UNL CropWatch July 15, 2010: 2010 GDDs Ahead of 2009 and Near Long-term Norms

UNL CropWatch July 15, 2010: 2010 GDDs Ahead of 2009 and Near Long-term Norms

July 15, updated July 20, 2010

July 22, 2010 Update

It appears that, based on a May 1 emergence date, most locations east of the Panhandle are running ahead of last year in GDD accumulation. Compared to last year, daily  temperatures have been an average 10 degrees warmer. If normal to warmer temperatures continue, early corn in southeast and south central Nebraska could mature from very late August to early September. Currently, northern Nebraska is accumulating approximately 180 GDD a week and southern Nebraska is collecting 210 GDD.

Western Nebraska and some areas of northern Nebraska are behind normal in GDD accumulations. While projected temperatures for the next two weeks are normal to above normal, little reduction in GDD deficits would be expected since maximum temperatures in the GDD calculation are capped at 86°F (see below). Deficits can be reduced on the low temperature side if they remain above normal.  Expect a 1 unit GDD reduction for each 2°F that the low temperature is above normal.  Maximum temperature normals will begin to drop below 86°F by mid-August in northern Nebraska and August 20-25 in southern Nebraska.  If Nebraska has above normal temperatures in September, there could be a significant reduction in the deficit.

Use the following tables to compare GDD accumulations at specific sites for this time last year with accumulations on the same date this year:

Al Dutcher
Extension State Climatologist

July 15, 2010

As summer begins to really heat up, growing degree day (GDD) accumulations will increase, likely reaching the maximum accumulation each day.  GDD accumulations across the state have been near the long-term average, with many sites reporting numbers from 1% to 5% below average to 1% to 3% above average

GDD Primer

GDDs are used to estimate plant and pest growth stages and help provide a timeline for management.

GDDs are calculated based on the optimal temperature range for plant growth. A crop would not be expected to grow much below the minimum temperature or above the maximum temperature.

To estimate GDDs for corn, use a minimum temperature of 50°F and a maximum temperature of 86°F. Minimum temperatures below 50°F are counted as 50°F and maximum temperatures above 86°F are counted as 86°F.

The simple calculation for one method of estimating GDDs is:

GDD = Max. Temp + Min Temp.    -   Base Temp.
                              2

Using this calculation, if the minimum temperature one day is 65°F and the maximum temperature is 92°F, you would use 65 and 86 in the calculation.

GDD  =  86 + 64    -   50
                  2

GDD =      150     -   50
                  2

GDD = 75 - 50     or      GDD = 25  

According to records from the High Plains Climate Center comparing 2009 and 2010 GDD accumulations (Table 1), in every case more GDDs had accumulated by July 8, 2010 than by this date last year.  For examplle, in 2010 in Holdrege 1056 GDDs had accumulated by July 8, while in 2009, the number was 979. The long-term average is 1009, placing 2010 slightly ahead of the norm by 2% and 2009 slightly behind it by 1%.

Table 1 shows similar data for many other reporting sites. The same corn maturity – 2569 GDDs – was used for all sites and wouldn’t typically be planted at higher elevation levels with a shorter season, for example in north central and western Nebraska where GDD accumulations were furthest below the norm.

Early emerging crops may have gotten off to a slower start when much of the state experienced cooler temperatures the first two weeks of May.  For example, at York corn emerging May 1 was estimated to have only 100 more GDD than corn emerging two weeks later on May 15. At Alliance, corn emerging May 7 had only 29 more GDD than corn emerging 10 days later on May 17.  

If normal temperatures hold true for the rest of the season, the corn crop would be expected to mature before the average fall frost date, said Nebraska State Climatologist Al Dutcher.  (Also see GDDs Catching up from Early Season Fluctuations.)

CropWatch GDD and Et Data

CropWatch offers several resources for estimating evapotranspiration (Et) and GDD accumulation.  At the top of every CropWatch page, in the grey bar under the red bar under Weather, you'll find links to 

Lisa Jasa
CropWatch Editor

Al Dutcher
Extension State Climatologist



Table 1. Comparison of GDD accumulations for July 8, 2009 and July 8, 2010, based on a 2569 GDD maturity for corn.  A typical corn hybrid for eastern and central Nebraska would mature at approximately 2569 GDD.

City
Crop
Emergence
Date
GDDs
Norm
2009
% of Norm
2010
% of
Norm

Ainsworth

Corn
5/15
810 
-7
955
-2
1002 
Alliance
Corn
5/15
775
-5
860
-5
899

Arapahoe 

Corn
5/15
786
-8
860
-5
979
Beatrice
Corn
5/15
1076 
-3
1162
1
1147
Brule
Corn
5/15
911
-3
951
-1
981
Brunswick
Corn
5/15
880
-7
1018
-2 
1059
Cedar Point
Corn
5/15
873
-4
943
-2
982

Central City

Corn
5/15
986
-2
1089
2
1046
Champion
Corn
5/15
876
-4
951 
-1
986
Clay Center           
Corn
5/15
1003
-1  
1084
2
1036

Concord        

Corn
5/15
918
-6
1033
-2  
1077

Cozad

Corn
5/15
900
-4
960
-2
1003

Curtis

Corn
5/15
930
-3
1007
0
998

Dickens

Corn
5/15
842
-6 
925
-3 
992

Elgin            

Corn
5/15
918
-5
1014
-1
1045

Firth

Corn
5/15
1129
-1
1195 
2
1147

Gordon            

Corn
5/15
765
-7
822
-5
939

Gothenburg

Corn
5/15
913
-3 
999
0
1002

Grand Island

Corn
5/15
977
-2
1066
2
1024

Gudmundsen

Corn
5/15
751
-9
820
-6
975

Halsey

Corn
5/15
850
-6
917
-3
1002

Havelock

Corn
5/15
1120
-1
1183
1
1147

Holdrege

Corn
5/15
974
-1
1056
1009

Indian Cave             

Corn
5/15
1137
0
1263
1146

Kearney

Corn
5/15
982
-1 
1068
1014

Lexington

Corn
5/15
980
-1
1001
0
1005

Lincoln

Corn
5/15
1127
-1
1198 
2
1147

McCook

Corn
5/15
998
0
1053
2
1000
Meadow Grove
Corn
5/15
1060
-3
1152
0
1146

Merna

Corn
5/15
898 
-4
973
-1
1006

Merritt

Corn
5/15
813
-7
912
-3
988
Minden
Corn
5/15
981
-1
1072
2
1012

Mitchell

Corn
5/15
813
-3
853
-2
892

Monroe

Corn
5/15
1024
-2
1120
2
1075

Nebraska City

Corn
5/15
1131
-1
1228 
3
1146

Newport

Corn
5/15
884
-5
1016 
0
1006

North Platte

Corn
5/15
911
-3
993 
0
994

Oakland           

Corn 
5/15
1034
-3
1144
1
1114

O’Neill

Corn 
5/15
849
-7
970
-2
1022

Ord

Corn 
5/15
912
-4 
997
-1
1021

Red Cloud

Corn 
5/15
1068
1
1132
4
1036

Scottsbluff

Corn 
5/15
833
-2
877
-1
893

Shelton

Corn 
5/15
996
-1
1086
3
1018

Sidney

Corn 
5/15
780
-6
837
- 4 
944

Sparks

Corn 
5/15
837
-6
946
-2
987

West Point

Corn 
5/15
993
-5
1112 
0
1113
York
Corn
5/15
1033
-1
1118
2
1061