The first U.S. corn crop rating was released last week showing 63% rated in either the good or excellent categories.
Using our usual rating system where we weight the crop based on the percent in each category and assign that category a factor of 0.2 for VP, 0.4 for P, 0.6 for F, 0.8 for G, and 1.0 for EX and then sum the results show a number of 73.0.
That is slightly below the five and ten year average June 1 rating but not too bad given how slow plantings have been this season with a mere 46% of the crop in the ground as of May 15.
This graphic shows the percent of the U.S. corn crop planted by May 15 and the crop rating around June 1 vs. the percent that final corn yields deviated from the 30 year trend.
Looking at other years of lagged seedings shows 1993 with 37% seeded by May 15, the lowest percent since 1986 with the June 1 crop rating at 68.8.
That is the second lowest June 1 rating with 1992 lower yet record yields were seen that season.
The year 1995 saw 39% planted by May 15 with the June 1 crop rating at 72.0.
Therefore, the only two other slower planting seasons did have lower initial crop ratings and both years saw final yields well below trend.
On the other hand, seasons of fast corn plantings and high June 1 crop ratings still resulted in below trend yields with last year a perfect example.
We suspect that in slow planting years, early season (June1) crop ratings are low based on the short and yellow appearance of the corn plants due to saturated soil conditions.
Nonetheless, the correlation between early season crop conditions and how much final yields deviate from trend is a low 0.17.
Most studies continue to point to summer weather conditions, primarily July temperatures and precipitation as having the greatest influence on yield variability.
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