August Rainfall Welcome

August 20, 2018


Many areas of the Upper Midwest were starting to get somewhat 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. Large portions of Missouri and Southern Iowa, as well as eastern Kansas and Nebraska remain under moderate to severe drought conditions. Portions of Northwest Southeast Minnesota are also quite dry.

The University of Minnesota Southern Research and Outreach Center at Waseca, received only 0.93 inches of rainfall during the first half of August, but did receive some additional rainfall on August 16. This followed 4.38 inches of rainfall in July at Waseca, which was near normal, and 5.78 inches in June, which was over one inch above normal. For the year, total 2018 precipitation at Waseca through mid-August is slightly above normal. The number of growing degree units (GDU’s) at Waseca was approximately 10 percent above normal during the first three weeks of August, continuing a trend of higher than normal GDU accumulation since May 1. For the season, the 2018 GDU accumulation is about 10 days head of normal, resulting in continued rapid crop development.

The U of M Research Center at Lamberton, in Southwest Minnesota, received 2.35 inches of rainfall during the first two weeks of August, which followed 6.17 inches of rainfall during July and 7.18 inches in June. As of August 17, the Lamberton location received had received over 20 inches of total precipitation since May 1, which was about 7.5 inches higher than normal. Some areas of Southwest Minnesota have received over 30 inches of rainfall since May 1. Similar to Waseca, the GDU accumulation at the Lamberton location since May 1 is about 12 percent above normal.

The USDA Crop Progress Report on August 12 rated 70 percent of the U.S. corn and 66 percent of the soybeans as “good-to-excellent”, with only 10 percent both crops rated as “poor or very poor”. There has been a slight decline in the percentage of “good-to-excellent” rated crops in recent weeks, probably reflecting the worsening drought conditions in portions of the southwest region of the Corn Belt. By comparison, a year ago in mid-August of 2017, 62 percent of the corn and 59 percent of the soybeans in the U.S. were rated as “good-to-excellent”.

The August 12 Crop Progress Report reported “good-to-excellent” ratings of 77 percent for corn and 73 percent for soybeans in Minnesota. Similarly, Iowa had the higher ratings on 75 percent of the corn and 72 percent of the soybean crop. Nebraska had the highest crop ratings of the major corn and soybean producing States, with a “good-to-excellent” rating of 83 percent for corn and 80 percent for soybeans. Other States with very high crop ratings for corn were North Dakota at 79 percent, Wisconsin at 78 percent, Illinois at 76 percent, and Ohio at 75 percent. Other States with high soybean ratings included Wisconsin at 76 percent and both Illinois and Ohio at 74 percent.

Even though we are getting fairly late into the growing season, some crop challenges remain. The very wet growing season in portions of the Upper Midwest has resulted in shallow root systems for some corn, which could lead to lodging problems as we approach harvest. Another challenge in corn this year could be uneven maturity and field dry-down, due to the varying corn maturity in the same field, which has resulted from the very wet weather in June and early July. Many farm operators have been spraying for soybean aphids during the first half of August, due to rapidly increasing aphid counts.

Based on the August 10 USDA Crop Report, the 2018 U.S. corn yield is estimated at the record level of 178.4 bushels per acre, and the 2018 U.S. soybean yield is estimated at 51.6 bushels per acre. These yield projections are higher than many private grain marketing analysts are estimating. Minnesota’s 2018 corn yield is estimated at 191 bushels per acre, the State’s soybean yield for this year is projected at 49 bushels per acre. Iowa is projected to have a 2018 corn yield of 202 bushels per acre, and a State average soybean yield of 59 bushels per acre.

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 2000, the average variation in the U.S. corn yield from August USDA Report to the final yield the following January has been around 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 2017, the final U.S. corn yield was 178.4 bushels per acre, following an August 10 estimate of 169.5 bushels per acre. Similarly, Minnesota’s final 2017 corn yield was a state record 194 bushels per acre, after an August estimate of 183 bushels per acre. Iowa saw a 14 bushel increase in the final 2017 corn yield to 202 bushels per acre, after an August estimate of 188 bushels per acre. Given the growing season weather patterns, we are not likely to see a similar corn yield increase from mid-August to harvest yields in 2018. The final 2017 U.S. soybean yield of 49.1 bushels per acre was very close to the August 10 estimate, as were the final 2017 soybean yields of 49 bushels per acre in Minnesota and 56.5 bushels per acre in Iowa.



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

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

E-mail —


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