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August 1, 2018

August Weather will determine Final 2018 U.S. Corn Yield

Author: Michael Cordonnier/Soybean & Corn Advisor, Inc.

The condition of the U.S. corn crop held steady last week at 72% rated good to excellent. The corn crop continues to develop ahead of the average pace with 91% pollinated compared to 82% last year and 82% average. The grain filling process is also advanced with 38% in dough compared to 21% last year and 20% average. This year, the corn crop is generally at least a week ahead of its normal development.

I left the U.S. corn yield unchanged this week at 178.0 bu/ac with the weather during August being the determining factor for the final corn yield. The temperatures during the first half of this week are going to be cooler than normal, but they are forecasted to be hotter than normal by the end of the week and over the weekend with the 6-10 day also forecasted to be hotter than normal. The rainfall this week looks generally dry for most of the Corn Belt with rainfall in the 6-10 day forecast favoring the northwestern Corn Belt.

The near term forecast looks beneficial, but I am concerned about the longer term forecast calling for hotter and dryer weather for the next two weeks. The soil moisture dried out somewhat last week and it will dry out some more this week. The first half of August looks hot and dry and that is not a beneficial forecast.

Enumerators are currently in the field conducting the survey for the August Crop Report which will be released on Friday, August 10th. The survey for the August Crop Report is generally conducted too early to accurately judge the final ear weights, so a key component for the August corn yield estimate is the number of ears found in the field.

Antidotal reports from the field indicate that the plant population is very good this year and as a result, the number of ears should also be very good as well. Even if the USDA uses an average ear weight, the high number of ears should result in an above average corn yield. My guess is that the August Crop Report might estimate the U.S. corn yield in the range of 175.5 to 176.5 bu/ac compared to their current trend line estimate of 174.0 bu/ac.

There have been some expressions of concern that the rapid development of the corn may end up cutting short the grain filling process, resulting in potentially smaller kernels that are shallow, less dense, and lower yielding. Certainly this year's corn crop is ahead of schedule in its development, and if the weather during August ends up being hotter and dryer than normal, that would likely shorten the grain filling period, so this needs to be watched.

There has also been a lot of talk this year about how the weekly crop ratings correlate to the final yields. Many people are skeptical that the final corn yield this year will be as high as the current crop ratings would suggest. The skepticism is due to what happened last year. The 2017 corn crop had mediocre crop ratings for most of the summer, but the yield estimates kept getting higher and higher in the late summer and early fall and the crop ended up with a record yield of 174.6 bu/ac.

I think the key to what happened last year was the weather during August. The soil moisture was about average for the first half of the summer and then it started to improve in early August and it continued to improve until early September. The improved moisture was accompanied by cooler than normal temperatures in August, which extended the moisture supplies even further. As a result, the corn condition rating, which had been running slightly below average for the first half of the summer, moved above average in early August and stayed above average for the remainder of the growing season.

Therefore, I think it was the very good weather during August is what really set the stage for a strong finish and a record corn yield in 2017.

Right now, the 2018 corn crop is rated 50% good and 22% excellent compared to the last week of July in 2017 when it was rated 48% good and 13% excellent. The weather during August will determine if the 2018 corn crop ends up good or very good.