Keep up with the latest research information on cereal diseases including Septoria tritici blotch of wheat, crown rot, rust, Fusarium head blight, and yellow leaf spot. The following papers were presented at the GRDC Updates across Australia in February and March 2017.
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We’ve also pulled together all the:
Authors: Nick Poole and Tracey Wylie (FAR Australia)
- There should continue to be a focus on the principles of an integrated disease management (IDM) approach to control diseases such as STB, using rotation, cultivar resistance, later sowing, and other aspects of cultural control to complement fungicide control.
- New research on foliar fungicides indicates that the principal foliar fungicides still give good in-field control of STB up to 30 days after application when applied at full label rates.
- There are significant differences in disease control of STB and leaf rust amongst the different fungicide products and rates of application when monitored leaves are assessed more than 30 days after application.
- Single spray timings of foliar fungicide for control of STB made during the late tillering phase gave less effective disease control than applications made at first node (GS31). Spray application delayed until flag leaf gave the poorest control of STB but gave superior leaf rust control later in the season.
- Combining two adult plant resistance (APR) genes in Avocet Near Isogenic Lines (NILs) reduced the maximum yield response to stripe rust control from (significant responses) 0.98 and 0.4t/ha where the single genes were used along down to non-significant response of 0.22t/ha where the genes were combined.
Authors: Clayton Forknall (DAFQ), Steve Simpfendorfer (NSW DPI) and Alison Kelly (DAFQ)
- Response curves provide an additional tool to aid growers in varietal selection decisions to maximise returns in the presence of disease.
- An experiment conducted near Macalister in 2015 revealed variation in the yield response of varieties to crown rot, along with their resistance to this disease.
- The variety Suntop, although displaying crown rot symptoms similar to that of a susceptible variety, demonstrated a greater ability to maintain yield in the presence of disease than other varieties considered (tolerance).
- The selection of varieties based purely on current resistance categories may be overlooking genetics with improved tolerance, such as the variety Suntop.
Authors: Greg Platz, Lisle Snyman and Clayton Forknall (DAFQ)
- Losses in yield to a given disease epidemic vary with the levels of resistance in the varieties affected.
- The GRDC funded project “Yield loss response curves for host resistance to leaf, crown and root diseases in wheat and barley” is gathering data on yield losses of varieties with different levels of resistance under epidemics of different severities for a range of pathogens of wheat and barley.
- The barley foliar disease module of the project is being led by DAFQ, with experiments conducted nationally to explore the impact of leaf rust, net blotch (spot form and net form), scald and powdery mildew on current commercial barley varieties.
- NVT disease resistance ratings categorize varieties into 9 resistance categories (R – VS). Data collected from the project will add precision to assignment of these resistance categories.
- Growers and agronomists will be able to make better informed and more accurate decisions on disease management by implementing information gathered from the yield loss response curves project in their calculations.
Authors: Jean Galloway (DAFWA), Ciara Beard (DAFWA), Pip Payne (DAFWA), Geoff Thomas (DAFWA) and Moin Salam (Freelance Consultant, Bangladesh)
The fungus that causes yellow spot survives from one season to the next on infected wheat stubble. In the Western Australian (WA) Grainbelt yellow spot fruiting bodies mature and ascospores are released from the previous season’s stubble earlier in the southern coastal cropping areas (Albany and Esperance) compared with central (Northam) and northern (Eradu) cropping areas. The timing of fruiting body maturation is influenced by environmental factors, predominantly rainfall and temperature.
The early maturation of the yellow spot fungus in the southern coastal cropping area, usually before crops have emerged, results in limited primary infection opportunities. This, combined with cooler temperatures, can limit yellow spot impact in most years in this region. The later maturation of the yellow spot fungus in the central and northern cropping areas is often after crop emergence and can result in multiple primary infection opportunities. These multiple primary infection opportunities, coupled with warmer winter conditions which favour secondary spread, result in continuous wheat crops in the northern and central areas having a high risk of developing yellow spot.
The timing of the onset of yellow spot ascospore release from stubble does vary from year to year. In years when the stubble has been exposed to several summer rainfall events the fruiting bodies mature earlier in the autumn compared with years that have had limited rainfall events between harvest and the autumn break. Progress has been made towards developing and validating a decision support tool (DST) that predicts the timing of yellow spot ascospore release. This is being developed and tested with data from WA, SA and Victoria. This DST will assist wheat growers, advisors and researchers make informed decisions about yellow spot management.
Authors: Nick Poole and Tracey Wylie (FAR Australia)
- Results with the new Succinate Dehydrogenase Inhibitors (SDHI’s) have been very promising against a range of barley and wheat diseases including net blotches and scald in barley and in wheat yellow leaf spot and Septoria tritici blotch (STB).
- The wet spring encouraged greater issues with wet weather stubble borne diseases such as STB and net form of net blotch which has been more widely reported in 2016.
- 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.
- Combining two Adult Plant Resistance (APR) genes in Avocet Near Isogenic Lines (NILs) reduced the maximum yield response to stripe rust control from (significant responses) 0.98 and 0.4 t/ha where the single APR genes were used alone down to a non-significant response of 0.22 t/ha where the APR genes were combined.
- Controlled environment studies have shown that the curative activity of fungicides such as epoxiconazole against stripe rust is approximately 7-14 days depending on the mean temperature.
- 2016 research work shows that multiple APR genes reduce the need for fungicide applications.
Authors: Fran Lopez and Alex Kay (CCDM)
- Fungicides are key resources for sustainable farming practices.
- Misuse of fungicides and poor disease management practices have an impact on everybody.
- Overuse of fungicides with the same mode of action will speed up the development of resistance.
- Fungicide resistance is already present in nature but resistant populations get selected and build up under continuous use of fungicides from the same mode of action.
- Resistance is a numbers game and the only viable option to slow it down is to limit the size of pathogen populations. We can do this by use of appropriate rotations, use of clean seeds, early spraying and the use of fungicide mixtures and alternation.
- Fast (and cheap) monitoring of pathogen populations is central for the sustainable chemical management of diseases.
Author: Andrew Milgate (NSW DPI)
- The widespread occurrence of septoria tritici blotch (STB) across southern NSW was exacerbated by the unusually wet winter of 2016.
- The risk to crops in 2017 is higher than average with inoculum carryover expected to be high but disease development will be dependent on rainfall and timing of sowing.
- The fungicide resistance status of the NSW population will be provided during the update.
- Current popular varieties are vulnerable to infection and yield loss under favourable disease conditions.
- Fungicide resistance management strategies need to be implemented on-farm.
- Integrated disease management complements fungicide resistance management.
- To slow fungicide resistance, do not apply the same triazole active ingredient more than once in a season.
High crown rot risk and should growers plant barley or wheat in northern NSW and southern Queensland
Authors: Steven Simpfendorfer, Rick Graham and Guy McMullen (NSW DPI)
- In 62% of trial comparisons the barley variety Commander provided a significant yield benefit (av. 1.04 t/ha) over the bread wheat variety EGA Gregory when grow in the presence of crown rot infection.
- In 30% of trial comparisons the effect of choosing Commander or EGA Gregory was neutral in the presence of crown rot infection.
- In 8% of trial comparisons Commander resulted in a significant yield penalty (av. 0.48 t/ha) compared to growing EGA Gregory, likely due to stress occurring earlier in the season.
- Barley and bread wheat varieties do vary in yield response in the presence of crown rot infection.
- Barley is very susceptible to crown rot infection and will not reduce inoculum levels for subsequent cereal crops.
Authors: Lislé Snyman, Greg Platz, Clayton Forknall Dept of Agriculture and Fisheries Queensland
- Crop rotation and reducing surface stubble decrease inoculum levels
- Do not sow susceptible wheat varieties into wheat stubble
- Economic response to fungicide application is a factor of varietal susceptibility, severity of the epidemic, product choice and timing of application.
- Increasing moisture periods increase the incidence and severity of yellow spot
Authors: Steven Simpfendorfer (NSW DPI), Daniele Giblot-Ducray (SARDI), Diana Hartley (CSIRO) and Alan McKay (SARDI)
- Low levels of Fusarium head blight (FHB) observed in central and northern NSW in 2016 were predominantly caused by Fusarium pseudograminearum (Fp).
- This was the crown rot fungus (Fp) reminding growers that it does not disappear in a wet season.
- FHB infection caused by Fp has reduced risk for mycotoxin accumulation in infected grain but could have detrimental impacts on crop establishment if retained for planting in 2017.
- Planting Fusarium infected grain can also introduce seed-borne crown rot infection into clean paddocks, undoing rotational benefits associated with growing non-host crops.
- Growers are urged to test both their crown rot inoculum levels in paddocks prior to sowing and ensure their 2017 planting seed has no or low levels of Fusarium infection if they observed FHB in 2016, especially if considering durum production.
Authors: Lislé Snyman, Clayton Forknall and Greg Platz (DAFQ)
- Compass is very susceptible to leaf rust and crops should be closely monitored for the disease
- Barley varieties differ in yield response to leaf rust across resistance ratings
- Resistance ratings of current commercial varieties are available on the NVT website
- Growing resistant varieties is the most practical and economical way of controlling barley leaf rust
- Varieties characterised as S to VS are impacted most by disease and also contribute to inoculum increase, leading to pathogen mutations putting available resistance genes at risk
- The use of resistant varieties forms part of a bigger disease management plan, which also includes green-bridge control, regular crop monitoring and the timely application of fungicides.
Authors: Greg Platz, Lisle Snyman and Ryan Fowler (DAFQ)
- Annual seed treatment with an effective fungicide is the best means to control loose smut.
- Loose smut infects heads at flowering and survives inside the seed.
- Some varieties are more susceptible to loose smut than others.
- Fungicides differ in their efficacy against loose smut and 100% control is difficult to achieve.
- Resistance to loose smut is not considered a high priority of barley breeding programs in Australia and control relies on the use of effective seed treatments.
- Effective seed treatment depends on choice of product, thorough application of fungicide and treatment of planting seed annually or not less than biannually.
Authors: Greg Platz, Lisle Snyman & Ryan Fowler (DAFQ)
- Disease epidemics are a function of presence of a virulent pathogen, availability of a susceptible host and environmental conditions favourable to the pathogen.
- Environmental conditions that are optimal for a particular pathogen signal potential for that pathogen to develop into an epidemic.
- Foliar diseases have a propensity for rapid increase where there are widespread sowings of susceptible varieties and environmental conditions are favourable for pathogen infection, sporulation and dissemination.
- Mild, wet seasons should trigger more frequent crop monitoring to detect unexpected increases in disease.
- Good disease control can usually be achieved by application of an appropriate fungicide before diseases become well established.
Authors: Steven Simpfendorfer (NSW DPI) and Maurie Street (Grain Orana Alliance)
- Spot-form of net blotch (SFNB) caused at least 18-21% yield loss in the susceptible barley varieties La Trobe and Spartacus CL in trials conducted at Tamworth and Dubbo in 2016. Note Dubbo also had another leaf disease, scald develop late in the season.
- Foliar fungicides provided effective suppression of SFNB + scald with associated yield benefits when applied at both GS31 and GS49.
- The seed treatment Systiva® provided useful levels of SFNB suppression post GS49 under moderate disease pressure at Tamworth but activity appeared to have waned by this growth stage under higher disease pressure at Dubbo.
- Systiva® basically had similar efficacy to the GS31 application of foliar fungicides when both strategies were backed up by a second foliar application at GS49.
- Product Z, an experimental foliar fungicide, appears to have improved SFNB activity compared to Amistar Xtra® which was then slightly better than Tilt®250 in these experiments.
- Barley growers are still urged to use integrated disease management (IDM) strategies to limit losses from SFNB and scald, with fungicides being only one component. IDM of barley leaf diseases will reduce disease pressure and the reliance on fungicides as the sole management tool but importantly also delays the development of resistance to these valuable chemical options.
Authors: Ryan Fowler and Greg Platz (DAFQ)
- Prolonged and widespread sowing of Commander and Shepherd barley has allowed net form net blotch (NFNB) to adapt to these varieties.
- Pathotypes able to infect Commander and Shepherd, that were once rare, have increased in prevalence in recent years.
- NFNB can be spread via the sowing of infected seed that has not been treated.
- Sowing barley on barley or more specifically, sowing a variety back into stubble of that same variety, causes the disease to increase within paddocks over time.
- Environmental conditions play a major role in the development of NFNB, with wet conditions favouring infection and spread of the disease, like the spring of 2016.
- NFNB is best controlled by crop rotation, sowing of varieties with a disease rating of MS or better, treating seed prior to sowing, monitoring crops for NFNB during the season and timely application of a registered foliar fungicide before disease becomes conspicuous in an S to VS variety.
Authors: Greg Platz, Lisle Snyman, Ryan Fowler, Dept of Agriculture and Fisheries
- Systiva® is a new seed treatment fungicide registered by BASF for the control of several foliar diseases of barley, smuts in barley, bunt in wheat and suppression of Rhizoctonia root rot in both.
- Systiva gives very good control of most foliar diseases for about 8 weeks of crop life.
- One or more supplementary sprays may be required for whole of season foliar disease control.
- Systiva is registered for loose smut control in barley but is ineffective against covered smut.
- Early season disease control slows disease epidemic development and increases yields where conditions after flag leaf emergence do not favour disease development.
- In 2017, seed treatment with Systiva is likely to cost approximately $15/ha or $30/100kg of seed.
- Systiva is a Group 7 fungicide and introduces new chemistry to seed treatment. Responsible use of the product is encouraged to prevent breakdown of efficacy.
Fungicides at seeing for the management of cereal foliar diseases including Spot Type Net Blotch (STNB)
Authors: Geoff Thomas, Ciara Beard, Kithsiri Jayasena, Andrea Hills, Jason Bradley and Anne Smith (DAFWA)
- Systemic seed dressing or in-furrow fungicides are applied preventatively (prophylactically) to address potential disease risk. They can delay onset, reduce severity or eliminate occurrence of disease often resulting in significant yield responses. In the absence of disease however, they are unlikely to provide yield or economic benefit.
- In four field experiments in at-risk environments in 2016, wheat powdery mildew was evident at three sites and reached yield limiting severity at one site.
- At two sites where powdery mildew infection commenced during stem elongation, seed dressings containing fluquinconazole, triadimenol or fluxapyroxad and in-furrow products containing flutriafol, triadimefon or azoxystrobin had significant impact on disease severity and incidence. Product differences were evident between sites.
- At the one site where powdery mildew was yield limiting, in-furrow and foliar fungicide treatments gave a significant yield response in a susceptible wheat variety.
- In three of four sites where disease severity was not yield limiting, neither foliar, seed dressing or in-furrow fungicides provided a yield response and would not have given positive return on investment.
Authors: D. Hüberli, K. Gajda, M. Connor, A. Van Burgel (DAFWA)
- Yield loss from crown rot infection varied among barley and wheat varieties in all three years tested, ranging from 0 to 1.85 t/ha (0-59% yield loss) for barley and 0 to 1.11 t/ha (0-42% yield loss) for wheat.
- An understanding of the crown rot disease history of a paddock and choosing varieties with the appropriate disease resistance ranking can improve crop yield substantially in the presence of crown rot.
Authors: Andrea Hills (DAWFA), Phil Goulding (DAFWA), Daniel Huberl (DAFWA), Geoff Thomas (DAFWA) and Lachlan Beveridge (ThinkSpatial)
- Rhizoctonia patches can be easily identified on both normal (RGB) and NDVI images captured by UAV.
- Mapping shows the pattern of patch distribution across a paddock, highlighting areas of crop with high and low levels of rhizoctonia patches.
- Maps can be used to determine the best fungicide treatment approach for susceptible crops such as blanket applications or zoning to optimise economic returns.
Authors: Hugh Wallwork and Marg Evans (SARDI)
- Eyespot was once again found more widely in 2016 than in previous years and higher inoculum levels are likely to be present in 2017. As yield losses are becoming more common, growers in disease prone areas should be aware of the symptoms and effective management strategies.
- Septoria tritici blotch inoculum which spread widely across the state in 2015 is likely to be present at much higher levels in 2017 given the large number of rainy days in 2016 which allowed the fungus to spread through crop canopies. Differences in virulence are becoming apparent between isolates of the fungus collected in the South-East and in the Mid-North.
- Increased virulence to net form of net blotch (NFNB) became apparent on Hindmarsh, La Trobe and Spartacus in barley trials at Elliston, Freeling and Kingsford. These varieties should now be considered similar to varieties rated as moderately susceptible (MS) or moderately susceptible-susceptible (MSS) for Spartacus, at least in the above areas.
- Leaf rust could be more severe in 2017 depending on summer survival owing to the large area sown to susceptible varieties. Take note of ’Free for February’ campaign to provide a more reliable summer break.
- Loose smut has been detected in many Spartacus crops. Effective treatments are available but powdery mildew control needs to be maintained for all susceptible barley crops.
- Another disease to watch out for in 2017 is take-all. Where growers have had a history of take-all or where barley grass populations have built up, then be aware that take-all inoculum will have had a favourable season for build-up in 2016. Significant summer rain of 25mm or more will, however, reduce those inoculum levels appreciably. Consider using a PreDicta B test if in doubt.
- Crown rot did not cause problems in 2016 and inoculum levels should have reduced significantly where paddocks had a break from cereal. Crown rot may still be a problem in 2017 if cereals were grown in 2016 in paddocks with existing inoculum levels. Consider using a PreDicta B test if in doubt, particularly if planning to sow a durum wheat crop.
Wheat disease management in Victoria: 2017
Authors: Grant Hollaway, Joshua Fanning, Melissa Cook, and Mark McLean (Agriculture Victoria)
- Wheat diseases will need active management in 2017 following carry-over of high levels of inoculum on stubble and the green bridge after the wet 2016 spring.
- Growers need to consider variety choice (consult a current disease guide), paddock selection (consider paddock history and take a soil test if unsure about root disease risk), the green bridge (rust carry over on cereal volunteers) and then put in place a fungicide plan for the control of potential disease threats.
- Yellow leaf spot reduced yields in susceptible varieties by ~20% in field experiments in the Wimmera and Mallee during 2016. Losses were less than 6% where resistant varieties were grown. Fungicide control was shown to be variable, but the best control was achieved with two sprays applied at growth stages Z31 and Z39.
- Septoria has continued to be important in high rainfall zones, and surveys during 2016 has shown that it is now present in the Wimmera at low levels.
- Rust will require control during 2017, especially if there is a green bridge (volunteer cereals growing over summer and autumn). The green bridge should be removed by the end of February and following consultation with a current disease guide, a plan developed for rust management.
- Root diseases levels will be higher than normal (especially take-all) following the wet spring. A PreDicta B test prior to planting will identify paddocks at risk to enable appropriate management to be implemented.
Proactively manage barley diseases during 2017
Authors: Mark McLean (Agriculture Victoria), Cameron Taylor (BCG), Hugh Wallwork (SARDI) and Grant Hollaway (Agriculture Victoria)
- Barley disease inoculum will be high in many fields during 2017 due to favourable seasonal conditions during 2016.
- Consult a current disease guide to review your varieties and plan ahead.
- Stubble-borne barley foliar diseases such as pot form of net blotch (SFNB), net form of net blotch (NFNB) and scald will require a proactive fungicide application strategy to minimise losses. Foliar fungicide at Z31 and Z39 or Systiva(R) and foliar fungicide at Z39 are most effective.
- Barley leaf rust will need to be monitored and managed in susceptible varieties such as Compass, if conditions are favourable.
- Apply effective seed treatments ensuring good coverage to control loose smut, especially in very susceptible varieties, HIndmarsh, LaTrobe and Spartacus CL.