Research is underway in Victoria that might help the faba bean shake off its reputation as a ‘failure bean’ in high-rainfall zones (HRZs).

Notoriously fickle and labour-intensive, the nitrogen-fixing legume can return vastly different yields season to season, even when inputs are the same.

This is because faba beans are highly sensitive to environmental conditions and vulnerable to disease in a wet spring. Plus, as an indeterminate species, the plant will keep growing after flowering, which, unlike cereals, has made a targeted fungicide regime based on particular growth stages a challenge.

“The recipe for fungicide use in cereals is quite well known – you spray at (growth stage) GS32 and then at GS39; but in beans there’s no equivalent because the plant will continue to grow new leaves and produce new flowers as long as conditions allow,” says Field Applied Research (FAR) Australia senior field research officer Aaron Vague.

However, Mr Vague says the research focusing on integrated disease management, nutrition and canopies is showing that inputs can be strategically applied to reduce disease risk and achieve higher yields more reliably. This could provide growers, particularly in the HRZ, with a more viable and profitable pulse break crop in their rotations.

The research is being undertaken at spoke sites of the GRDC Pulse Agronomy project running across three states: New South Wales (led by Brill Ag); South Australia (led by the South Australian Research and Development Institute) and Victoria (led by Agriculture Victoria). Managed by FAR Australia, it has involved trials over several years at Daysdale in NSW, Bundalong on the Murray River, and Gnarwarre in Victoria’s HRZ.

Mr Vague says the trials at Gnarwarre are important for growers in Victoria’s HRZ whose acidic and wet soils are unsuitable for lentils or chickpeas and so rely on faba beans as their nitrogen-fixing legume break crop.

“In south-western Victoria, faba beans really are our only winter crop option for increasing adoption of grain legumes,” he says. “So we want to make sure we do it well.”

While disease management has been the major focus of the research, Mr Vague says, it has also been important to look at nutrition and canopy management because the three factors are interdependent. “For example, you might be adding extra nutrients to achieve a bigger yield, which potentially creates a crop with a bigger canopy and a greater disease burden,” he says.

The research is showing that, with targeted inputs, growers can maintain and maximise yield while better controlling disease, gaining the legacy benefits of a legume in their rotation and another genuine income stream.

Changing fungicide strategies

When it comes to refining integrated disease management, much of the opportunity for greater control has been made possible through new SDHI (Group 7) fungicides, Mr Vague says. These chemistries contain an enhanced protectant action along with a mechanism that stops spores from germinating and infecting new leaves as they come out.

These longer-lasting effects mean fungicide can potentially be applied to faba beans, like cereals, at strategic times, he says – a significant shift from the established practice of applying older protectant chemistries such as chlorothalonil every two to three weeks.

While effective, and for many years the ‘backbone’ of disease management, the use of older-style protectant fungicides is both time-consuming and costly. Plus, finding enough spray days with appropriate conditions among other on-farm demands can be challenging, Mr Vague says.

Although more expensive, new SDHI chemistries are required less often. For example, these longer-lasting products may provide adequate crop protection with two strategic uses in a season, Mr Vague says. “This is a reason that they are so popular,” he says. “If a product allows you more flexibility in your farming system, you’re more likely to use it.”

Using fewer fungicides not only saves money and time but also provides another option to help manage fungicide resistance, Mr Vague says. “It is important to remember that SDHIs are susceptible to the development of resistance by diseases, so this is just one tool in the strategy and part of this project is about trying to determine under what sorts of seasonal conditions or scenarios would these chemistries be best utilised in rotation,” he says.

“The more precise we are with their usage, the longer we can extend their use before they break down through fungicide resistance.”

The trials

Given the appeal of the new chemistries, the FAR Australia disease management trials have been aimed at identifying optimal application times and strategy.

It is an approach that was also born from necessity because, unlike some older chemistries that have more than one site of activity and are less likely to promote fungicide resistance, SDHIs are more susceptible. “If we use the new SDHI chemistries in the old style of ‘many and often’, then we are at risk of losing their efficacy faster,” he says.

At Gnarwarre, trials using the SDHI fungicide Miravis Star found that it was most effective against chocolate spot when applied 14 days after the first flower, followed by an application of an older-style product such as carbendazim or chlorothalonil.

“So a two-spray program using an SDHI fungicide and the old chemistry is just as effective as using three units of the old protectant chemistry,” Mr Vague says.

Widespread global trends indicate this combination of new and old is the most-effective way to slow the onset of fungicide resistance. He says the trials have also found there is no benefit from using SDHI chemistries in winter, before plants start flowering. “If we want to get best bang for our buck, we’re going to use it after flowering, and this is when environmental conditions match the temperature and humidity to produce conditions that support a lot of disease,” he says.

Similar to targeted applications of fungicide used on cereals, this approach would be more cost-effective for faba beans, he says. “We are saying wait until the key components of the plant that contribute to yield are starting to develop – that’s when you need to use these products.”

Greater yields

Disease management through inputs is important, Mr Vague says, because – unlike wheat or canola – there are no faba bean varieties available to Australian growers that have a strong genetic resistance to the diseases that plague it.

While PBA Amberley still appeared to be the most resistant to disease, “we still don’t have an insurance policy of a variety that’s well-protected from the get-go. Yields are still highly dependent on spring disease pressure based on the environment and the prevalence of blown-in infection”.

Given the plant’s sensitivity to the conditions, he says it has been important to conduct trials over several years. With multiple data sets a more-accurate picture of key timings for fungicides could be drawn.

Most recently, trials in 2021, 2022 and 2023 at Gnarwarre provided a fascinating insight into the nature of the faba bean plant and its relationship with fungicides and the environment, he says.

In 2021, a trial of PBA Amberley untreated control yielded 4.29 tonnes per hectare. A neighbouring plot that received the full fungicide treatment (three timings of conventional fungicides paired with one Miravis Star at 14 days after the start of flowering) returned 7.45t/ha.

A year later, in a wet and disease-riddled season, faba beans under the same optimal fungicide program yielded more than double those that were untreated, at 2.99t/ha and 1.2t/ha respectively.

Then, in 2023, when spring conditions were markedly drier than the previous two years and there was very little disease pressure around, there was no fungicide response in the crop. Faba beans in the trial returned the same yield of 3.5t/ha despite the amount of fungicide applied – from nothing through to the highest application of four units. In that year, because of the dry conditions, crops were also smaller, with more-open canopies which also worked to reduce disease risk.

Figure 1: Faba beans in the HRZ

“So, 2023 is a nice reminder that sometimes the weather in spring is the best fungicide because hot, dry conditions aren’t conducive to disease development,” Mr Vague says.

While 2023 brought low disease pressure and no economic benefit from fungicide application, in other years the benefit is significant, and the most important input to manage in terms of return on investment.

Without a failsafe mechanism to accurately predict spring conditions, he hopes that the trials will help to provide some confidence around the value of using a targeted disease management approach.

Nutrition and canopies

The same economic and agronomic philosophy can be applied to nutrition.

In an evolving area of the research, Gnarwarre trials have shown that in some years an application of 200 kilograms/ha of nitrogen resulted in a yield gain only five per cent, a gain that does not appear to provide an annual benefit financially.

But, he says, while on paper there appears to be no economic benefit from nitrogen application in the year of application, which is not unexpected given faba bean’s ability to fix nitrogen, there may be a positive impact in the longer term. “Part of this project is looking at the long-term consequences or residual effects of different strategies..”

In terms of canopy management, researchers are looking at how to create an architecture that maximises disease resistance while minimising impact on yield. This is a challenge because optimal yields rely on big canopies, and big canopies correlate with greater levels of disease.

Trials are underway looking at the impact on yields and disease under different sowing rates, and the use of mechanical and chemical defoliation early in the season to reduce biomass.

“The key take-home message is that currently yield is king and if we are looking to achieve high yield, then high plant density is ideal. And any manipulation or reduction in early season biomass through defoliation treatments caused a reduction in yield as well.”

With 2024 marking the final year of trials, Mr Vague hopes their work will have built a more comprehensive agronomic picture of faba beans to provide growers in the HRZ with confidence in a crop that brings both environmental and economic benefits.

“You’ll still want to make money from the area on which you are growing faba beans, so we are trying to find not only ways to increase sustainability and profitability around the use of fungicides, as the main in-crop cost, but also using less of it to hopefully deliver on the bottom line as well.”