"What to do with fields with poor plant populations is an urgent question now that all of the plants that are going to emerge have done so," says Joel Ransom, North Dakota State University Extension Service agronomist for cereal crops.
"For wheat fields with few or no plants in low-lying parts of the field, replanting only the affected areas is probably the best solution. Any advantage of using a different variety that might be better adapted for later planting is probably offset by other logistical considerations, so using the same variety that was planted earlier seems to make sense."
Decisions on when and how to apply herbicides and fungicides to fields with two distinct planting dates should be based on label restrictions, as well as product efficacy and logistical factors.
For wheat fields that have low populations throughout the field, replanting is recommended when the plant density falls below eight plants per square foot. Replanting should be done as soon as possible because yield losses can exceed 1.5 percent per day after May 15. When planting spring wheat after June 1, consider growing the earliest varieties that are available in addition to using a higher seeding rate.
For corn fields with poor stands, but few large gaps and no significant areas without any plants, use the publication "Estimating Yield and Dollar Returns From Corn Replanting" by R.L. Nielsen and published by the Purdue Extension Service to assist in planting decisions. The publication is available at www.agry.purdue.edu/ext/pubs/AY-264-W.pdf. This guide considers biological factors and economics to help the producer determine if replanting will be profitable.
Relative to small grains, corn is thought to be very responsive to plant populations. Nevertheless, corn does have the capacity to compensate when stands are suboptimal. For example, data from the central Corn Belt indicates that a half stand (14,000 plants per acre) planted in early May will yield about the same as a full stand planted at the end of May.
"If you decide to replant,in most circumstances, the original stand of corn should be destroyed before you do it," Ransom says. "Late-planted corn that grows next to early planted corn will be at a competitive disadvantage and very likely will not produce an ear.
Data suggest that destroying the original stand before replanting will improve the yield of the replanted crop by 10% However, if there are few plants in the original stand, there will be limited benefit from destroying these plants because the chance for plant-to-plant competition will be minimal.
Replanting should occur as soon as possible in order to minimize yield losses and limit the amount of moisture in the grain at harvest. Consider switching to a hybrid five relative maturity units earlier, now that June has arrived."
Source: NDSU Extension Communications