Degree Days - Slow and Steady Wins the Race

September 15, 2009

By Rich Pope, Department of Plant Pathology

Soybean fields are now starting to senesce, and corn is filling well. The latest USDA crop forecast projected a 187 bushel per acre average for corn yields, and 52 bushels per acre for the beans. Both would be great accomplishments considering the wet spring and cool summer. As of Sept. 13, we are lagging for the season an "average" accumulation of between 300 and 400 degree days, which rivals the 1992 growing season.

Accumulated degree days from May 1 through September 13, 2009

Average temperatures and clear, sunny days the next two to three weeks are still the ideal for Iowa crops. Soybean aphids are still persisting with sizeable populations in some fields, but in Ames we are seeing winged aphids fully engaged in the migration to buckthorn for overwintering.  Nearly all soybeans well past the point of gaining benefit from treatment to control aphids.

Regardless of how the season finishes, wet grain, especially corn, is highly likely. That is all the more reason to ensure harvest equipment is properly adjusted and that grain is handled properly during and after binning.



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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