Keep up with the latest research information on cereal diseases including Septoria tritici blotch of wheat, spot and net blotch of barley, rhizoctonia root rot, crown rot and the cereal rusts. The following papers were presented at the GRDC Updates across Australia in February and March 2016.
By Nicke Poole and Tracey Wylie (FAR Australia).
- More evidence of fungicide resistance (or insensitivity) in triazoles has emerged in the 2014 and 2015 seasons
- These developments emphasise the need to use both an integrated disease management approach that capitalises on cultivar resistance and cultural control measures as well as adhering to anti resistance guidelines for new fungicides entering the market place
- Fungicides with a new modes of action, such as the succinate dehydrogenase inhibitors (SDHIs) (FRAC Group 7 classification) are now being commercialised in the Australian market and offer a step forward in disease control for a range of wheat and barley diseases
- Initial results with these products have been very promising against diseases such as yellow leaf spot, Septoria tritici blotch and net blotches.
- New research shows that adult plant resistance genes reduces the need for multiple fungicide applications and gives greater timing flexibility to single fungicide applications.
By Marg Evans and Hugh Wallwork (SARDI). Presented at Adelaide, February 2016.
This paper covers:
- Eyespot was found more widely in 2015 than in previous years. Yield losses are becoming more common and growers in the disease prone areas should be aware of the symptoms and effective management strategies. At least one fungicide to manage the disease should be registered in 2016
- Septoria tritici blotch has spread from the South East through a large area of medium rainfall areas of South Australia. New virulences in the pathogen population mean that most varieties are now susceptible to some degree and caution should be taken with early sown crops
- Loose smut continues as a problem in Hindmarsh crops. Effective treatments are available, but powdery mildew control needs to be maintained for all susceptible barley crops at the same time
- Check crown rot risk levels before sowing susceptible cereals in 2016, because low 2015 rainfall may have reduced the break-down rate of infected cereal residues under break crops last year
Impact of soil openers, seeding time and nematodes on Rhizoctonia fungicide wheat and barley yield responses
By Alan McKay (SARDI). Presented at Bendigo, February 2016.
- Results indicate yield responses are likely to be greater in barley than wheat, and in crops sown within the optimum seeding window. Applying fungicides to low yield potential paddocks and areas within paddocks is less likely to provide a positive return
- Increased root growth associated with application of Uniform® fungicide in all treatments did not always translate to a significant yield increase in field trials conducted in the SA Murray Mallee in 2015. Low spring rainfall is likely to be a key factor, and interactions with other diseases including Pratylenchus neglectus are also potentially important
- Application of post emergent nitrogen (N) is likely to be beneficial, but the economics requires further investigation
- Rhizoctonia levels are greater following barley than wheat, so barley following barley could be especially vulnerable
- Pratylenchus neglectus multiplication is greater on early sown crops, under wheat compared with barley
- To increase the reliability of a positive return on investments to control rhizoctonia root rot, further work is needed to better understand responses in different seasons, interactions with other diseases and farm practices including post emergent N application
By Grant Hollaway (DEDJTR). Presented at Bendigo, February 2016.
- Plans to effectively manage cereal diseases need to be developed for 2016, even though diseases levels were low in 2015. If diseases are not effectively controlled, and favourable climatic conditions occur, diseases can develop rapidly and cause yield loss
- A new strain of wheat leaf rust has become dominant in eastern Australia and resulted in many cultivars being rated more susceptible
- Septoria tritici blotch has become the most important disease in Victoria’s high rainfall cropping zones. Due to the occurrence of strains with reduced sensitivity to some fungicides, an integrated management approach is required
- A new seed applied fungicide, Systiva® provides very good suppression of SFNB and other stubble-borne foliar diseases of barley during the early stages of crop development
- Cereal root disease levels will remain similar in 2016 with little breakdown in the presence of break crops during the dry 2015 season. Root disease risk can be monitored using a PreDicta B soil test
By Steven Simpfendorfer (NSW DPI) Presented at Coonabarabran, Goondiwindi, Nyngan and North Star, February and March 2016.
- Stripe rust has not gone away!
- Know the difference between a ‘hot individual plant’ and a ‘hot-spot’ before creating panic.
- If you had stripe rust in your EGA Gregory in 2015 it is likely a seed purity issue. Consider freshening up your seed source.
- EGA Gregory remains MR to stripe rust and does NOT require fungicide application
- Consider ‘up-front’ or early season fungicide management of stripe rust in Suntop in 2016, especially under higher nitrogen status
- Be aware of the development and spread of new wheat leaf rust pathotypes in your region
- The north is on track with rust management, do not slip on minimum disease standards, any perceived short-term gains are likely to result in long-term pain for ALL.
By Steve Simpfendorfer (NSW DPI). Presented at the Coonabarabran, Goondiwindi and Nyngan, February 2016
- Barley and bread wheat varieties do vary in their yield response to crown rot infection.
- Variety choice can provide a 20-50% yield benefit over growing the susceptible variety EGA Gregory in the presence of high levels of crown rot infection.
- However, all varieties are susceptible to crown rot infection and will not significantly reduce inoculum levels for subsequent crops. Variety choice is NOT a sole solution to crown rot.
- Crown rot tolerance should not be the only consideration in variety choice, impacts on other pathogen populations, especially Pratylenchus thornei, resistance to other pathogens, grain quality and delivery should all be considered along with relative grain prices.
Yield impact of crown rot and sowing time on winter cereal crop and variety selection (Tulloona 2015)
By Rick Graham, Neroli Graham and Steven Simpfendorfer (NSW DPI). Presented at Coonabarabran, Goondiwindi and North Star, February/March 2016.
- Sowing date and variety maturity choice is a balance between the risk of frost versus terminal heat stress.
- Earlier sowing can increase frost risk but also generally maximises yield potential and reduces the extent of yield loss from crown rot.
- Cereal crop and variety selection can have a significant impact on yield in the presence of high levels of crown rot infection.
- Durum wheat and barley or bread wheat varieties with increased susceptibility to crown rot should only be grown in paddocks known to have low risk inoculum levels based on testing (e.g PreDicta B®).
- All winter cereal varieties are susceptible to crown rot infection and will not significantly reduce inoculum levels for subsequent crops. Cereal crop and/or variety choice is not the sole solution to crown rot.
By Steven Simpfendorfer, Rick Graham and Greg Brooke (NSW DPI). Presented at Nyngan, February 2016.
- Barley and bread wheat varieties varied in their yield response to crown rot infection at Nyngan in 2015.
- Cereal crop and variety choice provided a significant 48-182% yield benefit over growing the susceptible bread wheat variety EGA Gregory under high levels of crown rot infection.
- Barley tends to have improved tolerance to crown rot but is very susceptible to infection and will not reduce inoculum levels.
- All winter cereal varieties are susceptible to crown rot infection and will not significantly reduce inoculum levels for subsequent crops. Cereal crop and/or variety choice is NOT the sole solution to crown rot.
By Steve Simpfendorfer (NSW DPI). Presented at Coonabarabran and Goondiwindi, February and March 2016
- Treating EGA Gregory seed with Rancona® Dimension reduced establishment losses associated with the addition of crown rot inoculum to 6% compared to 23% when no seed treatment was used.
- In this instance Rancona Dimension did not provide a significant or consistent yield benefit in the presence of high levels of crown rot infection across the 12 trial sites in 2015.
- Growers should not expect Rancona Dimension to provide a significant and consistent reduction in yield loss from crown rot infection when used as a standalone management strategy.
- Growers considering the use of Rancona Dimension should follow the manufacturer’s advice and only consider it as part of an integrated management strategy against crown rot.
Barley disease update: Pathotype surveys of powdery mildew and net form net blotch and implications for management
By Greg Platz and Ryan Fowler (DAF Queensland). Presented at Goondiwindi, March 2016.
- Disease populations are in a constant state of change – change that is often directed by resistance genes in commercial varieties.
- Annual pathotype surveys are the best means of monitoring the presence of existing virulences and detecting the evolution of new virulences in disease populations.
- Keep abreast of significant changes in disease populations that may alter the resistance ratings of commercial varieties to plan appropriate management strategies.
By Lisle Snyman and Clayron Forknall (DAF Queensland). Presented at Goondiwindi, March 2016.
- Resistant varieties are the most practical way of controlling barley leaf rust. Yields of S and VS varieties are impacted most by the disease and increase the amount of inoculum exerting pressure on available resistance genes. If using S and VS varieties, be pro-active in terms of removing the green bridge, monitor crops regularly and apply fungicides early.
By Andrew Milgate (NSW DPI). Presented at Wagga Wagga, February 2016.
- Monitoring the root disease complex in southern New South Wales (SNSW) is vital to minimising losses
- Early sowing combined with wet winter favoured many cereal diseases in southern NSW during 2015
- Fungicide resistance is real and is present in New South Wales (NSW)
- Integrated disease management aimed at reducing the overall disease burden on crops will improve yields
By Jeremy Whish (CSIRO) and John Thompson (University of Southern Queensland). Presented at Coonabarabran, Goondiwindi and North Star, February 2016.
- Know your soil’s Root-lesion nematode (P. thornei) population size
- Test your soil for Root-lesion nematodes. P. thornei populations greater than 40,000 per kg at harvest will require a double break of around 40 months free of a host to reduce the population below the accepted threshold of 2000 Pt/kg. P. thornei populations greater than 10,000 per kg at harvest will require a single break of around 30 months free of a host to reduce the population below the accepted threshold of 2000 Pt/kg
- Weeds can be a host so fallows must be weed free and free of volunteers
By Nicole Seymour (Queensland Department of Agriculture and Fisheries), Graham Stirling, Jady Li. Presented at Goondiwindi, March 2016.
- Biological suppression does occur in most soils we tested from the northern grain-growing region, showing that populations of P. thornei are being reduced by parasites and predators.Suppression was found to be greater in the top 10cm of soil than at deeper layers (e.g. 30-45 cm). Practices such as zero tillage with stubble retention enhanced suppression. Without these practices, we estimate that RLN multiplication would be significantly greater, especially in top soils, and this would result in much greater losses in the productivity of susceptible crops.
- Suppression was found to be greater in the top 10cm of soil than at deeper layers (e.g. 30-45 cm). Practices such as zero tillage with stubble retention enhanced suppression. Without these practices, we estimate that RLN multiplication would be significantly greater, especially in top soils, and this would result in much greater losses in the productivity of susceptible crops.Several antagonists of Pratylenchus were found in northern grain-growing soils such as nematode trapping fungi, predatory nematodes, parasitic bacteria and root-colonising fungi that enhance the plant’s resistance to nematodes. Further research is focussing on these organisms as they are likely to be contributing to the suppressiveness of the soils.
- Several antagonists of Pratylenchus were found in northern grain-growing soils such as nematode trapping fungi, predatory nematodes, parasitic bacteria and root-colonising fungi that enhance the plant’s resistance to nematodes. Further research is focussing on these organisms as they are likely to be contributing to the suppressiveness of the soils.
By Andrew Verrell (NSW DPI). Presented at Coonabarbran and Goondiwindi, March 2016
- Sow chickpea crops between standing wheat rows
- Sow the following wheat crop directly over the row of the previous year chickpea crop
- Keep wheat stubble intact and do not spread it across the surface
By Brendan Burton and Linda Bailey (Northern Grower Alliance) and Kedar Adhikari (Sydney University Narrabri). Presented at Goondiwindi, March 2016.
- Multi-crop and variety trials were conducted over strips of ‘medium’ and ‘high’ Pratylenchus thornei (Pt) pressure.
- Site characterised by generally high crop yields (cereals~4-5.5t/ha, chickpeas ~3.5-4.0t/ha) combined with lower levels of Pt yield impact.
- Negligible decline in Pt population during the 21 month fallow leading up to the winter trials being planted.
- No evidence of yield impact from Pt in the brassica, faba bean, chickpea and barley trials.
- Greater yield loss observed in the wheat trials compared to the barley and broadleaf crops at this site.
- Addition of crown rot inoculum together with ‘high’ Pt pressure significantly increased mean yield loss (~30%) over a set of six wheat varieties compared to either the effect from crown rot inoculum alone (~13%) or Pt alone (~8%).
By Kirsty Owen, Tim Clewett, Jason Sheedy and John Thompson (USQ) Presented at Goondiwindi, March 2016.
Take home message
- Test soil for nematodes and plan crop rotations that target the species identified.
- Resistant crops will reduce high root-lesion nematode populations but several consecutive resistant crops and fallow may be needed to reduce very high populations.
- Tolerant crops can produce good yields when root-lesion nematodes are present but try to select tolerant varieties with high levels of resistance to have the biggest impact.
- Chickpea yield loss of current varieties due to P. thornei was 6.5% (provisional result).
- Liverseed grass (Urochloa panicoides) was susceptible to P. neglectus; grass weeds were poor hosts of P. thornei(provisional results).
By N. F. Poole and T. Wylie,(FAR Australia). Presented at Goondiwindi, March 2016.
- Fungicides with new modes of action, such as the Succinate Dehydrogenase Inhibitors (SDHI’s – FRAC Group 7) are now being commercialised in the Australian market.
- Initial results with the SDHI’s have been very promising against a range of barley diseases such as net blotches and scald as well as wheat diseases such as yellow leaf spot and Septoria tritici blotch (STB).
- The SDHI fungicides are at a moderate to high risk of pathogen resistance development so it is imperative that we don’t overuse these products and adhere to anti resistance guidelines.
- As more evidence of fungicide resistance (or insensitivity) in triazoles emerges it emphasises the need to use fungicides as part of an Integrated Disease Management (IDM) approach that capitalises on cultivar resistance and other cultural control measures.
- New research shows that Adult Plant Resistance genes reduces the need for multiple fungicide applications and gives greater timing flexibility to single fungicide applications.
The title links for the following papers will download the PDF version of the paper. The size of the PDF is given at the end of the paper title.
Wheat Powdery Mildew – Using New Fungicide Resistance Detection Methodologies to Stay Ahead of the Game (PDF 382kb)
By Madeline Tucker et al. Presented at Perth, February/March 2016.
- Wheat powdery mildew caused by the fungal pathogen Blumeria graminis f. sp. tritici (Bgt) was a surprising threat to the West Australian (WA) wheat industry in the 2015 cropping season, with many growers reporting some degree of infection.
- Recently Cyp51 mutations (Y136F and S509T), have been identified in barley powdery mildew isolates exhibiting some degree of resistance to many triazole fungicides, particularly tebuconazole. The Y136F mutation, although having minimal effect in the field, acts as a gateway mutation, initially present in isolates who mutate further translating to field level resistance.
- Digital PCR (dPCR) is a new technology in fungicide resistance mutation detection that can be used to screen several million fungal spores simultaneously.
- For the first time, dPCR was used to screen for the Y136F gateway mutation in Bgt. The mutation was found in significant numbers in the east of Australia but not in WA.
By Andrea Hills et al. Presented at Perth, February/March 2016.
- Grain yield response to fungicide application occurred in more than half (58%) of trials analysed. Grain yield gain from STNB control ranged from 0.19 to 2.18t/ha (5 – 59%) of the untreated yield. Grain screenings reduced by a third and there were also improvements in grain weight, hectolitre, brightness and protein levels.
- Double applications of fungicide, with the first made at stem extension, gained the greatest yield responses in the medium and high rainfall areas.
- Variety yield response reflects the disease rating – the highest gains are with SVS varieties.
- Spring rainfall, particularly rainfall and number of rainy days in September, determines the likelihood of a yield response to fungicide application. Growers in the medium and low rainfall areas need to take the spring rainfall outlook into account when deciding if a second fungicide application is necessary – in a dry spring there is no additional benefit from a second application.
- Propiconazole and Prosaro® performed comparably in nearly all situations where they were head to head.
By Ciara Beard, Geoff Thomas, Anne Smith, and Andrea Hills (DAFWA); Elly Wainwright (Liebe Group); Michael Macpherson (Imtrade Australia); Brad Westphal and Phil Smyth (Landmark); Leigh Nairn (Northampton Agri Services). Presented at Perth, February/March 2016.
- Application of a single foliar fungicide spray at a registered rate to a susceptible variety gave a significant yield response in four out of six trials located across the wheatbelt in 2015, when powdery mildew infection occurred from stem extension onwards. Average yield response across all trials to a single fungicide spray was 8%. Timing of application (as soon as possible after disease observed moving up canopy) was more important than product choice. In 6 trials, the difference between untreated versus treated yield was more significant than differences between product or active ingredient used.
- The best timing was: 1) before disease became severe and before flag leaves and particularly heads were infected and 2) where disease onset was later, once all leaves had emerged (i.e. after Z39) so maximum canopy area was protected. An earlier sown crop was more vulnerable to head infection than a later sown crop alongside it. Fungicide application after head emergence was too late to provide effective head protection and was not economic.
- Fungicides are more efficient as protectants than eradicants. To get most value from fungicides and achieve optimal yield benefit it is crucial to control the disease before it becomes too severe and develops in upper canopy and on heads. The value of applying a second fungicide was variable and in the two trials where it was tested was not justified by a significant yield response, possibly due to the dry hot spring in most locations.
Broad spectrum suppression of wheat and canola fungal diseases by endophytic biocontrol agents (633 kb)
By Margaret M. Roper, Cathryn A. O’Sullivan, Cindy A. Myers, Louise F. Thatcher (CSIRO Agriculture). Presented at Perth, February/March 2016.
- Several bacteria from the Actinobacteria phylum with antifungal properties were isolated from paddocks across WA.
- These Actinobacteria are effective at suppressing a range of fungal pathogens of wheat and canola including Fusarium crown rot, Pythium damping off, take-all root rot, Rhizoctonia hypocotyl rot and Sclerotinia stem rot.
- They have enormous potential for development as biocontrol agents because they can be delivered as a seed coat, they are endophytic so they will take up residence within crop roots, they are easy to culture and grow, and they form spores that allow them to survive adverse environmental conditions.
By Professor Robert F. Park and Dr Will Cuddy (The University of Sydney). Presented at Perth, February/March 2016.
- Rust pathogens spread freely and rapidly through the Australasian region. While this is predominantly in a west-to east direction, recent years have seen two examples of east-to-west transport.
- Monitor for the presence of the green bridge, and if present, make sure it is destroyed at least 4 weeks before crops are sown, either by heavy grazing or herbicides.
- Warm, moist autumn conditions favour the development of leaf rust.
- Monitor crops of vulnerable varieties for leaf rust in 2016 and send samples for pathotype analysis to the Australian Rust Survey. This service is free to all, and is funded by the grower levy paid to the Grains Research and Development Corporation.
- The identification of rust pathotypes involves greenhouse tests in which seedlings of indicator varieties are infected, and takes about 3 weeks. These tests are increasingly being supplemented with DNA-tests that are much quicker (less than 48 hours). The DNA tests provide useful basic information but are nowhere near powerful enough to identify pathotypes.
- Genetic resistance to rust in wheat and barley delivers significant benefit to Australian grain growers, estimated at $1.1 billion annually, and remains the basis of rust control especially in wheat.
- Minimum disease standards remain important for industry-wide benefit from genetic resistance.