Don’t Suffer Yield Loss from These Soybean Diseases

Don't let brown spot and white mold hurt your yields

If you grow soybeans, limiting common soybean diseases like white mold and Septoria brown spot are always on your list of tasks to complete. Now growers have another way to limit yield losses through effective crop protection programs. But before you can solve the issue, growers need to understand how to assess their risk, recognize the contributing factors and know how to resolve issues efficiently to limit yield loss and plant damage.

Be Aware of Risks

Plants are generally more at risk to white mold when they are in early flowering, or the R1 growth stage, because blossom petals are the typical medium for infection. The disease typically thrives in wet, cool, humid environments. These conditions are common early in the season, though they can redevelop later in the season after the summer’s heat recedes. Extended wet periods without large changes in temperatures can also increase risk. Growers planting acres with past issues need to pay extra attention, because the resting bodies, called sclerotia, of the causal pathogen can survive for long periods in the field.

Other contributing factors according to Purdue University are:

  • Planting varieties that have a bushy architecture or are more likely to lodge, as they have an earlier closing canopy.
  • High soil fertility and those that have very high levels of nitrogen help white mold development.
  • Tillage practices can return dormant sclerotia to the soil surface, giving resulting white mold spores an opportunity to infect soybean plants.

Brown spot affects plants a little later in the growth cycle, around the R3-R6 growth stages, although lesions can be seen earlier. Similar conditions that contribute to white mold can increase risk of brown spot. For a full list of symptoms, please visit Protect Yourself from Septoria Brown Spot.

Identification is Key

In order to quickly take care of infection problems from white mold and brown spot, it’s good to know the symptoms of the disease. That way, regular scouting can catch problems in their infancy to limit yield loss and protect plant health.

soybean pod infected with white mold

White Mold

Purdue University Extension researchers tells growers to look for the following signs:

  • White, fluffy, cottony growth on the outside of the stem and on the pods.
  • Wilted leaves and stems that appear bleached, along with tearing of the stem tissue.
  • Sclerotia can also be found on and inside plants that have been infected by white mold.

A soybean pod and stem infected with white mold.

Septoria brown spot or brown spot

Brown Spot (Septoria Brown Spot)

Brown spot thrives during cooler, wet conditions. If left unchecked, it can damage plant leaves and stunt pod fill. Signs include:

  • Brown or black spots on plant leaves that are angled or include a yellow ring or halo around spots.
  • Late-season infections force leaves to turn yellow and defoliate from plants prematurely.

Septoria brown spot, or brown spot, usually starts on the lower section of the soybean plant, moving up through the tissues under favorable conditions. Photo courtesy of Daren Mueller, Iowa State University,

Protect your Soybean Fields

Timely foliar fungicide applications help protect soybean plants from fungal diseases, including Septoria brown spot and white mold. For growers, a fungicide decision is a matter of considering production needs, past history in the fields, commodity prices, proper timing and risk management.

Delaro™ fungicide offers an unmatched broad spectrum control. Its advanced formulation delivers best-in-class dual mode of action residual and improved plant health. In soybeans, the ideal time to first apply Delaro is prior to disease development, between R2 and R5, with applications repeated as necessary. To manage white mold, the ideal time to first apply Delaro is prior to disease development, at R1, followed by a second treatment at R3 or R4. Disease-susceptible cultivars and seed soybeans are most likely to benefit from a Delaro application. For cost efficiency, Delaro can be tankmixed with insecticides and applied in the same trip across the field.

Before applying any fungicide, please read the entire label for the best possible results and to confirm that the product is effective on the disease you need to control. Not every product is suitable for every situation, and correct application technique will ensure the best results.

To limit yield loss in soybeans from other common issues, you might be interested in reading:

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