Predicting corn silage harvest date

Mike Rankin
Crops and Soils Agent
University of Wisconsin - Extension

      As we move into August, thoughts begin to turn from crop maintenance to crop harvest.  One of the first items of business is corn silage.  As documented throughout this growing season, our Growing Degree Unit (GDU) accumulations have lagged behind normal.  Hence, crop development is also slow.  Does this mean a later than normal corn silage harvest?  Probably.  How much later?  We can use growing degree units (GDU) to make our predictions.  A lot of the early-planted corn was silking around the last week in July.  From silking to "full dent", or when corn reaches 65 to 70 percent whole plant moisture, it takes about 900 GDU's.  The 30-year average number of GDU's accumulated in our area from July 29 to September 15 is 881.  Hence, corn fields that silked in late July will be ready to chop during the middle of September assuming we have near "normal" temperature and rainfall conditions.  However, there is a significant amount of corn that will silk from early to mid-August.

     The GDU method for predicting corn silage harvest begins to break down a bit with late planted corn. There are only 900 GDU’s normally accumulated from August 12 through the end of October.  Rather, it’s probably best to start counting calendar days.  From silking to “full dent” the general rule of thumb is to figure about 45 days.  Although fewer GDU’s are accumulated, later planted corn tends to move through developmental stages more quickly.  However, the tradeoff is generally less yield.  Like the last few years, there will be a relatively long corn silage harvest season because of the wide fluctuation in planting dates from late-April to mid-June.  It will be important to monitor corn maturity on a field by field basis.  There is also an extreme amount of variability in plant maturity within some fields.