Which of the following is a common annual grass weed found in Iowa?

Crabgrass is considered a common annual grass weed found in Iowa due to its widespread presence in lawns, gardens, and agricultural fields. It thrives in warm temperatures and can quickly establish itself in disturbed soils, where it competes with desirable plants for nutrients and water. Its ability to germinate and grow rapidly during the summer months allows it to dominate areas where turfgrass or other crops may be stressed or poorly maintained.

The other options, while they may be present in Iowa, do not fit the description of a common annual grass weed. Coarse Bluegrass is a perennial grass, not an annual, and its growth habit differs significantly from that of Crabgrass. Common Mallow is a broadleaf weed typically classified among dicots rather than grasses. Quackgrass, while a grass, is a perennial species known for its invasive nature and persistence, contrasting with the annual growth cycle of Crabgrass. Thus, Crabgrass is accurately identified as the correct answer concerning common annual grass weeds in Iowa.