Peronospora manshurica

Peronospora manshurica is an oomycete in the family Peronosporaceae that causes downy mildew, also called leaf spot, on soybeans and other crop plants, and is found wherever soybeans are grown. As a biotrophic pathogen it requires a living host to survive and reproduce, producing pale green to light yellow leaf spots that enlarge into bright yellow lesions before turning brownish with a yellowish-green border. The disease is historically considered low risk and rarely warrants fungicide treatment in the United States, but it consistently reduces seed weight and can cause yield loss in infected soybean crops.