HRZ disease adapting to drier climes

Image of septoria tritici blotch on wheat

Septoria tritici blotch is a stubble-borne disease that is most likely to affect early-sown cereals and cereals sown into wheat stubble.

PHOTO: Evan Collis

Septoria tritici blotch (STB) has spread beyond the confines of the southern high-rainfall zone (HRZ) and into more medium-rainfall environments in South Australia, prompting warnings for growers across the state to be vigilant in monitoring and, if required, treating the disease this year.

STB is a stubble-borne disease that is most likely to affect early-sown cereals and cereals sown into wheat stubble.

Reports from South Australian Research and Development Institute (SARDI) principal cereal pathologist Dr Hugh Wallwork indicate low levels of STB were present through parts of the Mid North, Yorke Peninsula and eastern and lower Eyre Peninsula regions in 2015.

Dr Wallwork says STB has rarely been seen in these regions for more than 20 years.

“There is a little pocket north of Kapunda and west of Point Pass in SA where I believe STB established in 2014 as a result of ascospores spreading up from the south-east,” he says.

“From there, a weather system must have picked up the spores and blown them further west soon after sowing in 2015.”

The disease was mostly found in Mace wheat, which has previously had good resistance against STB. However, Dr Wallwork says there has been a significant change in virulence of STB on Mace, Wyalkatchem and related varieties, with the potential for more damage in subsequent years.

Foundation for Arable Research (FAR) Australia managing director Nick Poole is reminding growers that it is best to take an integrated approach in trying to manage STB.

He says there are some key levers in an integrated approach outside of the fungicide arsenal that growers can employ for controlling this disease.

“A key message for growers is to try to pick more-resistant cultivars for earlier sowing in areas where STB is problematic,” Mr Poole says.

“It is also important for growers outside the HRZ who might not have experienced this disease for a while to know that fungicides are less effective against STB at rates used to control diseases such as stripe rust. That, combined with a long latent phase, makes STB a potentially dangerous adversary for growers.”

Currently, the severity and frequency of mutations in the Septoria pathogen population that confer fungicide, resistance may not be serious enough to affect the field performance of fungicides but problems will increase if growers are too dependent on chemicals to control the disease, Mr Poole says.

Extremely dry conditions, such as those experienced in spring 2015, are normally the best for fungicide use, but Mr Poole says early-sown crops still experienced issues with STB.

However, in most cases the infection has been restricted to leaves underneath the flag leaf rather than the flag leaf itself.

“One key learning from 2015 was that where cultivars developed earlier in the spring as result of their intrinsic phenology, the more important top three leaves of the crop canopy emerged earlier and predisposed them to greater risk of infection,” he says.

“In some cases this resulted in a moderately susceptible cultivar behaving as if it were a susceptible cultivar.”

Integrated disease management levers for STB control

  • Use less-susceptible cultivars, particularly for early sowing (mid to late April).
  • Reducing surface stubble loads to reduce disease inoculum (burning, grazing, stubble incorporation) may assist in reducing infection pressure where wheat is sown on wheat.
  • If susceptible cultivars have to be grown, sow them at the end of their safe sowing window.
  • In high-rainfall areas graze crops before GS30.
  • Fungicide management: ensure that fungicides are used to reduce infection on the top three leaves.

More information:

Dr Hugh Wallwork, SARDI,
08 8303 9382,

hugh.wallwork@sa.gov.au;

Nick Poole, FAR Australia,
03 5265 1290,
poolen@far.org.nz

A GRDC technical workshop on fungicide resistance and management of STB will be held at Riverton, SA, on Wednesday 30 March 2016. Register

Septoria Tritici Blotch fact sheet

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