The main disease to be controlled by fungicide in dry beans is white mould (Sclerotinia sclerotiorum) (Figure 1). In order for a disease to develop, all three factors of the disease triangle must be present (Figure 2): 1) susceptible host, 2) virulent pathogen and 3) conducive environment. In this case, the susceptible host is the dry bean crop. However, other crops grown in Manitoba are also hosts, such as soybeans, canola and sunflowers. This means any of these crop residues from a previous year can contribute to the presence of a virulent pathogen. Finally, the decision to apply fungicide often comes down to a conducive environment.
The MPSG Fungicide Decision Worksheet for Managing White Mould in Dry Beans (also available in the Bean App) can help determine the risk of disease development, based on environmental and agronomic factors, and aid in the decision of whether or not to apply a fungicide.
About White Mould
- The life cycle begins with fungal sclerotia bodies in the soil, from which apothecia (small, mushroom-like structures) form. Apothecia release ascospores in to the crop canopy, infecting blossoms and other dead or senescent plant tissues.
- Warm (15 to 25°C), wet soil about ten days before flowering favours the development of apothecia. Prolonged plant surface wetness for 40+ hours is favourable for infection.
- Disease development begins low in the crop canopy (Figure 1). Leaves, branches, stems and pods can all show symptoms. A thick plant canopy will contribute to disease development, as it helps maintain ideal moisture and temperature conditions for white mould.
- Crop rotation including non-host crops, upright plant architecture, resistant varieties, tillage and wider row spacing can reduce white mould pressure in dry bean crops. However, even sclerotia bodies buried 12 inches deep in a bean field can survive for 3+ years.
The R2/early pin bean stage is the best time to apply fungicide for effective white mould control. This stage coincides with flowering and early pod development. See the MPSG Dry Bean Growth Staging Guide. Research from North Dakota State University has indicated that later fungicide application at the R3 stage may be more beneficial under more prolonged dry conditions, such as those experienced in 2017.
If conditions are consistently favourable for disease development throughout flowering and pod development, two fungicide applications should be considered. However, double application results are variable and would largely depend on highly conducive environmental conditions and the expected time of infection.
On-Farm Network Research Results
The On-Farm Network has been investigating the impact of foliar fungicide application in dry beans. To date, only two out of five years (2013 and 2015) have resulted in a significant dry bean yield response to fungicide application.
July is when dry beans begin to flower and when most foliar fungicides are applied. Comparing July rainfall from 2013 to 2017, there were two years (2014 and 2017) where rainfall was considerably below normal (Table 1). In these years, we did not see a response to foliar fungicide. In 2013, 2015 and 2016, rainfall was either slightly above or below normal. However, significant yield responses to foliar fungicide only occurred in 2013 and 2015, and not in 2016.
If you are on the fence about applying fungicide and find yourself in the “moderate risk” category according to the decision worksheet, consider leaving one more more check strips to determine the effectiveness of fungicide in a given year. Refer to the additional resources below for more information on white mould and fungicide efficacy from Manitoba, Alberta and North Dakota. Also refer to the On-Farm Network single-site research reports or sign up to conduct this type of trial on your farm!
Are Foliar Fungicide Applications Necessary in Dry Beans to Control White Mould in a Dry Year? – Pulse Beat article by Greg Bartley, MPSG On-Farm Network Specialist
White Mould Fungicide Efficacy Research in Dry Beans – Pulse Beat article by Michael Harding, Alberta Agriculture and Dr. Syama Chatterton, Agriculture and Agri-Food Canada
Improving the Management of White Mold in Dry Beans – 2018 Bean Day presentation by Dr. Michael Wunsch, North Dakota State University