CORN Newsletter: 2009-24, July 28, 2009

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C.O.R.N Newsletter 2009-24
July 28, 2009 - August 4, 2009

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Will Cooler than Normal Temperatures Adversely Affect Corn Yields?
by Peter Thomison


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Some Ohio growers are concerned that the lower than normal temperatures we experienced in July will negatively impact corn growth and grain yields. Jim Noel noted in his “Weather Update”, that this summer is far cooler than 2004, 2000, 1996 or 1992, and that this month will go down as the coolest or near coolest July in anywhere from 25 to over 100 years - depending on where you are in the state and how the month ends. So, should these “cool” temperatures concern us? Probably not…it’s important to remember that corn actually yields best with moderate temperatures (and adequate soil moisture). Temperatures that occur in Ohio in July (especially at night) are often warmer than optimum for corn. The ideal daytime temperatures for corn are about 80 to 86 degrees F (and higher if moisture is plentiful at all times). Although some believe that corn grows best when nights are hot, past research shows that warm temperatures adversely affect yield potential. While temperatures in the 40’s may impair photosynthesis, high night temperatures (in the 70’s or 80’s) result in wasteful respiration and a lower amount of dry matter accumulation in plants. With high night temperatures, more of the sugars produced by photosynthesis during the day are lost; less is available to fill developing kernels, thereby lowering potential grain yield. Research conducted at the University of the Illinois indicated that corn grown at night temperatures in the mid-60’s out-yielded corn grown at temperatures in the mid-80’s. High night time temperatures result in faster heat unit (GDD) accumulation that can lead to earlier corn maturation, whereas cool night temperatures result in slower GDD accumulation that can lengthen grain filling and promote greater dry matter accumulation and grain yields.

Corn yields are often higher with irrigation in western states, which have low humidity and limited rainfall. While these areas are characterized by hot sunny days, night temperatures are often cooler than in the Eastern Corn Belt. Low night temperatures account in part for some of our highest corn yields in Ohio - 143 and 158 bu/A in 1992 and 2004, respectively (the highest yields recorded to date at that time). During most of the 2004 growing season, temperatures were below normal. From late June through most of August, a period of time that included most of the grain fill period, weekly temperatures were cooler than normal - as much as 4 to 7 degrees below normal in August. Cool night temperatures in 2004 may have reduced respiration losses during grain fill.

In parts of the Ohio this year where rainfall has been below average since mid June, the cooler than average temperatures were critical in minimizing what could have been severe drought stress if we’d had normal or higher temperatures. The cool temperatures may have also slowed the development of foliar diseases and insect problems.

So what’s the “downside” to these lower than average temperatures? Cooler temperatures (if they continue) could delay grain harvest and result in higher grain moisture. Growers may want to consider this possibility when they estimate fuel costs for drying grain. Cool temperatures have also been associated with certain ear disorders and reduced kernel set (“scrambled silks” or “silk balling” and “blunt ear syndrome”). However, these problems are usually uncommon and limited to certain hybrid genetic backgrounds.

This article contains information I’ve adapted and cited from the “Climate and Corn” section in Modern Corn and Soybean Production by R.G. Hoeft, E. D. Nafziger, R.R. Johnson, and S.R. Aldrich. (Published 2000. MCSP Publications, Champaign, IL).

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C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

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Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868


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