Answer: What you describe sounds like quackgrass. Quackgrass is a common lawn weed that offers nothing desirable and is very difficult to eradicate. In fact, it is often classified as one of the most objectionable grass-like weeds. Like crabgrass, it doesn't blend in with the lawn and can choke out the desirable turf grasses.
Quackgrass (Agropyron repens) is a perennial and has a really tough root system. It has long, tapered blades around 1/3 inch wide attached to hollow stems. The plant is much more upright growing than crabgrass. The seed heads are single, upright stems, not branched like crabgrass. Quackgrass has a strong root system with white, fleshy rhizomes that spread out from the main plant, sending up new plants.
The most common way for weed seeds to enter a yard is birds. Quackgrass seed is a favorite of sparrows and other birds and some of it passes through their systems to be deposited in your yard as they fly by. Weed seed can also be introduced by winds and contaminated grass seed. Once a plant is in your yard and goes to seed, hitting it with the lawn mower spreads it to the surrounding area.
You need to be aggressive in dealing with quackgrass, since it is aggressive in your yard. Unfortunately, there are no selective herbicides for quackgrass and with its rhizomatous root system, it is almost impossible to pull. The only real alternative in dealing with quackgrass is killing it with a nonselective herbicide such as Roundup or Finale. Keep in mind that these herbicides will kill anything with leaves so you'll want to cover desireable plants and apply it carefully.
Quackgrass, like crabgrass, leaves thousands of seeds in the lawn for the new season. Pre-emergence herbicides, such as crabgrass preventers, will inhibit germination of quackgrass seed. Such seeds germinate as the soil temperature reaches around 55-60 degrees in spring, so timely application is important.
After using Roundup or Finale to kill the quackgrass while it is actively growing, you can re-seed within 7 days. If you are using a pre-emergence herbicide in the spring, you need to wait a minimum of 30 days before seeding grass. Again, pre-emergent herbicides continue to affect germination rates after the 30 days, so if you can wait until the fall seeding season, you will have more success.
Once you've gotten rid of the quackgrass, put your lawn on a regular feeding and watering schedule. A lush, thick lawn will help crowd out undesireable weeds.
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