2019. At sowing, use of the fungicide flutriafol on fertiliser or fluquinconazole on seed has proven successful in delaying the onset of stripe rust epidemics in seasons where a significant green bridge risk existed.
Septoria tritici blotch
Septoria tritici blotch (STB) is currently the most important foliar disease of Victorian wheat crops. It is most severe in the high rainfall zone and widespread in the Wimmera, but did not develop to damaging levels in 2018 due to the dry spring. AgVic, with support from GRDC, assesses National Variety Trial (NVT) lines for their reaction to STB in the field at Hamilton to ensure new varieties have current Victorian relevant ratings.
An integrated approach that incorporates crop rotation (avoiding paddocks with infected wheat stubble), variety selection (avoid susceptible varieties) and in-crop fungicide application can provide effective suppression of STB. Identification of pathogen strains with partial resistance to common fungicides highlights the need to adopt an integrated control approach that is not solely reliant on fungicides.
Yellow leaf spot
Yellow leaf spot (YLS) is a common stubble borne foliar disease of wheat that is favoured by growing susceptible varieties and stubble retention practices. Previous studies by AgVic have demonstrated yield losses of up to 23%. Partial disease control which significantly reduces the level of yield loss in susceptible varieties is achieved with the application of a foliar fungicide (i.e. Prosaro®, (prothioconazole/tebuconazole)) at both stem elongation (Z31) and flag leaf emergence (Z39).
During 2017 and 2018, AgVic conducted field experiments near Horsham to compare fungicides and fungicide combinations for their ability to control YLS in comparison to a disease-free and an unsprayed control (Table 1). YLS infection was established by applying 1kg of infected wheat stubble to each plot. Disease severity, measured as percentage leaf area affected (%LAA), was assessed multiple times between mid-tillering (Z25) and mid anthesis (Z65). In 2018, no assessments were done post mid ear emergence (Z55) due to dry conditions. Grain yield and quality were also measured from harvest samples.
Table 1. Fungicide products applied at Z31 + Z39 (except Uniform® applied to fertiliser), active ingredients, rate and application method, and controls tested for suppression of YLS at Horsham during 2017 and 2018.
Rate of application
Example trade names
Multiple foliar fungicide
Amistar® Xtra, Titan Azoxystrobin Extra®
The effect of fungicide treatments on YLS severity during an average rainfall season in 2017 (393mm total) and a below average season in 2018 (204mm total) are shown in Table 2. Overall, no fungicide provided suppression comparable to the low disease treatment in either season, demonstrating that fungicides should not be relied on for complete suppression of YLS. Of the fungicide products, propiconazole (e.g. Bumper®) and the prothioconazole/tebuconazole combination (Prosaro®) provided the greatest disease suppression in 2017. During 2018, propiconazole (e.g. Bumper®), and combinations of azoxystrobin/epoxiconazole (Radial®) and tebuconazole/azoxystrobin (Veritas®) provided significant suppression of YLS, comparable to the prothioconazole/tebuconazole combination (Prosaro®).
Table 2. Percentage leaf area affected by YLS in wheat variety PhantomA on two occasions and AUDPC following different fungicide treatments at Horsham during 2017 and 2018.
Disease severity (%)
Disease severity (%)
Values that do not share the same letter in lowercase superscript are significantly different from each other and can be compared within columns only.
A AUDPC = Area under disease progress curve, denoting the cumulative disease severity over the growing season.
There were significant improvements to grain yield and quality following fungicide application during 2017 (Table 3), but not 2018 (data not shown). During 2017, propiconazole (e.g. Bumper®) and the prothioconazole/tebuconazole combination (Prosaro®) provided significant grain yield improvements over the nil control and the greatest grain quality improvements, comparable to the low disease control. This demonstrated that there were benefits to timely fungicide application with some products during a favourable season. Other fungicides products did not provide significant yield improvements, but did provide improvements to grain quality, compared to the nil treatment.
The findings from this study were comparable to previous studies that showed that foliar fungicide application at Z31 and Z39 can provide significant improvements to grain yield and quality during seasons favourable to the development of YLS, where yields are average or greater. However, fungicides did not provide economic benefit during dry seasons. Where possible, use variety and paddock selection to minimise risk from YLS as this will be more effective.
Table 3. Grain yield and loss plus grain quality of wheat variety Phantom in response to fungicide treatments to control YLS at Horsham during 2017.
Screenings (%) A
Retention (%) B
General analysis of variance with Fishers protected LSD used for analysis.
Letters in lowercase superscript can be compared within columns only.
n.s = non-significant differences from low disease control.
A Screenings = % of grain less than 2.2 mm wide. B Retention = % of grain greater than 2.5mm wide.
Barley foliar disease management
Foliar diseases had little impact on barley crops in Victoria during 2018 due to the dry conditions. Spot form (SFNB) and net form of net blotch (NFNB) and scald were at low levels while leaf rust and powdery mildew were generally absent.
Net form of net blotch
Net form of net blotch (NFNB) is becoming an important foliar disease of barley due to the cultivation of susceptible varieties such as RGT Planet and in some regions, Fairview and Oxford. Field experiments at Horsham during 2017 showed grain yield losses of up to 22% (2t/ha), as well as grain quality losses in a high yielding season (approx. 8 t/ha) with good spring rainfall.
Field experiments conducted near Horsham (Wimmera) and Birchip (Mallee) during 2018 determined grain yield and quality loss in three barley varieties with different levels of resistance to NFNB and one very susceptible old breeding line, VB9613. Two treatments were applied: 1) No disease - fungicide treatment which had Systiva® applied to seed and foliar applied Prosaro® at stem elongation (Z31) and flag emergence (Z39) to determine grain yield and quality potential, and 2) Disease treatment, which had no fungicide application and 1kg of NFNB infected barley stubble added, to determine loss.
The Horsham trial was in a paddock with good sub-soil moisture, supporting grain yields of approximately 4.5t/ha, despite growing season rainfall being well below average. Scald infection was present in Fathom, Commander and RGT Planet, which may have affected grain yield slightly. Up to 24% of leaf area was affected by NFNB in the very susceptible line VB9613. This resulted in a 12% reduction in grain yield (Table 4) and losses in grain plumpness and weight, demonstrating the importance of not growing very susceptible varieties as they can have losses during any season with good yield potential. NFNB developed late in the season in the susceptible to very susceptible (SVS) rated RGT Planet, but did not cause grain yield loss and only caused minor grain quality loss. This contrasted with the Horsham site during 2017, where RGT Planet had 22% grain yield loss and significant grain quality losses. This highlights that seasonal conditions are important to disease development and that NFNB is unlikely to be an issue during dry seasons except if a very susceptible variety (VS) is grown.
Fathom (moderately resistant to moderately susceptible (MRMS)) and Commander (moderately susceptible (MS)) had little or no NFNB infection and no losses to grain yield or quality, showing that MS or better rated varieties can be sufficient to avoid loss due to NFNB in low disease pressure seasons.
The Birchip site had less than 5% of leaf area affected by NFNB (data not shown) and grain yield was less than 0.7t/ha in all varieties and treatments (data not shown), indicating that water was the main limiting factor to yield. This demonstrated the importance of reviewing disease management plans during the season and not unnecessarily applying fungicides in such a dry season.
Table 4. NFNB severity, grain yield and quality loss of three barley varieties and one VS rated breeding line at Horsham during 2018.
NFNB Severity (%)
Grain yield loss
Grain quality loss (%)A
RGT Planet (SVS)
*=Significant difference between the fungicide and disease treatments at 0.05. ns = Not significant.
Red leather leaf of oats
Red leather leaf is a common stubble and seed-borne foliar disease of oats caused by the fungus Spermospora avanae. To date, there has been little research to determine its impact on oat production or identify effective control strategies. AgVic conducted separate variety yield loss and fungicide experiments near Horsham during 2018 to help develop management strategies.
The yield loss experiment consisted of four milling grade varieties (Table 5) with different resistance ratings to red leather leaf, with six replicates each of two treatments: 1) Disease free - three fungicide applications to minimise disease, and 2) Disease - no fungicide and 1kg of red leather leaf infected oat stubble applied to determine loss.
Despite the low rainfall during 2018, the oats yielded 3-4t/ha with up to 18% red leather leaf infection by season’s end. Kowari and Bannister both had significant grain yield loss in infected plots (Table 5). Kowari also lost grain quality, which is a potential concern for milling oat growers. No grain yield or quality loss was measured for Williams or Mitika, most likely due to crop maturity in relation to disease development.
These findings demonstrate that red leather leaf caused grain yield and quality loss in milling oats, even during a dry season. Losses were variable between varieties and are likely to be greater during wetter seasons that favour disease development later in the season.
Table 5. Red leather leaf severity, grain yield and quality loss of four milling oat varieties at Horsham during 2018.
Red leather leaf severity
Grain quality loss (%)B
2 Oct (Z72)
0.3 (10%)* B
A %LAA = percentage of leaf area affected.
B *=Significant difference between the fungicide and disease treatments at 0.05. ns = Not significant.
To evaluate fungicide strategies for the management of red leather leaf in oats, three fungicide applications timings (Z25, Z31 and Z39) were compared with an untreated control in the susceptible oat variety Mitika. Disease severity was assessed six times (27 July, 6 and 23 August, 5 and 11 September and 2 October) during the growing season and grain yield and quality measured. There was no significant effect of fungicide on grain yield or quality, so this data has not been presented.
Red leather leaf symptoms were first observed during mid-July which developed rapidly during late August and early September (Figure 1) in response to wet weather. There was little disease development during the spring months due to dry conditions. Red leather leaf suppression varied between foliar fungicide timings with application at tillering (Z25) providing the best suppression (Figure 1) and application at stem elongation (Z31) was the next most effective. This was due to fungicide application coinciding with the onset of early disease development in 2018. Foliar fungicide at flag leaf emergence (Z39) was less effective, due to the application being after the majority of disease had already developed.
Red leather leaf develops rapidly, given the right conditions. As a result, multiple fungicide applications may be required. Further studies are required to provide more robust management recommendations to oat growers.
Figure 1. Red leather leaf development in susceptible oat variety Mitika in response to application of foliar fungicide, propiconazole (125 g ai/ha) at different growth stages in comparison to a no fungicide, disease treatment.
Yield losses caused by root diseases often go unrecognised as symptoms are below ground and even if their effects become apparent, there are no in-crop management solutions available. A PREDICTA® B test taken before planting provides an effective way to detect paddocks at risk of root diseases and enables management strategies to be implemented.
Recent economic studies demonstrated annual average yield losses of 7% and 1% due to crown rot and root lesion nematodes, respectively, across Victoria and South Australia (SA). Within individual situations, however, field trials during 2018 in Victoria demonstrated yield losses from crown rot of 42% and 65% in bread and durum wheat crops, respectively (Table 6), demonstrating how damaging this disease can be.
Crown rot is now possibly the most important disease affecting wheat crops in Victoria and nationally. A recent study of 1502 PREDICTA® test results from across Victoria and SA (2015-2017) found that 36% of paddocks tested had a medium or high level of crown rot inoculum prior to sowing. Annual average yield losses across all wheat crops in Victoria and SA were estimated to be 6.6% with losses up to 10% in seasons conducive to crown rot. Field trials conducted by AgVic have demonstrated that in paddocks where crown rot is present, yield losses greater than 30% can occur.
The extent of yield loss caused by crown rot is related to the level of inoculum present in the paddock at planting, the seasonal conditions and variety susceptibility (Table 6). Hence, growers can use a PREDICTA® B test to establish the level of risk present in a paddock prior to sowing and implement appropriate management strategies if necessary.
Seasonal conditions have a large influence on the yield loss caused by a given level of crown rot infection (Table 6). For example, during the wet season of 2016, the medium crown rot inoculum levels caused no yield loss, but during the driest season (2018) the same level of inoculum caused a 35% reduction in grain yield in the susceptible variety Cobra.
Cereals vary in their extent of yield loss in the presence of crown rot. As shown in Table 6, during 2015 at the high inoculum level, yield loss in the bread wheat Emu Rock (MS) was 12%, while in the bread wheat Cobra (S) was 35% and the durum wheat WID802 (VS) was 63%. This clearly shows the benefit of avoiding highly susceptible varieties in paddocks with medium to high levels of crown rot inoculum.
In paddocks with high levels of crown rot, it is best to avoid growing cereals. Previous work has shown that cereals increased inoculum levels, while broadleaf break crops (e.g. canola and pulses) and fallow decreased inoculum levels of crown rot. In general, a two-year break from cereals is required to reduce medium to high inoculum levels to a low level. A three-year break may be required following the dry season of 2018 due to the decreased decomposition of cereal stubble.
Table 6. Effect of seasonal conditions, increasing crown rot inoculum levels at planting and varietal susceptibility on yield loss with yield potential and growing season (April to October) rainfall at Horsham during the years 2015 to 2018.
Yield Loss (%)
Yield Potential (t/ha)
Crown Rot Level (g/m row)
Bread Wheat, cv. Emu Rock (MS to crown rot)
Bread Wheat, cv. Cobra (S to crown rot)
Durum Wheat, cv. WID802 (VS to crown rot)
Rhizoctonia root rot
The dry 2018 season will have favoured the build-up of Rhizoctonia solani AG8 levels within paddocks. Significant summer rainfall will decrease inoculum levels if volunteer cereals and summer weeds (green bridge) are effectively controlled. The impact of rhizoctonia root rot on crops sown in 2019 will be reduced if the season breaks early and crops establish in warmer soil. Rhizoctonia is most damaging when root growth is restricted either by cold soils, compaction layers or lack of moisture. Crops that establish well can still be affected in mid-winter when soil temperatures drop below 10°C at which point Rhizoctonia can attack the crown roots causing uneven growth and reduced tiller number, rather than classic bare patch symptoms.
If growing cereals in 2019, a PREDICTA® B test can be used to identify paddocks at risk. If Rhizoctonia is present at high levels, control summer weeds and autumn green bridge and consider rotating to a non-cereal crop. If a cereal is to be grown, wheat is more tolerant than barley and early sowing in the seeding window with banding of nitrogen (N) below the seed to facilitate rapid root growth can also limit early impacts. Ensure good crop nutrition, with particular attention to trace elements, and increase seeding rates to reduce impact of lost tillers from Rhizoctonia damage to crown roots.
Consider fungicide seed treatments to protect the roots. Rainfall is needed to move fungicides into the root zone as roots outside the fungicide zone are not protected. Seed treatments tend to protect the seminal roots, whereas liquid streaming Uniform® above and below the seed can protect crown and seminal roots and tends to produce larger yield responses in above average rainfall seasons.
Root lesion nematodes
The root lesion nematodes (RLN), Pratylenchus neglectus and P. thornei are widespread in Victorian cropping paddocks. A recent study of 1,965 PREDICTA® B test results from across Victoria and SA (2013-2017) found that RLNs were present in 92% of paddocks with approx. 10% of paddocks having a medium or high test result. This report estimated the annual average yield loss across all wheat crops in Victoria and SA to be 1% with losses up to 2% in seasons conducive to losses from RLNs. Field trials conducted by AgVic and SARDI have demonstrated that in paddocks where RLNs are present, yield losses greater than 10% can occur.
Using data collected from many field trials conducted in Victoria and SA, the PREDICTA® B risk categories were updated for RLNs (Table 7). These revised risk categories reflect that yield losses due to RLNs do not occur in all seasons and our improved understanding of the extent of yield losses that they cause.
To keep nematode densities below yield limiting thresholds, it is important to grow varieties with a MR/MS or better resistance rating. If susceptible varieties are grown, it is important they are rotated with resistant crops or varieties and nematode densities monitored using a pre-sowing PREDICTA® B test. If medium to high nematode densities are present, consider growing resistant crops or varieties. Consult current Cereal and Pulse Disease Guides for the latest RLN resistance ratings as it is important to check the resistance rating of varieties due to varietal variation within crops for resistance/susceptibility to RLN species.
Table 7. Revised P. thornei and P. neglectus PREDICTA® B risk categories for Victoria and SA for seasons that range in their conduciveness for yield loss in intolerant varieties.
Seasonal Conditions and FrequencyA
RLN /g soil
Yield Loss %
A Conducive and non-conducive season are those where yield loss does and does not occur, respectively, due to the nematodes. The historical frequency of these occurrences is provided as percentages. The conditions that favour yield loss are not understood.
B BDL, below detection level.
Bunts and smuts
Seed treatments provide cheap and effective control of bunt and smut diseases. Seed should be treated every year as bunt and smut can increase rapidly, resulting in unsaleable grain. Good coverage of seed is essential and clean seed should be sourced if a seed lot is infected. Fertiliser treatments do not control bunt and smuts, so seed treatments are still required.
In the absence of proactive disease control, yield losses due to diseases can be greater than 20%. It is, therefore, important that plans are developed to effectively manage wheat diseases this season.
The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC — the author would like to thank them for their continued support.
Funding for this work was provided by the Victorian Government (Agriculture Victoria) and the GRDC through the GRDC projects DAV00129, DAV00128, DAV00144, DAV00136, DAN00175 and DAW00245.
Thanks to Agriculture Victoria’s Cereal Pathology Team: Graham Exell, Jordan McDonald, Tom Pritchett, Jon Baker, Laura Roden, Luise Sigel, Jennifer Cutajar and Winnie Liu Heang. Thanks also to the Birchip Cropping Group for field trials within the Victorian Mallee.
GRDC Project code: DAV00129, DAV00128, DAN00175, DAS00137, DAW00245, DAV00144, DAV00136
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