Stay Ahead of White Mold in Soybeans

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White mold in soybeans

As you’re scouting your soybean fields this summer, there is one particular disease to watch for. A lot of Midwest farmers dealt with white mold in 2021, and experts say — judging by the way this pathogen moves — it is likely to be a problem again in 2022.

“White mold in soybeans was the most common disease that I addressed last year,” says Gibson. “Through winter meetings, probably the No. 1 question I've had is what to do about white mold.”

What Causes White Mold?

White mold, also known as sclerotinia stem rot, is caused by the fungus Sclerotinia sclerotiorum. The disease has more than 400 alternate plant hosts — including many common weeds and crops — making it nearly impossible to eradicate once it infects soybean fields.   

Cool, cloudy and humid weather conditions, coinciding with soybean flowering, create a favorable environment for white mold development. Although these conditions are most likely to occur in northern areas, other Midwest and southern states are not immune from the disease. 

“A lot of farmers farther south than normal experienced white mold in 2021,” Gibson says. “So what we're trying to do is really encourage people to pay attention to whether they have the disease in the soybeans and take the time and to map out its progression field by field and pay attention to how it spreads or changes over time. This can help with disease mitigation.” 

White mold can jump from infecting 5% to 10% of your soybean crop in one season to 50% the following season. So Gibson says that timely preventive action is necessary to maximize soybean yield in the presence of white mold.  

Disease Identification

The first step in white mold management is identifying the disease early. Correct disease diagnosis and implementiation of an effective management strategy before harvest will help minimize the spread and reduce the risk of severely spreading the disease in subsequent years. 

To diagnose white mold, check stems of potentially infected plants. The first signs are gray to white lesions on nodes. Lesions rapidly spread above and below infected nodes and are often covered in fluffy, white growths.  

Cultural White Mold Management Practices

Farmers can implement common cultural practices to mitigate the risk of a white mold infection. These include, but are not limited to:  

  • Evaluating and adjusting seed density, if needed. “In lower-lying areas where moisture tends to sit, bean height gets a little taller. That’s where you’ll see more lodging — in those areas that don’t get as much air movement,” Gibson says. “If you can slightly reduce that plant stand and allow more spacing between plants, there will be typically less disease incidence.”  
  • Partitioning fields, and harvesting infected areas last. White mold persists in the soil over time by survival structures called sclerotia, which are hard black structures that resemble mouse droppings. Because sclerotia are released during the harvesting process, they can easily spread to new fields. Be sure to harvest any infected fields last and thoroughly clean equipment when leaving infected fields. 
  • Implementing strategic crop rotations. Rotation with a nonhost crop is an effective means of reducing disease pressure in a field. Nonhost crops include corn, sorghum and small grains. Susceptible crops to avoid in a rotation include alfalfa, clover, sunflower, canola, edible beans, potato and others. Depending on soybean tolerance, field history and other factors, reducing white mold problems may require more than one year away from soybeans.  

Making the Most of Fungicide Applications 

Despite the use of cultural best practices to limit the incidence of white mold, weather and other conditions conducive to disease development may still cause heavy infestations. July is a common month for white mold to surface in northern areas, so you’ll want to ensure your soybeans are protected ahead of that time frame.  

“Too often, when farmers pull the trigger on a fungicide for white mold, it’s applied in the R3 stage, which may be too late,” Gibson says. “It may be necessary to apply at R1 and then again at R2 to really maximize that protection.”  

You can count on Aproach® fungicide to stop the clock on crop diseases like white mold. Aproach provides uptake in plants that is nearly twice as fast as competitors, thanks to the active ingredient picoxystrobin, which utilizes four movement properties to quickly surround, penetrate and protect soybean leaves and stems. 

Learn more about the benefits of Aproach by talking with your Corteva Agriscience representative or visiting Corteva.us.  

You can also watch Gibson discuss tar spot in corn and white mold and how to control them in this video:

Aproach® is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Always read and follow label directions.