Dealing with Late Maturing Corn (8/25/11)

GDDs for all of the state are similar to those of last year, which turned out to be a relatively good year for corn.  So that is the good news.  Because of the extremely wet spring weather, however, most corn was planted late.  The fact that more than half of all the corn was planted after May 24^th means that much of the corn in the state is lagging significantly behind where it should be.  As an example, at Wyndmer, delaying the planting of corn until May 24 “cost” the crop 184 GDDs.  Delaying the planting until June 1^st “cost” the crop 317 GDDs.  Given the lateness of the season, it will be unlikely that late planted corn will be able to catch-up before the first killing frost.   Of course making it to physiological maturity (maximum dry wet of the grain) is only part of the challenge.  The other is to have the grain dry sufficiently so that it can be economically harvested, dried and stored.  The following are a few points to consider with regards to late maturing corn as we approach the end of the growing season and harvest. 

• Corn that reaches physiological maturity (PM) has a moisture content of 30-32%.  Moisture content prior to PM declines as additional starch is deposited in the developing kernel.  Moisture loss after PM is by evaporation.  Grain from plants that are killed prior to PM will be shriveled and have low test weight because they lack sufficient starch to fill out the kernel.
• The rate of moisture loss after the death of the plant via evaporation, whether the kernel has reached PM or not, will largely depend on air temperature.  Obviously relative humidity can play and important role in evaporation, but air temperature is the most dominant factor in ND.  Warm air has the ability to hold more water vapor than cold air, so warmer air temperatures are able to draw more air out of the drying kernel than cooler temperatures.  A good rule of thumb is that most field-drying that is going to occur in the fall will occur prior to November 1^st.  In some of our recent monitoring work, we found average moisture losses of between 0.25% to 0.33% per day during late September and October.  Moisture loss after 1 November was much less than these values.  Of course if we have a warm November, we can expect drying to continue through November.
• Leaving the corn crop over the winter has been found to be a profitable option when corn is excessively wet and difficult to harvest in the fall.  Because of the limited water holding capacity of our air in the winter, the rate of corn drying during the winter is very slow.  We observed an average moisture loss rate of about 0.1% per day for the period of December 1^st to February 21^st in 2009/2010.  Grain that had 32% moisture in early December reached 24% moisture on February 21^st.  In another study starting with relatively dry corn (18%) in 2008/2009 we observed minimal decline in grain moisture until the beginning of March, at which point the rate of decline accelerated until the corn was harvested in early May. 
• The test weight of wet corn increases with drying, except for corn with more than 42% moisture where the opposite is true.  Field drying during the winter may improve the test weight of corn that is excessively wet over high temperature drying, but don’t expect more than a couple of pounds difference.  A 45 lb/bu crop will be a low test weight crop regardless of how it is dried.  A shriveled kernel will be a shriveled kernel!
• Yield losses can be substantial during the winter due to snow, winds and wild animals.  Most yield loss is associated with ear drop and lodging.  If the crop goes into the winter with good stalk strength, it is more likely that yield losses will be less than if the crop has poor stalk quality.  We have not experienced much drought this year, so perhaps stalk strength will be good as we approach harvest.   

Joel Ransom - Extension Agronomist for Cereal Crops

Joel.ransom@ndsu.edu