Producers and agronomists may from time to time notice yellow leaves waving from the corn canopy early in the growing season (approximately June). This is due to a problem, which over the years has been described as buggy whipping, rapid growth syndrome, accelerated growth syndrome, roping, wrapped whorls, onion leafing, and twisted whorls.
Prior to showing yellow leaves, the affected plants will have leaves that do not unfurl (see photograph). Typically plants will unfurl within a week or two from when they began appearing this way. Once the trapped leaves are visible they will show varying degrees of crinkling and scorching in the leaf tissue. See a photograph of a 'crinkled' leaf in the Image Gallery. These trapped, sun-starved leaves will emerge with splotches of bright yellow amongst an otherwise dark green canopy.
In 2005, Bob Nielsen, extension agronomist at Purdue University, discussed this same phenomenon occurring in Indiana. "The cause of twisted whorls can be herbicide-related; particularly from post-emergence application of growth regulators like dicamba or 2,4-D. Recovery from these causes of twisted whorls depends on the severity of the actual herbicide injury to the plant. Twisted whorls can frequently occur in some hybrids as the plants transition from young pre-V5 seedlings to the rapid growth phase. The exact reason for the twisted and wrapped whorls is not known, but the good news is that the whorls of affected plants eventually unwrap with minimal, if any, effects on the yield of the plants. The younger leaves that had been trapped inside the twisted upper leaves emerge fairly yellow because they had been shaded for quite some time. By the time the affected plants reach waist to chest-high, the only evidence that remains of the previous twisted whorls is the crinkled appearance of the most-affected leaves."
Nielsen, R.L. 2005. Yellow tops and twisted whorls. Corny News Network, Purdue Univ. Available online at http://www.agry.purdue.edu/ext/corn/news/articles.05/TwistedWhorls-0605.html
Portions of this text, written by Roger Elmore, are taken from a Crop Watch article (University of Nebraska extension newsletter) published June 10, 2005.