Rapid test and fungicide resistant screening for Stemphylium leaf blight in onion (VN24003)

This project delivered new tools and evidence to help onion growers better detect, understand and manage three major canopy diseases – Stemphylium Leaf Blight (SLB), Downy Mildew (DW) and Purple Blotch (PB).

The project developed and validated rapid DNA-based diagnostic tests for SLB and DW, with a test for PB designed but not yet fully validated. These diagnostic tools were used to investigate the extent of each disease in the Lockyer Valley and determine any alternate plant hosts that might be harbouring the disease off season.

The research confirmed that SLB was the most significant disease affecting onions in the Lockyer Valley, ahead of DW and PB. The project also found clear genetic and laboratory evidence that some recent SLB strains had reduced sensitivity to commonly used fungicides, highlighting the need for more informed disease management.

Growers received individual disease, soil chemistry and soil health reports. The project also generated genome data and fungicide resistance results to support ongoing research and industry decision-making.

The work addressed a lack of accurate diagnostics and local data on disease pressure and fungicide resistance, which had contributed to crop losses and poor control decisions. The new diagnostic tools and resistance insights are expected to support earlier detection, better-targeted fungicide programs and more sustainable disease management for onion growers.