By Bob Kratochvil, Extension Specialist
University of Maryland, College Park
This spring, many producers west of the Bay have had planting delays caused by rain. The optimum planting window west of the Bay is between April 25 and May 15 with yield declining after that. As we near the end of that window, corn growers are likely asking if they should swap longer season hybrids for shorter season hybrids. The quick answer to that question is no, at least not yet. Hybrids have an ability to respond to a range of planting dates. They do so by adjusting the amount of time in vegetative and reproductive development either more or less depending on the planting date and the relative maturity of the hybrid planted.
Researchers at Purdue and Ohio State Universities (Nielsen and Thomison, 2003) studied the response of three hybrids with relative maturity (RM) ratings of 106, 111, and 115 days across three planting dates defined as early (April 25-May 10), mid (May 20-June 1), and late (June 10-15). After planting, they measured the time required to reach three developmental stages: (1) the number of days from planting to silk (R1); (2) the number of days from silk to physiological maturity (R6), and (3) the number of days from planting to physiological maturity. These measurements determined how hybrids vary in their (1) vegetative (V stages), (2) reproductive (R stages), and (3) complete growth and development based on the planting date. The research determined the following.
First, as planting date was delayed, the period between planting date and silk shortened. In other words, the vegetative growth period was reduced the later the planting date. Averaged across the hybrids, days from planting to silk were 75, 66, and 61, respectively, for early, mid, and late planting dates. The exact number of days for each hybrid differed based on their relative maturity (more for longer season, less for shorter season), but the downward trend was consistent for each hybrid.
Second, when planted late, all hybrids had an increase in the number of days between silk and physiological maturity. The actual number of days between silk and physiological maturity varied by hybrid and by planting date. However, averaged across the hybrids, days from silk to physiological maturity were 63, 66, and 68, respectively, for early, mid, and late planting dates. The longer season (115 RM) hybrid fluctuated by only 1-2 days in the time needed to go from R1 to R6 over the three planting dates; whereas the 106 and 111 RM hybrids had greater variation for this measurement. As planting was delayed, the 106 and 111 RM hybrids took up to 5 days longer to go from R1 to R6 compared with their early planting date response.
Third, for all hybrids, the change in length of time from planting to silk was greater than the change in amount of time from silk to physiological maturity. In general, the reduction in time spent in vegetative growth compensated for the increased time spent in reproductive growth. The study found that the response to delayed planting was a gradual shortening of the time spent in vegetative growth up to 14 days for the latest planting date coupled with a gradual increase in reproductive growth up to 5 days for the latest planting date. On average, the hybrids adjusted to the shorter growing season with a reduction of 9 days from planting to physiological maturity. It is clear that hybrids compensate primarily by shortening the time necessary to reach silk when planting is delayed.
At this point in time I recommend planting the hybrids that you selected for this year. If wet conditions continue, you will eventually have to consider how much growing season you will have before your average date of first frost. You do want to have your corn at physiological maturity by that date. For most of Maryland, we typically have an adequate number of growing degree days to easily get corn hybrids with 113-115 day RM to physiological maturity even if they are planted as late as June 1. If you will be planting your corn after that date, you should consider getting some shorter season hybrids.
R.L. Nielsen and P. Thomison. 2003. Delayed Planting & Hybrid Maturity Decisions. http://www.agry.purdue.edu/ext/pubs/AY-312-W.pdf