For generations, the standard measure for corn growth was knee-high by July 4th, 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-high, or higher, corn by July 4th 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, if corn is only knee-high or smaller on July 4.
In most of Minnesota and Iowa, the 2015 growing season started out earlier than normal, with most corn planted in the last half of April and first week of May. In recent weeks, excessive rainfall and severe storms with wind and hail have led to crop damage in some locations, as well as some unevenness in the corn and soybeans. Most corn in southern Minnesota and northern Iowa that was planted by early May will not only exceed knee-high by July 4, but will likely exceed waist-high. Some of the corn planted in mid-April in areas with favorable growing conditions will likely approach shoulder-high by July 4, which has not occurred in most parts of the region since 2012.
In Minnesota, Iowa and other Upper Midwestern states, nearly all of the 2015 corn and most of the soybeans were planted on a timely basis. This is not the case in portions of Kansas, Missouri and southern Illinois, as well as surrounding areas in other states, where corn was not planted until late May or early June, and soybeans until mid-to-late June. The later-than-normal planting, combined with extremely saturated soil conditions, has left the crop development well behind normal in portions of that region. The slower-than-normal development increases the likelihood that some of the corn in that region could have maturity issues this fall, especially if temperature trends remain cooler than normal in July and August. There are also thousands of prevented planting crop acres in this region that will likely not be planted in 2015.
Corn and soybean development in most areas of southern Minnesota and northern Iowa continues to be near normal, or slightly ahead of normal, as of late June, due to earlier than normal planting dates and near average temperatures in June. The accumulation of growing degree units (GDUs) is one measurement of crop development. The total GDU accumulation at the U of M Southern Minnesota Research Center from May 1 through June 29, 2015 totaled 839 units, which compares to a normal GDU accumulation of 850 on June 29. By comparison, on June 29 in previous years, there were 840 GDUs accumulated in 2014; 772 GDUs in 2013, and 970 GDUs in 2012.
June rainfalls have been quite variable across the region, with most areas of Upper Midwest receiving adequate to excessive amounts of rainfall during June. Total rainfall at the Waseca Research Center in the month of June was 7.61 inches as of June 29, which compares to a normal June rainfall of 4.22 inches. The total precipitation at Waseca through June 29 is now at 17.74 inches, which is about 1.50 inches above normal for the first six months of the year. The month of May broke a string of 10 straight months of normal to below-normal rainfall at Waseca. Some areas of Central and Southeastern Minnesota have received much higher amounts of precipitation in the month of June, while many portions of western Minnesota have received lower rainfall amounts during the month. Any concerns with continuation of drought conditions into the 2015 growing season have pretty much disappeared with the above normal rainfall in the month of June.
Stored soil moisture levels, which were below normal this spring, have been restored to near maximum levels in many areas by late June. As a result, any major rainfall events can quickly result in large amount of standing water in crop fields. Some portions of southern Minnesota have received frequent rainfall events during the month of June, which has lead to problems for timely applications of post-emergence herbicides for weed control, and has caused some leaching of available nitrogen in the soil profile. There are also some areas with yellow, chlorotic-looking soybeans, due to the excessively wet soil conditions. On the other hand, many areas of the region have experienced nearly ideal growing weather in the month of June, and have crop conditions that are good to excellent.