Source: Purdue University
Although scientists don't know exactly what causes corn to develop "twisted whorl syndrome," they have noted it often occurs when young corn plants shift quickly from weeks of slow development to rapid development.
The typical growth stage when growers notice the twisted whorls is late V5 to early V6 (five to six visible leaf collars, approximately knee-high). The lowermost leaves are typically normal in appearance, although some may exhibit some crinkled (accordion-like) tissue near the base of the leaf blade. Beginning with the sixth or seventh leaf, the whorl is tightly wrapped and often bent over at right angles to the ground.