Kakuya grass, also known as Kikuyugrass, was imported from Kenya early in the 19th century to be used for erosion control in warm areas such as Southern California. Unfortunately this grass, which grows as much as 1 inch per day, proved to be extremely invasive and now is classified by the state of California and the federal government as a noxious weed. Killing kakuya grass is not easy. The grass can be spread by stolons (above-ground branches), by seeds and by rhizomes (underground roots). Contaminated lawn mowing equipment, spreading small pieces of the grass from one lawn to another, is blamed for much of the spread of this hard-to-kill weed.
Water the kakuya grass thoroughly for a week to get as many of the seeds and rhizomes to grow as possible. Sprinkle for at least 1 hour for the first watering, moistening the soil to a depth of approximately 1 inch. Keep the ground moist but not saturated after that. Start this entire process in early spring, before the grass begins its vigorous summer growth.
Set your lawnmower to 1/2 inch and "scalp" the kakuya grass on the eighth day. Dispose of the cuttings.
Clean the lawnmower thoroughly. Wipe down all areas of the mower, removing every trace of kakuya grass.
Spray the area with a herbicide that contains glyphosate, following the manufacturer's label instructions. Do not to get any of the spray on plants you wish to keep, as this herbicide will kill any plant it touches. Do not spray on a windy day or if rain is forecast within the next 24 hours.
Wait seven days to allow any surviving kakuya grass to sprout. Spray a second time with the glyphosate herbicide.
Wait another seven days. Rake all dead vegetation from the area, using a thatching rake. Bag all vegetation in plastic trash bags and dispose of it. All traces of the kakuya grass and its thatch should be disposed of.
Spread 1 inch of organic manure on the entire area and till the manure into the top 6 inches of ground. Rake the area to remove any vegetation, rocks or other debris turned up by the rototiller. Level the area.
Spread grass seed using a seed spreader. Follow the manufacturer's directions as to the amount of seed.
Add 1/4 inch of manure on top of the grass seed. Water to keep the area moist but not soggy for 21 days, until the grass seeds have sprouted and taken hold. Set your lawnmower at 3 inches and mow the new lawn when the grass reaches 4 inches in length.