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Impact of the Recent Warm Weather on Growing Degree Days
By Mary Knapp
After a very cold April, May has been warmer-than-normal (Figure 1).  This has meant that despite the slow start, corn planting is near average for this time of year (Figure 2).  Producers may be interested in how that might influence corn development. Growing degree days (GDD) are the common method for tracking development. The new Degree Days page on the Kansas Mesonet is designed to provide flexibility for our users, including options to select the time period and more built-in calculations. Because of the flexibility, it is somewhat more complicated than the older version. An explanation of the features can be found in a previous eUpdate story from Issue 619.
Figure 1. Departure from Normal Temperatures for May 2 - May 8, 2018.
Figure 2.  Corn planting progress. Graphic by Ignacio Ciampitti, K-State Research and Extension.
For producers who planted early, the amount of GDD accumulation was limited. The graphs below show the GDD accumulation at Manhattan from April 1 – May 8 and from May 1 – May 8 (Figure 3).
Figure 3. Accumulated corn growing degree days at Manhattan (Kansas Mesonet)
The difference is even greater in northwest Kansas, where temperatures have been cooler. In Cheyenne County, temperatures averaged almost 2 degrees below normal.  The growing degree accumulation is only 9 degree days above normal (Figure 4).
Figure 4. Accumulated corn growing degree days in Cheyenne County (Kansas Mesonet)
Warmer temperatures are expected in the next week, but when the high temperatures exceed the upper threshold of 86 degrees F (Figure 5), accumulation won’t be as rapid as with more moderate temperatures
Figure 5. Formula for Corn Degree Days. Graphic taken from KSRE publication Corn Production Handbook.
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