DB Diseases

Foliar Fungicide Decision Making in Dry Beans

Managing White Mould

The main disease controlled by fungicide in dry beans is white mould (Sclerotinia sclerotiorum) (Figure 1). Fungicides can also offer control or suppression of anthracnose, powdery mildew and rust, depending on the product. However, these diseases are less frequent and less severe in Manitoba-grown dry beans. White mould has a wide host range, infecting other broadleaf crops such as canola, soybeans and sunflowers.

Foliar fungicides for suppression or control of white mould are preventative, meaning they must be applied before disease symptoms are visible. The R2/early pin bean stage is the best time to apply fungicide for effective white mould control. This stage coincides with flowering (100% of plants with an open blossom) and early pod development (first pin-pods are 0.5 to 1″ long).

If warm, humid conditions persist throughout flowering and pod development, consider a second fungicide application 7 to 14 days later.

The Fungicide Decision Worksheet for Managing White Mould in Dry Beans (available in the Bean App) was created to help determine the risk of white mould disease development, based on environmental and agronomic factors.

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.

Another option would be to conduct an on-farm trial by following the protocol on our On-Farm Network page. We still have product available to test foliar fungicide application in dry beans on your farm for 2020. Contact On-Farm Network Agronomist, Megan Bourns: 204-751-0439 | megan@manitobapulse.ca for more information.

White Mould (Sclerotinia) Life Cycle

  • The life cycle begins with fungal sclerotia bodies that overwinter 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 lower in the crop canopy. 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 help reduce white mould disease development.

On-Farm Network Research Results

Since 2016, 15 trials have been conducted by MPSG’s OFN investigating foliar fungicide application in navy and pinto beans to control white mould. A single application of foliar fungicide was applied at R2 (early pin bean) and compared to an untreated control.

To date, there have not been any significant dry bean yield responses to a single foliar fungicide application. The impact of fungicide on yield depends on the extent of fungal disease pressure in the field. Across all 15 trials, disease pressure was generally low. Under different environmental conditions that facilitate higher disease pressure, fungicide could have a significant impact on yield. The OFN will continue these trials to measure the effects of fungicide in dry beans across different environmental conditions and levels of disease pressure.

If you’re interested in testing foliar fungicide on your farm, we still have product available for dry bean trials in 2020. Contact On-Farm Network Agronomist, Megan Bourns: 204-751-0439 | megan@manitobapulse.ca for more information.

Additional Resources

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
Fungicide Efficacy Testing Results from NDSU’s Carrington CREC
Improving the Management of White Mold in Dry Beans – 2018 Bean Day presentation by Dr. Michael Wunsch, North Dakota State University
Optimizing fungicide application timing – 2019 presentation by Dr. Michael Wunsch, North Dakota State University