Take Home Messages
- Effective disease management requires tailoring strategies to crop variety, seasonal conditions and disease levels.
- Minimising fungicide use in low-disease years can improve profitability without compromising yield.
- Fungicide timing at key growth stages is essential for maximising yield and profitability in disease-prone seasons.
Aim
This study aimed to enhance cereal disease management in the southern Mallee region by:
- Assessing how various wheat and barley varieties with differing disease resistance ratings performed during the 2024 season.
- Identifying the most effective timings for fungicide application to control disease.
- Evaluating the effectiveness and economic viability of different fungicide options for disease control.
Background
The variable nature of disease, which is driven largely by rainfall, complicates in-crop disease management in the southern Mallee. In disease-prone seasons, poor fungicide management can result in significant yield losses, highlighting the need for effective control strategies. Conversely, in low-disease years, fungicide applications often provide no yield benefit, instead increasing costs and reducing profit. Wheat in the region is commonly affected by Septoria tritici blotch and stripe rust, while barley is impacted by spot form of net blotch (SFNB) and net form of net blotch (NFNB).
This report details the second year of a GRDC project. Results from 2023 emphasised the importance of avoiding highly susceptible cereal varieties to mitigate disease risk and demonstrated premium fungicide treatments do not always yield better economic returns (Jones and Plowman, 2023). Previous research by Agriculture Victoria and BCG in the southern Mallee found SFNB reduced yields of susceptible barley varieties by 17 per cent in 2016 and 10 per cent in 2017 (McLean et al., 2022). Another study in 2022 showed foliar diseases could reduce wheat yields by up to 50 per cent, underscoring the significant threat these diseases pose during a conducive season (Dadu et al., 2022). These yield losses were mitigated by using integrated disease management strategies, including variety selection and timely fungicide application (Dadu et al., 2022).
To support growers facing challenges with disease management amid seasonal variability, field trials focused on variety selection, optimising fungicide timing, and evaluating fungicide options. These trials aim to provide practical recommendations for enhanced disease control and improved profitability for growers in the southern Mallee.
Paddock Details
Location: Nullawil
Crop year rainfall (Nov–Oct): 361mm
GSR (Apr–Oct): 178mm
Soil type: Loamy clay
Paddock history: Vetch brown manure
Trial Details
Crop type/s: Wheat and barley
Treatments: Refer to Tables 2, 3 and 4
Target plant density: 130 plants/m²
Seeding equipment: Knife points, press wheels, 30cm row spacing
Sowing date: 22–24 May 2024
Replicates: Three or four
Harvest date: 12 November 2024 (barley), 9 December 2024 (wheat)
Trial Inputs
Nutrition, weeds and insects were managed as per best practice.
Method
Six trials were set up at Nullawil, in the Victorian southern Mallee, with three trials each dedicated to wheat and barley. The trials aimed to investigate different varieties, fungicide timings, and fungicide product selection for foliar disease management. Wheat and barley varieties with varying resistance ratings were sown (Table 1) and subjected to either a high (nil control) or low (full control) disease treatment (Table 2, Trials 1 and 4). Additional trials focused on wheat varieties Scepter and LRPB Matador, as well as barley varieties Maximus CL and RGT Planet, to examine various fungicide timing applications (Table 3, Trials 2 and 5) and fungicide product selection (Table 4, Trials 3 and 6).
All trials were set up using randomised complete block designs with three or four replicates. Assessments included disease severity, establishment counts, and yield parameters. Disease severity was visually assessed by estimating the percentage of leaf area affected with disease on eight occasions during the season, from GS15 to GS55. These severity estimates were used to calculate the Area Under the Disease Progression Curve (AUDPC), providing a cumulative measure of disease severity over time (Brown and Keane, 1997).
Results & Interpretation
Seasonal conditions and diseases present
Nullawil received 178mm (Decile 1) of rainfall during the growing season, leading to dry seasonal conditions and low overall disease pressure. Despite the dry conditions, Septoria, rust, and yellow leaf spot (YLS) were observed in wheat, while barley was affected by spot form of net blotch (SFNB), net form of net blotch (NFNB), and scald. Stored soil water resulted in higher yield than would have been expected based solely on in-crop rainfall.
Trial 1:
Wheat varieties with and without disease
Disease presence and resistance rating alignment Disease progression was monitored throughout the season, with Septoria detected in all plots during the early growth stages (GS31 to GS39). By mid-season (GS39), additional diseases, including stripe rust, became evident. Late-season assessments (GS55 and two weeks post-GS55) revealed the presence of stripe rust, Septoria, and YLS across all varieties.
In the high disease treatments, a clear relationship was observed between disease severity and variety susceptibility to stripe rust. The lowest disease severity was recorded in the Sunblade CL Plus low disease treatment (MRMS, AUDPC 111), while the highest was in the Vixen high disease treatment (SVS, AUDPC 435) (Table 5). Even under low disease treatments, susceptible varieties such as Vixen exhibited substantial disease loads (AUDPC 231) (Table 5). Although low disease treatments significantly reduced disease severity (p<.001), complete suppression was not achieved (Table 5). Susceptible varieties consistently retained higher residual disease loads compared to those with moderate resistance, underscoring the importance of avoiding highly susceptible varieties as part of an effective disease management strategy.
Disease effects and yield
Despite differences in disease levels between varieties and high and low disease treatments, the disease did not significantly affect grain yield in this trial (Table 5). This indicates that while disease was present, levels were not sufficient to limit yield. Despite the lack of yield impact, high disease levels did affect protein content, with reduced protein in treatments with greater disease severity (p=0.001) (Table 5). However, the differences in protein levels were not enough to alter grain quality ratings. Partial gross margin (PGM) analysis suggests small impacts of disease on PGM in all varieties, except for LRPB Matador, which recorded the highest PGM under the high disease treatment ($944). In contrast, the Valiant CL Plus high disease treatment recorded the lowest PGM ($576), reflecting the significant cost of uncontrolled disease for highly susceptible varieties (Table 5).
Trial 2: Wheat under various fungicide applications and timings
This trial involved two wheat varieties, Scepter and LRPB Matador, treated with various fungicide application timings (Table 3). These varieties were selected for their resistance ratings. Since statistical analysis showed no significant variety effect, the data from both varieties was combined for analysis.
Disease presence across treatments
Septoria was the predominant disease throughout the growing season, with occasional occurrences of stripe rust and dead leaf symptoms (senescence), particularly during the later stages of crop maturity. Treatments incorporating flutriafol, either alone or in combination with additional fungicide applications, significantly reduced disease severity (p=0.047) and AUDPC (p<.001); however, complete suppression was not achieved (Table 6). GS31+GS39 (Treatment viii) and Flutriafol+GS31+GS39 (Treatment ix) exhibited the most effective disease suppression, with AUDPC values of 224 and 228, whilst the Nil control (Treatment i) experienced the highest disease pressure (AUDPC 459) (Table 6). These results highlight the importance of well-timed, dual fungicide applications for achieving optimal disease control.
Yield and fungicide timing
Fungicide treatments significantly affected yield (p=0.003), with the dual application at GS31 and GS39 (Treatment viii) achieving the highest yield (4.93t/ha) and PGM ($1331/ha) compared to other treatments (Table 6). Among single applications, GS39 (Treatment v) was the most effective timing for disease control; however, it did not result in increased yield or PGM (Table 6). These findings underscore the importance of applying fungicides at both GS31 and GS39 to maximise yield and economic returns, aligning with the results of Dadu et al., (2023), who reported similar outcomes in a more disease-conducive year.
Trial 3: Wheat fungicide strategy
This trial involved two wheat varieties, Scepter and LRPB Matador, treated with various fungicide strategies (Table 4). As statistical analysis showed no significant difference between varieties, data from both was combined for analysis.
Disease severity
Disease severity two weeks after the GS55 spray ranged from 28 per cent for the Mid-range 1 strategy (Treatment iii) to 43 per cent for the Nil control (Treatment i) (Table 7). Fungicide treatments significantly reduced disease severity (p<.001), with all strategies outperforming the Nil control (Treatment i). Similarly, AUDPC values, which indicate disease progression over time, ranged from 276 under the Full control (Treatment v) to 363 for the Nil control (Treatment i), demonstrating a significant reduction in disease progression with fungicide applications (p=0.003) (Table 7).
Grain yield and economic outcomes
Despite reductions in disease severity and AUDPC, fungicide treatments did not result in a significant increase in grain yield, with no strategy delivering a statistically higher yield compared to the Nil treatment (Treatment i) (Table 7). However, PGM analysis highlighted the importance of cost considerations. The Triazole only strategy (Treatment ii) achieved the highest PGM at $970/ha, while the Expensive strategy (Treatment ix) recorded the lowest PGM at $917/ha. Moderate approaches, such as the Mid-range 1 strategy (Treatment iii) and Mid-range 2 strategy (Treatment iv), balanced effective disease control with economic return. In contrast, the Expensive (Treatment ix) and Full Control (Treatment v) strategies incurred higher costs without corresponding yield or financial benefits. These findings suggest that targeted, cost-effective fungicide strategies are optimal under the low to moderate disease pressure conditions observed in 2024.
Trial 4: Barley varieties with and without disease
Disease presence
Barley exhibited lower overall disease levels compared to wheat. Disease progression was consistent across trials, with SFNB appearing early in the season (GS31 to GS39). By mid-season (GS39), both SFNB and NFNB were detected in most treatments. Late-season assessments (GS55 and two weeks post‑GS55) revealed the presence of SFNB, NFNB, and scald across all plots. Despite the presence of multiple diseases, overall disease pressure remained low throughout the growing period.
Disease effects and yield
Fungicide treatments significantly reduced disease severity (p<.001) and AUDPC (p=0.023). However, no significant yield differences were observed, due to limited disease development in this experiment (Table 8).
Trial 5: Barley under various fungicide applications and timings
This trial involved two barley varieties, Maximus CL and RGT Planet, treated with various fungicide application timings (Table 3). These varieties were selected for their resistance ratings. Since statistical analysis showed no significant variety effect, the data from both varieties was combined for analysis.
Disease presence across treatments
Throughout the trial, SFNB appeared early in the season (GS31–GS39), while NFNB became more prominent by mid-season. Late-season assessments (GS55 and two weeks post-GS55) revealed a combination of SFNB, NFNB, and scald across most plots. Fungicide treatments significantly reduced disease progression (p<.001) (Table 9). The Nil control (Treatment i) recorded the highest AUDPC (273), while dual fungicide combinations, GS15+GS39 (Treatment vii) and GS31+GS39 (Treatment viii), achieved significantly lower AUDPC values of 176 and 170 respectively, indicating enhanced disease control (Table 9). Despite this, complete suppression of disease was not achieved.
Yield and fungicide timing
Due to low rainfall during the growing season, disease pressure was minimal and did not significantly affect yield (Table 9). In years where disease does not limit yield, the cost of production can be increased by unnecessary fungicide applications, as reflected in several negative profit margins shown in Table 9.
Trial 6: Barley fungicide strategy
This trial involved two barley varieties, Maximus CL and RGT Planet, treated with various fungicide strategies (Table 4). These varieties were selected for their resistance ratings. Since statistical analysis showed no significant variety effect, the data from both varieties was combined for analysis.
Disease severity
Low disease pressure was observed throughout the trial, and no significant differences in disease severity and AUDPC were detected between treatments (Table 10). This outcome reflects the dry seasonal conditions, indicating that in a low-pressure disease environment, disease impacts were minimal across all treatments.
Grain yield and economic outcomes
Grain yield did not vary significantly between treatments (Table 10). The Nil control (Treatment i) achieved the highest PGM at $1424/ha, suggesting the economic benefit of applying fungicides was limited (Table 10) under the dry conditions experienced in 2024. These results indicate that reducing fungicide inputs during seasons with low disease pressure may optimise profitability without compromising yield.
Commercial Practice and On Farm Profitability
Research into disease management remains critical, even during dry seasons like 2024, as it highlights the economic risks of unnecessary fungicide applications and reinforces the importance of tailoring fungicide decisions to crop variety and seasonal conditions. Consistent with the findings from BCG’s 2023 disease trials, variety selection and timely fungicide applications are key to effective disease control, with wheat exhibiting greater sensitivity to fungicide timing than barley (Jones and Plowman, 2023). Protecting the critical money leaves, flag-3, flag-2, flag-1, and the flag leaf, during GS31 to GS39 proved pivotal in wheat. These leaves play a crucial role in grain fill, and fungicide applications at these stages had the most significant impact on yield and partial gross margins.
The dry conditions of 2024 reduced disease pressure, highlighting that fungicide applications may not always be necessary, particularly for less susceptible varieties. In low-disease years, minimising or avoiding fungicide use can enhance profitability. Conversely, during wetter seasons with higher disease risk, such as 2022, well-timed fungicide applications are essential for protecting yield (Dadu et al., 2022). Research by Agriculture Victoria and BCG in the southern Mallee demonstrated that foliar diseases could reduce wheat yields by up to 50 per cent under conducive conditions. However, these losses were mitigated through varietal selection and timely fungicide applications (Dadu et al., 2022). Similarly, Agriculture Victoria and BCG studies from 2016 and 2017 revealed barley yield losses due to SFNB of 17 per cent and 10 per cent, respectively, emphasising the importance of effective disease management during conducive seasons (McLean et al., 2022).
Avoiding unnecessary fungicide use during dry seasons also helps preserve the longevity of available fungicide options. Fungicide resistance is an increasing concern nationally, and the Australian Fungicide Resistance Extension Network (AFREN) emphasises the importance of reducing fungicide use when possible. For more information on fungicide resistance, go to the website.
Overall, strategic and adaptable disease management is essential for optimising profitability. While intensive fungicide regimes offered little economic benefit in 2024, continued research across diverse seasonal conditions will further refine best-practice guidelines for wheat and barley growers in the southern Mallee.
References
Brown J.F., and Keane P., 1997, Plant Pathogens and Plant Diseases, ‘Assessment of disease and effects on yield’ pp 315–329.
Dadu H., Hollaway G., McLean M., and Clarke G., 2022, 2022 BCG Season Research Results, ‘Stripe rust management during a high-pressure season’ pp 92–99. <https://www.bcg.org.au/research-article/stripe-rust-management-during-a-high-pressure-season-2022> (Accessed 17 January 2025).
GRDC, 2024, NVT Disease Ratings, <https://nvt.grdc.com.au/nvt-disease-ratings> (Accessed 19 September 2024).
Jones T., and Plowman Y., 2023, 2023 BCG Season Research Results, ‘Management of disease complexes in southern Victorian Mallee cereals’ pp 140–147. <https://www.bcg.org.au/research-article/management-of-disease-complexes-in-southern-victorian-mallee-cereals/> (Accessed 19 September 2024).
McLean S., Poole N., Munoz-Santa S., and Hollaway G., 2022, Crop Protection, ‘Efficacy of spot form of net blotch suppression in barley from seed, fertiliser and foliar applied fungicides’.
Zadoks J.C., Chang, T.T., and Konzak C.F., 1974, Weed Research, ‘A decimal code for the growth stages of cereals’ pp 415–421.
Acknowledgements
The research undertaken as part of this project has been made possible by the significant contributions of growers through both trial cooperation and the GRDC (BWD2303-002RTX); the authors would like to thank them for their continued support. BCG would like to acknowledge and thank Thomas Jones for his involvement, James Considine, from Nutrien Ag Berriwillock, and Rik Maatman, from Nutrien Ag Birchip, for their advice on product pricing and selection used in this trial, as well as Danny Conlan, from Dodgshun Medlin, and Matt Bissett, from Exceed Ag, for providing supplementary product pricing information. BCG sincerely thanks the Watts family for generously hosting the trial site at Nullawil and for their support throughout the project.
