Most people drive by a corn field and view it as.....well....a corn field.  However, as tassels emerge from the green stalks, they mark the beginning of the most interesting and critical period in a corn plant’s life.  It is also a time when we can begin to predict harvest dates.  So let’s take a close look at what these corn plants are currently doing and what they also may be telling us.

     Recall that corn has both male (tassel) and female (ear) flowers.  The pollination process is initiated when the tassel emerges (this either has happened or will soon happen in many area corn fields).  Typically, the tassel is fully emerged before any pollen is shed.  Each tassel has from 500 to 1000 spikelets and each of these contains two florets.  Within each floret are three anthers.  The anthers are those “little dealies” that hang from the tassel during pollination and drop yellow pollen grains like confetti on a downtown parade.  Walking through a corn field during this period leaves you looking like a lemon. 

     The female flower includes the ovule (kernel) and stigma (silk).  Every potential kernel develops its own silk and each one must be pollinated by receiving a dropped or blown pollen grain once the silk has emerged from the husk.  A well-developed ear shoot has 750 to 1000 potential kernels, although fewer normally develop.  All silks will emerge and be ready for pollination within 3 to 5 days and this is usually enough time for all silks to be pollinated before pollen shed ceases.  The amount of pollen needed for fertilization is rarely a problem as each tassel produces from 2 to 5 million pollen grains, enough for 2,000 to 5,000 grains per silk.  Pollen is very light and can travel a distance of up to 600 feet by wind but most lands within 20 to 50 feet of its plant (tassel) origin.

     Pollen shed is not continuous.  If anthers are wet from rain or dew, no pollen grains are released from the anthers.  Typically, peak pollen shed occurs between 9:00 and 11:00 a.m.  Because of whole field variability, an individual field may take as long as fourteen days to complete pollen shed. 

     Any stress during the pollination period will have a significant impact on final grain yield. "Severe" moisture stress during tasseling and silking can decrease final yields by 5 to 15 percent per day of stress.  Severe stress is defined as leaf rolling for several hours during the mid-day period.  Yield reductions will be on the high end of this range when temperatures are high, and at the low end when temperatures are cool.  Moisture stress has its greatest impact on silk elongation.  Under optimum conditions, silk emergence occurs one to two days after pollen shed begins.  With moisture stress, silk growth and emergence is delayed, such that under severe stress, silks may not emerge until pollen shed is complete.  Insects that feed on the lush silks can also prevent complete fertilization (an ear with missing kernels).

     All of these previously discussed events are contingent on timing and synchronization for successful kernel pollination, which in turn sets-up the possibility for high grain yields.  Silking also provides a mechanism for predicting silage or grain harvest.  Silage harvest usually begins about 42-47 days after silking.  This translates to a date of about August 20 for early planted corn in our area.  Kernel black layer, also referred to as physiological maturity, occurs about 55-60 days after silking.  The bottom line is that silage choppers and grain combines will roll earlier in 2007 than in the past several years.