Rain systems moving across Indiana this past week continue to delay corn planting throughout Indiana. With only 17% of the state corn acreage planted as of May 7, Indiana's 1995 corn planting season is currently among the four slowest in the past 12 years. 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).
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' hybrids you usually plant. For the week ending June 2, I would recommend hybrids that mature 150-200 GDD fewer than the 'adapted' hybrids you usually plant. For the week ending June 9, I would recommend hybrids that mature 200-250 GDD fewer than the 'adapted' 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' hybrids they usually plant. For the week ending June 9, I would recommend hybrids that mature 100-150 GDD fewer than the 'adapted' 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' hybrids they usually plant. Growers in the southern third of Indiana shouldn't worry about switching to earlier maturities until the middle of June.
