Frogeye Leaf Spot

FLS Top Side of Leaf Photo Credit: Heather Kelly

FLS Top Side of Leaf
Photo Credit: Heather Kelly

Frogeye leaf spot (FLS) is caused by a fungus (Cercospora sojina) which can overwinter on soybean debris and can be introduced on infected seed. Symptoms usually appear during reproductive growth stages and include circular to angular leaf lesions with a purple to dark brown margin around the tan/gray center. Lesions begin as dark water-soaked spots on younger leaves and as they age the centers become ash-gray to light-brown. Examining the underside of leaves, FLS lesions will have a tan to gray center and if sporulating there will be a dark black area in the center of the lesion where spores are being produced.

  • Variety selection – FLS resistant varieties are available, see yearly variety disease ratings pdf publications and searchable database
  • Fungicide application during reproductive growth stages can help reduce disease and protect yield, although caution is advised as fungicide resistance to the QoI/Strobilurin group has developed. Links to Fungicide Efficacy Table – mobile version or pdf

  • The fungus that causes frogeye leaf spot (FLS), Cercospora sojina, has developed resistance to the QoI/Strobilurin fungicide group (FRAC 11). This means if a QoI/Strobilurin fungicide is applied to a field that contained the resistant fungus the disease will not be controlled and yield may be lost.
  • We are currently screening FLS samples to better understand the pathogen population and assess the risk of fungicide resistance. Producers in Tennessee are encouraged to contribute to this effort by mailing in soybean leaves with frogeye leaf spot symptoms along with the information requested on the ‘Frogeye Leaf Spot Sample’ sheet. Samples will be tested, free of charge, for strobilurin/QoI fungicide resistance and results will be emailed to producers. Funding was provided by the Tennessee Soybean Promotion Board for this service.
  • TN Map of FLS Fungicide Resistance – counties where at least one FLS sample contained QoI/Strobilurin fungicide resistant spores
  • National website that monitors resistance – http://frogeye.ipmpipe.org
  • More information on fungicide resistance and a webcast on Management of Frogeye Leaf Spot and Fungicide Resistance can be found on the Plant Management Network – Soybean Fungicide Resistance Hub

close up with microscope of sporulating fls lesion
Close up with Microscope of
Sporulating FLS Lesion
Photo Credit: Heather Kelly

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FLS Underside of Leaf
Photo Credit: Heather Kelly

fls in canopy
FLS in Canopy
Photo Credit: Heather Kelly

fls variation in susceptibility - right highly susceptible variety-crop-u5095
FLS Variation in Susceptibility –
Right Highly Susceptible Variation
Photo Credit: Heather Kelly

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Underside of FLS Lesions
Photo Credit: Heather Kelly

burn on left - FLS on right-2
Underside of Leaves – Chemical Burn on Left –
FLS on Right
Photo Credit: Heather Kelly

FLS on right - burn on left-2
Upper-side of Leaves – Chemical Burn on Left
FLS on Right
Photo Credit: Heather Kelly