Which soybean foliage disease causes small brown spots on unifoliate leaves?

The correct answer is Septoria brown spot, which is a common foliage disease affecting soybean plants characterized by small, round brown spots that typically appear on the unifoliate leaves. This disease is caused by the fungal pathogen Septoria glycines. The small brown spots often have a yellow halo and can result in premature leaf drop, ultimately affecting the overall yield of soybean crops.

Recognizing the symptoms of Septoria brown spot is critical for effective disease management, as early detection allows for timely interventions to minimize its impact. Unlike other diseases, such as bacterial blight, which presents differently on the leaves with water-soaked spots, or powdery and downy mildew, which present with powdery fungal growths or downy mycelium, respectively, Septoria brown spot specifically results in those characteristic small brown lesions, making it distinct among soybean foliage diseases. Understanding these identifiers helps farmers and agronomists implement appropriate control measures tailored to the specific disease present.