We've all seen it, been fascinated by it, know that it is referred to as Crazy Top, because that is exactly what it looks like. But what really is it and what causes it?
According to Iowa State Extension, it is a disease caused by Sclerophthora macrospora – a soil-borne fungus.
Crazy Top is a pathogen closely related to water molds. It tends to develop when soils have been flooded shortly after planting or as the plants are in the four- to five-leaf stage. The combination of soil and water accumulating and sitting in the whorl of these corn plants for anywhere from 24-48 hours can allow the infection to occur.
Symptoms or signs can vary, like excessive tillering and rolling and twisting of the upper leaves. Eventually the tassel proliferates in part or completely where it appears to be a tight bunch of leaves.
Another oddity that might be showing up in fields is "tassel ears." It looks just like an ear of corn, only it is growing on the tassel. They are mostly found on tillers or suckers of the plant in thinly populated areas of a field. It lacks the protective husk and therefore the kernels that do develop are exposed to weather and birds.
"Some folks lump the tassel-ear symptom into the same category as the malformed tassel symptom of the so-called 'crazy top' disease," writes Bob Nielson, Purdue Agronomy Department. "These two odd tassel symptoms are not related and, in fact, look totally different."
Tassel-ears are what happen when the normal development of the tassel becomes altered. It is a physiological change that is likely hormonally driven while the environmental trigger that alters those hormones is unknown.
Currently there is not much that can be done to prevent or manage crazy top or tassel ears. There is usually not a significant amount of yield loss from either corn oddity.