I often get the question, "So given the weather we have had so far, what will corn yields be like?" Unfortunately, my crystal ball is no better than anyone else's. In 2011, corn planted progress has been slower than average. There is some concern that yields have been compromised due to delayed planting. Can the corn crop recover? In similar previous years what has been the corn crop response?

Since 1979, USDA-NASS has been collecting data on crop progress during the growing season. By correlating crop progress with final yield we might be able to predict some trends. Figure 1 shows crop progress (planted, silking, dented and mature) of selected years. Years were selected on the basis +1 standard deviation of the 30-yr normal for the week when the planted stage reached 67% planted. The charts show the 30-yr normal, slow- and fast-planted years, and 2011 planting progress. The table in the middle of the figure is the final USDA yield regressed against year to give a predicted trendline and a departure from the trendline (residual).

Figure 1. Corn progress (planted, silking, dented and mature) of selected years. The table in the middle of the figure is the final yield regressed showing predicted yield and the departure from the trendline (residual). Data source is USDA-NASS.

Somewhat surprisingly there were more fast-planted (n=7) years than slow-planted (n=2) years. The 2011 growing season has gotten off to a slow start, but it has not been significantly slower than the 30-yr normal. Two years have been extremely slow, 1983 and 1996. During 1983, silking, dented and mature data were not collected by USDA-NASS, but the crop finished 4 bu/A below the yield trendline. During the 1996 production year, crop progress was slower than the 30-yr normal at each crop stage and ended 13 bu/A below the yield trendline.

For Wisconsin, high yielding seasons tend to have earlier than normal planting dates. Over the last 30-yrs this has been the case in 5 of 7 years, with the exceptions being 1988 and 2007. One interesting production season was 2000 when planting got off to an early start, but then due to a cool June and July crop progress slowed and finished 1 bu/A above the yield trendline.

Weather at the Arlington and Marshfield experiment stations is shown in Figure 2 for accumulation of Growing Degree Units (GDUs) and Precipitation from April 1 to May 31. Years were selected that were + 1 standard deviation from the 30-yr normal for this period and then follows what happens to October 31. In 2011, precipitation accumulation is similar to the 30-yr normal. However, GDU accumulation is one of the slowest seasons in the last 30 years at both Arlington and Marshfield. Of the 5 years that were cooler than normal for the April 1 to May 31 period, only one year ended the growing season above average. Generally warm years during April 1 to May 31 ended at or above the 30-yr normal.

Figure 2. Season Growing Degree Unit and Precipitation deviations from April 1 to May 31 at Arlington and Marshfield. Years were selected using + 1 standard deviation from the 30-yr normal. Weather data is obtained from Bill Bland (AWON, UW-Soils) and the Midwest Regional Climatological Center.

To view previous weather patterns of these unique years at Arlington and Marshfield see http://corn.agronomy.wisc.edu/Research. Again, a lot can still happen yet in the 2011 production season. The crop that has emerged seems to be off to a good start, even though it is somewhat late planted. Some things to consider include:

Scouting for increased pest pressure in late-planted corn,
Locking in fuel prices for corn grain drying in the fall.