First corn crop rating vs. trend yields

To great anticipation, the USDA released its first weekly crop condition report for U.S. corn this week.

Ample precipitation this spring along with cooler than normal temperatures has made corn plantings a challenge this season, especially in the Missouri Valley and Eastern Corn Belt regions. This had raised questions about how the USDA would assess the crop in its initial crop ratings report.

Using our usual ratings system (where we weight the crop based on the percent in each category and assign that category a factor of 2 for very poor, 4 for poor, 6 for fair, 8 for good, and 10 for excellent and then sum the results), the first corn crop rating this year was 730 vs. 758 a year ago, and the five, ten year and 15-year averages respectively at 761, 754 and 744.

This graphic shows the initial crop ratings along with the percent that the final U.S. corn yield deviated from the 30-year trend.

US Corn Crop Rating Chart

We also added the date that the first crop report of the year was issued to help gauge whether an early release perhaps presaged a good yield or conversely a late release was related to a below trend yield.

The highest first rating of the year was seen in 1991 at 794 points on June 2nd but an unfavorable second half of that growing season resulted in final yields coming in 8.1% below trend.

A look at some very low initial crop ratings ( a number below 700) show 1990 at 698 and a yield 1.9% above trend, 1993 at 688 and a yield 17.4% below trend, 1996 at 688 and a yield right at trend and 2002 which has the lowest initial crop rating of 654 resulting in final yields 7.1% below trend.

A final note is the two years that had the latest first crop rating release; 1993 coming out June 6th and 1995 on June 18th had yields 17.4% and 9.8% respectively below trend.

Making some general observations is that a high first crop rating is no guarantee of good yields as the key pollination period is still more than a month away.

Secondly is that in 2008 an even lower 728 rating saw final yields that year 2.1% above trend and in 2005 an even lower 726 rating sill resulted in final yields 2.0% above trend.


Joel Karlin, DTN Contributing Analyst