What to do? 2013 growing season
The weather has put us in a bind. About a third of the corn crop has been planted in Southeast Minnesota, which has led to questions on the "correct" course of action. There will be no one "correct" course of action and with fields unsuitable for planting and more rain in the forecast there will be no easy decisions. One choice could be to utilize prevented planting, a choice that is appropriate for some and will lead to many other decisions to be made. A second option is to switch corn acres to soybeans; this may also be a wise and appropriate decision for some acres. Remember when planting soybeans after June 10th it is generally recommended to drop 0.5 RM from your typical full season varieties. The final choice is to stay the course and plant corn, a perfectly viable option for some acres.
Remember corn needs heat to complete its life cycle and we have lost a month. The following figure is from the National Corn Handbook, it indicates how many Growing Degree Days 50/86 (GDD 50/86) it takes for different relative maturity corns to reach physiological maturity (when planted by May 1st).
|Corn Relative Maturity||GDD 50/86 to Reach Physiological Maturity|
Similar information generated from commercial seed literature is as follows:
|Corn Relative Maturity||Approximate GDD 50/86 to Reach Physiological Maturity1|
1 = Values are approximate and can vary from hybrid to hybrid within a relative maturity
Late planted corn does not need as many GDD's to reach physiological maturity. In general there is a 6.8 GDD reduction per day for corn planted after May 1st. For corn planted June 1st that would mean a reduction of 210 GDD required to reach maturity. In other words a 100 RM corn hybrid planted in April takes about 2400 GDD to achieve physiological maturity. That same hybrid planted on June 1st would only take about 2190 GDD to reach maturity.
How much heat can we expect for the 2013 growing season? The following are a set of GDD 50/86 scenarios for different planting dates and locations in Southern Minnesota. Scenarios are based on the 1971 to 2000 temperature normal, information was derived from the Climatology Working Group (climate.umn.edu). October was excluded because there is about a 20% probability we will freeze before the end of September and about a 90% probability we will freeze before the mid of October. In addition we can only expect about 150 GDD 50/86 in October. Another cautionary note is that these scenarios are based on the 1971 to 2000 normal, and there is the possibility of accumulating more or less GDD's during the course of the summer (i.e. nothing is guaranteed).
|GDD 50/86 Accumulation by Month|
|GDD 50/86 Accumulation by Month with 3 Weeks in June|
|Location||3 wks June||July||August||September||Total|
|GDD 50/86 Accumulation by Month with 2 Weeks in June|
|Location||2 wks June||July||August||September||Total|
|GDD 50/86 Accumulation by Month with 1 Week in June|
|Location||1 wk June||July||August||September||Total|
Bottom-line: as the season progresses we will accumulate less GDD's, and with the full month of June in a "normal" year we won't quite reach 2300 GDD 50/86. There is a good chance that if we plant corn with Relative Maturity of 95 or greater we will not reach physiological maturity. What to expect when we don't reach physiological maturity: lower test weights, excessive moisture, and the potential for harvestability issues. Harvestability issues will really depend on the amount of GDD's we accumulate, and the shorter we are on GDD's to reach physiological maturity the more issues we will have.
Shorter maturity hybrids, if available, will have less yield potential but will be more likely to reach physiological maturity. This means test weights should be better, but at this point in the season even short season hybrids will have significant moisture levels at harvest.
The scenarios are intended to give you a better assessment of risk for the relative maturities you intend to plant. Remember nothing is guaranteed.
For a more comprehensive look at corn hybrids and grain production, see Selecting corn hybrids for grain production.