Degree Days - The Finish Line Looms

September 29, 2009
ICM News

By Rich Pope, Department of Plant Pathology

As of Sept. 27, 2009, we are close to winning the race between early frost and crop maturation across Iowa. The average date of first killing frost ranges from around Oct. 5 in central Iowa; about a week earlier to the north and west ,and a week later in southeast Iowa. It appears now that the 2009 first killing frost will occur at least at the average, and hopefully a bit later.

This good news is coupled with fairly favorable daily weather the last two to three weeks, with ample sunshine and mild evening temperatures. Reports from the field have both corn and soybean fields at or close to physiological maturity, with a few exceptions of late-planted or replant fields and other odd areas.

Degree day accumulation map for September 27, 2009

About six weeks ago, I posted a comparison of 2009 degree day accumulations through the season with other recent and notable years. As seen below, the favorable month of September is illustrated in the red line (2009). The red asterisk shows the line position as of September 27. Note that the last 3 to 4 weeks have led to a near-normal to slightly above normal temperature accumulations. Again, this is great news.

Degree day comparison with other years

Fall harvest is now just beginning in many areas.  As operators take to the field, a last check for pests while in the field is a great idea.  Because of the record cold July that limited vegetative growth and canopy fill in soybean, some weeds were allowed to flourish late in the season.

A final note that open, windy days can cause some lodging problems in corn fields, especially where stalk rots are developing. Scheduling corn harvest to take corn based on stalk strength monitoring can possibly net you a few extra bushels this year.

Stalk and ear rots are especially a concern in fields that were hail-damaged in July and August.  


Rich Pope is a program specialist with responsibilities with Integrated Pest Management. Pope can be contacted 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 September 29, 2009. The information contained within may not be the most current and accurate depending on when it is accessed.