Take Home Messages
- Economical and premium fungicide options performed similarly in many cases.
- Spot blotch and net blotch were common in the southern Mallee barley site.
- Septoria tritici blotch, leaf and stripe rust were observed in the southern Mallee wheat site.
- Disease resistance of varieties plays an important role in disease management
Aim
To showcase diverse management strategies for disease complexes and identify optimal economic strategies that suit different crops grown in the Mallee region.
Background
The Mallee region experiences substantial fluctuations in seasonal conditions, with varying rainfall and patterns in recent years. This variability poses challenges for predicting the risk of disease and timing of application to produce economic returns for growers from fungicide use to manage disease. Given the inconsistencies in economic returns for fungicide use in the Mallee environment, this project was established to support growers in making real-time decisions for disease control and to maximise benefits from fungicide use. The objective of this project is to showcase diverse management strategies for disease complexes and identify optimal economic strategies that suit different crops grown in the Mallee region. This involves conducting plot trials at multiple locations, emphasising various fungicide management approaches in wheat, barley, and lentils. The trials are designed to encourage facilitated discussions and peer-to-peer learning regarding critical disease management decisions
Trial Details
Location: Kinnabulla Pyramid Hill
Crop year rainfall (Nov–Oct): 276mm 379mm
GSR (Apr–Oct): 187mm 250mm
Soil type: Sandy clay loam Clay
Paddock history: Lentil brown manure Oats
Trial Inputs
Trial managed as per best practice with varying fungicide treatments (Table 1).
Method
Site establishment
In 2023, Birchip Cropping Group (BCG) established five small-plot research trials across two locations in regional Victoria: the Mallee, located in Kinnabulla, 20km northwest of Birchip, and the North Central region, 13km south of Pyramid Hill. Data from the two Pyramid Hill trials (barley and wheat) has been omitted from this report, as the trials experienced heavy pressure from kangaroo grazing throughout the year. The three trials at the Kinnabulla site were sown to wheat, barley, and lentils, with different disease management strategies applied (Table 2). Data collected from the lentil trial showed the disease load was lower than expected, and the trial results have been omitted from this report. All trials were established as randomised complete block design with four replications. The sites experienced timely early season rainfall of 57.4mm in June, resulting in good trial establishment as well as early season disease development. During the growing season, the trial received 187mm of rain. Rainfall received during the growing season was classified as decile 3, however, there was sufficient soil moisture due to above average rainfall (decile 10) in 2022.
Crop varieties and disease susceptibility
Three different varieties within each crop type were selected with varying disease susceptibility ratings (Table 1).
Treatments
Results & Interpretation
Wheat
Variety was a primary driver in differentiating disease prevalence at growth stages GS31 and two weeks post-GS39, p <0.001 and p=0.036, respectively (Table 3). Septoria tritici blotch (STB) was detected on lower leaves early in the season (GS31). At GS39, STB had migrated into the upper canopy in all varieties. The presence of rust was also noted at this growth stage in some untreated Hammer CL Plus plots. Two weeks following the GS39 treatment application, rust had formed hotspots in the trial, with rust appearing in most plots.
Both variety and treatment imposed statistically significant effects on grain yield (t/ha), p=0.008 and p=0.005, respectively (Table 4). Between the untreated controls, LRPB Matador was the highest yielding variety, and Scepter the lowest, illustrating the impact of disease, as shown in Table 3. Within varieties, Scepter was the most responsive to disease control, with all but one treatment (iii) showing a significantly higher yield compared to the control. Double spray applications (GS31 and GS39) resulted in the highest yield for Scepter (treatments vii and viii), with little difference between the economical and premium products. The partial gross margin (PGM) for treatment vii (GS31 and GS39 economical) showed a slightly higher return on investment (ROI), but the highest PGM for this variety was achieved by treatment vi, which was one application of propiconazole and benzovindiflupyr at GS31.
Differences in yield between treatments were observed to a lesser degree for Hammer CL Plus, and less again for LRPB Matador. A common trend across both varieties was the high yields achieved for treatment iii (one application of propiconazole and benzovindiflupyr at GS39) versus the premium version of this treatment (v) which included Flutriafol. Treatment iii across both varieties showed high yields and the highest PGM.
Pre-emergent herbicides: Star of Bethlehem (SoB) bulb production
Herbicide treatment had significant effect on SoB bulb production (Table 5). However, this significant result was only due to a reduction in bulb production by Glean® compared to the untreated control and all other herbicide treatments. In herbicide treatments other than Glean®, SoB bulb density doubled in response to the treatment, which was very similar to the untreated control. These results clearly highlight high tolerance of SoB to most selective pre-emergent herbicides used in cropping systems. Results obtained from the assessment of bulb production were supported by the data from plant establishment counts in the next season (data not shown)
Wheat
As observed in the wheat, barley establishment was aided by timely rain and soil moisture, which was also likely to increase disease load. Spot form of net blotch (SFNB) was detected in every barley trial plot. RGT Planet suffered substantially higher damage from SFNB than other varieties (Table 5), which is not surprising as it is considered more susceptible to this disease than Maximus CL and Leabrook. At the time of the GS39 spray application, net form of net blotch (NFNB) was the main disease present in RGT Planet plots. Two weeks post-GS39 treatment application, NFNB had spread throughout the trial, however it was prevalent mainly in RGT Planet plots. At the same time, leaf scald hotspots were beginning to appear within Maximus CL plots.
Both treatment and variety imposed significant effects on the yield (t/ha) (p=0.041) and variety (p<0.001) for yield (t/ha). In the control plots, the mean yield in Maximus CL was significantly higher than the mean yields recorded for Leabrook and RGT Planet (Table 6). It is possible that the difference in yield between Maximus CL and the other varieties is due to slightly lower disease loads for this variety later in the season, as shown in Table 5. Given that Leabrook is the more resistant variety to SFNB, this may indicate the environmental conditions in this trial favoured Maximus CL. Unlike the wheat trial, no varieties responded strongly to treatments across the board, and for RGT Planet, no disease management treatment resulted in significantly different yields compared to the control.
Within the RGT Planet variety data, no significant differences were detected between treatments, including the control. The highest yield was obtained by treatment viii, the complete treatment strategy (two sprays with premium products) however, this did not translate to return on investment, as shown by the PGM: the highest PGM for RGT Planet was for the control treatment. The opposite was true for Leabrook and Maximus CL; the highest return on investment occurred for plots where yields were significantly higher than the respective controls for each variety. These findings suggest a strong influence of variety choice and disease management strategies on each other.
Only one instance of significant difference between economic and premium products was detected; this was for treatments iv (economic) and v (premium) for Maximus CL, where the economic treatment sprayed only at GS31 yielded higher than the premium treatment sprayed at GS31. As a result of the higher yield and lower input cost, the PGM showed a higher ROI for the economic option. Nevertheless, the yield for this treatment was lower than that for both the economical and premium double-spray option, indicating the double-spray choice was the ideal strategy for this variety, regardless of product choice, as the PGM showed a comparable ROI between the two double-spray strategies.
Commercial Practice and On Farm Profitability
Interim findings of this project suggest complex interactions between variety choice and disease management strategy. For wheat, Scepter was more receptive to fungicide treatment than LRPB Matador and Hammer CL Plus. Despite this, no substantial difference in yield was detected between economic and premium products for this variety, and in this case the choice may be driven more by ROI, rather than yield alone. Similar observations were made for barley, however RGT Planet did not exhibit receptivity to any treatment when compared to the control. Like the wheat trial, only one product comparison showed a significant difference in yield between the single-spray economic and premium treatments at GS31. It is hypothesised these effects may vary season to season, and that variety susceptibility plays a significant role. BCG will continue this work in 2024 to build on the work presented here.
References
2023 Victorian and Tasmanian Crop Sowing Guide <https://grdc.com.au/__data/assets/pdf_file/0026/580580/GRDC2023_SowingGuide_VIC-TAS_Final.pdf>.
Acknowledgements
The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of GRDC, the authors would like to thank them for their continued support. BCG would also like to acknowledge former BCG employee Genevieve Clarke for designing the trial, Dr Hari Dadu from Agriculture Victoria for his advice and assistance throughout the year, and Rik Maatman from Nutrien Ag Birchip for providing indicative prices for products used in this trial.
