Degree Days - Off on a Muddy Track

May 6, 2009
ICM News

By Rich Pope, Corn and Soybean Initiative

Today's article is the first weekly post that monitors accumulation of degree days through the 2009 growing season. The map below shows the base 50 degree F days that have accumulated in each of Iowa's nine crop reporting districts, and the departure in accumulations from long-term averages.

Accumulated degree days May1 through May 4, 2009

As of the morning of May 4, approximately 70 percent of corn has been planted in Iowa. Most of this corn was planted prior to the heavy rains that struck central and eastern Iowa the weekend of April 25.  Just like the Kentucky Derby, many acres started on a muddy track. Although that isn't itself a major problem, farmers are advised to watch fields where corn is emerging for successful stand establishment, particularly where driving rains may have caused crusts to form.  Soybean planting was estimated at less than 5 percent complete for the state.

For plantings prior to May 1, the map below shows degree day accumulations prior to May 1.  As an example, for a field that was planted on April 10 in central Iowa, 135 degree days accumulated for crop development in addition to those listed since May 1.  So for that field, as of May 4, there would be 35+135 or 170 degree days currently accumulated.

2009 degree days accumulated prior to May 1

Several ISU field agronomists are seeing corn emergence. A general rule of thumb for degree days required between planting and emergence is from 100 to150, and several fields have passed 150 with no emergence. Remember that the degree days posted here are based on air temperatures, and that until emergence, the corn plant is underground. Wet soils warm more slowly, especially when there are cloudy days that limit solar warming. That said, with warmer and sunny days forecast this week, many fields planted in mid-April should be emerging this week.


Rich Pope is a program specialist with responsibilities with Integrated Pest Management.


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 May 6, 2009. The information contained within may not be the most current and accurate depending on when it is accessed.