Replant decisions are seldom clear cut. The ambiguity of these decisions arises from concerns over the adequacy of the remaining stand, the prospects of getting another crop started in time, the costs versus potential benefits, and limitations placed on replanting created by soil applied herbicides.
Although a correlation does exist between the number of healthy plants remaining in a stand, it is not a one-for-one relationship. If plants are removed or otherwise rendered non-viable, surrounding plants can take advantage of the extra space and resources and increase their yield. This is true if gaps in plants are scattered more or less randomly and if gaps occur early in the season (between VE and V3). Typically there is little justification for replanting if the stand remains above 75% of the original seeding rate, whereas if less than half of the expected population remains replanting is often necessary.
Where a substantial portion of the corn plants emerge late, due to heavy soil crusting or poor seed to soil contact, yield reductions are also likely. For VE to V1 plants which emerge more than 4 days after the majority of the crop, there is a high probability that they will act like weeds during the duration of the season and be barren at harvest.
The timing of a replant operation must also be considered. Because planting too late in the season may prevent the crop from having sufficient time to fully mature, a determination must be made regarding how quickly any necessary tillage and replanting can occur. While planting a short season hybrid can reduce the risk, it may also reduce the yield potential and result in a necessary ‘adjustment’ in your expected returns.
Besides a yield reduction that is possible from planting late in the season, there are costs associated with seed, tillage operations, and possibly additional herbicide applications. If replanting a field takes some of the time away from other essential tasks, those costs also need to be included in the calculations. Of course the market price of corn is the biggest factor.
Replanting a field to soybean could possibly be restricted by the type of herbicides used on the corn crop. Confirm by checking with the pesticide label if there are restrictions that could further delay planting.
One final note to keep in mind. Corn which has been damaged by hail or heavy winds and rain early in the season can become more susceptible to diseases as lesions are open to infection. Stands which have been damaged in this manner may require a fungicide application. The need for a fungicide will of course be determined by hybrid susceptibility and other risk factors associated with disease infections.
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