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Know Your Corn Staging Methods
Canada - January 15, 2001
There's only a certain window of time when the growth stage of the weeds and the crop are appropriate for optimum control. To get all your acres sprayed within the optimum crop stage, you'll need to be familiar with corn staging and especially the different methods used.
- Most of the Ontario research work on the "critical weed free period" bases leaf staging on the time the tip emerges from the whorl of the corn plant.
- In OMAFRA Publication 75, however, corn leaves are counted on the "leaf over" basis. In this system a leaf is counted once it has emerged far enough out of the whorl to no longer stand vertical but begins to arch and the end of the leaf blade leans over.
- The "collar" approach (used predominantly in the U.S.) counts a leaf only when it is completely out of the whorl. Using this system there is perhaps less ambiguity as to whether a leaf "tip" has actually emerged from the whorl or if a leaf is in the "leaf over" position.
Comparing systems
| If using the... |
the critical weed-free period is from... |
| Leaf tip method (as per Swanton research) |
4 to 10 leaf stage. |
| Leaf over method (as per Publication 75) |
3 to 8 leaf stage. |
| Collars method (i.e. V2 stage) |
2 to 6 leaf stage. |
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The key point is that when discussing corn growth stages and leaf numbers in the critical weed free period, be sure everyone is talking about the same system. And remember:
- The same rain that shuts down post spray operations can activate soil-applied herbicides.
- A soil-applied pre-plant herbicide helps reduce the difficulty in staging and scheduling large acres of over-the-top post spraying.
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