Beneficial August Rainfall

August 21, 2017


Many areas of the Upper Midwest were starting to get quite dry in early August; however, recent rainfalls have alleviated these concerns in many areas. Most of Minnesota, Northern Iowa, and the Eastern Dakota’s received some very beneficial rain during the first three weeks of August, with some locations receiving excessive amounts of rainfall as part of severe thunderstorms. Much of Central and Western North and South Dakota remain under a moderate to extreme drought, and portions of Western Iowa continue to be extremely dry.

The University of Minnesota Southern Research Center at Waseca, received 1.21 inches of rainfall during the first half of August, but did receive some additional rainfall on August 16 and 17. This followed 6.56 inches of rainfall in July at Waseca, which was over two inches above normal. For the year, total 2017 precipitation at Waseca through mid-August is slightly above normal. The number of growing degree units (GDU’s) at Waseca was approximately 20 percent below normal during the first three weeks of August; however, the 2017 GDU accumulation since May 1st remains slightly above normal.

The U of M Research Center at Lamberton, in Southwest Minnesota, received 1.39 inches of rainfall  during the first two weeks of August, which followed 4.01 inches of rainfall during July. As of August 14, the Lamberton location received had received 14.08 inches of total precipitation since May 1, which was about 1.5 inches higher than normal. Some areas of Southwest and South Central Minnesota received rainfall amount of 3-9 inches on August 16 and 17, which resulted in considerable standing water in some locations. The GDU accumulation from May 1 through August 14 at the Lamberton location was about 4 percent below normal.

Even though we are getting fairly late into the growing season, some crop challenges remain. The very cool, moist growing season in early August can be favorable for the development of corn and soybean diseases. Some of these diseases that occur before plants reach maturity can cause plants to die-down earlier than normal, which can ultimately reduce yields. Root-rot diseases also occur more frequently when crops are continually in saturated soil conditions. This can cause lead to more frequent lodging, as crops reach maturity. If the cool weather pattern continues, there could also be concern in some areas of corn and soybeans reaching maturity, prior to the first killing frost this Fall.

Another issue in portions of Minnesota and surrounding States has been the numerous severe storms that have occurred in August with strong winds, hail, and very high rainfall amounts. These storms can lead to late season crop yield loss, in addition to yield losses from late planting and drown-out damage earlier in the growing season. The severe storms have also caused property damage to houses, buildings, and grain bins on farms and in rural communities at some locations.

Based on the August 10 USDA Report, the 2017 U.S. corn yield is estimated at 169.5 bushels per acre, and the 2017 U.S. soybean yield is estimated at 49.5 bushels per acre. These estimates are higher than many private grain marketing analysts are estimating. Minnesota’s 2017 corn yield is estimated at 183 bushels per acre, trailing last year’s record State average yield of 193 bushels per acre. Minnesota’s soybean yield for this year is projected at 49 bushels per acre, again below the 2016 record average yield of 52.5 bushels per acre. Iowa is estimated to have a 2017 corn yield of 188 bushels per acre, and a State average soybean yield of 56 bushels per acre, which significantly trail the 2016 record yields of 203 bushels per acre for corn and 60.5 bushels per acre for soybeans.

History has shown that the final U.S. corn and soybean yields can vary considerably from the mid-August USDA Report to the final yield results, which are usually released in January, following the completion of harvest. USDA uses plant population counts, crop conditions, crop maturity, ear counts, kernel rows, pod counts, etc., as of August 1 to make the U.S. crop yield estimates for the mid-August Crop Report. The final USDA yields are based on actual reported yields.

Since 1990, the average variation in the U.S. corn yield from August USDA Report to the final yield the following January has been over 5.5 bushels per acre, with a variation of about 2 bushels per acre for soybeans. The final U.S. corn yield has increased slightly over half of the time from the August report until the final yield numbers in January, while final soybean yield numbers have decreased slightly more than half of the time. In 2016, the final U.S. corn yield dropped slightly from the August estimate, and final U.S. soybean yield increased slightly from the August estimate. It will be interesting how the final U.S. corn and soybean yield numbers end up for the 2017 crop year.


Note — For additional information contact Kent Thiesse, Farm Management Analyst and

Vice President, MinnStar Bank, Lake Crystal, MN.  (Phone — (507) 381-7960);

E-mail —


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