Crop conditions across the Midwest are quite variable in late July, depending on planting date, as well as impacts from heavy rainfalls in June and the recent dry weather conditions in late July. Overall, across the southwestern and the western portions of south-central Minnesota, a large percentage of corn and soybeans are in fair to good condition; however, excessive rainfall, along with very dry weather recently, in some locations could reduce 2013 yield potential. Crop conditions in the balance of Southern Minnesota and adjoining areas of Northern Iowa are much less favorable, due to the significant amount of late and prevented planting in 2013.
As of July 24, a total of 1,360 GDUs had been accumulated since May 1 at the U of M Southern Research Center at Waseca, which is about 1% behind normal for July 24. This has been an amazing recovery in GDU accumulation, considering most areas were ten days to two weeks behind normal in early June. The GDU accumulation has slowed considerably in the past week with some very cool daytime and overnight temperatures. Long-range weather forecasts continue to call for below normal temperatures for the next 7-10 days in the upper Midwest. By comparison, on July 24, 2012, a total of 1,626 GDUs were accumulated, and corn and soybean development was well ahead of normal.
A majority of the corn and soybeans in the region were planted 7-10 days later than normal in 2013, or later, so the warm temperatures in late June and early July have helped the crops make up for the late planting. As a result, most corn and soybeans that were planted in May were only slightly behind normal development, as of July 24; however, the later planted crops continued to lag well behind normal development. Most crops in the areas of eastern south-central Minnesota and southeastern Minnesota that were hardest hit with late and prevented planting continue to look fair to poor.
Corn takes about 60 days from the time of tasseling and pollination until the corn kernels reach physiological maturity, with normal accumulation of GDUs. Once the corn kernel is black-layered, it is usually free of significant damage from a killing frost. Much of the earlier planted corn in southern Minnesota tasseled and pollinated from July 15-25, and should adequately mature in 2013, assuming fairly normal GDU accumulation in August and early September, and a normal date for the first killing frost. Some of the later planted corn in south-central and southeast Minnesota, which is tasseling in late July or early August could have some challenges being fully black-layered by the first frost, especially if temperatures turn cooler, or if the first killing frost is earlier than normal. Corn also will likely have higher moisture content at harvest this fall, which will increase drying costs.
There are similar concerns with soybean maturity, as hundreds of thousands of acres of soybeans in the Upper Midwest were planted in mid- to late June. The recent very cool weather trend has increased concerns regarding the late planted soybeans reaching maturity before the first killing frost. Overall, most soybeans in many areas on southern Minnesota and northern Iowa are shorter than normal in 2013; however, less vegetative growth on soybeans does not necessarily correlate to lower yields. The weather pattern in August will likely be the key factor for final determination of 2013 soybean yields.
Some areas received some beneficial rainfall on July 25; however, some of the driest portions of Southwest Minnesota and Northwest Iowa received very little precipitation. Total precipitation at Waseca in July, as of July 24, was 4.10 in., compared to a normal total July precipitation total of 4.47 in. Many areas of southwestern Minnesota have received less than 2 in. total in July.