Faba bean agronomics for Tasmania

Take Home Messages

• Of the current varieties available, PBA Amberley is the faba bean variety that is likely best suited to the HRZ of Tasmania due to its potential yield and disease resistance.
• Chocolate spot control is key to ensuring yield potential can be achieved. Using an SDHI fungicide in season allows for less applications of fungicide and greater protection windows.
• Mid-late April sowing is the optimum sowing window, providing a balance between yield potential and disease pressure.
• 20 plants/m² is the ideal plant number for high rainfall zones, allowing for good disease management and harvestability.

Introduction

The development and understanding of faba beans in the high rainfall zones of Australia has come a long way in the past decade. The agronomic development and varieties available have enabled growers to successfully grow faba beans despite having previously been nicknamed “failure beans”. There are a number of agronomic levers covered throughout this paper, such as plant density, variety and disease management that growers and advisors can utilise to grow a successful faba bean crop.

The demand for faba beans in the market is increasing and, as such, there are great opportunities for growers to be planting them. While interest in faba beans continues to grow in the overseas markets, the use of faba beans in a domestic market is also steady and there is a real opportunity for the use of faba beans in stockfeed (either grain or stubble grazing).

Faba beans have become essential for some farming systems in the western districts of Victoria, and often have other benefits aside from its price per tonne.

Varieties

PBA Amberley^A

PBA Amberley^A is a high yielding variety that is best suited to the high rainfall zones, particularly Tasmania. PBA Amberley^A has been bred to have better resistance to different diseases, especially chocolate spot. It is also well suited to the longer growing season and has good standability.

PBA Amberley^A has been the variety of choice in south-west Victoria, particularly in the last three years due to its disease resistance rating of moderately resistant moderately susceptible (MRMS) for chocolate spot and resistant to moderately resistant (RMR) for Ascochyta blight. PBA Amberley^A has consistently had the highest yield out of several varieties over the last four years of trials run by

Southern Farming Systems (SFS) in south-west Victoria, and has been the top performer against chocolate spot, particularly in 2022 which was a high-pressure disease year.

PBA Samira^A

PBA Samira^A is another high yielding variety; and is more widely adapted to different environments. It’s later flowering again makes it a suitable fit for the longer season in Tasmania. However, PBA Samira^A has poorer disease resistance to chocolate spot compared to PBA Amberley^A. While still rating RMR to Ascochyta blight, it is only rated moderately susceptible (MS) for chocolate spot. Despite poorer chocolate spot resistance, PBA Samira^A has yielded well in most years, even when compared to PBA Amberley^A. PBA SamiraA could also be a suitable choice for the Tasmanian growing conditions.

PBA Bendoc^A

PBA Bendoc^A is a Group 2 tolerant faba bean. However, it is not well suited to the high rainfall zone due to its poor disease resistance observed in SFS trials over the past three years. This is also reflected in its disease ratings with susceptible (S) for Cercospora, S for chocolate spot and very susceptible (VS) for rust. Despite its advantages for better broadleaf weed control due to the Group 2 tolerance, the poor disease ratings and low yields make it a poor fit for Tasmania (and other high rainfall zones).

Sowing date

SFS having been running time of sowing by variety trials from the 2019-2022 seasons to understand how sowing dates can influence phenology and grain yield. Traditionally in the HRZ, faba beans have been sown in May, however in the past few years, growers have shifted the sowing date earlier. This is, in part, due to research by SFS through the Southern Pulse Agronomy project, which showed that in five years’ worth of trials, a mid-late April sowing date resulted in an increase in grain yield of 0.5–1.3t/ha on average compared to a mid-May sowing date.

An early April sowing date can increase yield through more pods/plant and pods/m², however, it also makes the crop more susceptible to disease, as the disease cycle begins as soon as the crop has emerged. Therefore, the longer the plant’s growing season, the more it is exposed to disease pathogens. Earlier sown faba beans will also have more biomass and denser canopies compared to later sown. This creates a more favourable environment for pathogens to develop and can further increase disease pressure. Growers will need to evaluate the trade-off between yield potential and disease pressure when planting earlier.

A mid-late May sowing date (as per tradition) can mean improved disease management but can increase the risk of heat and moisture stress during springtime. Disease management is improved as the canopy is more open, meaning less humidity and better penetration of fungicides when applied.

Whereas a mid-late April sowing date allows growers to generate adequate yield potential when balancing disease, climate, and lodging risk. An economic analysis from 2021 showed that sowing at a mid-late April sowing date increased profitability due to the increase in yield compared to mid-late May.

Plant density

SFS trials (SFS Results Book 2021)found that generally the higher the sowing rate*, the more yield is maximised. However, with the large seed size of faba beans, there is often a limit to how much seed can physically fit down the seed tubes on a seeder. With higher sowing rates, there is also a risk of increased disease pressure, especially depending on sowing date as well. Higher sowing rates result in a denser canopy, which creates a more humid and warmer environment and is more conducive to disease development and pressure.

In 2021 trials, SFS found that yield potential is decreased from plant densities below 20 plants/m², especially from earlier sowing dates. It was found that by increasing plants/m² from 14 to 21, yield increased by up to 2t/ha (Table 1). This was the best response recorded in SFS faba bean sowing rate trials to date.

Plant density can also influence disease pressure. By reducing plant numbers from 18 plants/m² to 10 plants/m², there was a 15% reduction in chocolate spot symptoms. However, there was also a grain yield penalty of 30%. This indicates that plant numbers had a larger impact on yield potential than disease, and management through genetic resistance and fungicides will help to protect yield potential at higher plant densities.

Targeting a plant density of 20 plants/m² balances the risk of increased disease pressure from denser canopies with the influence of plant density on maximising yield potential.

Table 1 highlights how different plants/m² impact grain yield and highlights how both 28 plants/m² and 21 plants/m² generate significant yield gains compared to lower sowing rates.

*Please note: Plants/m² is often used to describe sowing rate in trials as kg/ha can be variable depending on germination percentage and one hundred grain weight.

Table 1: The relationship between plant density and grain yield in a 2021 SFS plant density trial

Disease management

Disease management in faba beans is critical to ensure yield maximisation. Chocolate spot (caused by Botrytis fabae) is the most common disease, which can cause severe yield loss. There are several key management techniques that can assist in reducing chocolate spot severity, such as paddock selection, paddock hygiene, seed source, sowing date, sowing rate and fungicide products and timings.

Chocolate spot is present during the months of June and July, however usually in lower levels. Once canopy closure has occurred and throughout spring, chocolate spot tends to rapidly spread due to

increased temperatures (15–25°C) and humidity (>70%) which damages potential yield. Below is an excerpt from Fanning et al. (2023) at the Victorian GRDC Update in 2023 at Bendigo, where Dr Fanning gave an update on disease after the 2022 season.

With the 2022 season highly conducive to Chocolate Spot, the 2020 Hamilton trial results (next to Lake Linlithgow, Vic) are highly relevant to the recent season.

Newer dual active fungicides including, tebuconazole + azoxystrobin (Veritas®), bixafen + prothioconazole (Aviator® Xpro®) and fludioxonil + pydiflumetofen (Miravis® Star) were compared against the single active chemistries carbendazim or procymidone (Table 2). All treatments received a 4-node tebuconazole application to prevent Cercospora leaf spot. Treatments were applied at early flowering as these newer chemistries were expected to have longer efficacy and this timing is the latest permissible application timing.

It was a very conducive year, hence additional applications of carbendazim and procymidone were applied in addition to the fungicide treatments to be more realistic in a very conducive environment. These additional fungicides struggled to limit disease progression and highlights the need for proactive disease management, as disease epidemics can develop rapidly.

Table 2: Fungicide treatments and timings in faba bean experiments conducted at Hamilton during 2020.

^A These fungicides are additional to all treatments receiving a tebuconazole application at the 4 to 6 node growth stage. There was significant disease pressure later in the season. Therefore, an additional two carbendazim (250gai/ha) and an extra one procymidone (240gai/ha), or two extra procymidone applications on the carbendazim treatment were applied alternately every 2-4 weeks to control the Chocolate Spot;
^B The control treatment is a rotation of fungicides applied to ensure minimal to no disease as a control in the experiment. This control had significant levels of disease despite multiple fungicides.

PBA Bendoc^A and Fiesta consistently showed greater levels of Chocolate Spot compared to PBA Samira^A and PBA Amberley^A, with disease symptoms observed and progressing under the ‘Full Control’ fungicide treatment (Table 3). The fungicide treatment containing fludioxonil + pydiflumetofen resulted in disease severity similar to the ‘Full control’. These results highlight the requirement for fungicides to be applied to PBA Amberley^A, to prevent a severe disease presence.

Faba bean grain yield indicated greater fungicide efficacy in the dual active chemistries, with fludioxonil + pydiflumetofen, providing higher yield gains compared to the other fungicide strategies (Table4). The economic benefit of applying the fludioxonil + pydiflumetofen, was similar to the strategy involving carbendazim with the canopy closure application, further highlighting the need to minimise disease early in the season.

Table 3: Chocolate spot severity in four varieties with different fungicide strategies applied at Hamilton, assessed on 20 October 2020.

^AFungicide strategies are described in Table 2
^B Different letters indicate significant differences (P<0.05) between means of varieties or treatments.

Table 4: Grain yield of four varieties, with seven different fungicide strategies applied at Hamilton during 2020.

^AFungicide strategies are described in Table 2
^BDifferent letters indicate significant differences (P<0.05) between grain yield means across varieties and treatments.

Following on from the high-pressure season of 2022, a key message around disease management has been reflected in both Dr Fanning’s pathology work and numerous trials run throughout Victoria. Using an SDHI (for example, fludioxonil + pydiflumetofen) fungicide as a part of your fungicide program can allow for less applications and provide longer protection between sprays, with the same (if not better) disease control as standard fungicides. This is of upmost importance in the HRZ as spray opportunities during winter and early spring are often very limited due to weather conditions.

Conclusions

Faba beans have a place in the HRZ cropping rotation and could be a good fit in Tasmania. However, it is important that disease is managed properly, as chocolate spot, in particular, can have a big impact on yield. Using sowing date and plant density can have an impact on pod development and yield formation. A mid-late April sowing date with a higher plant density can maximise yield potential, but it is also important to be aware of the trade-off for disease management and harvestability (in terms of lodging). However, using an SDHI fungicide can enable longer protection windows and less applications and still result in acceptable disease control. A good fungicide program will rotate through chemistries and be applied at timely intervals to prevent disease from developing and/or rapidly spreading.

This paper only touches on the main findings from several years’ worth of research from several organisations. For more information, please contact author Greta Duff, SFS.

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 the GRDC. The authors would like to thank them for their continued support. The authors would also like to thank all those involved in running these trials through various years and locations. A special thank you to the team at Southern Farming Systems who have managed many of these trials.

References

Fanning J., Findlay C., Manson J.,& Brand J. 2023) Pulse Disease Research Update. In Victoria GRDC Research Updates- 2023, Bendigo, Victoria. NVT disease ratings (https://nvt.grdc.com.au/nvt-disease-ratings?crop=23&state=VIC)

Manson J (2021) Managing faba bean canopies for yield, disease control and harvestability; A synthesis from 2021 data. Southern Farming System 2021 Results Book. Faba Bean Grow Notes, Southern
(https://grdc.com.au/__data/assets/pdf_file/0027/292833/GRDC-GrowNotes-Faba-Southern.pdf?utm_source=website&utm_medium=download_button&utm_campaign=pdf_download&utm_term=South&utm_content=Faba%20Bean%20Southern%20Region%20-%20GrowNotes%E2%84%A2) Pulse disease guide (https://agriculture.vic.gov.au/biosecurity/plant-diseases/grain-pulses-and-cereal-diseases/pulse-disease-guide)

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