NCSU Turfgrass Centre, Turffiles.NCSU.edu
Speedwell is a low-lying weed that grows mostly in the winter and thrives in open turf where it grows more upright as it matures. It covers the ground and produces round and toothed lower leaves and pointed upper leaves. It also blooms small bright-blue flowers with white in the middle; the seed pods grow below the flowers. This weed doesn't tolerate warm temperatures very well and will usually die off not long after flowering.
To get rid of speedwell weeds, increase your turfgrass density. You'll need to minimize the amount of open turf in your yard by mowing, fertilizing and irrigating regularly. It's best to use a pre-emergent herbicide before the winter as this weed will emerge by then. Apply a broadleaf herbicide in the late summer or early fall before it has a chance to germinate and spread.