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Corn+Soybean Digest

Crop Maturity Concerns

As we approach the end of the 2009 growing season, there are some concerns with crop maturity for the corn and soybean crop across most of the upper Midwest. Below-normal temperatures and accumulation of growing degree units (GDUs) throughout most of June, July and August has left the 2009 corn and soybean crop behind normal development as we enter September. The total accumulated GDUs from May 1 to Aug. 31 at the University of Minnesota (U of M) Southern Research and Outreach Center (SROC) at Waseca, MN, was 1,830, which is approximately 266 GDUs –13% – behind normal GDU accumulation. The average temperature during that four-month period has been 64.1° F, which is the eighth coolest in 95 years of weather records at the U of M site at Waseca.

The 2009 GDU accumulation at Waseca from May 1 through Aug. 31 is very similar to the 2004 growing season, when there were also concerns about crop maturity. However, in 2004, September was a very warm month, with accumulated GDUs at Waseca 55% above normal. As a result, most corn and soybeans reached maturity by the time the first frost came to the region on Oct. 2, 2004. The normal first frost date in southern Minnesota ranges from the last few days of September until around Oct. 7, depending on the location. The first week of September in 2009 has at least returned to normal temperatures and GDU accumulation across southern Minnesota. Any major killing frost prior to those normal first frost dates in 2009 could result in some crop loss in portions of the region.

On Sept. 1, the National Ag Statistics Service listed 52% of Minnesota’s corn crop in the dough stage, compared to a five-year average of 79%. Corn is considered safe from a killing frost once the corn reaches physiological maturity, which is when the corn kernel reaches the black layer stage, and this is still three to four weeks away in many cases. When the corn reaches back layer, it is still usually at a kernel moisture of 28-32%. Ideally, corn should be at 15-16% kernel moisture for safe storage in a grain bin until next spring or summer. So even beyond the corn reaching maturity in the coming weeks, some nice weather conditions will be required to allow for natural drydown of the corn in the field, in order to avoid high corn drying costs this fall.

Dry Weather Pattern Continues
The overall dry weather pattern continues in many areas of southern and western Minnesota. At the U of M SROC in Waseca, a total of 3.33 in. of rainfall was received in August 2009, which was the highest monthly total since July 2008. However, the total rainfall in August at Waseca was still 1.25 in., or 27%, below normal. Monthly rainfall totals for 2009 at Waseca were 2.94 in. below normal in July, 1.46 in. below normal in June and 2.06 in. below normal in May. The 2009 four-month total rainfall from May 1 to Aug. 31 at Waseca has totaled only 9.52 in., which is about 7.7 in. below normal, and is the sixth driest year on record in the past 95 years.

Of course rainfall amounts and timeliness of rainfall events have been quite variable across the region in 2009. Some areas of southern Minnesota, especially near the Iowa border, have received much higher total rainfall amounts than at Waseca during the growing season, and have had much more timely rainfall events. However, other areas of south-central and west-central Minnesota have received even lower rainfall amounts than those listed at Waseca. Many of the rainfall events were quite variable from farm to farm, and even from field to field. As a result, we are likely to see a wide variation in crop yields across the region, even in the same county or township.

Given the limited rainfall we have received in most areas of southern and western Minnesota in 2009, it is pretty amazing that the corn and soybean crop has the yield potential that it does. This is partly due to early planting, good early season growing conditions, limited early season plant loss and the cool temperatures in July and late August that reduced crop stress. Also, some of the credit must go to our seed companies for the improved crop genetics in recent years that have made our corn and soybeans more tolerant of variable weather conditions during the growing season. It will be a very interesting harvest season in 2009 to see where corn and soybean yields end up.

U of M SROC Open House
The U of M SROC at Waseca, MN, will its their annual open house event on Thursday, Sept. 10, from 4 to 8 p.m., at the center site on the west edge of Waseca. This year’s theme will be Agriculture in the 21st Century: Growing a Strong Bio-Economy.Several U of M specialists and Extension educators will be on hand for presentations and to answer questions. The event is free and open to the public, and will include a free picnic supper.

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

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