Signs of Crazy Top in Corn

July 6, 2009
ICM News

By Fanny Iriarte and Alison Robertson, Department of Plant Pathology

The Plant Disease and Inspect Diagnostic Clinic recently received some corn samples with symptoms and signs of crazy top, a disease caused by Sclerophthora macrospora

Symptoms of this disease crazy top, caused by Sclerophthora macrospora, vary greatly with time of infection and degree of host colonization by the pathogen.  Generally, excessive tillering, rolling, and twisting of the upper leaves appear first.  Later, infected plants produce a "leafy" tassel. 

Crazy top develops when soils have been flooded shortly after planting or before plants are in the four to five leaf stage.  Pooling of soil and water in the whorl of small plants can also lead to infection. Saturation for 24-48 hours is sufficient for infection to occur, since it allows the overwintering soilborne oospores to germinate and produce zoospores that swim in the water to infection sites on corn.  

Diseased grasses may also be a source of inoculum.  According the the Compendium of Corn Diseases infection occurs at a wide range of soil temperatures.  Although seed transmission of the pathogen has been demonstrated from freshly harvested seeds, it is generally considered unimportant in the spread of the pathogen. 

Crazy top is not a severe disease but it can cause significant losses in low-lying areas of fields that are prone to flooding, since infected plants are often barren. This disease is best managed by improving field drainage or by avoiding low, wet areas in fields. Rotation may be helpful if care is taken to keep rotational fields free of grassy weeds. 

Therefore, there's not much that can be done to manage this disease in season.  Pulling up and discarding infected plants can reduce buildup of inoculum in the field, and thus reduce the risk of disease in subsequent years. 

crazy top


Alison Robertson is an assistant professors of plant pathology with research and extension responsibilities in field crop diseases. Robertson may be contacted at (515)294-6708 or by emailing

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on July 6, 2009. The information contained within may not be the most current and accurate depending on when it is accessed.


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...