Perennial Grasses Hardest to Lick
These are grass-like weeds that can not be killed using a broadleaf herbicide such as "Weed and Feed". 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 still be carefully confined to the weeds being killed. A splash or drift from them will blemish other plants, and any runoff into the storm drains will impact creek and river life. If the treated area is walked on while still wet, shoe soles will spread the treatment to other areas and you'll end up with orange footprints on your lawn.
When a pressure sprayer is used to spot-spray the weeds, keep pressures low to reduce the mist that might drift to good plants. You will want drops, not a fog. 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 only through the 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.
Next: Other Lawn Problems