In rangeland pest management, what is a 'pre-emergent' herbicide and when is it applied?

• A. A herbicide placed in the soil to prevent weed seed germination; applied before weed emergence, often to control annual grasses.
• B. A herbicide that is applied after weeds have emerged.
• C. A weed-control method that does not involve chemical herbicides.
• D. A herbicide used to promote weed germination.

Answer: (D)

Pre-emergent herbicides are soil-applied chemicals that create a barrier in the topsoil to stop weed seeds from germinating. In rangeland management, they’re applied before the weeds start to emerge, timed to the season when target annual grasses are about to sprout. They act as the seedling never gets past the germination stage, and they don’t affect weeds that are already growing. This is different from post-emergent herbicides, which are used after weeds have emerged. The description that fits this idea is a herbicide placed in the soil to prevent weed seed germination and applied before weed emergence. The notion of promoting germination is the opposite of how these products work.