Dr. Joe Lauer, UW-Madison Agronomy and UWEX state corn specialist, has added a new article to his blog. Below, find an excerpt and link to his website.
http://wisccorn.blogspot.com/2017/05/B087.html
Figure 1. Wisconsin corn planting progress from 1987 to 2017. The bold blue line is the 30-year normal. Other lines are years that were earlier- or later-than normal using + one standard deviation. Click figure to enlarge.