Brown Spot


Brown Spot, also known as Septoria leaf spot, is a foliar disease caused by Septoria glycines that primarily targets the lower canopy of soybeans.

The disease primarily targets the plant's principal photosynthetic organ. Brown Spot can also disrupt the physiological processes of the soybean plant. For example, the disease can hinder the plant's ability to absorb nutrients and water, impacting its overall health and productivity.

Additionally, defoliation triggered by Brown Spot can leave the pods exposed, increasing their vulnerability to other diseases and pests.

Brown Spot is not known to cause substantial yield losses. However, the actual impact on yield can fluctuate based on the timing of infection, disease severity, and the management strategies employed.

(Image Credit: R.J. Reynolds Tobacco Company,

Brown Spot Disease in Soybeans close up

How to Identify Brown Spot Disease

The disease presents as small, dark brown spots on both upper and lower leaf surfaces. These spots, usually 2-5mm in diameter, can coalesce to form larger blotches.

As the disease evolves, the infected leaves turn yellow and may prematurely fall from the plant. In extreme cases, Brown Spot can cause defoliation of lower leaves, leading to a decrease in yield.

Geographic Impact of Brown Spot Disease

Brown Spot thrives in warm, humid climates and often hits hardest in fields with a history of soybean cultivation. The disease can persist in infected crop residue, making it a perennial issue in fields where soybeans are the primary crop.

(Image Credit: R.J. Reynolds Tobacco Company,

R.J. Reynolds Tobacco Company,

Timing of Brown Spot Disease

Brown spot typically makes its appearance early in the growing season, often as the first foliar disease. However, it can also strike later in the season.

How to Manage Brown Spot Disease in Soybeans

Effective management of Brown Spot is a key determinant of successful soybean production.

Many fungicides work to reduce disease. Our experts recommend applying GCS Azoxyprop during soybean growth stage R3.


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This content was generated with the assistance of Norm℠, FBN’s artificial intelligence (AI) Ag Advisor, based on a dataset of information containing general industry best practices and research. The AI model did not use specific external sources to generate this content. Our process involves using AI to aid human subject matter experts with the initial drafting and/or refinement of content.

Every product that labels BROWN SPOT as a weed, pest, or disease the product can be applied against is shown below. Click any product for label and more information.
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