(L. R. Jones).
The chemicals used as herbicides, the worth of which has been established, are the following: Salt (sodium chlorid), is more commonly used than any other compound, chiefly because of cheapness and handiness. It should be applied dry or in strong solution; and it is most effective in hot, dry weather. Salt can be used in any weed-killing operation, but it is most valuable on roadways and like surfaces and for certain lawn weeds. Hot brine (one pound salt to one gallon water) is useful on walks and roadways.
Blue vitriol (copper sulfate). - This is more powerful in herbicidal action than salt, but its cost prohibits its general use. For most purposes it is best used in solution, 2 to 10 per cent being effective. It is often used on gravel walks and similar surfaces, but salt will generally be found cheaper and arsenical poisons more effective. Its chief value is against charlock or mustard.
Copper sulfate solution, containing 8 to 10 pounds of blue vitriol to 50 gallons of water, and applied at the rate of 40 to 50 gallons per acre, is a good formula.
Iron sulfate (copperas) solution, containing 13/4 to 2 pounds of iron sulfate to the gallon of water (100 pounds iron sulfate to 52 gallons of water), is a good herbicide. Use at the rate of 50 to 75 gallons per acre.
Kerosene. - This and other coal-oil products will kill plants. It is weak in efficiency, and relatively more costly than any other chemical here listed. A pint of crude carbolic acid will do better service than two gallons of kerosene, and costs much less.
Carbolic acid. - This is one of the quickest and most valuable herbicides. The crude acid is relatively cheap. It is not quite equal to the arsenical poisons for penetrating the soil, or in lasting effects, but it is often preferable because of cost or convenience. It does not corrode metals, and therefore may be applied with any spray-can or pump. An effective method is to squirt the strong acid from an ordinary oil can on the roots or crown of individual weeds. If it is to be sprayed or sprinkled broadcast on the foliage or ground, it should be diluted with 15 to 30 parts of water, and this mixture agitated frequently during use.
Sulfuric acid (oil of vitriol). - This is destructive to everything it touches. It can be applied in the crown or about the roots of coarse or especially hardy plants, provided the user is willing to kill the adjacent vegetation also. In general, carbolic acid will be preferred, partly because sulfuric acid can be handled only in glass vessels.
Caustic soda. - A strong solution of this material makes a cheap and effective herbicide, commended especially for pouring on soil where it is desired to destroy poison ivy or other deep-rooted or woody plants. Soil so treated will be rendered sterile for some time, but the soda will gradually leach away. Like salt, this is most effective if applied in hot, dry weather.
Arsenical compounds. - One or another of the soluble arsenical compounds form the most effective herbicides known, to use on roadways and other plain surfaces. These form the basis of all, or nearly all, of the various proprietary " herbicides " or " weed-killers." The simplest to employ is arsenite of soda. This needs only to be dissolved in water for use, the rate of 1 pound in 3 to 9 gallons of water. White arsenic is still cheaper, but according to Schutt's formula it must be combined with sal soda, which is somewhat bothersome. (White arsenic, 1 pound; washing soda, 2 pounds; water, 3 to 9 gallons.) An important characteristic of these arsenical poisons is that they endure for a long time and do not readily wash or leach away.
Application of Herbicides
Gravel roadways, gutters, tennis courts, walks, and like surfaces can be kept free from weedy growths by the application of any of the above.