Cereal disease status and 2017 outlook

Author: | Date: 07 Feb 2017

Take home messages

  • 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. 

Eyespot

Eyespot, which causes eye-like lesions on stem bases and lodging in cereal crops, continued to be a problem in 2016. Disease severity was increased by the wet seasonal conditions and it is highly likely eyespot inoculum will have increased as a result. This makes it particularly important to know eyespot inoculum levels prior to sowing 2017 cereal crops in paddocks at risk from eyespot.

The main control strategy used for eyespot management overseas is fungicide application early in stem elongation. No fungicides are currently registered for managing eyespot in cereals in Australia, but one plant growth regulant and two fungicides are being submitted this year for label extension/registration for assisting in managing eyespot. Trials undertaken in South Australia (SA) in 2014 and 2015 gave results which indicate fungicide efficacy is consistent with overseas experience.

Varietal resistance is also important in eyespot management. Screening trials undertaken in 2014-2015 have demonstrated that a range of resistance levels are present in current SA cereal varieties (see 2017 Cereal Variety Disease Guide for full list). Ranges were:
  • Main season wheats – S (Axe, Cobra, Grenade CL+, Mace, Scout); MS (Trojan; Emu Rock).
  • Barleys – MS (Compass, Scope); moderately resistant-moderately susceptible to susceptible (MRMS-S) (La Trobe, Hindmarsh); MRMS (Fathom, Oxford).
  • Durum wheats – S (Aurora); MS (Hyperno).
  • Long season wheats – S (Orion, Wedgetail); MS-S (Bolac); MS (Manning, Forrest); MRMS (Beaufort).

Septoria tritici blotch

Septoria tritici blotch was observed over a wide area throughout the mid and high rainfall regions of SA in 2015, although only as small hotpots of infection at each location. These observations were repeated in 2016 although with higher levels of more uniform disease observed in each instance. The past season with plenty of rain throughout the growing season was ideal for rain splash spread up the canopy and will lead to significantly higher levels of infection in crops in 2017. The severity of the disease in 2017 will depend on the sowing date (early sowing increasing infection), the amount and frequency of rain during the season and on the variety sown. Chemical control will likely be very important for some growers (see paper in these proceedings by Nick Poole).

Two NVT variety trials sown at Turretfield and Conmurra were inoculated with mixed isolates from each region. Results revealed some differences in virulence between the two locations with the Mid-North ratings being higher on many varieties but not all varieties. Most of the main varieties are now rated as MSS-SVS. The Mid-North results will be used for main season variety ratings and the Conmurra data will be used for long season varieties.

Wheat leaf rust 

Wheat leaf rust was widespread in 2016 but caused less of a problem than expected because of the cool weather for much of winter and spring. Depending on where the rust is able to survive on volunteer wheat, the disease could be a problem in 2017 largely because most varieties are susceptible to some degree. Treatment of Mace with fungicides to control stripe rust will have helped suppress leaf rust as well. Where Mace is replaced with Scepter and the fungicide was not used because the improved stripe rust resistance of Scepter then leaf rust may become a bigger issue. A campaign ’Free for February’ aims to promote a region wide break in the green bridge without impeding on many growers who wish to sow early where rains provide an opportunity. Sowing of susceptible summer cereal crops in long season areas should be discouraged.

Net form net blotch 

Net form net blotch had a relatively quiet year as this disease is favoured by warmer temperatures. Despite this, an increase in virulence on the varieties Hindmarsh, La Trobe and Spartacus was recorded in the NVT trials at Elliston and at Kingsford and in breeding plots at Freeling. In these areas, at least Hindmarsh and La Trobe should be considered as MS, while Spartacus should be considered as MSS.

Loose smut 

Loose smut has been reported from many crops of Spartacus barley similar to Hindmarsh in previous years. Trial data has also shown that Rosalind seed in NVT trials has significant levels of loose smut which may lead to problems in crops if the levels of infection in supplied seed are similar.

Seed treatment tests conducted by SARDI have shown that products containing just triadimenol provide only about 50% control of loose smut in Hindmarsh. Products containing flutriafol and tebuconazole, as well as the low rate of Rancona® Dimension (80mL), also allow some infection to persist in crops. Effective control is provided by products containing carboxin and the higher rates of the succinate dehydrogenase inhibitor (SDHI) fungicides, EverGol® Prime, Vibrance® and Rancona® Dimension. 

Growers should be aware that use of seed treatments for the control of barley mildew should continue as a high priority for effective long term management of this disease. Where control of rhizoctonia or loose smut is a priority, growers planning on using treatments specific for these diseases should consider mixing it with triadimenol or flutriafol for mildew control unless they know their barley variety has good mildew resistance.

Take-all

Take-all (Gaeumannomyces graminis var. tritici) has generally been kept under good control for many years. However, inoculum of this disease has persisted at moderate levels in some areas, particularly where rotations away from cereals and pastures have been limited. In paddocks where there has been a risk, then 2017 is a year to watch out.

Powdery mildew in wheat 

Powdery mildew in wheat has been an increasing problem in SA as crops have been getting thicker and more nitrogen (N) has been applied to them. Wyalkatchem (SVS) made the problem particularly severe and when this variety was largely replaced by Mace (MSS) on the Lower Eyre Peninsula (EP), the problem abated to some degree. We foresee the disease increasing in other medium to high rainfall areas in future, notably the South-East which has not experienced the disease to any extent so far. It is of interest that 10-15 years ago mildew was not a problem in Tasmanian wheat crops, but now it has become very severe in crops of Trojan and Forrest according to agronomist Geoff Dean.

Powdery mildew exists as a range of pathotypes and it is not clear that the disease ratings applied from nurseries at the Waite accurately reflect the pathogen population in different parts of the state. Ratings should therefore be taken as a guide and a more resistant rating treated with some degree of caution.

Acknowledgement

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

Hugh Wallwork
South Australian Research and Development Institute
Plant Research Centre, Gate 2b Hartley Grove, Waite Campus
hugh.wallwork@sa.gov.au  
08 8303 9382

Marg Evans
South Australian Research and Development Institute
Plant Research Centre, Gate 2b Hartley Grove, Waite Campus
marg.evans@sa.gov.au
08 8303 9379