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Septoria Brown Spot of Soybeans

Gail Ruhl, Senior Plant Disease Diagnostician

(Click on smaller image to view larger image.)

Close-up Septoria Spot on Soybean Leaf Top Photos of Soybean Leaves by Gail Ruhl

Bottom Photos by Peggy Sellers

Septoria Spot on Soybean (Front and Back of Leaves Shown)
Close-up Septoria Spot on Soybean Leaf Septoria Spot on Soybean (Front and Back of Leaves Shown)
Septoria Spores at 100X Septoria Spores at 400X Fungal Fruiting Bodies Close-Up
Septoria Spores at 100X Septoria Spores at 400X
Fungal Fruiting Bodies
Close-Up       

Septoria Brown Spot has been confirmed on several samples that have been submitted to the Plant and Pest Diagnostic Lab. This fungal disease causes chocolate-reddish brown spots that are visible on both the upper and lower leaf surfaces, as well as on cotyledons. The fungus, Septoria glycines, overwinters in soybean residue. During wet weather in late May/early June, spores are produced on the residue and are splashed or blown to healthy soybean leaves. Angular red-to brown spots that vary from the size of a pinpoint to about 5 mm in diameter first appear on unifoliolate leaves. Lesions on older, trifoliolate leaves may coalesce as the season progresses causing an overall rusty brown discoloration. Defoliation of the lower part of the plant may occur with severe infections. Although lesions are primarily found on leaves, it has been reported that this disease may also infect stems, petioles and pods.

Control measures vary according to the severity of the problem. It is important to plant pathogen-free seed, practice crop rotation and plow under crop residue where erosion is not a problem. Areas with poor drainage favor spread of the disease. If the infection is causing severe premature leaf drop, a foliar fungicide application at the R-3 stage might be beneficial.

Please contact Dr. Greg Shaner at 765-494-4651 if you have further questions.


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Last updated: 8 June 2001/tlm.
The Plant & Pest Diagnostic Laboratory at Purdue University.