Q: What is the best way to get rid of (and then prevent) goosegrass in my fescue lawn?
A: Goosegrass is an annual grass just like crabgrass. It comes up from seed every summer but it germinates much later than crabgrass. Therefore, the pre-emergent herbicide that you might have applied in mid-March for crabgrass control will be gone from the soil by the time goosegrass is ready to sprout in May.
My advice is to first be sure your turfgrass is maintained properly so it grows vigorously and thickly. This is one of the best ways to combat any weed. If you have had goosegrass previously, apply a pre-emergent herbicide labeled for goosegrass/crabgrass control . Consider putting out two applications of pre-emergent each year: one in mid-March and one in early May.
If the goosegrass gets ahead of you, products containing sulfentrazone (click for sources) are labeled for grassy weed control in a lawn. You may need more than one application but read and follow the label.