Corn Replant Decisions Based on Maturity Zone, Plant Stand, Planting Data, and Hybrid Characterization.

Early planting and unfavorable weather afterwards can result in poor emergence and final plant stands that are much less than satisfactory for high yields.  In these cases, a decision must be made whether to replant or not.  Accurate decisions based on planting dates and existing plant stands are needed to ensure profitability.  We hypothesize that the decision to replant will not only depend on the plant stands and planting dates, but also on the maturity zone and hybrid.  Our main objective was characterize popular, modern corn hybrids for sustaining grain yields despite low plant populations or when planting late in the season.  Each hybrid was traited by their respective seed company with ear development as “fixed” or “flex” type.  The first experiment was conducted in three maturity zones across Ontario, Canada, for four years between 2006 and 2009, for a total of 12 location-years.  At each location, eight corn hybrids were planted at three different timings (early, normal, late) and thinned uniformly to five different plant populations.  In Experiment Two, multiple hybrids were planted at three locations during two years with different mixtures of conventional and glyphosate resistant seed.  In addition, full-season adapted hybrids were compared with shorter-season hybrids for late planting.  The corn performance data generated from artificially-created but realistic variable plant stands in Experiment Two validated work from Experiment One, where corn populations were uniformly spaced (it has been argued that these uniform stands did not reflect field conditions of variability).  Hybrid ear characteristics of “flex” vs. “fixed” was not a factor in replant decisions.  On average, replanted yields were higher than those recommended to producers in Ontario via earlier work from Illinois.  Planting a full-season hybrid in early June resulted in grain moisture 4-6% higher than planting an earlier hybrid.  The replant decision was highly dependent on planting date, plant population density of the early planting, and the hybrid.