Degree Days - We Don't Need Stress!

August 4, 2009
ICM News

By Rich Pope, Department of Plant Pathology

It is beyond time to get hot summer weather started! Both corn and soybean are (finally) in reproductive stages, and parts of Iowa are over 200 degree days behind normal. 

But we don't want to make up that deficit with significantly above-normal temperatures, as high August temperatures mean stress that can cut yield potential dramatically. In 1992, we were nearly as far behind as now, and the cool August weather then produced an above-normal yielding crop, however the grain was wet and fall grain handling and dry down were significant issues. 

We cannot say yet if there will be a repeat of 1992. The ideal weather recipe now is not too cold and not too warm, with a little rain mixed in. Anything cooler and we delay maturation, anything warmer and we cut yields.  

 Accumulated degree days from May 1 through August 2, 2009

Observations indicate soybean aphid numbers are increasing, most notably in northern and central Iowa. Scouting fields is critically important. Foliar corn diseases also warrant monitoring -  eyespot in norther parts of the state and gray leaf spot towards the south.

There is an interesting graphic and story of the July 24, 2009 hail storm that struck northeast Iowa on the Iowa Environmental Mesonet (IEM) website. The IEM contains a weatlth of weather and climate related information for Iowans.

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.

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on August 4, 2009. The information contained within may not be the most current and accurate depending on when it is accessed.