Dandelion (Taraxacum officinale) 

Dandelion is particularly vigorous in cold-winter climates. It grows from a deep, fleshy taproot and spreads by windborne seeds. Flowering begins in spring and often continues until frost.

A healthy lawn can outcompete dandelions, so thicken the turf by overseeding and by proper fertilizing, watering, and mowing.

Pull dandelions while they're small, before they produce a taproot and set seed. Once the taproot has formed, you must remove all of it, since new plants can sprout from even a small piece. A dandelion weeder with a forked blade is helpful, or use a hand weeder with a bent shaft.

For chemical control, use a selective postemergence herbicide labeled for dandelions in turf.