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

Unfortunately, it is time for an update on selecting relative maturity (RM) for grain corn and silage hybrids and Maturity Groups for soybean varieties.

May 25th has come and gone so any grain corn that was planted last week should have been about 5 days shorter in RM. Given the recent rains, most planting won?t resume until about June 1 so it is time to scale back by another 5 days in RM for grain corn when planting from June 1-June 5 or so. So if growers typically plant a 100 day hybrid by May 15th, a 90 day hybrid should be planted for the week of May 31-June 6. We average about 170-190 growing degree days (GDD) from May 16th-May 31st so we cannot make that up even with the more rapid maturity for late-planted corn.

I realize that many are saying that the cut-off date for grain corn in Ohio and other Midwestern states is June 5th but I think that we can go to June 10th with the appropriate RM. We average about 125-150 growing degree days during the first 10 days of June so hybrid RM has to be scaled back another 10 days or so. So if a grower typically gets a 100 day hybrid to mature and yield well with a planting date by May 15th, the grower should be planting an 80 day hybrid or so from June 5-10 for dry shelled corn.

Another option for cash croppers is to switch some of the corn acres to soybeans (although soybean on soybean ground is not the most preferred practice but there is only about a 5% yield hit if white mold is not a problem in that field) during that first week of June. Again, soybean has a much broader optimum planting date window so the yield penalty is minimal up until June 5th or so. We conducted a study at Aurora in 1992-1993 (I know-old varieties!) with Group 00,0,I, and II Maturity Groups planted about May 15, May 25, June 5, and June 15 (What?s Cropping Up?, Vo.4, No.1, p.6-7, 1994). The two Group II varieties yielded about 55, 53, 50, and 32 bushels/acre, whereas the two Group I varieties yielded 44, 48, 48, and 31 bu/acre, respectively across the four planting dates. So it looks like Group II varieties should be planted up until June 5th or so. The Group 0 varieties yielded 40, 43, 43, and 33 bu/acre, respectively. So I would suggest Group II varieties until about June 5th, Group I varieties from June 5th to June 15, and Group 0 varieties from June 15-20th. After June 20th, I would probably call it quits on soybeans. If growers are planning on planting wheat after soybeans, Group I or Group 0 varieties should be planted as soon as they can get into the field.

How about hybrid RM for corn silage? Well, May 29th is upon us so it is time to scale back 5 days in RM for the June 1-5 period. Once the dairy producer is planting in the June 5-10 period, it is time to scale back another 5-10 days or so. For corn silage, I think that we can plant until June 10-15 with a scale back in RM of another 5-10 days because we are rapidly losing GDD as June progresses. So if a dairy producer typically plants a 100 day RM hybrid by May 20th, the producer should be planting a 95 day hybrid until about June 5, an 85-95 day hybrid from June 5-10, and a 75-80 day hybrid from June 10-15. Unlike grain corn, corn silage needs a timely harvest for quality so we need a little wider spread on the RM.  Once we get past June 15th, I defer to the forage people.

So it is a dire situation. I remember back in 1994, a grower was bemoaning the delay in corn planting but lo and behold his Pioneer 3925 (about 10 days earlier in RM than he usually planted) planted on June 3rd yielded 180 bushels/acre. Also, in 1991 and 2005, our June 15th soybeans yielded the highest-better than mid-May or late-May planted beans. So to quote that great 20th century philosopher, ?it is not over until it is over?.