Perennial grasses, such as quackgrass and nimblewill, are some of the most difficult weeds to control in the lawn. Control is difficult because there is no herbicide that will selectively destroy these weeds. Also, pulling or digging these perennial grasses is often unsuccessful.
Quackgrass (Agropyron repens) is a cool-season perennial grass. It spreads rapidly by underground stems or rhizomes. Its leaf blades are bright green, coarse in texture, and twice the width of leaves of bluegrass. Quackgrass is objectionable in lawns because of its coarse texture and spreading habit. Quackgrass also can be a major problem in flower and vegetable gardens.
Nimblewill (Muhlenbergia schreberi) is a warm-season perennial grass. Nimblewill is a thin, wiry grass that is pale green or gray-green. It spreads by aboveground shoots or stolons, often forming circular spots in the lawn. Nimblewill is easy to spot in the lawn because it greens up late in the spring and turns brown in early fall. Nimblewill is objectionable in the lawn because of its gray-green color and delayed green-up in the spring and early browning in fall.
The best way to control quackgrass, nimblewill, and other undesirable perennial grasses in the lawn is to spot treat the weed-infested areas with glyphosate (Roundup, Kleenup, Kleeraway, etc.). Glyphosate is a systemic, nonselective herbicide that is absorbed through the foliage and translocated to all parts of the plant. Visible symptoms (yellowing or browning of foliage) usually develop in 7 to 10 days of the application. Death typically occurs in 2 to 4 weeks. Glyphosate is most effective when applied to actively growing plants.
Midsummer is an excellent time to control undesirable perennial grasses in the lawn. Most perennial grasses, such as nimblewill, are actively growing in summer. Also, midsummer control efforts allow adequate time to kill the weedy grasses and to prepare the areas for seeding or sodding in late summer. Complete destruction of the weeds is necessary to prevent their reappearance. Spray the weedy patches and a few inches beyond these areas to ensure their complete destruction. If the treated areas are not dead in 2 to 4 weeks, a second application is necessary. Treated areas can be seeded or sodded 7 days after the application.
After the treated areas have been completely destroyed, reestablish the lawn by seeding or sodding. If you plan to sow seed, it's not necessary to dig up the destroyed areas. Small areas can be raked vigorously with a garden rake to remove some of the dead debris and to break the soil surface. After seeding, work the grass seed into the soil by lightly raking the areas. Large areas can be seeded by a turf-type or slit seeder. A turf-type or slit seeder cuts small grooves into the soil and deposits the seed in these grooves. The best time to sow grass seed is mid-August through mid-September. After seeding, keep the soil moist with frequent, light applications of water.
If you plan to lay sod, remove the dead debris before sodding. Late summer and fall are excellent times to lay sod.
Destroying undesirable, perennial grasses in the lawn is difficult. However, if done properly, your efforts should produce an attractive lawn free of grassy weeds.
This article originally appeared in the May 23, 1997 issue, p. 77.