Originally published in Purdue Pest Management & Crop Production Newsletter (10 May 1996)

More Thoughts on Switching to Earlier Maturing Hybrids as Planting is Delayed

• Some Indiana corn growers may want to begin talking with seed dealers.
• Northern and eastcentral Indiana corn growers will be affected first.

(Author's note: This is another modified replay from the 1995 newsletter. When will it end?)

Rain systems moving across Indiana this past week continue to delay corn planting throughout Indiana. In fact, corn planting progress is now behind that of 1995 (which we thought was a terrible start to planting), with only 8 % of the state corn acreage planted as of May 5, 1996. Last week, I cautioned against getting excited about switching to earlier maturing hybrids. This coming week, some corn growers may want to begin talking with their seed dealers about possible replacement hybrid maturities IF planting is further delayed to the end of May.

Corn growers in the northern third of Indiana and eastcentral Indiana will be the first to face the decision of switching to earlier maturities if planting delays continue. These areas of the state historically accumulate fewer heat units or Growing Degree Days (GDD) during the growing season than other regions of Indiana. Delayed planting further reduces the availability of GDD for the corn crop and increases the risk of a crop not maturing before a killing fall frost. Furthermore, the rate of GDD loss with delayed planting increases as we approach June simply because the days are warmer.

The good news is that the corn plant adjusts its thermal requirements as planting is delayed. Based on research conducted from 1991-1994 by graduate research assistants Greg Brown and Tony Halter, under the direction of myself and Dr. Peter Thomison (Ohio State Univ.), we estimate that a typical corn hybrid's GDD requirements decrease about five GDD per day of delayed planting from late April - early May through at least the early part of June. This means that a 30 day delay in planting may result in a hybrid maturing in 150 fewer GDD (30 days times 5 GDD per day).

Let's set the scene by briefly defining what an adapted' full-season hybrid means for the different parts of the state. These definitions are mostly my interpretations, based on observations of the industry and my own experience. Since hybrid maturity ratings are not standardized across the industry, I've elected to define the full-season hybrids on the basis of Pioneer Hi-Bred Comparative Relative Maturities (CRM) and their approximate correlated GDD.

Based on our research and considering historical records of GDD accumulation throughout the various regions of Indiana, corn growers in northern and eastcentral Indiana should consider switching to earlier maturity hybrids by the last week of May. For the week ending May 26, I would recommend hybrids that mature 100 GDD fewer than the adapted' full-season hybrids you usually plant. For the week ending June 2, I would recommend hybrids that mature 150-200 GDD fewer than the adapted' full-season hybrids you usually plant. For the week ending June 9, I would recommend hybrids that mature 200-250 GDD fewer than the adapted' full-season hybrids you usually plant.

Corn growers in other parts of the state can avoid switching to earlier hybrid maturities until planting is delayed into early June. For the week ending June 2, corn growers in central Indiana should consider switching to hybrids that mature 100 GDD fewer than the adapted' full-season hybrids they usually plant. For the week ending June 9, I would recommend hybrids that mature 100-150 GDD fewer than the adapted' full-season hybrids they usually plant.

For the week ending June 9, corn growers in westcentral Indiana should consider switching to hybrids that mature 100 GDD fewer than the adapted' full-season hybrids they usually plant.

Growers in the southern third of Indiana shouldn't worry about switching to earlier maturities until the middle of June.

Return to the the Chat 'n Chew Cafe.

The Corn Growers Guidebook , a WWW resource for corn management systems in Indiana and the eastern CornBelt.

Purdue University Agronomy Extension WWW Home Page.

Purdue Agronomy On-Line! , Purdue's Agronomy Department WWW Home Page.

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