What is the purpose of preemergence herbicides in turf and when are they typically applied?

• A. To prevent weed seed germination by forming a chemical barrier.
• B. To kill established weeds.
• C. To improve turf color.
• D. To reduce soil moisture retention.

Answer: (A)

Preemergence herbicides work by preventing weed seed germination through a chemical barrier in the soil. They act on seeds that haven’t sprouted yet, so they won’t kill weeds that are already established. Because they rely on seeds not germinating, timing is critical: apply before the weed seeds are expected to germinate and then water in so the product moves into the root zone. In turf, that usually means applying before the typical germination window for the target weeds—often in late summer to early fall for cool-season grasses to curb winter annuals, or in late winter to early spring for warm-season grasses to curb summer annuals. The label will specify how long the barrier lasts and when to reapply. This purpose differs from killing established weeds, improving turf color, or altering soil moisture, which are not the goals of preemergence products.