Resistance finding prompts net blotch warning

Author: Natalie Lee | Date: 20 Apr 2015

Image of CCDM fungicide resistance group program leader Fran Lopez-Ruiz

Growers are urged to carefully plan fungicide management strategies for net blotch in barley crops this season, following the discovery of a population of the disease resistant to commonly used fungicides.

Curtin University researchers have discovered a barley net-type net blotch (NTNB) population from Western Australia resistant to the triazole (DMI) fungicide tebuconazole, as well as some other types of triazole fungicides.

Net blotch – a disease that can cause substantial yield and quality losses in barley - reached damaging levels in WA barley crops last year, especially in high rainfall, southern areas of the State.

Samples of the fungus causing net-type net blotch in barley treated with tebuconazole. Resistant fungi (bottom two samples) discovered by the GRDC-supported Centre for Crop and Disease Management’s fungicide resistance group are still able to grow at high concentrations of the fungicide. 
Photo: CCDM/Curtin University



The discovery of the resistant population of NTNB, also known as net form of net blotch, was made at the Centre for Crop and Disease Management (CCDM), supported by the Grains Research and Development Corporation (GRDC) and based at Curtin University.

CCDM fungicide resistance group program leader Fran Lopez-Ruiz said that to minimise the risk of NTNB in 2015, growers should use a range of fungicide and crop management strategies.

“Management strategies include reducing the risk of disease carry-over by avoiding sowing barley on barley stubble, and avoiding barley varieties susceptible to NTNB in disease-prone environments,” he said.

“Growers need to avoid spraying barley crops with straight tebuconazole products, which are registered to control powdery mildew and scald, because there is a high risk that this will encourage the development of NTNB resistant populations.

“They should instead ensure that they use alternative fungicides mixes that contain a quinone outside inhibitor (Qol), as NTNB is unlikely to develop significant resistance to Qol.

“Examples of Qol are azoxystrobins, although it should be noted that some products are registered for suppression only of net blotch on barley.”

Dr Lopez-Ruiz said that if a second treatment was required, growers should then use fungicides with a different mode of action such as a prothioconazole, cyproconazole, propiconazole or epoxiconazole product that is registered for NTNB in barley.

The full range of fungicides available for managing NTNB can be accessed through the Australian Pesticides and Veterinary Medicines Authority (APVMA) Public Chemical Registration Information System Search (PubCRIS) database.

Growers should always use the recommended label dose.

Dr Lopez-Ruiz encouraged growers who suspected fungicide resistance issues to contact the CCDM for testing and advice.

“CCDM researchers will continue to work on determining the full extent of the issue to ensure that better resistance management strategies can be deployed to minimise its impact,” he said.

The CCDM was set up at Curtin University in 2014 to conduct cutting-edge crop disease research into genetics, breeding and fungicides, and to improve agronomy and farm management practices.

The GRDC has committed $30 million over five years to the $100 million CCDM as part of its long-term bilateral agreement with Curtin University signed in April 2014. The centre’s goal is to be delivering savings of $400 million a year to the grains industry by 2020.

GRDC Project Code CUR00022

Region West