Flooded corn fields and what diseases might you expect to see

June 25, 2024 3:37 PM
Blog Post

The torrential rains that northern Iowa experienced last week may have favored several diseases of corn including crazy top, Physoderma brown spot and node rot, Goss’s wilt and bacterial stalk rot. While there are no in-season management practices for these diseases, correct diagnosis can help with disease management options in future years including choosing hybrids with resistance.

Crazy top

The most characteristic symptoms of crazy top are distorted tassels with prolific leaf-like growths, or stunted plants with numerous tillers. Crazy top is caused by a soilborne oomycete that produces swimming spores (zoospores) in flooded conditions. The zoospores infect the growing points of young plants. 

Photo of crazy top disease in corn
 Crazy top expressed on a corn tassel.  

Physoderma brown spot and node rot

This disease is most common when heavy rains occur when the corn is at growth stage V5 to V9. This articledescribes the characteristic symptoms of the two phases of the disease. Note that hybrids that are susceptible to Physoderma node rot rarely have Physoderma brown spot symptoms on the leaves; while hybrids that get Physoderma brown spot, rarely have Physoderma node rot.

Photo of Physoderma brown spot on a corn leaf
 Physoderma brown spot on corn leaf and leaf sheath. 


Photo of physoderma node rot in corn
 Physoderma node rot. 

Goss’s wilt

It’s been a few years since Goss’s wilt was prevalent in Iowa, however I still hear reports of it each year. While most hybrids have good resistance to the bacterium, there are some hybrids that are susceptible. Remember to look for dark “freckles” in the lesions, which become translucent when they are backlit.

Photo of Goss's wilt in corn
Backlit corn leaf showing Goss's wilt translucent "freckles".  

Bacterial stalk rot

We rarely see bacterial stalk rot in Iowa but it’s possible to find this disease in areas where water sat, and where plants may have been wounded. This stalk rot often occurs mid-season. Infected plants may be scattered across the field and die prematurely. The stalk is soft, slimy and brown; and perhaps the most characteristic symptom – infected plants stink.

As mentioned earlier, there is no in-season treatment for these diseases, therefore fungicide applications are not efficacious. 


Alison Robertson Professor of Plant Pathology and Microbiology

Dr. Alison Robertson is a professor of plant pathology and microbiology. She provides extension education on the diagnosis and management of corn and soybean diseases. Her research interests include Pythium seedling disease of corn and soybean and Goss's wilt. Dr. Robertson received her bach...