Corn School: Staging post-emergent herbicides

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The race is on for many corn growers as they hustle to apply post-emergent herbicides to control yield-robbing weeds.

The duration of the post-emergence application window depends on the herbicide. A product like glyphosate can be applied all the way up to the 8-leaf stage. But other herbicides have tighter timing and need to be sprayed in-crop at the 4 or 5-leaf stage or at 7 or 8 leaves, for example.

On this episode of the RealAgriculture Corn School, BASF technical development manager Rob Miller looks at three crop staging methods growers can use to determine whether the crop is in the correct development stage required to optimize their herbicide choice.

“That’s why it’s really important to know which herbicide you’re using and always check the label because they do vary in terms of crop leaf stage,” stresses Miller.

The primary method used to stage corn in Canada is the ‘leaf over’ method. In this case, growers need to count the leaves that have unfurled and rest horizontal to the ground. The coleoptile, the first leaf with the rounded tip at the base of the plant, is considered Leaf 1. From there, moving up the plant, growers can count the horizontal leaves to determine the leaf stage of the crop.

‘Leaf tips’ is another method that is less commonly used. Here growers can simply count the leaf tips starting at the base of the plant. As Miller notes in the video, it’s critically important to understand what method is being used to count leaves.

“In Canada, it’s important to understand that for our herbicide labels we reference the ‘leaf over’ method to get that timing right,” adds Miller. He points out that the same plant used in this video is at Leaf 6 using the leaf over method but when the leaf tips method is used the plant would be rated at Leaf 9.

Miller also explains the  vegetative or V stages method, which is predominantly used in the U.S. This method is based on counting leaf collars that are fully formed on the plant.

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