Cereal disease update

Take home messages

• Eyespot expression in many areas of South Australia (SA) in 2017 was generally low in cereal crops due to the late start to the season, followed by low rainfall until mid to late tillering. In these areas (or paddocks), eyespot inoculum levels, and so the eyespot risk for 2018, are likely to be reduced. In areas of the state (and in paddocks) which experienced good or normal rainfall, the eyespot risk will depend on inoculum levels in individual paddocks.
• Consider using a PREDICTA® B test if you are in any doubt about the risk of yield losses from crown rot or eyespot in at-risk paddocks as, given the past two seasons, it will be difficult to predict risks based on paddock history.
• Be cautious in selecting barley varieties susceptible to net form net blotch (NFNB) as this disease is likely to increase in significance in coming years.

Eyespot

Eyespot causes eye-like lesions on stem bases and lodging in cereals, continues to be a problem. However, seasonal conditions in many areas in 2017 meant eyespot expression was limited even where the risk (inoculum) levels were high. Limited disease expression occurred because of the late start to the season and lack of rainfall during early crop growth stages. With little increase in inoculum from these 2017 crops, it is possible there will have been a net decrease in inoculum levels as infected residues from 2015 and 2016 will have decreased during this period. Whether the decrease is sufficient to afford a practical reduction in risk of yield loss from eyespot will only be determined by undertaking PREDICTA® B tests in paddocks.

The main in-crop control strategy used for eyespot management overseas is fungicide application early in stem elongation, prior to canopy closure. No fungicides are currently registered for managing eyespot in cereals in Australia. A number of products are in the process of label extension or registration for eyespot management and, providing the reviewers support the applications, they should be available over the next one to four years:

• Registration of Aviator® Xpro® @ 500mL/ha (Bayer) has been applied for and is expected (but not guaranteed) by the end of May 2018.
• Registration of Soprano® 500 SC @ 125mL/ha (Adama) has been applied for and might be available by the end of 2018.
• A label extension for Radial® @ 840mL/ha for eyespot management will be submitted by mid-2018 and might be available by mid-2019.
• Syngenta expects to have two products with label extensions for suppression of eyespot in place by 2020.

Varietal resistance is also important for in-crop eyespot management. Screening trials undertaken 2014 to 2016 have demonstrated that a range of resistance levels are present in current SA cereal varieties.

Abbreviations: S=susceptible; MS = moderately susceptible; MR = moderately resistant. Ranges were:

• Main season wheat – S (Mace, Scout); MS-S (DS Pascal ); MS (Trojan, Emu Rock).
• Barley – MS (Compass, Scope); MRMS-S (La Trobe, Hindmarsh); MRMS (Fathom, Oxford).
• Durum wheat – S (Aurora); MS (Hyperno).
• Long season wheat – S (Orion, Wedgetail); MS-S (Bolac); MS (Manning, Forrest); MRMS (Beaufort).

Results from 2017 trials will be presented at the 2018 Adelaide GRDC Grains Research Update. A full list of varietal resistance levels will also be available in the 2018 Cereal Variety Disease Guide which will be available via the website following the 2018 Adelaide GRDC Grains Research Update or on request from the authors.

The best long-term management option for eyespot would be to reduce inoculum levels and keep them below a level which will cause yield losses. However, for eyespot, this means at least a two year break from cereal crops or burning infected crop residues and then having a one year break from cereal crops. These options are usually considered to be undesirable and uneconomic and eyespot management generally relies on fungicides and, to a lesser extent, varieties. Preliminary information from 2016 to 2017 suggests that it might be possible to reduce inoculum using the combination of a variety with some resistance to eyespot and fungicide application. This would mean that a one year break from cereal could be followed by cereal without incurring yield loss due to eyespot while reducing inoculum levels. A research program has been designed to validate and quantify the combined effects of variety resistance and fungicide application for reducing eyespot inoculum on lower Eyre Peninsula and in the South East.

Crown rot

Crown rot has not caused significant problems in cereal crops over the past few years, so it is difficult to make a general prediction of the risk from this disease for 2018. Knowledge about the crown rot history of individual paddocks will assist in decision-making. Consider using a PREDICTA® B test if in doubt, particularly if planning to sow a durum wheat crop.

Foliar diseases

Foliar diseases in cereal crops had a relatively quiet year in 2017. In some areas, this was due to dry conditions and late sowing, while in others the cold winter helped to suppress some of the pathogens. The good spring conditions, however, favoured late development of some diseases, particularly in the longer season areas.

Septoria tritici blotch

Septoria tritici blotch was observed at higher levels in cereal crops across the medium and high rainfall areas. The disease was favoured by a significant build-up of inoculum in the previous two years. Most varieties are susceptible to varying degrees. There is some indication that the septoria population is adapting to different regions through increased virulence to local varieties. Confirmation of these changes will require further testing.

Net form net blotch (NFNB) and spot form net blotch (SFNB)

NFNB and SFNB in barley were at lower levels in 2017 than previous years and this will have resulted in lower inoculum levels leading into 2018. However, the very high yields of RGT Planet will possibly lead to large areas sown to this variety in coming years and this could lead to significant future issues with NFNB as this variety is very susceptible (SVS) to this disease.

Leaf rust

Leaf rust in wheat was observed early in 2017 but was kept in check by cold temperatures through winter and through effective fungicide management of crops, in most cases as a precaution against stripe rust and/or septoria. Barley leaf rust was also present at much lower levels than previous years. Stripe rust arrived very late and caused little or no problems owing to its late arrival and effective use of fungicides.

Useful resources

Cereal Variety Disease Guide 2018 (available soon via the website or by contacting either of the authors).

Acknowledgements

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.

Contact details

Margaret Evans
SARDI
Plant Research Centre, Gate 2b Hartley Grove, Urrbrae
marg.evans@sa.gov.au
08 8303 9379

Blake Gontar
SARDI
1 Hindmarsh Street, Port Lincoln
blake.gontar@sa.gov.au
0430 597 811

Hugh Wallwork
SARDI
Plant Research Centre, Gate 2b Hartley Grove, Urrbrae
hugh.wallwork@sa.gov.au
08 8303 9382