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Knee High By Fourth of July?


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-high or highercorn by July 4 is 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 shorter on July 4.

In extreme southern Minnesota and northern Iowa, the 2011 growing season started out a bit late, with most corn planted in early to mid-May. However, the corn rebounded nicely with some fairly good growing conditions in late May and early June. In recent weeks, excessive rainfall in most areas, along with cooler-than-normal temperatures, have provided for fair-to-poor growing conditions, which has slowed the crop development. Most corn in southern Minnesota and northern Iowa will exceed knee-high by July 4, and some will exceed waist-high; however, no corn will be approaching shoulder-high, which occurred in some parts of the region in 2010.

In central Minnesota, a considerable amount of 2011 corn was not planted until early June, leaving the crop development well behind normal. As a result, a significant amount of corn in this region will fail to reach knee-highby July 4. What this means in agronomic terms is that the corn in this region is two to three weeks or more behind normal development. This increases the likelihood that a large amount of corn could have maturity issues this fall, and that the 2011 corn crop is much more susceptible to a normal or earlier-than-normal first frost. It also increases the odds of wetter corn at harvest, which will likely lead to higher corn drying costs this fall.

Corn and soybean development in most areas continues to run well behind normal, due to cooler-than-normal temperatures in the middle of June. The accumulation of growing degree units (GDUs) at the University of Minnesota Southern Research and Outreach Center totaled 728 from May 1 through June 24, 2011, compared to a normal GDU accumulation of 747 on June 24. By comparison, there were 761 GDUs accumulated by June 24, 2010; only 679 GDUs were accumulated by June 24, 2009. GDU accumulation has been even slower in most areas of central Minnesota, which, along with the very late planting dates, has lead to the very slow start for corn and soybeans in that region.

June rainfalls have been quite variable across the region, with most areas of southern Minnesota and northern Iowa receiving adequate to excessive amounts of rainfall during June. Total June rainfall at the Waseca research center was 5.12 in. as of June 24, which compares to a normal June rainfall of 4.22 in. The total precipitation for 2011 through June 24 at Waseca is now 18.7 in.; normal is 16.24 in. At the U of M Southwest Research and Outreach Center at Lamberton, they have received more than 150% of their normal rainfall since May 1.

Some portions of southern Minnesota have received frequent excessive rainfall amounts during the last two weeks, which has lead to some large drowned-out field areas. The excessive rainfall has also lead to problems for timely applications of postemergence herbicides for weed control, and has caused some leaching of available nitrogen in the soil profile. There are many areas with yellow, chlorotic-looking soybeans, due to the excessively wet soil conditions and the cool temperatures. Close to maximum levels of stored soil moisture exist in most areas of southern Minnesota, so any major rainfall events can quickly result in large amount of standing water in crop fields.


Editor’s note: Kent Thiesse is a former University of Minnesota Extension educator and now is Vice President of MinnStar Bank, Lake Crystal, MN. You can contact him at 507-726-2137 or via e-mail at [email protected]

TAGS: Soybeans Corn
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