When should pre-emergent herbicides be applied for turf weed control?

• A. After weeds have germinated.
• B. Prior to weed seeds germinating.
• C. During heavy rainfall.
• D. Only in summer.

Answer: (B)

Pre-emergent herbicides create a chemical barrier in the soil that stops weed seeds from germinating or early seedlings from establishing. Because they act on seeds as they try to sprout, they must be applied before germination begins. If weeds have already germinated, the barrier won’t save them, so the product won’t provide effective control. Timing is tied to when weeds are expected to emerge and to the product’s label, and often requires irrigation to activate the barrier after application. Applying during heavy rainfall can wash or dilute the product and reduce efficacy, and limiting applications to summer misses the common emergence windows for many turf weeds. So the best practice is to apply before weed seeds germinate.