Leaf Symptoms of Frogeye Leaf Spot

  • Symptoms begin as small, circular-to-somewhat-irregular spots on the upper surface of the leaf
  • These dark, water-soaked spots develop into lesions with dark brown centers surrounded by red or dark reddish-brown margins 
  • As lesions age, the center becomes light brown to light gray, and the border remains dark 
  • Leaf lesions may coalesce to form larger irregular spots on the leaf
  • Heavily diseased leaves may wilt and drop prematurely, or dead tissue may weather away, leaving tattered leaflets
Frogeye Leaf Spot on soybean leaf
Center of frogeye leaf spots becomes light brown to light gray, and the border remains dark.

Leaf symptoms of Frogeye Leaf Spot.

Stem, Pod and Leaf Symptoms

  • Stem lesions are reddish brown with a narrow, dark margin 
  • The centers of the lesions become brown to gray with age 
  • Lesion development on pods is similar to that of the leaves 
  • Symptoms begin as water-soaked spots that progress to dark reddish-brown lesions 
  • Lesions are circular to elongated in shape, and may appear slightly sunken and lighter colored in the center 
  • The fungus can also grow through the pod wall to infect maturing seeds 
  • These seeds may show cracking of the seed coat and discoloration ranging from small specks to large blotches
soybean pod with frogeye leaf spot lesions
frogeye leaf  spot fungus growing through soybean pod wall


Frogeye Leaf Spot Facts

  • Caused by Cercospora sojina, a fungus found throughout the world
  • In the U.S., frogeye leaf spot is most common in the mid-South, Mississippi Delta and southeastern soybean growing areas
    • Development of resistant varieties by Pioneer soybean breeders has limited disease impact in these areas
  • In the past decade, it has been detected in soybean fields in the Midwest US
  • Infects leaves, stems and pods of soybeans
  • Disease development is favored by warm, humid conditions and frequent rains following disease onset can lead to serious epidemics
  • Dry weather severely limits disease development

Disease Cycle

  • Disease survives and overwinters in soybean residue and seeds
  • Initial infection occurs as spores produced on infected residues or cotyledons are spread by splashing rain or wind
  • Secondary infection occurs as lesions on the soybean plant produce spores
  • Diseased soybean residue (leaves, stems and pods) left on soil surface provides inoculum to continue disease cycle in next soybean crop

Impact on Crop

  • Yield losses depend on disease severity and varietal susceptibility
    • With severe leaf blighting on susceptible varieties, losses may approach 30%
    • Minor symptoms on moderately resistant varieties unlikely to result in economic losses


Management – Resistant Varieties

  • Plant resistant soybean varieties if fields had frogeye leaf spot in recent years 
  • Pioneer rates its varieties and makes ratings available to customers
  • Ratings range from 2 to 9 (9 = resistant) indicating excellent resistance is available in elite soybean varieties 
  • Select varieties with resistance to most important diseases first
  • Soybean cyst nematode, sudden death syndrome, and Phytophthora root rot may present a greater risk than frogeye leaf spot
  •  Select for other key traits required for your fields 

Other Management Practices

  • Consider tillage to reduce infected residue left on soil surface. Reduced inoculum levels can delay the onset and spread of the disease
  • Rotate crops to break the disease cycle and reduce disease inoculum
  • Apply a foliar fungicide if disease levels exceed thresholds established by your state extension soybean disease specialist
    • Timely application of a fungicide with multiple modes of action can preserve green leaf material and prevent disease spread by sporulation.
    • Strobilurin-resistant strains of frogeye leaf spot have been identified in several states, including Arkansas, Kentucky, Illinois, Tennessee and Missouri.
    • DuPont™ Aproach® Prima fungicide combines a strobilurin with a triazole for better control of resistant frogeye leaf spot to protect yield and input investments. Apply a full rate (6.8 fluid ounces per acre) of Aproach® Prima to soybeans at R2 to R3.
    • Be sure to read and follow all label instructions
  • Your Pioneer sales professional can help you select suitable varieties for your farm