Soybean Diseases to Watch

Frogeye Leaf Spot

• Infection most often occurs after flowering.
• Fungicide seed treatments can reduce the risk of infection. Fungicide application can reduce disease severity. In some states there are populations that are resistant to the strobilurins.
• Symptoms include discrete, roundish lesions with light centers and dark reddish-purple margins are apparent on leaves.

Septoria Leaf Spot

• Also known as brown spot has caused defoliation in fields before R2 stage. Infection occurs as early as the V2 growth stage on lower leaves.
• Symptoms start as dark brown, irregular spots on both upper and lower leaf surfaces. Typically lesions have a yellow or chlorotic halo when held up to a back light.
• Irregularly shaped blotches form as adjacent lesions merge. Leaves become yellow to rusty brown.

Soybean Rust

• Soybean rust can cut yields by 50% or more in favorable conditions.
• First, tan or reddish-brown lesions form on the underside of leaves. Then, in those lesions small pustules/blisters develop, which break open and release masses of spores.
• Diagnosis at an early stage is necessary for successful management.

Sudden Death Syndrome (SDS)

• Typically the damage isn’t visible until fl owering or later in the season.
• Damage can be greater with high soybean cyst nematode (SCN) populations.
• SDS is sometimes mistaken for brown stem rot. To diagnose, split the lower stem of plants to determine which fungal disease is present.

White Mold

• The infection is active at the R1 stage. However, symptoms show later in the season when individual plants wither and die in an otherwise healthy field.
• The stems of infected plants have a bleached area, which radiates several inches from the leaf axil.
• The most telling symptom is the fluffy, stringy, white mycelium on the stem.