Cercospora Leaf Blight - UT Crops Pest Guides

General Information

Photo Credit: Trey Price – LSU

Cercospora leaf blight (CLB) is caused by a fungus (Cercospora kikuchii) which may come from infected seed and/or debris from previous crop. Upper leaves exposed to the sun develop light-to-dark purple areas, depending on variety. This discoloration can deepen and extend over the entire upper surface of affected leaves, giving them a leathery, dark, reddish-purple appearance, highlighted with bronzing and/or blighting. Symptoms do not usually appear until reproductive growth stages. Numerous infections cause rapid necrosis (deadening) of leaf tissue, resulting in defoliation. The same fungus causes purple seed stain which varies from pink or pale purple to dark purple. Infected seed may not show symptoms.

Management Options

Variety selection – some varieties may have higher tolerance to CLB and earlier maturing varieties may escape any infection, ratings can be found on UT pdf publications and searchable database
Timely fungicide, prior to disease development, may limit disease and protect yield, although fungicide resistance to QoI/Strobilurin and MBC fungicide groups has developed. Links to Fungicide Efficacy Table – mobile version or pdf

Fungicide Resistance

The fungus that causes Cercospora leaf blight (CLB), Cercospora kikuchii, has developed resistance to the QoI/Strobilurin fungicide group (FRAC 11) and the MBC fungicide group (FRAC 1). This means if a QoI/Strobilurin or MBC fungicide is applied to a field that contained the resistant fungus the disease will not be controlled and yield may be lost.
Consult the Fungicide Efficacy Table for best treatments – mobile version or pdf
More information on fungicide resistance and a webcast on Fungicide Resistance in the Cercospora Leaf Blight and Purple Seed Stain Pathogen of Soybean can be found on the Plant Management Network – Soybean Fungicide Resistance Hub

Images

Cercospora Leaf Blight Symptoms
Photo Credit: Trey Price – LSU

Cercospora Leaf Blight Bronzing Symptoms
Photo Credit: Heather Kelly – UT

Close-up of Blight Symptoms
Photo Credit: Trey Price – LSU

Purple Seed Stain
Photo Credit: Trey Price – LSU

Variety on Right is Susceptible to CLB
Photo Credit: Heather Kelly – UT