Details:
Soybeans were scouted at the R6 (full seed) growth stage and yellowing discoloration and a bronzing purple/brown color of leaves was observed in patches across the field. This issue was confirmed by the NC State Plant, Disease and Insect clinic to be Cercospora Leaf Blight. This foliar disease is caused by the pathogen Cercospora kikuchii, which is also the causal agent of purple seed stain. This disease is common in soybeans, it rarely causes significant yield losses for North Carolina producers. Symptoms associated with cercospora leaf blight includes yellowing leaf discoloration with a purple or bronze tint, and as the disease progresses, small dark spots along major leaf veins.
Conclusion:
Rotating with a non-host crop (corn, small grains) and tillage may help reduce pathogen levels. Consider variety susceptibility for future years. There are fungicides registered for cercospora leaf blight, and they may help reduce visual symptoms in the field. However, fungicides have not been shown to effectively reduce the incident of purple seed stain.
Resources:
Cercospora Leaf Blight | NC State Extension
Disease Management | NC State Extension
