Corn School: How to count leaves for herbicide timing


Proper staging is critical when applying in-crop herbicides in corn, but there are multiple ways to measure corn’s growth stages, and herbicide labels don’t always use the same method.

Agronomists often use the “leaf collar” — or V-stage — method to describe growth stages, while others use plant height. However, herbicide labels often refer to slightly different methods that involve counting leaves.

Many product labels use either the “leaf over” method or the “leaf tip” method, explains Jeanette Gaultier, senior technical services specialist with BASF, in this episode of Corn School.

As she demonstrates in the video below, the leaf over method involves counting the number of leaves, starting from the coleoptile leaf with the rounded tip at the bottom of the plant, to the last leaf that is bent over, with its tip pointing down. Less mature leaves that are still pointing up are not counted.

For the leaf tip method, all the leaves are counted, including any leaf tips pointing up from the whorl at the top of the plant, explains Gaultier.

The leaf collar method, meanwhile, involves counting the number of leaves with visible collars, starting from the coleoptile all the way to the last leaf with a visible collar.

Wind, dry conditions, frost, and other stressors — all of which have been seen in Western Canada in 2021 — can cause lower leaves to fall off, but those leaves should still be counted to determine the crop’s physiological stage, notes Gaultier.

Check out this Corn School episode with Jeanette Gaultier for more on corn staging, and weed control strategies for corn in Western Canada:

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Corn School (view all)Season 10 (2021) Episode 20

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