Perennial grasses, such as quackgrass and nimblewill, are some of the most difficult to control weeds 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. 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, etc.).
Glyphosate is a systemic, non-selective herbicide. Glyphosate is absorbed through the foliage and is then translocated to all plant parts. It kills nearly all plants that are directly sprayed. Visible symptoms usually develop in 7 to 10 days of the application. Death occurs in 2 to 4 weeks.
Efforts to control undesirable perennial grasses in the lawn should begin in mid-summer. This allows adequate time to kill the weedy grasses and prepare the areas for seeding or sodding in late summer. Complete destruction of the weeds is necessary to prevent their reappearance. 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 application.
If you plan to sow seed, it's not necessary to dig up the destroyed areas. Vigorously rake these areas with a garden rake to remove some of the dead debris and to break the soil surface. After seeding, work the seed into the soil by lightly raking the area and keep the soil moist with frequent, light applications of water. The best time to seed bare spots is mid-August through September. If you plan to sod, remove the dead debris before laying the sod.
The establishment of a thick, healthy lawn and its proper maintenance will help prevent future weed infestations.
This article originally appeared in the July 22, 1994 issue, p. 115.