University of Missouri Extension

G4442, New December 2004

Soybean Rust

Frogeye leaf spot
Cercospora sojina

Frogeye Leaf Spot, upper leaf surface Upper leaf surface
 

Frogeye Leaf Spot, lower leaf surface Lower leaf surface
 

Upper leaf surface symptoms

Lesions of frogeye leaf spot are small, circular to somewhat irregular spots that develop on the upper leaf surfaces. Initially the spots are dark and water-soaked in appearance. As the lesions age, the center becomes light brown to light gray in color. Although lesions may merge to kill large areas of leaf tissue, the individual lesions do not increase significantly in size (~0.25 inch in diameter) Older lesions have a light center with a darker red to purple-brown border.

Lower leaf surface symptoms

Lesions oare evident on the lower leaf surface and appear similar t those on the upper leaf surface.

Canopy symptoms

Young leaves are more susceptible than older leaves to infection. The disease may be evident throughout the canopy of the plant, if weather conditions remain favorable for disease development.

Weather

Development of frogeye leaf spot is favored by warm, humid weather. Spores are spread short distances by wind or splashing rain. Dry weather severely limits disease development.

Survival

The fungus that causes frogeye leaf spot survives in infested soybean residues and infected seed.

Distribution in Missouri

Until about 1998 frogeye leaf spot was found only in the southern parts of Missouri. Since then the distribution of this disease has expanded and it is now found throughout the state.

 

G4442 Soybean Rust | University of Missouri Extension

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