Following the discovery of fungicide-resistant net form of net blotch (NFNB) in Western Australia (Figure 1), a costly problem may be about to get a whole lot bigger. The resistance was detected by fungicide resistance researchers of the Centre for Crop and Disease Management (CCDM), with NFNB estimated to cost the Australian grains industry $19 million in losses annually.
The GRDC and Curtin University supported CCDM has revealed the resistance has led to a large reduction in sensitivity to tebuconazole and a lower reduction in sensitivity to other demethylation inhibitor fungicides such as epoxiconazole, prothioconazole and propiconazole.
Dr Fran Lopez-Ruiz, leader of CCDM’s Fungicide Resistance Group, said such fungicides are relied upon for the control of NFNB in products and that growers should monitor the level of disease control they receive when using these fungicides.“However tebuconazole is not registered for the control of NFNB, so growers should be mindful that NFNB may be present when applying tebuconazole to control other barley diseases. This may contribute to NFNB issues in subsequent seasons,” Dr Lopez-Ruiz said.
NFNB evolved two defences against fungicide
The resistant NFNB was found to have the target enzyme in much higher amounts. More fungicide targets means more fungicide molecules are required to control the disease.
The researchers also found a mutation that changes the shape of the target enzymes, meaning the fungicide binds to it less effectively.“This means the resistant NFNB are working against fungicides in two key ways; they are producing more fungicide targets, and the shape of those targets has changed.”
Prevention is better than the cure
Growers and agronomists should think of fungicide applications as complementary to disease prevention strategies with Dr Lopez Ruiz emphasising;“It is more important than ever to implement stubble management, crop rotations and disease resistant cultivars. When fungicides are used, play it safe and use fungicide mixtures, or rotation of fungicides from different modes of action when possible,” he said.
Submit a sample for fungicide resistance testing
Whilst a small number of NFNB samples from across the eastern states of Australia have tested negative for signs of resistance, a large scale analysis is required to determine whether NFNB resistance has developed outside of WA.
The CCDM will continue to monitor the resistant disease over next year’s season and are also calling for samples from the eastern states.
For a net-form net blotch sampling kit, contact the Fungicide Resistance Group by email firstname.lastname@example.org or phone 08 9266 1204.