Key points
Field Applied Research Australia research manager Tom Price says:
- the grain yield response of faba beans to foliar fungicide varies according to season, with Victorian trials showing a grain yield response in 50 per cent of years
- aim to sow disease-resistant faba bean varieties where possible to reduce reliance on foliar fungicides. This is most important in higher rainfall areas
- there is merit in saving fungicide applications for when there is a more reliable rainfall outlook for the season
- fungicide applications just before canopy closure are often most effective in wetter-than-average seasons
When it comes to faba bean diseases, Field Applied Research (FAR) Australia’s Tom Price says chocolate spot is the biggest threat.
The FAR Australia research manager outlined his observations from trials in a presentation to growers and agronomists at a GRDC–Brill Ag workshop in March at Ganmain, New South Wales.
Brill Ag and FAR Australia trials, with GRDC investment, show that selecting a disease-resistant variety should be one of the first considerations when growing faba beans.
Mr Price said FAR Australia faba bean trials in the southern Victorian high-rainfall zone at Gnarwarre (with an average annual rainfall of 462mm), Victoria, from 2015 to 2023 demonstrated a grain yield response to foliar fungicides in four out of eight years (2016, 2020, 2021 and 2022).
In 2023, at Ganmain (with an annual average rainfall of 500mm), NSW, he said there was no grain yield response to fungicides because of the dry September (Table 1).
Table 1: Faba bean grain yield response to fungicide at Ganmain, NSW, in 2023.
1 Targeted = fungicides targeted at the crop reproductive stages.
Source: Brill Ag and FAR Australia
“The trials showed a significant difference between the grain yields of PBA Samira and PBA Nasma, but there was no grain yield response to any fungicide treatment,” he said.
“Some infection was evident on the faba beans early in their development, but the dry September stopped disease progression.”
At Daysdale (with an average annual rainfall of 542mm), NSW, in 2023, Mr Price compared PBA Bendoc, PBA Samira and PBA Amberley faba beans for grain yield (Table 2).
Table 2: Faba bean grain yield response to fungicide at Daysdale, NSW, in 2023.
Notes: 1 S = susceptible to chocolate spot. 2 MS = moderately susceptible to chocolate spot. 3 MR-MS = moderately resistant to moderately susceptible to chocolate spot.
Numbers with different superscript letters are significantly different to each other.
Source: Brill Ag and FAR Australia
“The results showed a 300-kilogram-per hectare grain yield response in PBA Bendoc faba beans to fungicide,” he said.
“However, in a low-disease-pressure year, there was no economic difference between a complete fungicide program and when two applications of old and new chemistry were applied at mid-flowering and podding.”
For PBA Amberley, rated MR-MS for chocolate spot, he said there was no significant difference in the grain yield response to any fungicide treatment applied in the low-disease-pressure year of 2023 and PBA Amberley without fungicide yielded similarly to PBA Bendoc with fungicide.
Mr Price said the 2023 results showed no grain yield response to applying an old-chemistry fungicide at the eighth node growth stage.
“Using new-chemistry fungicides 14 days after the start of flowering, followed by a new chemistry fungicide applied mid-flowering, enabled the start of fungicide application to be delayed without any grain yield loss,” he said.
“Delaying when we start applying fungicide buys more time to check whether the next 14 days is likely to be wet and high risk for the disease.”
Fungicide management
In 2022, at Ganmain, NSW, seven fungicide applications were used in the complete control treatment because the season was wetter than average (Table 3).
Table 3: Faba bean grain yield response to fungicide at Ganmain, NSW, in 2022.
1 Targeted = fungicides targeted at the crop reproductive stages.
Notes: The faba beans were sown on 10 May because the ground was too boggy to traffic before this date. The data shows no significant difference between the reactive treatment (three fungicide applications) and the complete control treatment (seven fungicide applications).
Source: Brill Ag and FAR Australia
Mr Price said one discovery in 2022 was that although PBA Nasma had a lower rating for chocolate spot than PBA Samira, the PBA Samira faba beans were lower yielding when no fungicide was applied.
This was possibly due to the early maturity of PBA Nasma and fewer rain events falling on a green canopy.
“In 2022, there was no statistical difference between PBA Samira and PBA Nasma grain yields treated with the targeted approach,” he said. “The targeted approach may enable you to delay the first fungicide application until crop canopy closure and only apply fungicide when needed to reduce canopy infection.”
He said this approach was based on the principle that some developmental stages of faba beans are more important for protecting against disease than others, and these stages coincided with canopy closure.
Late sowing
Brill Ag’s Rohan Brill said the 2022 trial at Ganmain was sown on 10 May because the site was too boggy to seed during mid-April.
Accordingly, he said mid-April-sown crops would likely yield less grain if the fungicide application program began at the start of flowering.
“Sowing the crop later reduced disease pressure in 2022, but I wouldn’t advise those with mid-April-sown crops to start their fungicide program at the start of flowering,” he said. “Sowing later will often reduce nitrogen fixation and grain yield.”
Mr Price said the newer systemic chemistry fungicides enabled a more-targeted approach with faba bean diseases.
Nonetheless, he emphasised the value of proactive fungicide application timing and said this was more important than product choice when managing disease in faba beans.
He stressed the importance of rotating fungicide groups and continuing with the partial inclusion of older multi-site chemistry, such as chlorothalonil, which had helped to protect against fungicide resistance in grain legumes.
“Relying on new products, such as fungicides from Groups 7 and 11 only, could quickly lead to the loss of these very effective products.”
Impact on profit
Mr Price concluded his presentation by discussing which fungicide treatments were worth the investment when conditions turned dry as they did in 2023.
“With PBA Bendoc faba beans, two sprays with old-chemistry fungicides were not any cheaper than two sprays with new chemistry fungicides, with both returning $120/ha additional income above the nil fungicide treatment,” he said.
“With PBA Samira faba beans, two sprays with old-chemistry fungicides were not worthwhile, while two sprays with new chemistry fungicides returned $129.60/ha above the nil fungicide treatment.”
However, he said, when factoring in costs of $112/ha for old-chemistry fungicides and $118/ha for new-chemistry fungicides, you would only make your money back with a margin of about $10/ha in both cases.
“For PBA Amberley faba beans, which are MR-MS to chocolate spot, two sprays with old and new-chemistry fungicides produced a negative return on investment, demonstrating the value of planting a faba bean variety with higher tolerance to disease.”
GRDC grower relations manager – north – Graeme Sandral said the main factors impacting returns were variety resistance level, seasonal outlook (wet versus dry) and potential yield.
“If faba bean variety resistance is in the low range and the seasonal outlook is wetter than average, it is likely fungicide application will provide an economic benefit.”
More information: Tom Price, tom.price@faraustralia.com.au