As we approach the end of the 2013 growing season, there are remaining concerns with this year’s corn and soybean crop across most of the Upper Midwest. Below-normal temperatures and accumulation of growing degree units (GDUs) throughout late July and early August, along with later-than-normal spring planting, has left some of the corn and soybean crop behind normal development. Continued dry weather, associated with the recent high temperatures, is also a major concern in many portions of southern and central Minnesota, as recent rainfalls have been quite variable.
The total accumulated GDUs from May 1 to Aug. 26 at the U of M Research and Outreach Center at Waseca was 1,917, which is approximately 89 GDUs – or about 3-4 days – behind normal GDU accumulation. The GDU accumulation at the U of M Research and Outreach Center at Lamberton was 1771 from May 1 to Aug. 19, which is about 8% below normal. The much warmer-than-normal temperatures during the last 10 days of August are likely to close the GDU deficiency in most areas that planted a majority of corn and soybeans in May.
The recent very warm temperatures may be helpful for crop maturity, but these higher temperatures are now causing considerable crop stress in areas that have received very limited rainfall during the months of July and August. Most rainfall events across central, southwest and south-central Minnesota in recent weeks has been highly variable, with some locations receiving very beneficial rainfall amounts, and other locations receiving very little precipitation. Until Aug. 20, crop stress had been fairly minimal, due to the cooler temperatures; however, the recent hot weather trend is causing crops in some areas to deteriorate rapidly. There will likely be some significant yield reduction in the hardest hit areas.
Even though we are having a late summer heat wave, there are still concerns for corn and soybeans reaching maturity prior to the first frost, especially in south-central and southeastern Minnesota, and adjoining areas of northern Iowa. These areas experienced corn planting dates into early June, and had soybean planting into late June and early July. A majority of the corn and soybeans in this area need another 30-45 days of normal temperatures to reach maturity. The normal first frost date across southern Minnesota ranges from the last few days of September until around October 7.
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 4-5 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 in order to avoid high corn drying costs this fall.