Sometimes, plant stands are reduced by disease, herbicide injury, hail, insects and flooding. If crop insurance covers the damage, consult the insurance agent before taking action. When all plants of a field are lost, it is realistic to replant if adequate growing season remains for the crop to mature. Areas of fields may be replanted while leaving the remainder of the field as is, and areas of inadequate stands can be thickened by interplanting additional seed. If the stand loss is random or erratic throughout the field, a stand count should be taken to determine the number of plants remaining. For dark soils, do not interplant more seed unless the number of plants per foot of row is less than 45 percent of the recommended seeding rate for the date on which replanting could be accomplished (see Table 5-4). For light-colored soils, do not interplant unless the number of plants per foot of row is less than 60 percent of the recommended seeding rate for the date on which replanting could be accomplished.
For example: A stand count reveals that for most of the field there are about 1.5 plants per foot of 7.5-inch row. The date is June 10 and a replanting can be made on June 15 when the recommended seeding rate for 7.5-inch wide rows is 2.8 seeds per foot of row. If the soil in the field is dark in color and good vegetative growth is anticipated, then replanting would likely not be profitable. However, for a field with light-colored soil or where plants will likely be small, interplanting may be warranted and the interplant rate should be 1.65 seeds per foot of row. That replant rate is the difference in the current stand and the recommended seeding rate for the date on which the interseeding could take place, plus about 10 percent to compensate for the plants killed while interplanting. For example:
The recommended seeding rate for June 15 is 2.8 seeds per foot of 7.5-foot row.
There are currently 1.5 plants per foot of row.
2.8 seeds per foot - 1.5 plants per foot = 1.3 plants per foot of row needed.
1.3 seeds per foot X 110 % = 1.43 seeds per foot of row or about 100,000 seeds per acre or 40 pounds of seed if there were 2500 seeds per pound.
If low plant populations are due to root rot diseases, the guidelines for replanting also include planting a variety with disease resistance genes or partial resistance plus the use of a fungicide seed treatment.
Table 5-4: Suggested Seeding Rates for Combinations of Planting Date, Relative Maturity and Row Spacing.
*For good growth environments these seeding rates can be reduced to 75 percent of the table values, and for poor growth environments, they should be increased by 30 percent of the table values.