Grass Weeds Unmasked: Identifying and Controlling Crabgrass & Its Cousins

Any fast-growing grassy weed invading your lawn gets labeled "crabgrass." But witchgrass, quackgrass, goosegrass, dallisgrass, and true crabgrass each have distinct habits—and knowing the difference helps you fight smarter.

In turf, the best defense is a thick, healthy lawn that crowds out invaders. In sparse lawns, targeted herbicides are needed: post-emergent products with clethodim or fluazifop, or pre-emergents like Dimension® (dithiopyr) or Tupersan® (siduron). Most turf experts favor pre-emergents.

Pre- vs. Post-Emergent

Pre-emergents stop weed seeds from germinating. Apply fall and spring to catch annuals and perennials. Post-emergents require contact with growing foliage and don't prevent seed germination. Read labels carefully—each product differs.

The Real Challenge: Reproduction

These grasses spread by both underground rhizomes and seeds. Digging chops rhizomes into pieces that each become new plants if left in soil. Seeds disperse by wind, mowing, and birds into flower beds, restarting the cycle. Young plants pull easily but are hard to treat with herbicides without risking desirable plants. (For safe spot-treatment, see "How To Spray Weeds and Insects Without Killing Everything.")

Meet the Usual Suspects

Crabgrass (Digitaria spp.) — Annual. Low-growing, dark green 5-inch smooth leaves. Seed heads resemble bermudagrass. Control: boost turf vigor, mow regularly to prevent seeding.

Witchgrass (Panicum capillare) — Annual. Branches from base with hairy stems, swollen nodes. 1–2 feet tall, large spikelets with single seeds at branch tips.

Quackgrass (Elytrigia repens) — Perennial. Creeping with sharp-tipped rhizomes traveling far before surfacing. Plantlets form at every rhizome node. Up to 4 feet tall, smooth round stems, gray-green or dark green leaves to 12 inches. Wheat-like seed heads. Grows in all soils, highly drought-tolerant. Sometimes used as forage.

Goosegrass (Eleusine indica) — Annual. Rosette of flat stems to 2 feet, fibrous roots (no rooting at nodes). Dark green leaves to 12 inches. July–September bloom on flattened zipper-like spikes. Thrives in poor soil, full sun, tolerates close mowing.

Dallisgrass (Paspalum dilatatum) — Perennial. Clump-forming, center dies out. Short rhizomes with short internodes distinguish it. Leaves ½-inch wide, 4–10 inches long, stems often purplish at base. Flower stalk to 65 inches with drooping branchlets bearing two seed rows. Loves heat, poor drainage, most soils; drought- and frost-tolerant. Highly susceptible to toxic ergot fungus—rarely used for forage.

Armed with identification skills and persistence, you can keep these grass invaders out of your yard and garden.

Resources: UC IPM Online; Ohio State University OARDC Perennial & Biennial Weed Guide.