I found this homemade weed killer recipe attached to a review of quikpro on amazon:
2. The most inexpensive herbicide is to mix a "home made solution" from cheap household products. For killing grass and sterilizing the soil as well, I mix a quarter cup of liquid laundry detergent and 2.0 pounds of salt in a gallon of water. DO NOT USE POWDER DETERGENT, it clogs up the sprayer.
. . . . .CASH AND CARRY of Seattle sells a 50 pound bag of salt at $5.90, and COSTCO sells a 1.3 gallon container of ECO LIQUID LAUNDRY DETERGENT at $13.89.
. . . . .This $0.32/gallon solution is applied via a hand-pump sprayer. The detergent removes the shiny protective waxy layer of the vegetation and forces it to quickly absorb the toxic solution. The detergent is also sticky. As a result, the salt sticks to the plant during drying. You can see the crystals of it on the blades of grass during a sunny day.
. . . . .Within an hour, it is curling. In one to two days, certain parts of the grass turn dark purple-black in color. Within a week, the area is brown. It is best to do spraying on a dry week in late July, for rain tends to wash off the dried saline and negate the killing process. When a summer shower does come later, the salt goes into the soil, attacks the grass roots, and sterilizes the ground.
I have an area that is covered in Japanese Knotweed at my house that I am going to try this on.