What is a post-emergent herbicide and give an example used in rangeland?

• A. A post-emergent herbicide is applied after the target weed has emerged; example glyphosate.
• B. A post-emergent herbicide is applied before weeds germinate; example atrazine.
• C. A post-emergent herbicide is always soil-applied; example trifluralin.
• D. A post-emergent herbicide only affects woody plants; example 2,4-D.

Answer: (A)

A post-emergent herbicide is applied after the weed has emerged and is visible, typically targeting actively growing foliage so the chemical moves inside the plant to kill it. In rangeland, glyphosate is a classic example: it’s applied to the green, growing plants and is absorbed through the foliage, then translocated to growing points to stop the plant’s development. This makes it effective for clearing patches or establishing desired species because it works on weeds that are already present.

Think about why the other statements don’t fit post-emergence. Pre-emergents are used before weeds germinate, which is the opposite timing. Some post-emergents are applied as foliar sprays rather than strictly to soil, and many are systemic, moving within the plant rather than staying on the soil surface. The idea that a post-emergent only affects woody plants isn’t right, since many post-emergents target a range of broadleaf or herbaceous weeds, not just woody species.