cattered
plants with distinctly yellow-green upper leaves are evident in some fields
of early-planted corn while driving down the road at 60 mph. Closer examination
of these fields reveals other plants with tightly wrapped whorls similar to
what is sometimes referred to as “onion leafing”.
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.
Just as frequently, twisted whorls 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.
For more descriptions and images of this curiosity, revisit the articles I wrote last year (Nielsen, 2004a & 2004b).
Nielsen, R.L. (Bob). 2004a. Twisted Whorl Symptoms in Corn. Corny News Network, Purdue Univ. Available online at http://www.kingcorn.org/news/articles.04/TwistedWhorl-0607-Gallery.html [URL verified 6/5/05].
Nielsen, R.L. (Bob). 2004b. Wrapped & Twisted Whorls in Corn. Corny News Network, Purdue Univ. Available online at http://www.kingcorn.org/news/articles.04/TwistedWhorl-0607.html [URL verified 6/5/05].