• To study the epidemiology of Septoria tritici blotch in wheat grown in the medium and low rainfall zones of the Southern region.
• To assess the impact of Septoria tritici blotch (STB) in wheat and identify effective integrated disease management (IDM) strategies for its control in the MRZ and LRZ of the Southern region.

Key findings and achievements

1. STB epidemiology and disease risk factors

1. The lifecycle of Zymoseptoria tritici is polycyclic and involves both sexual (ascospores) and asexual (pycnidiospores) reproduction phases in Southern Australia.
2. Spore trap data confirmed that wheat stubble is a major source of early-season STB infection, with peak spore release occurring in winter months where average temperatures are low (10-15°C).
3. Rainfall is a key driver of in-crop STB risk, with higher spring rainfall increasing spore dispersal and disease severity.
4. Late-season disease pressure is primarily driven by spores traveling from neighbouring fields, limiting the long-term effectiveness of localized stubble management alone.
5. Early sowing significantly increases disease risk, particularly in susceptible (S, SVS) wheat varieties, due to prolonged exposure to early inoculum under wet conditions.

2. Economic analysis of integrated disease management (IDM) strategies

A combination of variety resistance, targeted fungicide use, stubble management, and crop rotation provided the best economic and disease control outcomes.

Variety resistance: the most cost-effective STB management tool

1. Less susceptible wheat varieties consistently reduced disease severity and minimized yield loss, offering an economic advantage of up to $433/ha compared to susceptible varieties in MRZ.
2. Growing susceptible varieties (S, SVS) in high-risk seasons such as 2022 resulted in substantial yield losses (up to 43%) and required greater fungicide inputs, reducing profitability.

Fungicide applications: effective in high-risk seasons but not always profitable

1. Fungicide profitability varied depending on disease pressure and yield potential:
   • In high-disease years (e.g., 2022), fungicide applications increased gross margins by up to $459/ha in MRZ.
   • In low-disease years (e.g., 2021), fungicides resulted in financial losses, reinforcing the importance of seasonal disease monitoring.
   • In crops with <3 t/ha yield potential (low-rainfall regions and dry seasons), fungicide applications often failed to provide a positive return on investment.
2. The most effective fungicide strategy was two foliar sprays at Z31 and Z39, but profitability was highly dependent on seasonal conditions and variety selection.

Stubble management: reduces early-season risk but not late-season disease

1. Higher stubble loads were associated with increased early-season STB risk.
2. Baling, burning, and cultivation significantly reduced early inoculum levels, but due to long-distance spore movement from neighbouring paddocks, stubble management had minimal impact on late-season disease.
3. Economic benefits from stubble reduction were site-specific, as growers in high-risk areas benefited more from variety selection and fungicide strategies than from stubble management alone.

Crop rotation and sowing time: reducing disease risk and maximizing economic returns

1. Rotating wheat with non-host crops (e.g., canola, pulses) effectively reduced inoculum loads, resulting in lower STB risk and improved profitability.
2. A minimum one-year break between consecutive wheat crops is recommended to effectively reduce STB risk. However, since the stubble source is not a limiting factor, infection can still occur from spores dispersed from neighbouring fields during the season.
3. Early-sown wheat (April) had up to 21% greater yield loss due to STB, while delaying sowing (May) reduced disease pressure and minimized fungicide dependence.

Industry impact and recommendations

When and how industry can benefit

This research provides practical, data-driven management strategies that can be immediately adopted to enhance disease control, reduce input costs, and maximize farm profitability:

1. Variety resistance should be the primary strategy for STB management, with MSS or better-rated varieties offering significant cost savings and reduced reliance on fungicides.
2. Fungicide applications should be targeted based on seasonal disease risk and yield potential:

• For crops with >3 t/ha yield potential, two foliar sprays at Z31 and Z39 provided the highest economic returns in high-disease years.
• For crops with <3 t/ha yield potential, fungicide use should be carefully evaluated, as returns were often minimal.

1. Stubble management reduces early-season risk but does not eliminate late-season disease, so a combination of variety resistance and fungicide application remains essential in high-risk regions.
2. Crop rotation with non-host crops reduces STB inoculum loads, improving wheat productivity.
3. Delaying sowing to May in the MRZ and LRZ can significantly lower early STB pressure and fungicide reliance, leading to higher economic returns.

Who can benefit

1. Growers in MRZ and LRZ looking to maximize economic returns through variety selection, strategic fungicide use, and crop rotation.
2. Advisors and agronomists developing seasonally adaptive STB management plans tailored to regional disease risk and economic conditions.
3. Breeders and seed companies working on improving STB resistance in wheat varieties to reduce the reliance on fungicides.

Conclusion

This project highlights the importance of IDM strategies that combine variety resistance, targeted fungicide use, stubble management, and crop rotation. Implementing these findings will enable growers to reduce unnecessary fungicide applications, optimize input costs, and sustain wheat productivity across MRZ and LRZ, particularly in high-rainfall seasons and variable-yield environments.