The application of fungicides to corn between V12 and tasseling (VT) is not recommended.
This recommendation is based on the potential for arrested development of corn ears, or the formation of “beer can” ear syndrome. The syndrome was termed by Dr. Bob Nielsen of Purdue University in 1996, who described the ears with the expected number of rows, but with much fewer kernels per row than normal, giving the ears a stubby or “beer can” appearance (Figure 1).
The physiology behind the formation of the stubby ears is poorly understood, but the effect seems to be associated with the application of non-ionic surfactants contained in, or added to fungicides, between V12 and tasseling (VT). (Nielsen, 2008). Coincidentally, it is within this stage in development when kernel numbers per row are being determined (or ear length). The number of kernels per row is extremely sensitive to environmental stresses during this phase of development (Nielsen, 2007). Surfactants may play a role in stress during this time.
Nielsen, R.L. 2008. Arrested Ears Resulting From Pre-Tassel Applications of Pesticide & Spray Additive Combinations. (accessed June 27, 2012).
Nielsen, R.L. 2007. Ear Size Determination in Corn. Corny News Network, Purdue Univ. (accessed June 27, 2012).