Septoria brown spot (Septoria glycines)

Septoria brown spot: biology

Septoria brown spot is a fungal leaf and stem disease found in soybean crops. It does not typically cause a major yield impact, but losses of up to 10% have been observed in very susceptible varieties that have been infected early and under prolonged stress conditions.

The Septoria glycines fungus overwinters on seed and crop residue. It is dispersed by airborne spores, and infection occurs in the spring and early summer, during extended periods of warm, wet weather.

Septoria brown spot symptoms first appear on the primary unifoliate leaves shortly after trifoliate leaves have developed. They begin as small, dark brown, irregular spots (1-2 mm in diameter) with or without a yellow halo, which develop on upper and lower surfaces of lower leaves. Lesions may enlarge and coalesce, and are frequently concentrated along the leaf veins or at the leaf margin. Rapid yellowing and senescence (death) of infected leaves occurs. Septoria brown spot is distinguished from other leaf and stem diseases by its characteristic brown spots imbedded in the necrotic tissue of older lesions. Lesions are primarily found on leaves, but can also occur on stems, petioles, and pods.