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Proper planning can prevent gray leaf spot outbreak.

Agronomy Bulletin 38 ─ Gray Leaf Spot

Symptoms of gray leaf spot include orange-red lesions with yellow halos.


Increased use of reduced tillage and no-till production practices has increased gray leaf spot occurrence. Caused by a fungus, the disease leads to leaf tissue loss, resulting in a decrease in plant sugars and decreased grain production. Potential yield losses range from 5 percent to 40 percent.

Factors to Consider

  • Symptoms
  • Residue management
  • Crop rotation
  • Hybrid selection

Action Plan

  1. Recognize symptoms. Soon after tasseling, look for orange-red lesions with narrow yellow halos surrounding them. As lesions mature they appear tan or brown in color and are rectangular in shape. Lesions are ½ inch to 4 inches long and interveinal, giving them a straight-edge appearance.
  2. Understand the life cycle. Gray leaf spot overwinters in residue on the soil surface. Spores develop on residue in late spring when temperature and humidity increase. Rain and wind transport spores onto the corn plant, where they mature and move up the plant. Gray leaf spot infection occurs when relative humidity is more than 90 percent and the leaf surface remains wet for more than 11 hours.
  3. Manage residue. Crop rotation and clean plowing are effective methods to control fungus levels. A two-year crop rotation away from corn is effective under reduced tillage. A one-year rotation is sufficient with clean plowing. Weed control is essential to allow airflow to dry the canopy quickly.
  4. Select tolerant hybrids. Mycogen Seeds offers several hybrids that are time-tested through extensive research and in-field testing to ensure tolerance to gray leaf spot. Using tolerant hybrids provides an earlier, more extensive source of inoculums for gray leaf spot development.


With careful crop planning, gray leaf spot can be managed in a no-till or limited tillage situation. Under environmental conditions that are favorable to fungus development, fungicide use can be helpful. For more information, consult your local Mycogen Seeds customer agronomist or trusted agronomic adviser.

Published on Wednesday, August 14, 2013