In general, acreage response to late corn planting since 1996 has been smaller than anticipated, with meaningful differences (but in opposite directions) in only two years. In addition to the timeliness of planting, acreage decisions might be influenced by a change in the relationship of the prices of corn and competing crops. That is, more corn acres might be planted after the date for optimum yields if corn prices increase enough relative to other crops to offset the potential yield penalty. Compared to the ratio on March 31 when the USDA released the Prospective Plantings report, the ratio of November 2014 soybean futures to 2014 December corn futures now favors soybeans more than corn. It appears that the market is not yet concerned about the loss of corn acreage this year.
The U.S average corn yield relative to trend yield has varied considerably in years of late planting. In the 43 years from 1971 through 2013, we calculate that the percentage of the corn acreage planted late (after May 30 before 1986 and after May 20 since 1986) was 20 percent or more in 13 years. Compared to the unconditional trend yield from 1960 through 2013, the U.S. average yield was at or above trend yield in eight of those years and below trend yield in five years. The largest negative deviation from trend yield occurred in 1993 when record flooding occurred in parts of the western Corn Belt. The largest positive deviation from trend yield occurred in 2009 under the influence of a cool, wet summer. These results tend to support the notion that summer weather, not timeliness of planting, is the major determinant of the U. S. average corn yield.
Significant corn planting likely occurred in some areas last week, but prospects for a cool, rainy pattern over much of the northern Plains and Corn Belt over the next 10 days do not favor rapid corn planting. With over three weeks until corn planting is considered late by our definition, it is difficult to anticipate the potential impact of delayed planting on the magnitude of planted acreage. Without a more favorable corn price response, however, it would not be surprising for acreage to fall short of intentions, particularly in northern growing areas. Yield prospects will be up in the air until later in the season.