Assessing Need for Replanting Corn

I have received a couple of questions on how to take stand counts and with the storm damage and recent weather conditions decided to highlight some information from UNL’s CropWatch website on Time to Dig In and Assess Need for Replanting Corn written by Roger Elmore, Extension Cropping Systems Agronomist and others. First, let’s review how to take stand counts. In short, after you know your row width (inches), there are given numbers that correspond to row width you will need to measure and count the plants in a row and multiply that by 1000 to calculate plants/acre. For example, most corn in our area is planted into 30-inch rows. The row length in feet to equal 1/1000 of an acre is 17’5” so you would measure out 17’5” in a row, count the number of corn plants in that length and multiply is by 1000. This would tell you how many plants/acre you have in that row.  Do this several times in the field.

After you have your average plant populations, calculate the losses from planting to final stands. University research trials suggest 4-7% is typical, but final stands are within 1-4% of seeding rates for top managers. If your attrition losses are 10% or more, examine what happened. Elmore and others suggest considering the following: seed viability, insect such as cutworms, wireworms and white grubs, diseases, compaction and soil crusting and cold soils.  One should also scout for weed management issues. Scout weeds within two weeks of corn emergence to evaluate efficacy of burn down and pre-emergence herbicides. Early emerging weeds such as marestail should be controlled early on to avoid early-season competition.

After examining these factors, one must decide if replanting is necessary. For example, if plants have emerged but have variable heights or development, even though a yield reduction is possible, it’s not necessarily a reason to replant. Plant height differences may reflect lack of uniformity in emergence timing or other issue the plant faced. Replanting may however be necessary with reduced planting populations. The most important factor in deciding whether to replant is to calculate expected yield with the current stand versus what you could potentially have if you replanted. Finally, one must estimate the replanting costs of seed, fuel, additional pesticides and labor. Also, be sure to contact your crop insurance agent, Farm Service Agency and others with an interest in your crop.

The full CropWatch article provides more information and some useful tables to help you with your consideration of replanting.

(Source: cropwatch.unl.edu, article Time to Dig In and Assess Need for Replanting Corn by Elmore, Jackson-Ziems, Grassini, Jhala, & Wright)