Note DetailFinding Growing Degree Days for Iowa
1/9/2011 4:25:00 PM

Finding Growing Degree Days for Iowa
Are the Growing Degree Days (GDD) behind or ahead
of normal for your county?  You can start the
report on the day you choose.   Go to the Iowa
Mesonet and make you own graph showing the “normal”
and the accumulation for the period of interest.
  In most of Iowa it is good to be normal to 
100 GDD above normal from corn planting to silking
(300 ahead of normal is getting bad).  Above normal
between silking and dent usually results in a
reduced yield.  100GDD behind normal increases the
yield potential (remember there are other factors
as well) for corn by about 10%, 200GDD behind
increases by 13% -t 15%, if GDD fall 300 behind
between silking and dent the yield is still likely
high but harvest is likely a high moisture.  400GDD
behind usually results in poor test weight, moist
grain at harvest and still yields somewhat above
normal bushels (+8% is average).   Get the
information at:     
then click on  “Ag Weather” and under Growing
Degree Days select “Single Site Graphs”    select
the site (city) on the list and input the year,
start date, and end date (remember this only works
for periods older than yesterday).

Iowa State University Extension