Rapid growth syndrome is a phenomenon where corn leaves don’t unfurl properly and the whorl becomes twisted or tightly wrapped. It usually occurs in 5th to 7th leaf corn but can also occur as late as 12th leaf corn. This is also described as buggy whipping, twisted whorls, wrapped whorls, accelerated growth syndrome, roping, and onion leafing.
Most of the time this occurrence is due to rapid growth as plants benefit from warm temperatures, rainfall after being dry, or development of nodal roots. Some hybrid genetics have a greater propensity for occurrence than others do. Rapid growth syndrome does have distinctly different symptoms then genetic strip. Growth regulator and acetamide herbicides can also be the culprit. Rapid growth syndrome is not a symptom of biotic diseases but, something like smut infection may be increased on plants following unfurling.
The twisted whorls typically unwrap on their own within 3 to 7 days. Wind can help speed the natural process up. When the whorl unfurls, the outer leaves will have a rippled appearance and the inner leaves will be yellow to white. As photosynthesis ramps up those yellow leaves will green up rapidly.
This should have minimal, if any, impact on grain yields, so just be patient and let nature work itself out. Loss of yield could occur if there is a resulting delay in development.