By Mike Witt
With another planting season comes the inevitable situation of Mother Nature creating a headache for some farmers. The best plans of any farmer can be dashed by too much rain, wind, hail or frost. But the decision-making process on replanting a corn crop cannot be made hastily or on looks alone. The normal reaction, after a bad weather event has occurred, is to run to the planter and “fix” what is broken or lost in the fields. This natural tendency to jump first should be avoided and replaced with analysis and strategy. Taking a deep breath and evaluating the replant decision-making process will help get the maximum yield out a bad situation and not compound the losses.
The real-life decision-making scenario described below is one a farmer may face in Iowa this spring. A field of corn was planted on May 2 with population of 35,000 plants per acre at 30-inch row spacing. A storm struck the field May 18 and has reduced the stand to 20,000 plants per acre. A decision is to be made to replant the field on May 23 or to keep the field as is. The following steps outline how the decision to replant should be determined to help maximize profits from this bad situation.
Step 1. Determine the remaining plant population or stand in the field
Calculating plant population is an easy first step to survey actual damage done to the field on a large scale. Select several “random” areas of the field to determine the existing population. Use a zig-zag pattern and avoid taking all of the measurements in the worst area of the field, as it will not be a good representation of the field as a whole. Count the surviving plants in the affected field at the given distance in Table 1 for your row spacing. Multiply your number of “good” plants by 1,000 to get your population, and take the average of sampled random areas. In this scenario, we determined that the new plant stand has decreased from 35,000 plants per acre to 20,000 plants per acre.
Step 2. Determine the expected yield potential of your remaining stand
By using Table 2, farmers can get a fair yield estimate from the population determined and the planting date. This estimation is represented as the relative yield potential from maximum yield potential at original planting. In the scenario, the original planting date of May 2 with a population of 35,000 plants per acre resulted in a 100% yield potential. With the population reduction to 20,000 plants per acre, with the planting date of May 2, the yield potential has now been reduced to 89% of maximum.
Step 3. Estimate your replant yield
Using Table 2 also allows determination of the potential for yield in a replant situation. Continuing our scenario, the replanting at 35,000 plants per acre on May 23 would result in about 87% of maximum yield. Compare this to the original crop, which was planted May 2 and has an existing population of 20,000 plants per acre, and an expected yield of 89%. Thus, the expected yields are 89% of maximum for the original plants versus 87% for a replanted stand. Other important factors to note are there is no guarantee of getting a good stand with replanting. Also, insect and disease pressure may be greater, and the chance of fall frost damage is higher for late-planted corn.
Step 4. Estimate the cost of replanting fields
Replanting a field, regardless of the scenario, is a costly endeavor and usually the deciding factor for farmers. Some things to consider include seed costs, tillage, fuel (for tillage and planting), additional pesticides, labor, time, etc. Another important factor is to consider the hybrid that was originally planted will potentially not be the same as the replant. A shorter-day hybrid may be needed, which can cause unevenness within the fields with plant stature, flowering time and harvest maturity. These cost versus potential yield estimations are key in the decision-making process.
In the scenario discussed here, the decision to replant or not seems clear. However, the decision is still ultimately based on what level of cost versus yield potential a farmer is comfortable with. Numerous factors determine a field's yield potential, and the tables and scenario presented should be used as a guide in the decision-making process. It’s important to understand that actual yield losses may be greater or less than what is shown, but the general ranges and principles hold true.
Decisions on replanting a stand are never a “one-size-fits-all” scenario. However with proper scouting, evaluation of actual stand losses and understanding yield potential available in fields, a farmer can make the best of a bad situation. Leaping before looking is not a sound practice for those who wish to be successful in farming or life.
Witt is the ISU Extension field agronomist in west-central Iowa. Contact him at [email protected].