Making corn replant decisions

Now is the time when corn producers should be out in their fields assessing stands to determine if replanting is necessary. Replant decisions are never easy and are ultimately determined by which decision provides the greatest net income. Each field will have its own set of circumstances that will influence the decision. Remaining stand level and likely replant date will be the key issues.

Recent thunderstorms have wreaked havoc on localized areas across the state. Some brought high winds, heavy rain, and hail. Once again, stand assessment will be important to determine if the damage will be economic. Young corn plants (<V5 stage of development) can tolerate significant leaf damage and loss and yet remain viable and produce new leaves. This is because the growing point remains below the soil surface until approximately the V6 stage. However, flooded areas in fields also may cause stand losses. Small corn plants are not tolerant of flooding and may succumb to this condition in one to three days. Warm, sunny days may accelerate these losses. Soybean shows slightly better tolerance to flooding but still will not tolerate this condition for very long.

Corn damaged by early season hail.
Flooded field.

The table shows the most recent data on stand levels and planting dates. Although season, location, hybrid, and other factors may cause some variation in the data, the information in the table will serve as a good starting point for making replant decisions.

Attempt to "thicken" a thin stand of corn.

Attempts to "thicken" stands by interseeding directly into an existing stand generally result in additional complications. Larger plants compete strongly for space, water, and nutrients and complicate subsequent management decisions. Thus, it is always recommended that if a replant is warranted, destroy the original stand and start over. If the original stand is adequate, leave it alone and be willing to accept it as is.

Another major consideration that goes hand-in-hand with making a replant decision is whether or not a hybrid change is needed or perhaps a change to an alternate crop such as soybean. Switching to an earlier maturing hybrid can be done at any time if so desired. Hybrid and planting date studies, however, show an advantage to switching to a hybrid that is roughly five days earlier in maturity if planting is delayed beyond May 20 and another five days earlier if delayed beyond June 1. Switching to soybean generally will not be an economical choice unless planting is delayed beyond June 10.

Corn yield at various planting dates and stand levels, expressed as a percentage of the optimum stand and date.

Planting date
Established stand* April 20-May 5 May 20 June 1 June 10
(% yield)
26,000 to 30,000 100 90 81 67
22,000 96 86 78 64
18,000 91 82 74 61
14,000 80 72 65 54
10,000 65 59 53 44

*Assumes reasonably uniform stands.

This article originally appeared on page 91 of the IC-480(12) -- June 1, 1998 issue.

Updated 05/31/1998 - 1:00pm