A lack of uniformity in plant heights typically means that the vegetative stages between plants vary. The severity of yield loss associated with uneven heights is dependent on the percentage of plants affected and how far behind they are. Although the field may look very poor, the yield loss may not be as severe as thought by the producer or agronomist. Use the following tools to assess what the estimated yield loss will be for your particular field.
First: Use the worksheet to derive the percentage of late plants you have and how many days they are behind the original stand. You will need to determine the growth stage of both the late and original plants. To do this, you may have to take an average for the late plants as there may be considerable variation. For example, if the late plants vary from V3 (third leaf) to V5 (fifth leaf); then use V4 in the chart.
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Second: Your calculations in the worksheet are now used in the figure to estimate yield loss. There are many arrows within the figure but it is not difficult to use if you have your worksheet filled out. First, use your (c) value to find the percentage of plants that are late on the x-axis. Because this figure is based off of research reports, we do not have every value available - so use what is closest. You will only look at the arrows directly above your x-axis value to estimate yield loss. Now, use your (e) value to find the arrow which is most similar in the number of days difference between the original and late plants. This arrow will then display the estimated yield loss you should expect from uneven corn heights.
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Text written for the ISU Corn Production website in October 2006.