Friday, March 21, 2014

Wheat Development Delayed about 2 Weeks this Year

Carrie Knott, Extension Agronomist-Princeton, University of Kentucky

We all know that this year has been an unusually cold year.  I am sure many if not all of you have visited your wheat fields to determine the effect this year has had on wheat growth and development.  At the University of Kentucky Research and Education Center at Princeton, KY, visually the wheat crop is about 2 or 3 weeks delayed.  Typically by this point on the calendar we are either at Feekes 5 or 6.  Right now we are only at about Feekes 2 or 3. 

I have also spent considerable time analyzing the weather data to determine how many growing degree days, or heat units, we have accumulated this season.  Growing degree units per day are calculated by subtracting 32°F from the average daily.  The 32°F is considered the “base” temperature or the temperature that wheat stops actively growing.

For example, on March 1, 2014 the average daily temperature was 48.5°F.

                48.5°F - 32°F =16.5 growing degree days (GDD)

If you add up all the GDD between November 1, 2013 and March 16, 2014 the total is 1411.5 (Figure 1).  If you compare this to the 2013 growing season the total accumulated GDD from November 1, 2012 to March 16, 2013 was 1841.5 (Figure 1).  That is a difference of 430 GDD. 

Assuming that we will have “normal” temperatures from March 17 to April 7 we can calculate how long it will take to accumulate those 430 GDD we lack.  At Princeton, typically from March 17 to March 31, which is 15 days, we accumulate 19 GDD.  From April 1 to 7 we typically accumulate 23 GDD.

                15 days x 19 GDD = 285 GDD for March 17 to 31

                7 days x 23 GDD = 138 GDD for April 1 to 7

                285 GDD + 138 GDD = 446 GDD for March 17 to April 7

According to GDD calculations it will be between April 6 and 7 before we accumulate the 430 GDD that we are behind, compared to last year.  That is about 2 to 3 weeks late.  This matches our visual estimates of 2 to 3 weeks late.

It is very important to understand the delay in wheat development this year because it will complicate wheat management this year.  We will NOT be able to manage a profitable wheat crop this year by the calendar.  You are going to have to be diligent and make sure you wait for the appropriate development stages to apply inputs.

We have already put out numerous articles regarding this, especially for nitrogen management, but it is worth repeating.  Wheat prices are not projected to be great this year and to maximize profitability you must be an active participant for management, which will not allow passive management with the calendar.
Figure 1. Calculated Growing Degree Days (GDD) and Cumulative GDD for November 1 to March 16 for the 2013 and 2014 Wheat Crop.

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