Why is weed control so important during early season planting?

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Early control of weeds is important as it protects the potential yield of crops, especially corn which is not very competitive. Weeds and corn require the same resources, such as water, sunlight, and nutrients. Weeds that are small and young are easier to control and can absorb and move herbicides more effectively. Later applications of herbicides can be less effective during heat and drought conditions. A sequential weed control program that involves the use of pre-plant and post-emergence herbicides generally provides the most consistent and reliable results.


Critical Period of Weed Control

  • Defined as the growth stages or time during which weeds must be controlled to maintain maximum yield potential (assumes field is clean at the time of planting).
  • In Western Canada, weeds can reduce corn yield starting at emergence, so controlling weeds from before the VE (emergence) stage of corn to V6 (6-leaf stage) is recommended.
  • After this stage, the corn is generally too tall and susceptible to glyphosate herbicide injury.
  • Controlling weeds is essential for minimizing competitive effects and preventing weed seed production.

Photo - Field infestation of wild buckwheat and lambsquarters. June 27, 2018. Southern Alberta.


Illustration - Critical Period of Weed Control in Corn (VE-V6)

Critical Period of Weed Control in Corn (VE-V6).


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