There are three groups of weeds commonly found in lawns, and each group contains weed types that are invasive. The first group is grasslike weeds (they look similar to blades of grass). The second group of weeds found in lawns are called grassy weeds. They look similar to grass, but have thicker leaves. The third group consists of common broad-leafed weeds, which have rounder leaves.
Nut sedge is a grasslike weed. Although it looks very similar to desirable grasses, it grows a lot faster than lawn grasses do, making it easy to spot in a yard. Nut sedge is a perennial weed that will return year after year, quickly choking out your desirable lawn grass. It can reproduce through seeds or its tubers and bulbs. Nut sedge is difficult to manage. The best way to treat it is to pull up individual clumps the moment you spot them.
Crabgrass is a grassy, highly invasive weed that spreads very rapidly, making it difficult to remove even by hand. Mature plants are short and have dark green, thin leaves, although not as thin as blades of grass. Hardy and strong, crabgrass can invade and take over a lawn in just one growing season. It spreads easily by seed and rooting, which means that any bit of it left in the soil can take root and grow. Pre-emergent herbicides can be applied in the spring to help prevent the growth of crabgrass.
White clover is a widespread, broad-leafed weed that can be found in lawns throughout the United States. The weed creeps quickly through grass, covering the lawn and killing the blades underneath it. Clovers have a hard seed coat, which makes it harder to prevent germination through solarization or pre-emergent herbicide applications. Luckily, they are easily to pull up, so the best way to manage clover is to simply pull it up from the lawn. Pre-emergent herbicides can be used in very large areas, although several applications may be necessary.
Dallisgrass, a grasslike weed, looks much like crabgrass and is just as invasive. The major difference between the two is that dallisgrass is a perennial weed, returning year after year if not controlled Dallisgrass is also much taller than crabgrass at maturity, with flowers that can reach a height of 1 to 4 feet. The weed produces a large number of seeds and should be controlled with a pre-emergent herbicide and manual removal whenever possible.