Frogeye Leaf Spot

Agronomy

Symptoms

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

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

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 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

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