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Effective Foliar Disease Control in Faba Bean

There are three main diseases that are important to control in beans, Cercospora (Cercospora zonata), Ascochyta (Ascochyta fabae) and chocolate spot (Botrytis fabae and Botrytis cinerea).

There are critical periods to monitor for these diseases within a faba beans life cycle to ensure effective control and yield protection

 

The first period is the initial 5-8 weeks after emergence where cercospora begins to develop and is most effectivity controlled within this period with tebuconazole. Cercospora is similar to ascochyta in that it develops in prolonged wet and cold conditions and has similar symptoms although the cercospora lesions tend to be bit darker and more irregular. If left uncontrolled significant defoliation can occur. If growing a susceptible variety to ascochyta (refer to Table 2), the management focus needs to be more of proactive approach rather than reactive to ensure no yield loss is obtained.

Photo 1. Cercospora leaf spot (Cercospora zonata) lesion on Faba Bean leaf. Photo curtesy of Agriculture Victoria.

 

Ascochyta is prevalent throughout south-east south Australia and western Victorian regions. Infections develop in prolonged cool and moist conditions which is typical in our area. It forms sunken lesions on the stems, pods and leaves; these lesions can cause the plant to lodge or impact on grain colour and size if the lesion is on the pod, impacting the quality and quantity of beans produced.

 

The first period is the initial 5-8 weeks after emergence where cercospora begins to develop and is most effectivity controlled within this period with tebuconazole. Cercospora is similar to ascochyta in that it develops in prolonged wet and cold conditions and has similar symptoms although the cercospora lesions tend to be bit darker and more irregular. If left uncontrolled significant defoliation can occur. If growing a susceptible variety to ascochyta (refer to Table 2), the management focus needs to be more of proactive approach rather than reactive to ensure no yield loss is obtained.

Photo 2. Ascochyta leaf spot (Ascochyta Fabae) Lesions on Faba Bean leaf. Photo curtesy of Agriculture Victoria   

 

Chocolate spot forms black-brown spots on the leaves of the Faba Bean and can expand, turning the whole plant black. Chocolate spot often occurs when there is warm humid conditions over an extended period of time during flowering and after canopy closure. Chocolate spot impacts the plant by aborting pods and causing plant damage, therefore the plant is putting its energy into healing itself rather than pod development and seed set. 

Photo 3. Chocolate spot (Botrytis Fabae) lesions on a Faba Bean leaf. Photo curtesy of Agriculture Victoria.   

 

The second critical period is during flowering and prior to canopy closure as it allows penetration down to those lower leaves and protects against chocolate spot which when serious can cause pod abortion and flower drop; a protective spray prior to symptoms appearing is recommended. Both cercospora and ascochyta should again be targeted at this period, especially if early control of cercospora was unsuccessful or if a particular variety is susceptible to ascochyta (see table 1).

 

The final critical period is pod fill, this is where both chocolate and ascochyta need to be controlled if they haven’t been already. The control of chocolate spot is necessary at this period because lesions can cause the plants to lodge causing significant grain loss. Ascochyta needs to be controlled as the disease can cause seed staining, resulting in a downgrade of seed quality.   

Table 1.  Show a disease rating table of faba Bean varieties common in SE SA and Western Victoria, S = Susceptible, M = Moderate, MS = Moderate susceptibility, MR = Moderate Resistance, R = Resistant.  Table curtesy of Pulse breeding Australia sourced from GRDC grow notes faba bean. 

 

The disease rating of a variety determines how susceptible that variety is to different diseases. That is why it’s important to choose a variety that has good disease resistance to reduce disease build up and improve efficacy of the fungicide thereby improving yield (Table 1).

 

It is also critical to point out that growing faba beans in the high rainfall zone has added disease pressure due to moist humid conditions; ideal growing conditions for disease especially chocolate spot so when choosing a variety it needs to have a good disease rating to help protect from high disease pressure prevalent throughout SE SA and SW Victoria.  

 

These timings are just guidelines to when diseases may become an issue. It is critical that during these periods crops are checked regularly to ensure the diseases are kept under control and preventative fungicides can be applied. Adama have presented a performance guide to different fungicides; showing relative performance to controlling foliar diseases in faba beans.  

   

Table 2. Shows different control options of diseases using ADAMA products and how effective they are on different diseases. 

If you have concerns about disease levels in your Faba Beans please contact your local Western AG agronomist for a field assessment.

Article produced by - Zach Reardon, Western AG Bordertown