Pennsylvania Soybeans: What Factors Influence White Mold?

Characteristic white mold symptoms include white, cottony mycelium on the stem of soybean plants. Photo: Damon Smith, University of Wisconsin Madison

Looking at the 2019 USDA crop reports for Pennsylvania through June 23, estimated soybean planting has reached approximately 87%, and 81% of the crop condition is rated as good or excellent. The long planting period and the outstanding acres still to be planted indicates to us that we will be monitoring white mold risk around the state in different time windows.

Nonetheless this is a perfect time to begin our discussion of the factors that should be considered for determining if a fungicide application will be warranted. Early-planted soybean is now entering flowering and our current weather forecast over the next several days is for our first extended dry period of the growing season, with temperatures into the 80s throughout much of the state.

What factors influence white mold development?

There are several factors that we can consider when determining the risk of white mold, including:

  • Disease of high yield potential soybean
  • Field history of white mold
  • Type of crop rotation
  • Susceptible cultivar
  • Row width and plant population (canopy closure and flowering)
  • Light intensity (low light at soil surface)
  • High soil moisture and high relative humidity
  • Duration of leaf wetness > 12 hours
  • Cool temperatures (< 85°F)

Sporecaster app can help you make management decisions for white mold.

One tool that you can also try to examine the risk of white mold is called Sporecaster, an app that is available for Android and iPhone/iPad. This tool was developed in the Midwest from multiple years of research in several states to model the appearance of apothecia. The app and the model behind it forecasts the appearance of apothecia as a function of weather and soybean row closure for fields grown on 15” and 30” rows, as well as under irrigation or dryland conditions.

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In 2018, we began to test this app in Pennsylvania for many fields that we visited as part of field calls, research plots, or field days. For 2019, we are again monitoring those sites and we are assuming the same parameterization as we had in 2018 (some were 15” row spacing, others on 30” spacings) for those cases. Doing an update on June 24, we found that the majority of our marked fields were in the moderate risk stage. The recommendation when the risk is “medium” is to consult the app during the next several days to monitor the situation.

Foliar fungicides for white mold.

The North Central Regional Committee on Soybean Diseases (NCERA-137) updates annually the relative efficacy of foliar fungicides in its document, “Fungicide Efficacy for Control of Soybean Foliar Diseases.” If you are considering a fungicide application for white mold, we recommend that you consult this document since fungicide decision-making is different for white mold than for many of our primary foliar disease targets and product efficacy is variable.

Additionally, check the labels closely for recommendations on the use of these products and the recommended number of applications and timings, especially given the current commodity prices.

We want to take white mold and/or soil samples from your fields!

As part of a new project with support of the Pennsylvania Soybean Board, we are very interested in taking samples from fields that have white mold symptoms in 2019, or have had a history of white mold.

To help us with this project, please send an email with your name and contact information to:

Paul Esker (pde6@psu.edu) and Tyler McFeaters (tsm31@psu.edu)

Please send your message to both addresses as we will coordinate with you to take a sample. We are also interested in doing a short follow-up discussion regarding your production practices and learn more about the challenges you have had in managing this disease to help us improve our management recommendations for this disease.


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