Just How Important Was September 2004?

Joe Lauer , Corn Agronomist

Most farmers and agronomists I have visited with were grateful for the warm September experienced during 2004. Most feel that without it we would have had few crops develop to maturity. But, how good was September?

Data collected from the Arlington and Marshfield Agricultural Research Stations show that by May of the 2004 production year accumulated precipitation was above the 30-yr average (Figure 1). By the first part of September total precipitation was equal to the 30-yr average. No days at either location had maximum temperatures above 90 F, and rarely were daily maximum temperatures above the 30-yr average. Towards the end of August a scare occurred were the minimum temperature was 35 F on August 21. Growing degree units (GDUs) begin to lag behind the 30-yr average by early June. We needed a warm September to finish the crop.

Typical GDU accumulation during September averages 381 GDUs at Arlington and 330 GDUs at Marshfield . The coolest September on record at Arlington occurred in 1993 with 260 GDUs and at Marshfield in 1965 with 211 GDUs. The warmest September on record was 1971 at Arlington and 1931 at Marshfield (Table 1). During 2004 GDU accumulation was 419 GDUs (10% more) at Arlington and 446 GDUs (35% more) at Marshfield . At both locations a killing frost did not occur until early October.

Clearly September was one of the warmest on record at Marshfield and helped with the rate of crop development. We have seen warmer Septembers in other years at Arlington .

Table 1. Rank of years for Growing Degree Unit accumulation during September since 1962 for Arlington and since 1913 for Marshfield (modified GDUs base = 50 F, max = 86 F).
  Arlington Marshfield
Rank Year GDUs Year GDUs
1 1971 483 1931 452
2 1978 472 2004 446
3 1998 470 1948 444
4 2002 459 1998 443
5 1988 456 1933 430
6 1994 443 1994 426
7 1990 442 1920 421
8 2004 419 1936 406
9 1979 414 1921 403
10 1996 408 1990 399


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