By Roger Elmore, Department of Agronomy
Yellow leaves wave above V5 to V8 corn canopies in northern and central Iowa this week. These sun-starved leaves freshly emerged from twisted whorls will turn green soon after they begin intercepting sunlight.
Potential causes are numerous: rapid growth coupled with a wide range of temperatures, hail, strong winds or an application of a herbicide, insecticide or fungicide, etc.
This reference describes these symptoms and causes in more detail: Twisted whorls and 'buggy whipped' corn.
Yellow leaves resulting from twisted whorls associated with an application of a growth regulator herbicide. Broadleaf weeds in the photo were affected too. Photo by Brian Lang, ISU Extension Field Agronomist; 2011.
I would expect these plants to look almost normal within a few days to a week or so. If the malformation causes a delay in either growth or development, it could result in yield reductions. But any yield reduction would likely be hard to detect on a field basis unless the symptom is widespread.
Roger Elmore is a professor of agronomy with research and extension responsibilities in corn production. He can be contacted by email at firstname.lastname@example.org or (515) 294-6655.