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Frogeye leaf spot jumping up on corn belt growers.

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Traditionally a headache for soybean growers in Southern states, frogeye leaf spot is an increasing concern for growers in the central Corn Belt and soybean-producing states such as Indiana, Illinois and Iowa because of recent weather patterns. What is this yield-limiting foliar disease and how can growers manage it?

Factors to Consider

  • Infected seeds
  • Symptoms
  • Rotation
  • Disease cycle
  • Fungicides
  • Soybean varieties
  • Moisture
  • Tillage
A longtime nemesis of Southern soybean growers, frogeye leaf spot is a major threat to yield, usually infecting soybean plants under hot and moist conditions.

Action Plan

  1. Know the damage frogeye can inflict. The disease can pose a serious threat to yield potential and seed quality. Infected seeds germinate poorly, and the surviving seedlings are often severely weakened. Severe cases of the disease can also cause premature leaf drop and yield losses. Planting quality seed is a key management technique for growers pursuing a high yield potential soybean crop.
  2. Understand disease cycle and preferred conditions. The fungus Cercospora sojina ignites frogeye leaf spot and can survive in infected seed and plant residue. The fungus multiplies in warm, humid and wet conditions. Spores easily blow from field to field, and splashing raindrops can transport spores to younger leaves at any point during the growing season. Infections are most common after the initiation of flowering (R1 stage).
  3. Recognize the symptoms if conditions are ripe. Disease symptoms will usually appear about seven to 12 days post-inoculation. Lesions on leaves will first appear as yellow colored and circular in shape and will become more reddish-gray with age and elongate to about 1/4 inch in length. These lesions are irregularly shaped and can be mistaken for herbicide damage. Tiny hairlike spores will eventually appear on the underside of leaves which are infected.
  4. Leverage management options. If an outbreak occurs or if your farm has a history of frogeye leaf spot, consider a combination of the following management practices:
    • Using fungicide seed treatments helps reduce risk of infection and disease severity in crop applications when the fungicide is applied after growth stage R1
    • Tillage can incorporate residue and fungal residues that if left undisturbed, can overwinter on the soil surface
    • Crop rotation can help reduce inoculum levels and thus reduce potential disease exposure
    • Selecting the right variety helps provide resistance to frogeye leaf spot starting at planting


Under the right conditions, frogeye leaf spot can quickly diminish yield potential. If the disease is a concern for your fields, consider use of a seed treatment fungicide, tillage, rotating crops or choosing a soybean variety with resistance to the fungus. To help you scout and manage frogeye leaf spot, contact your local Mycogen Seeds customer agronomist or your trusted agronomic adviser.

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