Is It Crabgrass Or Quackgrass In Your Lawn?

Coarse, weedy, wide-bladed grass whose appearance mars the uniform texture of lawngrass is often all mistakenly referred to as crabgrass. Crabgrass preventer is widely sold in springtime at national chains, hardware stores and garden centers.

Here’s the problem: crabgrass preventer only works on what is truly crabgrass, when actually much of the weedy, wide-bladed grass in our lawns is also quackgrass. And crabgrass preventer has no effect on quackgrass. If crabgrass preventer products aren’t working to rid the lawn of wide-bladed grassy weeds, it’s possible it’s not crabgrass in the lawn.

How can we tell the difference between crabgrass and quackgrass?

  • Crabgrass is an annual, which must grow each year from seed that sprouts in spring, grows during summer and then dies over winter. Quackgrass is a perennial, living year to year, growing back each spring from a winter-hardy roots system.
  • Because crabgrass seed doesn’t germinate until soil temperatures warm to about 55 to 60 degrees in early May, crabgrass plants don’t appear in the lawn until later. Quackgrass, being a perennial, begins to grow from it’s established root system earlier in spring, usually growing about the same time that regular lawngrass begins to green and grow.
  • Both crabgrass and quackgrass are wide-bladed grasses, but an easy way to diagnose is to look closely at the leaf blades. Quackgrass has what are termed “clasping auricles,” which are easily seen at the point where the grass blade wraps around the lower stem. Crabgrass lacks these auricles.
    Quackgrass showing “clasping” auricles

    Crabgrass lacks clasping auricles
  • Crabgrass’s growth habit is noticeably “prostrate,” where the grass blades tend to lay more horizontally, giving the plant a squashed look. Quackgrass habit is upright.
    Crabgrass has prostrate growth habit

    Quackgrass has upright leaf blade habit
  • Crabgrass roots stay in a bunch. Quackgrass has very pronounced white/tan rhizomes that run horizontally underground, spreading the plant. Digging a plant is an easy way to identify between crabgrass and quackgrass. Crabgrass is easier to pull out, roots and all.
    Crabgrass roots

    Quackgrass roots and rhizomes
  • If allowed to go to seed and mowing doesn’t cut off the seedheads, crabgrass has a distinctive “goosefoot-shaped” seed head, while quackgrass has a straight seedstalk.
    Crabgrass showing “goosefoot” seedhead

    Quackgrass seed stalk
  • Crabgrass is killed and turns brown about the time of fall frosts. Quackgrass remains green late into fall.
  • Crabgrass seed can be prevented from germination if crabgrass preventer is applied before soil temperatures reach 57 to 60 degrees. Each year varies, but products can be applied in late April most years. There are “post-emergent” crabgrass killers that can be applied if the seed-preventers don’t work, or if you missed application. Follow the directions, but the post-emergent products are effective on very young crabgrass plants, such as before the four-leaf stage.
  • Quackgrass can only be killed with products like Roundup, after it’s actively growing. There are no products that selectively remove quackgrass from lawns. Roundup can be spot-applied to quackgrass, which will also kill the lawngrass, making re-seeding necessary.
  • A third type of coarse, weedy grass that grows in dark green bunches is Tall Fescue. A perennial grass, control is the same as for quackgrass – spot spray with Roundup followed by reseeding.

    Tall Fescue

So when wide-bladed weedy grasses appear in our lawns, the very important first step is identification.

Happy Gardening, and may all your lawngrass be fine!

2 Responses

  1. Corey S

    Thanks for the article Don. I have Tall Fescue in my yard and I’m wondering how long should I be waiting to re-seed after spraying Round-Up on those spots?

    Thanks.

    1. Don Kinzler

      Hi Corey. For best results the tall fescue should be up and growing well, even allowed to get at least 4 inches, if you can. I realize in a lawn that’s not always possible. Then apply the Roundup to the bunches of tall fescue. I would wait at least a week for the Roundup to be well-absorbed by the fescue, before cutting or removing it, then you can reseed. Roundup has no soil carryover, so technically you can reseed immediately after application, but it takes time for the fescue to absorb and translocate the Roundup through it’s system.

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