Downy mildew or crazy top is a condition that often results in wet or flooded fields. A crazy top results when plants are infected by Sclerophthora macrospora at flooding. It may result from soil and water pooling in the whorl of small corn plants in flooding scenarios.

Corn plants respond by excessive tillering and “crazy” growth on the upper plant. Yield losses are typically minimal except in low-lying areas or where excessive flooding has occurred. Heavily infected plants may not produce a viable ear.