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Latest on Cereal diseases – 2019 GRDC Update papers

Net form of net blotch in wheat

Keep up with the latest research information in cereal diseases: Stem Rust, Net Form of Net Blotch, Crown Rot, Yellow Leaf Spot, Powdery Mildew and Barley Loose Smut. The following papers were presented at the GRDC Updates across Australia in February and March 2019. The papers are sorted by region. Click the paper titles to view the full paper.

Northern region
Southern region
Western region

We’ve also pulled together all the:

Pulse disease papers
Canola disease papers

Barley Stem Rust On The Darling Downs In 2018

Author: Lislé Snyman (Dept. Agriculture and Fisheries, QLD)

  • All isolates identified as Scabrum rust – will not infect wheat crops
  • The stem rust pathogen is a biotroph and needs a living host for survival – not stubble-borne
  • Most barley varieties are vulnerable to stem rust infection and will host wheat, rye and scabrum rusts
  • Susceptible varieties contribute to inoculum pressure and increase the risk of breakdown of resistance in other varieties
  • Need to manage green bridge to limit pathogen survival

Virulence In Net Form Of Net Blotch In Barley

Author: Lislé Snyman (Dept. Agriculture and Fisheries, QLD)

  • Continuous barley cropping increases the risk of net form of net blotch (NFNB)
  • The NFNB pathogen is seed-and stubble-borne
  • NFNB is best controlled by using resistant varieties (rated MS or better), crop rotation, seed treatment, regular crop monitoring and timely fungicide application
  • Virulences are dynamic and fluctuate in response to available host genotypes
  • No new virulences were identified in 2018.

Fungicide resistance in net blotch

Author: Lislé Snyman (Dept. Agriculture and Fisheries, QLD), Fran Lopez-Ruiz & Wesley Mair (CCDM)

  • Reduced level of sensitivity of several DMI fungicides was detected in Western Australia in the net blotch pathogen
  • All isolates from the Northern region tested up to date remained sensitive to fungicides
  • Control measures for both Net form of net blotch & Spot form of net blotch

The Secret Life Of Crown Rot: What Happens After Harvest?

Author: Toni Petronaitis (NSW DPI), Clayton Forknall (Department of Agriculture and Fisheries, QLD) and Steven Simpfendorfer (NSW DPI)

  • A preliminary survey of cereal stubble from 2017 showed that in the northern region (NSW and Qld) the crown rot fungus is commonly present from the crown up to 18 cm, with detection up to 33 cm within tillers at harvest
  • However, moist conditions can promote further growth of the crown rot fungus post-harvest in inoculated cereal stubble (increasing by almost 1 cm up from the crown per day at 100% humidity)
  • Inoculum levels in post-harvest stubble are not static and may fluctuate as different weather patterns are experienced
  • Planting different bread wheat, durum wheat and barley varieties may not be useful for suppressing inoculum growth in stubble after harvest
  • Reducing cereal stubble height may limit inoculum build-up in crown rot affected paddocks by restricting the capacity for further fungal growth post-harvest. This could also help reduce dispersal of infected residues when harvesting shorter break crops such as chickpea, but field validation of this management option is required.

Crown Rot – What Is The Threat Coming Out Of A Dry Year?

Authors: Steven Simpfendorfer (NSW DPI) and Alan McKay (SARDI)

  • Dry seasons which reduce crop biomass production and yield still increase crown rot inoculum levels within paddocks, but to a lesser extent than in good seasons.
  • Decomposition of previous cereal stubbles which harbour the crown rot pathogen, even under break crops (e.g. canola), is reduced in dry seasons. Hence, inoculum levels may not have declined significantly since harvest of 2017 cereal crops.
  • PREDICTA® B is a reliable technique for assessing the risk of crown rot and a range of other soil-borne or stubble-borne pathogens prior to sowing in 2019.
  • PREDICTA® B also has new tests for sclerotinia stem rot in canola as well as pulses and yellow spot in wheat. Tests for septoria tritici blotch of wheat and net blotches in barley are under consideration for next season.
  • Follow sampling recommendations in the manual V10.2, including the addition of pieces of cereal stubble to improve the detection of stubble-borne pathogens such as the crown rot fungus.

What Pathogens Were Detected In Central And Northern Cereal Crops In 2018?

Authors: Steven Simpfendorfer (NSW DPI) and Alan McKay (SARDI)

  • Disease surveys are important to stay abreast of developing issues within farming systems
  • Fusarium crown rot and common root rot (Bipolaris) were widespread in cereal crops in 2018 and are potentially dominating other diseases such as take-all
  • The yellow spot fungus was detected in all 102 wheat crops surveyed and surprisingly also in 43 of the 46 (94%) barley crops. This presumably highlights how effective the yellow spot fungus is as a saprophyte of dead barley tissue
  • Spot form of net-blotch was detected more frequently and at higher DNA concentrations in barley crops than net-form of net blotch in 2018. Saprophytic colonisation of wheat as an alternate host appeared lower with net-blotch compared to yellow spot
  • PREDICTA® B assays appear to be a valuable tool to rapidly quantify a wide range of fungal pathogens, nematode pests and beneficial fungi within wheat and barley crops.

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Sowing Into Stubble — Impacts Of Row Spacing, Yellow Leaf Spot And Stubble Height On Crop Development

Authors: Nick Poole, Tracey Wylie and Michael Straight (FAR Australia)

  • Research results from the GRDC Stubbles Initiative and the preceding GRDC Water Use Efficiency (WUE) project have discovered several management challenges in a no-till environment where stubble loads often exceed 8t/ha.
  • Triazole fungicides give relatively poor control (25%-50%) of yellow leaf spot, Pyrenophora tritici-repentis, in a wheat-on-wheat scenario, whereas variety choice and cultural practice can give up to 90% disease control.
  • In comparison to the row spacing research in the GRDC WUE project (sown in late May/June), where yield decreased as row spacing increased, wheat sown in mid-April showed no negative effects of wider row spacing.
  • Increasing row spacing in mid-April sown wheat had little effect on crop structure but did in some cases decrease dry matter (DM) production.
  • Long stubble can have a negative effect on tiller number, DM and light interception of wheat, and in some cases cause a decrease in final grain yield.
  • An increase of up to 50% photosynthetically active radiation (PAR) has been recorded in the winter months when stubble height was decreased from 42cm to 12cm.

Cereal Foliar And Root Disease Update 2019

Authors: Grant Hollaway, Mark McLean, Joshua Fanning and Melissa Cook (Agriculture Victoria), Alan McKay (SARDI) and Steven Simpfendorfer (NSW DPI)

  • 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.

Crown Rot – What Is The Threat Coming Out Of A Dry Year?

Authors: Steven Simpfendorfer (NSW DPI) and Alan McKay (SARDI)

  • Dry seasons which reduce crop biomass production and yield still increase crown rot inoculum levels within paddocks, but to a lesser extent than in good seasons.
  • Decomposition of previous cereal stubbles which harbour the crown rot pathogen, even under break crops (e.g. canola), is reduced in dry seasons. Hence, inoculum levels may not have declined significantly since harvest of 2017 cereal crops.
  • PREDICTA® B is a reliable technique for assessing the risk of crown rot and a range of other soil-borne or stubble-borne pathogens prior to sowing in 2019.
  • PREDICTA® B also has new tests for sclerotinia stem rot in canola as well as pulses and yellow spot in wheat. Tests for septoria tritici blotch of wheat and net blotches in barley are under consideration for next season.
  • Follow sampling recommendations in the manual V10.2, including the addition of pieces of cereal stubble to improve the detection of stubble-borne pathogens such as the crown rot fungus.

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The Incidence Of Fungicide Resistance In Spot Form Net Blotch (SFNB) And Its Implications

Authors: Fran Lopez-Ruiz, Wesley Mair, Geoff Thomas, Kith Jayasena and Andrea Hills (DPIRD)

  • Fungicide resistance to Group 3 (DMI) fungicides in spot form of net blotch is spreading in the southern region of WA.
  • Overuse of fungicides with the same mode of action will speed up fungicide resistance.
  • We can limit the development of fungicide resistance by using the lowest effective dose, appropriate fungicide group rotations and employing IDM practices including crop rotation, stubble management and selection of more resistant cultivars (if available).
  • Fast (and cheap) monitoring of pathogen populations for fungicide resistance is central for the sustainable chemical management of diseases.

Wheat Powdery Mildew Epidemiology And Crop Management Options

Authors: Jason Bradley and Geoff Thomas (DPIRD)

  • Wheat powdery mildew (WPM) infection is favoured by temperatures of 15-23oC and is sensitive to periods over 25oC. Rate of infection and spore production are optimum at 20-23oC. Parameters favouring WPM can be used to identify the periods of increased epidemic risk and guide the need formanagement intervention in the different climatic regions of the WA wheatbelt.
  • Fertiliser applications can influence powdery mildew severity. With increasing nitrogen fertilisation, plants are effectively more susceptible to WPM and crop canopies are more dense favouring epidemic development. These crops will require more intensive monitoring and disease management. While responses were small and inconsistent, experiments suggest that maintenance of adequate potassium nutrition can benefit in helping reduce powdery mildew development.
  • All commercial wheat varieties tested were susceptible as seedlings to all powdery mildew isolates from across the wheatbelt. Some variability in virulence of isolates was evident on alternate resistance genes, however until varieties with improved resistance are released placing selection pressure on the powdery mildew population, variety responses should be consistent across the wheatbelt and reflect NVT disease ratings.

Barley Loose Smut – Control, Variety Susceptibility And Effects On Grain Yield

Authors: Andrea Hills, Geoff Thomas and Kith Jayasena (DPIRD)

  • All seed dressings tested reduced loose smut but the most effective were the SDHI fungicides EverGol® Energy, Systiva®, Vibrance® and Vitaflo® C.
  • The Dash/Hindmarsh family of varieties are particularly susceptible to loose smut and will require a seed dressing every year to maintain control.
  • Grain yield loss was generally equivalent to the percentage of infected plants present.
  • Management strategies to reduce loose smut in crop were of no or limited value although grading seed to retain the >2.5mm portion could be useful.

 

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