Degree Days - Average IS a Good Thing

August 11, 2009

By Rich Pope, Department of Plant Pathology

A nearly average week of heat and some rain to boot! August could not have started better for Iowans, except for the band of hail and wind damage along the U.S. 20 / Iowa 175 corridor.  For the week, we only lost around 10 to 15 base-50F degree days to average across Iowa. Like they say, just what the doctor ordered (except for the hail!).

Statewide, corn development ranges from brown silk (R2) to dough stage (R3), and soybeans are busily filling pods (R4--R5).

Accumulated degree days from May 1 through August 9, 2009

Soybean aphid numbers are increasing with some fields reaching the economic threshold of 250 per plant and increasing; most notably in the northeast, but in other scattered areas as well.

Corn leaf aphids have been bothersome in northwest and north central Iowa as well. There are not good thresholds available for treatment  for aphids on corn, but extension entomologist Erin Hodgson posted a recent ICM News article that highlights the corn aphid. Corn leaf aphid numbers typically decline after tasselling, so the problem may soon start to ebb.

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

ICM News