Which plant is a summer-annual turfgrass weed?

• A. Prostrate knotweed
• B. Foxtails
• C. Crabgrass
• D. Shepard's purse

Answer: (C)

A summer-annual turfgrass weed is one that germinates in warm weather, completes its entire life cycle in a single growing season, and often forms a dense mat that crowds out desirable turf. Crabgrass fits this pattern perfectly: it emerges in late spring to early summer as soils warm, grows rapidly through the hot months, and produces plenty of seeds before frost, then dies. This makes it the classic example of a summer-annual weed in turf.

Prostrate knotweed and Shepard's purse are broadleaf weeds, not grasses, so they don’t fit the “turfgrass weed” and grass-life-cycle pattern. Foxtails are also annual grasses and can behave similarly, but crabgrass is the most well-known and typical example used to represent summer-annual turfgrass weeds in management discussions.