Nearly all corn and soybeans across most of Minnesota have been planted and have emerged by the end of May. Crop growth has responded well to very warm temperatures in the past couple of weeks, following cooler-than-normal temperatures that existed from May 6 to 15. Most emerged corn in southern and western Minnesota was impacted by the hard frost on May 9, with the visible growth pattern being set back one to two weeks; however, the plant physiology has still advanced based on the mid- to late-April planting date that existed for most of the corn. There were some isolated reports of corn being replanted following the May 9 frost; however, most corn has recovered quite nicely from the frost damage. Soybeans received very little damage from the frost, and most soybeans are now emerged, with some excellent early growth. First cutting of alfalfa is nearly completed in many areas, and yields were quite good. Overall, the crop conditions across the region appear good to excellent for late May. Rainfall in the last half of May has been quite spotty across southern Minnesota, so there is beginning to be some concern with dry topsoil conditions, especially in fields with later-planted soybeans, and for re-growth of alfalfa following the first cutting.

At the University of Minnesota Southern Research and Outreach Center at Waseca, the average May air temperature through May 28 was 57.8° F, which is very similar to 2009, and just below the 30-year average May temperature of 58.4° F. The 2010 accumulation of growing degree units (GDUs) since May 1 at Waseca was 297, as of May 28, which is right on the long-term average Waseca. This is quite amazing, since the accumulation of GDUs during the cold spell from May 6 to 14 was only a total of 12.5; however, from May 23 to 28, the GDU accumulation was 133.5. The 30-year average for the entire month of May at Waseca is 337, and end of May GDU levels in recent years have been 327 in 2009, 258 in 2008 and 428 in 2007. The early development of the 2010 corn crop was also aided by the accumulation of approximately 150 GDUs during the last half of April, prior to the official GDU measurements at Waseca, which are initiated on May 1 each year.

The total precipitation in May, recorded through May 28, at Waseca, was 3.2 in., which is slightly below the long-term average precipitation of 3.96 in. for May. Total precipitation in April at Waseca was 1.60 in., compared to a normal of 3.23 in. It should be noted that some areas of southern Minnesota have received considerably less precipitation this spring, especially during late May, as compared to Waseca, and are now starting to have some concerns with rapidly drying topsoil.

Environmentally Friendly Herbicide Application
Most producers have begun applying postemergence herbicides for weed control in corn and soybeans, and will be continuing in the next couple of weeks. With the high amount of acres planted to Round-up Ready corn hybrids and soybean varieties, or similar crop genetics, a majority of the weed control in corn and soybean production is accomplished through the use of postemergence herbicides that are applied after the crop and the weeds are emerged and growing. By comparison, 10-15 years ago, post-emergence herbicides for weed control were secondary to the use of soil-applied pre-plant and pre-emergence herbicides to control weeds before they emerged. In addition to giving crop producers better options and more flexibility for weed control, usually at a lower cost per acre, the move toward a higher percentage of postemergence herbicides has also been more environmentally friendly. The postemergence herbicides are generally safer to use, and are much less likely to run-off into lakes, rivers, streams or tile lines, as compared to many of older soil applied chemicals. Biotechnology advances in seed genetics have allowed for these environmental benefits in last decade.

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].