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How to Eradicate Annual & Perennial Crabgrass

By Laura Reynolds ; Updated September 21, 2017

The name “crabgrass’ is used for several invasive, non-native plants that are large, coarse-leaved grasses. If not eradicated, these aggressive growers will strangle more sensitive turf grasses and form large, tangled clumps with strong, deep roots in gardens as well as lawns. Real crabgrass, also called "finger grass," is an annual, living and dying in one season. It is dull or blue-green, often with purplish stems. Perennial quack grass, or couch grass, grows taller; up to 20 inches. It is blue-green and sets rhizomes that will rise again next spring.

Annual Grass

Apply a pre-emergent herbicide in early spring to keep seeds from germinating. Follow the label instructions for dosage.

Apply post-emergent herbicides such as MSMA, fenoxaprop-p-ethyl and quinclorac, usually available in spray form, as soon after the plant emerges as possible.

Keep the lawn mowed to the proper height and well-irrigated. Most lawn grasses should be kept less than 3 inches tall as crabgrass seed spikes grow about 6 inches tall. Keep the grass cut to impair next year’s crop.

Dig out clumps of the crabgrass before the long spikes of seed begin to develop in August and September. Turn up pieces of turf or dig out long roots with a dandelion digger. Remove as much of the root as possible to prevent the plant from growing.

Repeat pre-emergent treatments each spring and keep after renegade plants.

Perennial Grass

Remove quack grass in early spring by digging it up.

Keep the lawn watered and mowed to a height of about 3 inches.

Fertilize turf grass to keep the lawn healthy. Apply two to three feedings of balanced lawn fertilizer (20-10-10) or a blend specially formulated for your soil. Follow the manufacturer's instructions for application.

Apply non-selective spray herbicides containing 2,4-D or glyphosate on stubborn or out-of-control patches. Reserve the use of grassy weed herbicides for serious infestations, as these chemicals will kill all vegetation.

 

Things You Will Need

  • Dandelion digger
  • Garden spade
  • Pre-emergent herbicide
  • Post-emergent herbicide
  • Fertilizer spreader
  • Herbicide sprayer

Tips

  • Herbicides containing dithopyr, ethofumesate and other chemicals are marketed in dry form to be dropped with a fertilizer spreader. Since annual seeds germinate in late spring, timing is critical.
  • Know which kind of grass you are trying to kill. Crabgrass (finger grass) and quack grass (couch grass) are coarse, rough, weedy grasses that grow in bunches. Crabgrass starts growing later and has branched seed blooms. Some quack grass has red bands where the leaf meets the stem, and most crabgrass has purplish stems or racemes (seed stems).
  • Names for weeds vary from place to place. Your local state university extension agent will have information on what's named what in your area and can make specific recommendations about management methods.

Warnings

  • Annual and perennial grasses send out rhizomes, special roots that run just under the soil surface and pop up new plants. When digging out plants, don't neglect the offspring.
  • Don't fertilize during the heat of summer. Most turf grasses are dormant during this period; the only grasses that benefit are the weeds.
  • Quack grass is more tolerant of mowing than crabgrass. Its seed spikes are about 6 inches long and it favors dry areas and thin lawns.
  • Once crabgrass sets seed, there is nothing that can be done to kill it until the next spring.

About the Author

 

An avid perennial gardener and old house owner, Laura Reynolds has had careers in teaching and juvenile justice. A retired municipal judgem Reynolds holds a degree in communications from Northern Illinois University. Her six children and stepchildren served as subjects of editorials during her tenure as a local newspaper editor.