Degree Days - What a Year It Was

November 17, 2009

By Rich Pope, Department of Plant Pathology

Heat or maybe lack of heat is a better description to use in this recap of the growing season. The degree day departure from average graphic shows how the season progressed by crop reporting district.

degree day graph

This year, the state was remarkably consistent in the heat that accumulated, with northwest and central Iowa faring just slightly better then the rest of the state. July, late August, and October were all very cold compared with historical records, with July ranking as the coldest on record, and October in the coldest five.


For most of Iowa, rainfall throughout the season was pretty average, with the slight exception in the east central and southeast districts, where rainfall was a bit above normal from July on.

rainfall graph

There were some very localized exceptions associated with summer thunderstorms that brought locally heavy rain to small areas.  Two of those storms were notable, because of devastating hail that destroyed crops and caused other damage. The first, on July 24, cut a swath from about Calmar in Winnesheik County to western Dubuque County.  The second was a remarkable storm that stripped crops from Ida County to Grundy County, and caused particularly intense damage in Hardin County near Eldora and near Callendar in Webster and Calhoun Counties.  This August 10 storm was unusual in that it formed and persisted across Iowa in the mid to late morning, associated with a slow moving cold front. 

The two graphics (below) from NASA show an image of the damage from space that was taken on August 23.  Note the defoliation scars that document the extent of these events.  ISU researchers have been analyzing damaged ears from these areas for ear rots and potential mycotoxin formation.


NE hail damage area

July 24, 2009 storm track, northeast Iowa


eldora hail damage

August 10, 2009 storm track, central Iowa

Rich Pope is a program specialist with responsibilities with Integrated Pest Management. Pope can be contacted at or by calling (515) 294-5899.


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