Perennial Grasses Hardest to Lick
Any weed killer strong enough to kill perennial weed grasses will kill good grass along with the bad. About the only thing to do is to dig out the unwanted clumps, spot-spray them with a general weed killer such as Roundup, or kill everything in the lawn and then replant. Sometimes a lawn can be upgraded gradually, simply by overseeding with good grass and managing the lawn so as to
give it every possible encouragement. Some perennial grassy weeds, including
quackgrass, nutgrass and dallisgrass may be eased out of a lawn by tending
the lawn well or by a change of cultural practices. Nutsedge likes wet
areas, and drying out the area will cause it to gradually disappear.
Chemicals that kill all vegetation are used to clean out old weedy grass before reseeding. While general weed killers such as Roundup are not quite so hazardous to use as volatile forms of 2-4-D, they should be carefully confined to the weeds being killed.
A splash or drift from them will blemish other plants. If the treated area is
walked on while still wet, shoe soles will spread the treatment to other areas.
When a pressure sprayer is used to spot-spray the weeds, keep pressures low to
reduce the mist that might drift to good plants. For small areas, the weeds
could even be painted with the solution, using a dauber of any absorbent
material, or even a paint brush. Since such herbicides are effective through
foliage, it is not good to douse them heavily as with a sprinkling can; most of
the chemical runs through to the soil rather than adhering to the weed.