For generations, the standard measure for corn  growth was “knee-high by fourth of July,” which meant that the corn plant should be able to produce a crop for that year. Of course, most farmers a couple of generations ago had much lower yield goals for their corn than the farmers of today. Today, waist/shoulder high corn by July 4 is a more typical, and has resulted in some very good corn yields in most areas in recent years. It is difficult to get exceptional corn yields in the southern half of Minnesota or in Iowa, if corn is only knee-high or smaller on July 4.
In most of Minnesota and Iowa, the 2012 growing season started out earlier than normal, with most corn planted in April or early May; it got the corn crop off to a good start. Adequate to excessive rainfall in many areas of southern Minnesota and northern Iowa during May, along with warmer-than-normal temperatures, have provided optimal growing conditions for crop development. Most corn in the region will exceed shoulder-highby July 4, with some corn tasseling and pollinating by that date, which is well ahead of normal, and far ahead of corn development a year ago.
Corn and soybean development in most areas is well ahead normal due to the warmer than normal temperatures during much of the early growing season in 2012. The accumulation of growing degree units(GDUs) in 2012 at the U of M Southern Research and Outreach Center totaled 947.5 from May 1 through June 28, which compares to a normal accumulation of 830 GDUs by June 28. By comparison, the GDU accumulation on June 28 was 792 in 2011, 847 in 2010 and 774 in 2009. The 2012 GDU accumulation is about 12-15% ahead of normal at most locations in southern and western Minnesota, which correlates the crop development being seven to 10 days ahead or normal development.
June rainfalls have been quite variable across Minnesota, ranging from very excessive amounts in central and northeast Minnesota to very limited amounts in portions of southern Minnesota. Very heavy rainfalls in mid-June caused flooding just south and west of the Twin Cities, as well as in northeastern portions of the state. Meanwhile, June rainfall in southern portions of the state ranged from near normal to well below normal. Total June rainfall at the Waseca Research Center was 4.25 in. as of June 28, which compares to a normal June rainfall of 4.22 in. The total precipitation at Waseca for April, May and June in 2012 is now at 13.07 in., compared to a normal of 11.41 in. The U of M Southwest Research Center at Lamberton received 10.33 in. of precipitation in May, which is about three times the normal amount, but had only received 1.23 in. during June, as of June 28.
Large areas of west-central and east-central Minnesota also had considerable crop damage  from hail and strong winds, in addition to the heavy rainfall amounts, resulting from several severe storms in mid-June. Except for the crops that were damaged by the heavy rainfall and severe storms in May and June, most of the corn and soybeans in the southern half of the state look good to excellent. However, there is a growing concern in some locations across the southern one-fourth of Minnesota with potential crop damage from the continued dry weather pattern and very warm temperatures. This will become more critical as we enter the critical corn tasseling and pollination period in early July.
As of June 28, about 70% of the main corn and soybean producing areas in the U.S. were listed as suffering some drought symptoms by the National Drought Monitor. Large areas of Illinois, Indiana, Ohio, Missouri and Kansas were listed as having moderate to severe drought conditions. Growing areas in Iowa, Nebraska and South Dakota were listed as abnormally dry to moderate drought. Only the Upper Midwest, including most of Minnesota, was considered to be drought free.