Australian Pulse Bulletin

Faba bean fungicide guide: 2021 season 

The four main fungal diseases of faba and broad bean that require monitoring are chocolate spot (Botrytis fabae and B. cinerea), ascochyta blight (Ascochyta fabae), cercospora leaf spot (Cercospora zonata) and rust (Uromyces vicia-fabae). By following the monitoring process recommended for these diseases, there is the opportunity to assess the impact or presence of other diseases, weeds or plant disorders. To be effective, crop monitoring and scouting needs to include a range of locations in the paddock, preferably following a ‘V’ or ‘W’ pattern.

Ascochyta blight

The initial symptoms will be lesions on the leaves and stems of young plants. A distinguishing feature is fungal fruiting structures (small black dots) visible within the centre of lesions.

Monitoring should commence 2–3 weeks after emergence, or 10–14 days after a rain event. This is to allow time for disease expression after an infection event, such as transmission from infected seed or rain-splashed inoculum. Infected seedlings may deteriorate quickly and affected plant parts above the lesion may break off, making symptoms difficult to detect.

Timing is critical! After the initial inspection, subsequent inspections should occur every 10–14 days after a rain or heavy dew event. During dry periods, inspections can be less frequent. When monitoring, look for signs of lesions on leaves, or if severe, wilting in upper foliage or small areas of dead or dying plants, and if present examine individual affected plants for symptoms of infection. This method will allow more of the crop to be inspected than a plant-by-plant check.

Chocolate spot

Chocolate spot is more likely to occur in bulky crops after canopy closure. The critical stage for the first inspection will be just before the commencement of flowering, as temperatures begin to increase, and then regularly through the flowering and seed filling period. Lesions occur on leaves and flowers first but can occur on stems and pods. Flower abortion and drop can occur.

Symptoms first appear as small brown spots on leaves and flowers, which then rapidly develop into large irregular shaped lesions on leaves and decay of flowers if conditions remain favourable.

Chocolate spot (Botrytis fabae) requires high leaf moisture or humidity (>70%) within the crop canopy and optimal temperatures are 15–28°C. However, disease progression can occur at lower temperatures, although at a reduced rate of spread. When humidity levels decrease or maximum daily temperature exceed approximately 28°C, the infection levels decline sharply.

More regular crop monitoring and protection may also be required in high risk situations such as:

• immediately adjacent to last year’s crop
• non-optimal paddock selection (e.g. waterlogging)
• high disease pressure in the previous season
• susceptible variety sown
• short rotation.

Cercospora

Cercospora leaf spot is most likely to occur in paddocks with a long term history of faba bean cropping. Cercospora monitoring must start 2–3 weeks after emergence, or within 4–6 weeks of sowing. This is particularly important where faba beans have been grown in the paddock in recent years or there has been quite a few beans grown in that paddock over time.

When disease risk is high protective fungicide needs to be applied 4-6 weeks after sowing to prevent initial infection, irrespective of symptoms. Fungicides applied at first signs of cercospora lesions will slow the spread of the disease. 

Subsequent monitoring should occur when checking for chocolate spot prior to and during flowering and podding.

Rust

The time to start monitoring for rust in faba and broad beans in southern Australia depends on sowing time and presence of infection on bean stubbles from the previous year.

With early sown beans, infection can occur at early emergence when temperature and rainfall conditions are suitable for its spread. Later sown beans may not get infected until spring, when temperatures, moisture and humidity are high.

Monitoring for rust needs to occur when monitoring for chocolate spot and late ascochyta.

For more detailed information: Faba bean: Integrated disease management

The need for repeated fungicide applications depends on the growth stage of the crop, the time since the last fungicide application and the likelihood of further conditions favouring disease development. Unprotected crops may be quickly defoliated and destroyed by the infection. The choice of fungicide is less important than the timing, but when multiple sprays are required during the season it is critical to rotate different products and modes of action to preserve the effectiveness of all the fungicide choices. Follow this link for advice on maintaining fungicide efficacy for the grain industry.

Seasonal Conditions in 2021

After a bumper season in 2020 that produced record yields in many areas of NSW, Victoria and South Australia, rainfall has been variable over summer in many regions. NSW and southern Queensland have had good rainfall over summer that has given full soil moisture profiles, Victoria and South Australia started with dry conditions for sowing winter crops but have recently received adequate rain to get crops germinated. In Western Australia conditions have been very favourable for sowing crops and regular rain events have followed. This season will be favourable for many diseases as we head into spring. Many of these diseases need only limited moisture to infect crops (heavy dew or fog may provide enough moisture), so monitoring needs to be continued through the different growth stages of the crop. With good access for ground sprayers this year, allowing for high water rates and canopy penetration, timely fungicide application will give the crop the best chance of a high yield. The crop needs continuing fungicide protection for good pod fill so timely application of fungicides by ground sprayers will give the spray coverage required. Rotate and mix fungicides from different groups to minimise the risk of fungicide resistance developing in the pathogens.

For more detailed information on disease management: 

• Faba bean: Integrated disease management
• CropPro faba bean disease manual
• Fungicide resistance in grain crops (including pulses)

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  Cercospora (SARDI)

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  Mouldy pods caused by chocolate spot

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  Early indications of chocolate spot

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  Chocolate spot on faba bean leaves and flowers (J Davidson).

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  Ascochyta blight on faba bean leaves (J Davidson).

Fungicides registered for use for faba bean in 2021

Many Minor Use Permits have short term expiry dates (e.g. 30/11/2022) 

Faba Bean Foliar Fungicide	Trade Name example	Chocolate Spot	Rust	Ascochyta	Cercospora	WHP Harvest
Chlorothalonil 720	CC Barrack 720	1.4 to 2.3 L/ha	1.4 to 2.3 L/ha	NR	NR	7 days
Mancozeb 750 (M3)	Dithane DF	NR	1.7 to 2.2 kg/ha	1.7 to 2.2 kg/ha	1.7 to 2.2 kg/ha	7 days
Carbendazim (Group 1)	Spin Flo	500 mL/ha	NR	NR	NR	28 days
Procymidone 500 (Group 2)	Sumislex 500	500 mL/ha	NR	NR	NR	9 days
Copper (M2)	Champ 500DF	1.2 kg/ha	1.2 kg/ha	NR	NR	1 day
Metiram 700 (M3)	Polyram DF	1.0 to 2.2 kg/ha	1.0 to 2.2 kg/ha	1.0 to 2.2 kg/ha	1.0 to 2.2 kg/ha	42 days
Tebuconazole (Group 3)	Folicur SC	NR	145 mL/ha	NR	145 mL/ha	21 days
Prothioconazole (Group 3) + Bixafen (Group 7)	Aviator XPro	600 mL/ha	600 mL/ha	400 to 600 mL/ha	400 to 600 mL/ha	35 days (Do not apply after early flowering)
Azoxystrobolin (Group 11) + Tebuconazole (Group 3)	Veritas	1.0 L/ha	NR	1.0 L/ha	NR	28 days

NR = Not Registered (not effective for this disease)  

Read the Label As with any chemical application, care should be taken to observe all the label conditions for each product. Some label advice is different for each state or region, so for best results, it is important that this is followed. Many of our pulse crops are exported for human consumption, so market access is dependent on having the product free of chemical residues. Australian has a reputation for providing clean and safe produce so it is vital that this is maintained by using chemicals according to regulations. All permits have label recommendations for use rate and withholding periods (WHP) that must be observed so grain will comply with Maximum Residue Limits (MRL) allowable for market access.

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Last updated: 9 July 2021