• Timely planting is critical for high corn yield. However, delayed planting is common when rainfall occurs near the intended planting time. This is especially problematic in the Upper Midwest due to the relatively short growing season and abundance of fine-textured soils.
• When corn planting is delayed, it is essential to know whether the hybrids intended for planting are of appropriate comparative relative maturity (CRM) for economically viable grain production, or whether they should be replaced with earlier-maturity hybrids to ensure corn reaches physiological maturity within the remaining growing season and has adequate time for drying prior to harvest.
• Advances in corn breeding and genetics have resulted in widespread release of hybrids with more rapid late-season dry down of grain, creating a need to reassess corn response to planting date. The objective of this study was to conduct an analysis of recent corn planting date trials conducted by researchers at the University of Minnesota.

• Grain yield and grain moisture content at harvest were obtained from corn planting date trials conducted over 26 site-years:
  • Sites: Crookston, Lamberton, Morris, and Waseca, MN
  • Years: 2009 to 2016
  • Planting dates: April 8 to June 16
  • Hybrid CRMs: 74 to 109
  • Grain yield: 87 to 251 bushels/acre
  • Grain moisture at harvest: 11 to 35%
• Each trial had at least three hybrids of differing CRM planted on at least three dates in four replications. Hybrids were categorized as early, mid, or late maturity based on the CRM and trial location (Table 1).

Table 1. Comparative relative maturity (CRM) of early-, mid-, and late-maturity hybrids included in planting date studies from 2009 to 2016.

• Relative grain yield was calculated as a percentage compared to the planting date and hybrid with maximum grain yield in the same site-year.
• Partial economic net return was calculated as gross return (grain yield × $3.50/bushel) minus drying cost ($0.045/bushel for each point of grain moisture above 15%).
• Data were analyzed by hybrid maturity group across all 26 site-years.

• The site-years and the hybrids included in this study represent a wide range of possible growing environments and hybrids for the Upper Midwest.
• Relative grain yield produced regression equations with better fit compared to grain yield and it allows results to be easily applied to growing environments with differing yield potential.
• Relative grain yield was greatest when planting occurred between April 16 and May 16 for mid- and late-maturity hybrids, and between April 28 and May 23 for early-maturity hybrids (Figure 1).
• For all hybrid maturity groups, relative grain yield declined rapidly when planting was delayed beyond May 25 (Figure 1). Late-maturity hybrids produced greater relative grain yield than mid-maturity hybrids when planting occurred prior to June 4.
• Early-maturity hybrids produced less relative grain yield than mid-maturity hybrids at all planting dates (Figure 1). Relative grain yield with early-maturity hybrids was also most negatively impacted by early planting (before April 23).

• Grain moisture at harvest was greatest for late-maturity hybrids and least for early-maturity hybrids (Figure 2). Grain moisture at harvest was least when planting occurred on May 20 or earlier, and it increased by 3 to 6 percentage points when planting was delayed until June 13.
• When planting was delayed beyond May 20, grain moisture at harvest increased more rapidly for late- and mid-maturity hybrids compared to early-maturity hybrids (Figure 2).

• Greatest partial net return occurred with late-maturity hybrids planted on May 10 or earlier, and with mid-maturity hybrids planted on April 21 or earlier (Figure 3). From April 24 to May 29, late-maturity hybrids produced greater partial net return than mid-maturity hybrids.
• Early-maturity hybrids produced the least partial net return when planting occurred prior to May 17 (Figure 3). From May 17 to June 2, partial net return did not differ significantly between early- and mid-maturity hybrids.
• When planting was delayed beyond June 9, early-maturity hybrids produced greater partial net return than late- and mid-maturity hybrids (Figure 3).

• This study confirms the importance of timely planting and appropriate hybrid CRM selection for corn grain production.
• Greatest economic net return after drying occurred with late-maturity hybrids planted on May 10 or earlier, and with mid-maturity hybrids planted on April 21 or earlier. Late-maturity hybrids produced greater net return than mid-maturity hybrids when planting occurred between April 24 and May 29.
• When planting was delayed beyond June 9, early-maturity hybrids produced greater net return than late- and mid-maturity hybrids. However, corn planted in June in the Upper Midwest is at high risk of freezing in the fall before reaching physiological maturity and having high grain moisture at harvest.