Fundamentally Speaking

Corn Crop Ratings Following Seasonal Pattern

Joel Karlin
By  Joel Karlin , DTN Contributing Analyst
Chart by Joel Karlin, DTN Contributing Analyst

We see that the trade felt corn and bean conditions would stay steady or increase by 1% when the USDA released its weekly crop progress and condition report, though we were skeptical in that regard as much less rain was seen last week than was the case in the prior three weeks of July, yet crop conditions really did not respond in much of a positive manner at all.

It does not seem surprising that corn and bean ratings went down this past week, as did the spring wheat ratings, and now one really must wonder about how likely attaining trend row crop yields will be this season.

Corn crop ratings instead of improving by 1% fell that much to 64% good or excellent vs. 72% a year ago and 69% for the average.

Along these lines, this graphic shows the seasonality of U.S. corn crop ratings from week 23 which is around the second week of June till week 39 which is usually around the last week of September.

We use 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.

We plot the 2021 ratings so far this season (week 29), the 1986-2020 average and then the plus and minus one standard deviation lines also for crop ratings as 68% of all year's ratings fall in between the two red lines which are the plus and minus one standard deviations.

Corn crop ratings on average usually start out the year at rather high levels around 748 but as the season progresses, ratings tend to fall bottoming out in weeks 35 or 36, right in the middle of September at a 705-706 rating.

There are some exceptional years where ratings are at or above the plus one standard deviation lines with particularly good growing seasons sometimes seeing ratings increase during the year on a contra seasonal basis, and there then are poor years where ratings are generally below the minus one standard deviation line most if not all of the season.

Interestingly this year's 2021 corn crop ratings are following the usual seasonal pattern quite well and are actually just above the average levels at least through the end of July as it appears that the other 14 top growing states have enough good areas to more than offset what are below average ratings in Iowa and really poor crop prospects in Minnesota and the Dakotas.

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