• Weeds are unwanted plants that can start competing with desired vegetation for nutrients and water if left uncontrolled. Oklahoma lawns are susceptible to a number of weeds. Weeds most commonly strike in lawns that have been weakened by poor maintenance practices, common pests and stressful environmental conditions. The Oklahoma State University Extension site recommends practices targeted to achieve vigorous, healthy grass as the first step toward defeating the growth of weeds.
  
  

Black Medic

• Black medic (Medicago lupulina) is a warm season annual or cool season perennial weed in Oklahoma lawns. The weed is also referred to as black clover, yellow trefoil and hop medic. The weed is a member of the legume family and grows low. The taproots of black medic grow deep into the ground, and the three-leaflet foliage closely resembles other clover leaves. The weed produces dense clusters of pea-like, bright yellow flowers, and the black seed pod contains a single light yellow seed.
  
  

Spotted Spurge

• Spotted spurge (Euphorbia maculata) is an aggressive lawn weed in Oklahoma lawns and is also referred to as eye-bright and milk purslane. The weed grows to form a round mat that kills all grass in its area of growth. Spotted spurge is one of the most rapid seed-producing and growing weeds. The foliage is a light reddish-green to dark green with a maroon spot in the center. The small, light pink flowers grow in the leaf axils. Spotted spurge produces three-sided, oblong, dark brown to black seeds.
  
  

Common Yarrow

• Common yarrow (Achillea millefolium) or thousand leaf, milfoil or bloodwort is a hairy, perennial weed that grows from sturdy, thick rhizomes. The weed has a strong scent and grows close to the ground, making it difficult to remove by mowing alone. The fern-like foliage has alternating, finely-divided leaves, and the erect stems are covered with gray-green hair. Common yarrow blooms with yellow-centered, white or light yellow flowers in the form of thick clusters at the end of the stems. The flat, oblong seeds are about 1/16 inch in length and white to gray in color with lines running along the entire length of the seeds.