From Dr. William J. Cox, Department of Crop and Soil Science, Cornell University:

I have received quite a few phone calls this morning (May 16, 2011) on keeping or staying with corn hybrid relative maturity (RM) groups, given the forecast for the remainder of the week. So I will venture out and make some comments. Two things to keep in mind:

If hybrids are planted later than normal, they require less growing degree days (GDD) to finish up or mature. For example, a 105 day RM hybrid planted on June 1 instead of May 1 would require only 2100-2150 GDD to be ready for silage harvest instead of the typical 2200 GDD when planted on time.

If growers got started last week, they planted their early or better-drained ground so now they will have to wait for their later or poorer-drained ground to be ready before they can plant.

Digging out some old data, I found a 3-year study (1988-1990) that we did at Aurora and Mt. Pleasant with planting dates on about April 25, May 10, and May 25. At Aurora, our 105-110 day hybrids yielded 23.9 tons/acre compared with 22.8 for the 101-105, and 19.5 for the 95-100 day hybrids when planted on April 24. For the May 8th planting date, the yields were 23, 22.4, and 20 tons/acre, respectively. For the May 22 planting date, the yields were 22.7, 22.3, and 19.7 tons/acre, respectively. At Mt. Pleasant, our 95-100 day hybrids yielded 15 tons/acre compared with 15.1 tons/acre for the 90-95 day hybrids, and 13.2 for the 85-90 day hybrids when planted on April 26th. For our May 10th planting date, the yields were 15.6, 15.6 and 13.9 tons/acre, respectively. For our May 24th planting date, the yields were 15, 15.4, and 13.7 tons/acre, respectively. So for regions where there is no real threat of an early fall frost (first frost is in October), the data indicate not to back off on maturity length just yet.

So if it was me and I have selected well-adapted silage hybrids that are typically ready by September 20-25, I would stick with what I have for silage up until May 29th or so. If I have some real late material (112 day hybrid when all my other hybrids are less than 105 days) that I took a chance on, I would return it immediately.  By Saturday of this week if the forecast is not good for planting next week (May 23-29), I would start scaling back my hybrids by 5 days. In general, a hybrid that is 5 days shorter in RM will be 1.5 points drier but will yield about 0.75 tons/acre less (http://css.cals.cornell.edu/cals/css/extension/cropping-up/archive/upload/WCU18-5.pdf). And I would keep scaling it back by 5 days as each week passes. I would do the same thing for high-moisture shelled corn.

For dry shelled corn, I would probably stay with the hybrids that I have selected up until May 25th or so as long as they typically black-layer by September 20-25th when planted during the first half of May. We found that 95-100 and 101-105 day hybrids planted around May 20th yielded as well (or even better due to weather factors) than planted around April 25th (http://css.cals.cornell.edu/cals/css/extension/cropping-up/archive/upload/WCUVol21No1.pdf). The hybrids planted on May 20th, however, were about 2.5 points wetter at harvest, which would translate into a $12/acre increase in drying costs for a 150 bushel/acre crop (or growers could wait another 7-10 days or so to get the moisture down further). The other option that cash grain growers have is to switch to soybeans once June rolls around and corn planting is not finished. There is less of a yield penalty for planting soybeans late than for planting corn late. We found that there is only about a 1/3 to 1/6 bu/acre/day decrease when soybean planting is delayed from May 15th until about June 15th (http://css.cals.cornell.edu/cals/css/extension/upload/WCUVol17No2Mar-Apr2007.pdf). Furthermore, late-planted soybeans on corn ground would have no extra drying costs to worry about because wheat was not slated to be planted in that field.