Post-frost stand assessment

Contributed by Robert Moloney, NK Brand Seeds

While I don’t expect that there will be a lot of fields with a significant number of plants killed by the May 9/10 frost, there will probably be a few low lying or muck fields with some stand loss. Since it’s still (relatively) early in the planting season some growers may be wondering if it’s worth replanting the field. Here are some points to consider:

1- get an idea of how many plants are dead or so severely damaged that they won’t come back (see previous articles). By now you will likely be able to see some signs of new growth on plants that are recovering. While the dead leaves may cause some leaf trapping, most of the time the plant will push through it given some time.

2 – do you still have an even stand? Moderate damage spread evenly through the stand may have more yield potential than less damage that leaves 3-4 foot gaps in the row. Depending on the field layout it may also make sense to replant only worst damaged part of the field.

3 – what plant population do you have remaining? Count 1/1000th of an acre and multiply by 1,000 in a number of spots to get an average population for the field.

Once you have a population estimate and if the stand is reasonably even over the whole field, the following table will give you an idea of what yield potential to expect with different combinations of planting date and final plant stands. Realize that these numbers are an estimate and will be influenced greatly by a number of factors other than final population and planting date (see below).

As an example if you planted on April 25th expecting a yield of 150 bu/ac and ended up with a final stand of 15,000 evenly spaced plants per acre after the frost, your yield potential is likely 150 bu/ac X 79% = 118.5 bu/ac. If you replant on May 19th and end up with a final stand of 30,000 plants/ac your yield potential is 150 bu/ac X 97% = 145.5 bu/ac. This means that theoretically if you can replant for less than the value of 27 bushels of corn (144.5 – 118.5 = 27 bushels) you should come out ahead.

This chart is a really simplified calculation that doesn’t take into account all the factors involved in replant. Some other things to consider:
– later planting increases the risk of higher moistures/higher drying costs at harvest.
– later planting exposes you to more risk of a fall frost damaging the crop before maturity (potentially resulting in higher drying/lower grades).
– if you move to a shorter maturity hybrid for the replant you will likely give up yield potential versus the longer maturity hybrid you originally planted.
– if the current planting conditions aren’t as good as the original (and this year it would be pretty tough to beat the early conditions), you may give up yield potential because of this.
– if it turns into a dry summer the earlier planted corn will likely have a better root system to deal with drought conditions.
– don’t forget to include the cost of killing the original stand. Thickening won’t work well in corn most of the time due to maturity differences and the fact that the uneven staging between the original plants and the replant plants means both stands become a weed to each other.
– pay attention to any herbicides that may have been applied already. Depending on the product you may end up with crop damage or loss of residual control from any tillage or coulters on the planter from a replant.

Since making a decision on a frosted (or otherwise damaged crop) can be an emotional issue, make sure you get a second opinion from your NK dealer or another competent authority before you do rip up the original stand. While it may look ugly, often the 1st stand will result in you coming out ahead at harvest.

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