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.

To combat white mold infections and other diseases, Bayer recommends treating soybeans soon after initial flowering, or R1, with an application of Proline® fungicide. It has shown to be a very effective tool in the management of white mold, especially when coupled with a later fungicide application.

A best practice following an application of Proline is a follow up spray of Stratego® YLD fungicide. In this 2-spray approach, Stratego YLD protects the leaf canopy from foliar diseases, while Proline protects the lower parts of the plant. Stratego YLD features the latest in triazole technology combined with strobilurin chemistry for soybeans. It offers two modes of action providing both preventive and curative benefits and systemic movement for broad-spectrum, long-lasting foliar disease control and higher yield potential. In trials where Stratego YLD was applied alone at early pod set, around R3, yields increased on average between 3 and 4 bu/A versus untreated soybean plots.

For added protection from insects, growers can also tankmix Stratego YLD fungicide with a powerful insecticide like Leverage® 360. Applications like this can help lower costs, improve yields and increase ROI by reducing the number of passes needed to ensure crop protection. In trial tests, 90 percent of growers that applied Stratego YLD tankmixed with Leverage 360 at R3 saw a positive yield response, increasing yields nearly 5 bu/A.

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

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