Wrapped or twisted whorls in corn can be referred to as Rapid Growth Syndrome. It is also commonly called accelerated growth syndrome, buggy whipping, roping, twisted whorl syndrome, wrapped whorls and onion leafing. This phenomenon occurs when leaves fail to unfurl properly and become tightly wrapped and twisted. Growers typically begin seeing twisted whorls at V5 to V6 corn. The lower most leaves are normal with the sixth or seventh leaf tightly wrapped. Young leaves inside the whorl continue to grow but are unable to emerge through the wrapped upper leaves. This continued growth creates pressure which causes the whorl to bend or kink at right angles to the ground.
Twisted whorl in corn
Photo Credit Purdue Univ. RLNielsen
The cause is typically due to an abrupt transition from slow growing conditions (cool, cloudy days) to rapid development (warm, sunny conditions) which we have observed for the past couple of weeks in June. Herbicides such as cell growth inhibitors or growth regulators can cause twisted whorls in corn and are often blamed for these symptoms. However, rapid growth syndrome has occurred over the years in many fields where neither class of herbicide was used. Instances of twisted whorls will vary by hybrid due to individual growth characteristics.
Yellow top symptom shortly after twisted whorl finally wraps
Photo Credit Purdue Univ. RLNielsen
In most cases, these whorls will eventually open up and growth will resume normally with no yield loss expected. As these wrapped leaves open up, yellow leaves will become apparent across the field. A few days of sunshine will green them up and the problem will no longer be visible, except for a few crinkled leaf edges left behind caused by their restricted expansion inside the twisted whorl.
Reference: http://www.agry.purdue.edu/ext/corn/news/timeless/TwistedWhorls.html