Revisiting Hybrid Maturity Issues
Greg Roth
Department of Crop and Soil Sciences
Penn State
March 1998
Many growers throughout Pennsylvania were plagued by corn that dried down slowly last year and resulted in late harvest, high drying costs and sometimes low test weight corn. This has caused many producers to wonder if they are growing hybrids that are too late for their region. This is a very valid question. But we need to realize that the slow drydown last year was also related to a cool season and drought stress.
In many areas of the state, the growing degree days available for corn growth and development were less than normal. Growing degree accumulations from May 1 to October 1 for State College for example, were about 2150, about 300 GDDs less than normal for our area. To compound the problem, when corn experiences drought stress silking is often delayed. Last year we noticed about a 4-5 day delay in silking at Rock Springs due to the drought. Basically, the corn plants went dormant and we effectively lost another 100 GDDs or so. So, we had about 2050 GDDs to mature a 2400 GDD hybrid in. It was not surprising that even our early planted hybrids failed to reach black layer and dried down slowly.
In our area, we have found that it generally takes about 2400 GDDs to get a 105 day hybrid to black layer. Frequently, this is about all of the GDDs we get. We can grow longer season hybrids, say 110 day maturity, that needs about 2600 GDDs, but they often only reach half milk line. If we are harvesting for high moisture corn, or want to harvest in December, we can utilize these hybrids. If we get a cool season, though, then the 105 day hybrid takes until December to dry down and the 110 day hybrids can sometimes result in wet corn and poor quality grain. These seasons are especially tough on grain producers who need to dry this corn or those who want to utilize it for ear corn.
We could also grow 100 day hybrids that mature in 2200 GDDs or so and very rarely encounter maturity problems, but in warm years we may sacrifice some yield potential. Also consider, though, these early hybrids have other advantages: opportunities for planting wheat after harvest, drying corn under warmer conditions, and harvesting under generally drier soil conditions resulting in less soil compaction.
Several other factors complicate the hybrid maturity question. Probably more than any other state we have wide maturity difference within many counties. So on one side of the county you might be able to get away with a hybrid 5 to 10 days longer than on the other side. Another factor is lack of standardization on corn hybrid maturity- a 108 d hybrid in one company is not the same as a 108 d hybrid in another company. Another factor is that we rarely get a normal year- and it is easy to let what happened last year dictate your decision too heavily. A fourth factor to add to the confusion is that seed company ratings for hybrid GDD requirements are often higher than their actual requirement by 200 GDDs or so- many of the 105 day hybrids have a GDD rating of 2600.
So how can we try to make a better decision on the maturity of hybrids we grow? First decide if this is an issue for you. If you have not had trouble with slow drydown or test weight in the past few years then you're probably all right. If you have, they consider evaluating some earlier hybrids in your mix. One good way would be to estimate the GDDs available in your area. Next try to match your hybrids with the available GDDs. Also consider a spread of maturities- to help offset the risk associated with warm or cool seasons. A good suggestion might be 20% that always mature (early season), 60% that usually mature (medium season) and maybe 20% that sometimes mature (full season). Then adjust that based on your own operation- if you harvest all grain and test weight is a critical issue move more toward the early hybrids. If you sell high moisture grain and can tolerate more risk perhaps you can move toward the fuller season hybrids.
Also start to do a little maturity monitoring on your own. Are the hybrids you are growing reaching black layer regularly? If not, then you are likely near or past your limit on maturity for shelled or ear corn harvest. Are you encountering other problems associated with late harvest- soil compaction, late planted wheat or difficulty completing harvest before the snow flies? Are you not seeing a yield advantage to the longer hybrids? If so, these are signals a move towards an earlier maturity may be necessary.
Corn maturity decisions are not always as simple as they should be. Take time to reevaluate your situation. Don't make knee jerk reactions. Base your decisions on sound observations and long term weather data.