by Alix Carpenter, Agronomy Specialist, University of Missouri Extension
With planting delayed by wet soils, and replant being necessary in some cases, the effect of planting date on yield should once again be reviewed.
There is still time to plant a successful corn crop this year. University of Missouri Extension research (based on four years of data collected through 2011) indicates that in northern Missouri, corn planted on May 11 can be expected to yield 89 percent of normal, planted May 16 86 percent of normal, May 21 83 percent of normal, May 31 77 percent of normal, and June 5 75 percent of normal.
In some cases, replanting is necessary. When replanting, planting into sparse, existing stands is not recommended, as plants of uneven size and maturity perform poorly. Existing stands (the entire field, or those portions which merit replanting) can be removed with the use of herbicides or tillage. The potential production from a reduced stand should be compared to the cost of replanting combined with the potential for reduced yield potential for a later planted crop. There are several factors to consider when evaluating a stand: the cause of the sparse stand, the stand density (and condition of the remaining stand), the estimated yield potential and expected gross revenue of the sparse stand, the estimated cost to replant, the estimated yield potential and gross revenue from a replanted stand, and will the replanting pay for itself?
To determine stand density, count the number of live plants: 1/1000th of an acre is 17 feet five inches of a row (at 30 inch spacing), 26 feet two inches of row (at 20 inch spacing), or 34 feet ten inches of row (at 15 inch spacing).
University of Missouri Extension research now indicates that in 30 inch rows, corn at a population of 26,000 plants per acre will yield 90 percent of normal, at 24,000 plants per acre 95 percent of normal, at 22,000 plants per acre 92 percent of normal, at 20,000 plants per acre 87 percent of normal, at 18,000 plants per acre 72 percent of normal, at 16,000 plants per acre 67 percent of normal, and at 14,000 plants per acre 62 percent of normal. These estimates are for normal yield environments; in high yielding environments (those which consistently produce yields of 200 bushels, or more, per acre), populations are higher.
The decision to replant is straightforward to make in fields (or portions of fields) which have crusted to the point where seedlings will not emerge, or where water has been standing for four days or more, or where germinating corn was exposed to low temperature water. In some cases the variables make such decisions more difficult; in such a situation, the MU Extension replant worksheet can assist with organizing pertinent information and making an informed decision regarding replanting. This tool takes into account the costs associated with replanting (seed, fuel, machinery, labor, pesticides, and other costs). The worksheet can be obtained at your local University of Missouri Extension office (ask for guide G4091); interactive worksheets are available online at http://extension.missouri.edu/scripts/explore/g04091.asp.