Degree Days - Cool Weather Continues

June 16, 2009

By Rich Pope, Department of Plant Pathology

A third straight week of cooler than average weather has slowed crop progress across Iowa. Sporadic rainfall has limited field work, and for many fields weeds are a growing concern (pun intended). There has been slow weed response to herbicides, especially with glyphosate. The answer to this lies in getting some warmer weather to stimulate growth. So patience is a virtue.

During the week of June 7-14 Iowa crops accumulated about 40 to 60 degree days fewer than the long term averages (30-year running average). That is equivalent to the crop putting in a four to five day week!

Degree day accumulations from May 1 through June 14, 2009

The degree day accumulations posted here are for the growing season that arbitrarily starts on May 1 each year, but many fields are planted in April. From April 15 through May1, base-50 degree day accumulations ranged from 107 in northwest Iowa, to 121 in central Iowa to 148 in the southeast.   All these values were close to average.


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

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