The faba bean joins other pulse crops such as chickpeas, lupins, lentils, and field peas as important rotational options.
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Research in ongoing farming systems across the Australian grain belt - from Grains Research and Development Corporation (GRDC), as well as state agencies like NSW Department of Primary Industries (NSW DPI - has shown faba beans frequently add to profitability when included in rotations.
As with most pulse crops, disease management is a critical part of faba bean success as a rotation option.
NSW DPI project officer Penny Heuston points out faba beans have had a reputation of being difficult to grow but if a robust disease management package is used, this does not need to be the case.
NSW DPI has published a detailed faba bean disease management guide that covers disease identification, including useful photos, along with tips on disease management.
The department's leading pathologists, including Joop van Leur and Kurt Lindbeck, have contributed to the guide.
Important diseases of faba bean include chocolate spot, rust, cercospora, ascochyta - which is a different species to ascochyta in chickpea - along with viruses, other minor diseases and root lesion nematodes (RLN).
For several of these threats, variety choice can help minimise disease impacts when combined with other control options.
There is useful resistance in some varieties to ascochyta, viruses, chocolate spot, rust and RLN.
Chocolate spot is the most important faba bean disease and can cause anything from minor damage to total crop failure in unprotected crops in conducive conditions.
It is favoured by bulky crops or ones with high leaf moisture or humidity over four-five days.
Optimal temperature range for disease development is 15-28 degrees.
The greatest risk period is normally from late July to late October, coinciding with canopy closure and flowering.
Faba bean rust is a bigger risk in northern NSW than southern NSW.
It is more likely to occur in early-sown crops appearing from mid-spring onwards when warm and humid conditions prevail - above 20 degrees.
Severe infections can cause early defoliation resulting in smaller grain.
Rust can cause losses of as much as 30 percent, especially in unprotected, susceptible varieties.
Ascochyta blight tends to develop under prolonged wet, cool conditions - from 5-15 degrees.
It appears earlier in the season than chocolate spot and is more prevalent in the colder, southern areas of NSW.
Cercospora, like ascochyta, develops early in wet and cold conditions.
It originates from soil-borne inoculum and previously infected plant material and only appears in areas previously sown to faba bean or adjacent paddocks.
Faba bean viral diseases can correlate with high aphid numbers early in the season due to late summer rains, the abundance of pasture legumes or the presence of volunteer faba bean plants.
Recently released varieties have greater varietal resistance compared with the older varieties.
Control of fungal diseases is focused on preventing disease establishment rather than curative control.
Seed-applied fungicides are generally not recommended for faba beans as they can harm rhizobia.
When applying fungicide to the seed, apply the rhizobia inoculum shortly before sowing.
The protection period of different fungicides varies from 10-14 days for older products and up to 4-6 weeks from newer semi-systemic ones.
Seasonal conditions and disease pressure may reduce periods of protection and require additional fungicide applications.
Authors of the guide emphasise the importance of monitoring weather events and being prepared to apply foliar fungicides when conditions are favourable for disease development.
It is important to have appropriate fungicides ordered well in advance.
Where possible, have aerial application booked in advance as a backup.
High water rates (100 litres per hectare by ground or 30L/ha by air) are advocated for good coverage and canopy penetration.
If necessary, apply foliar fungicides in light rain or when dew is present.
Water on the leaf can assist in product spread over the leaf.
Next week: Strategy to improve legumes with perennial grasses.
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact 0428 752 149.
