Don’t Suffer Yield Loss from Septoria Brown Spot, Frogeye Leaf Spot

Don't let frogeye leaf spot and brown spot hurt your yields

If you grow soybeans, limiting common soybean diseases like Septoria brown spot and frogeye leaf spot is 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 Your Risk

The lifecycle of Septoria brown spot and frogeye leaf spot begin when it overwinters in leaf and stem debris, crop residue and infected seed. The microscopic spores produced on living tissues or dead plants are released during wet weather. Wind and rainfall disperse the spores onto healthy plants and infection begins.

Brown spot affects plants a little later in the growth cycle, around the R3-R6 periods. Favorable warm, wet weather conditions – 59 to 86 degrees F with 77 degrees optimum – enhances infection and development of disease symptoms.

For frogeye leaf spot, leaf lesions will begin to appear around R2. Spread of the disease is common under similar conditions that foster brown spot infection. Risk will also be raised if minimum tillage is used consistently or soybeans are not rotated often enough.

Identification is Key


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, Bugwood.org.

frogeye leaf spot in soybeans

Frogeye Leaf Spot

Frogeye leaf spot is a serious disease annually affecting soybean growers. According to Loren Giesler, Extension Plant Pathologist at University of Nebraska, yield loss estimates due to frogeye leaf spot have been reported as high as 30 percent nationally with extensive leaf blighting. Symptoms to identify are:

  • Brown, grey or tan spots with dark brown or purple borders.
  • A layered appearance when leaves are young.
  • Under severe disease pressure, lesions may combine and cause leaf drop.
  • Stems with dark red to brown spots.

Circular to angular spots on leaves, which resemble the eyes of frogs, begin as dark, water-soaked spots and develop into brown spots.

Protect your Soybean Fields

Timely foliar fungicide applications help protect soybean plants from fungal diseases such as Septoria brown spot and frogeye leaf spot through the season. 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. 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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