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Angie Peltier

Angie Peltier
Former Extension Educator, Commercial Agriculture

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Hill and Furrow

Current topics about crop production in Western Illinois, including field crops research at the NWIARDC in Monmouth.
Figure. Figure. Daily high and low temperatures (between 50 and 86 degrees F) collected at the NWIARDC in 2013 were used to calculate growing degree days, a measurement of corn growth and development.

Temperatures drive corn plant development

Brian Mansfield and Marty Johnson at the Northwestern Illinois Research and Demonstration Center (NWIARDC) recently completed their last corn fungicide spray. It is a hot job: donning their personal protective equipment, mixing fungicides, and applying the fungicides with small backpack sprayers and hand-held spray booms.

This task, which is part of many experiments, often takes place when corn reaches the silking (R1) growth stage. One experiment looking at the effect of corn hybrid and planting date on grain yield takes place at six different University of Illinois research centers across the state. Fungicides are applied (or not) to subplots within each hybrid/planting date combination when corn plants have reached the silking growth stage.

Corn plants require heat (between 50 and 86 °F) in order to grow, develop and reach vegetative and reproductive milestones on their way to physiological maturity. Growing degree days are a measure of the accumulated heat and associated corn growth and development during the growing season. Chapter 2 in the Illinois Agronomy Handbook has a good description of daily GDD calculations and the number of GDD that typically must accumulate in order for corn to reach specific growth stages.

In the 2013 corn hybrid and planting date experiment at the NWIARDC, corn was planted on April 4 and 26, May 15 and June 4 (Table). Corn planted on April 4 took 90 days to reach silking, while corn planted on April 26 took 13 fewer days to reach this milestone. Corn at each subsequent planting date took a little bit less time to reach silking. This is due to the lower average temperatures and correspondingly lower GDDs accumulated during April compared to May, June, and July (Figure).


Table. Planting and silking dates, days to silking and growing degree days accumulated at R1 for a corn planting date study at the Northwestern Illinois Agricultural Research and Demonstration Center in Monmouth, IL.


Planting Date

Silking (R1) Date

Days to R1

GDD to R1*

Planting date 1

April 4

July 3



Planting date 2

April 26

July 12



Planting date 3

May 15

July 19



Planting date 4

June 4

August 1




Now that tasseling and silking have taken place and pollination has wound to a close (even in the latest planted corn) agronomists like University of Illinois' Dr. Emerson Nafziger recommend checking ears from each field to see whether pollination was successful. Dr. Nafziger recently wrote a Bulletin article both detailing how to check corn pollination success and discussing his concerns about potential suboptimal pollination in some areas of the state in 2013.

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