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Check growth stage of plants, not height

Three things became evident while checking plant-
to-plant spacing in
Indiana Prairie Farmer/
Precision Planting plots last summer at the Purdue University’s Throckmorton Research Center. These three discoveries could help you make better management decisions.

First, plants that get a slow start tend to fall behind in maturity. “The plots where seeds were planted 1 inch deep came up last and never caught up all season,” says Jeff Phillips, Tippecanoe County Extension ag educator.

Indeed, by late June when plant spacing was measured, some plots were already pushing the V7 growth stage, while plants in plots with seeds planted 1 inch deep were still at five leaves, some at four.

Since the growing point stays belowground until about the fifth leaf stage, that means some growing points were belowground and some above. The only difference was how deep the seeds were planted. Plots were planted May 27.

Key Points

Pay attention to growth stage, not plant height, when applying herbicides.

Maturity of plants that get a slow start may lag behind all season.

Height can be deceiving — it’s growth stage that counts.

The plots with seed planted 1 inch deep yielded 20 bushels less than plots planted 2 inches deep, and 25 bushels less than plots planted 3 inches deep. That’s significant.

Second, height doesn’t always signal growth stage. Differences of as much as a foot in extended height might come from two plants only one growth stage apart. This is why many herbicide companies label herbicides by growth stage, not plant height. Most list a maximum vegetative stage when herbicides can be applied. Depending on how fast or slow plants grow, there may be several inches difference in height at the same growth stage.

Fast growth

Once plants reach the V6 or V7 leaf stage, meaning six or seven leaf collars are exposed, they grow rapidly. Experts refer to this as the grand growth phase. That was obvious from observations made in the plot field last summer.

“If you still need to get nitrogen on, or make herbicide applications, and the weather is warm with enough moisture for growth, you need to pay close attention to growth stage,” Phillips says. “The corn can pass from one growth stage to another faster than you think.”

How do you determine growth stage?

Your best guide to determining growth stage for corn is the Corn & Soybean Field Guide published by the Purdue University Crops Diagnostic Training Lab. 2011 editions are now ready to purchase. Visit

As noted in the guide, there are two methods. The most common method used today is the leaf collar method. If the leaf collar is visible near the stem, then the leaf counts. A plant with three leaf collars exposed would be at the V3 growth stage.

Some people still use the droopy corn method. It tends to overestimate young corn by about one growth stage. Be sure you know which method is indicated on herbicide labels if you’re making determinations related to potential spray applications.


Side by side: Daniel Bechman, plot assistant, holds plants from adjoining plots at different growth stages. The shorter plant got off to a slow start due to shallow planting.

This article published in the February, 2011 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.