CHEMICAL WEED -KILLERS OR HERBICIDES 



117 



is to be sprayed or sprinkled broadcast on the foli- 

 age or ground, it should be diluted with 15 to 30 

 parts of water, and this mixture agitated fre- 

 quently during use. 



Sulfuric add (oil of vitriol). — This, of course, is 



Fig. 168. Poison hemlock {Oonium maeulatum). 



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 be- 

 cause sulfuric acid can be handled only in glass 

 vessels. 



Caustic soda. — A strong solution of this makes a 

 cheap and eflfective herbicide, commended especially 

 for pouring on soil where it is desired to destroy 

 poison ivy or other deep-rooted or woody plants. 

 Of course, 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 effec- 

 tive herbicides known. These form the basis of all 

 or nearly all of the various proprietary "herbi- 

 cides" or "weed-killers." Such compounds are 

 handled by leading horticultural supply houses, 

 and, so far as the' writer has tested them, are 

 highly efficient. The only reason for seeking 

 elsewhere is their high price. Soluble arsenical 

 poisons as a rule can be bought considerably 

 cheaper in the drug trade and are similar in action. 

 The simplest to employ is arsenate of soda. This 

 needs only to be dissolved in water for use, at the 

 rate of 1 pound in 3 to 9 gallons of water. White 

 arsenic is still cheaper, but according to Schutt's 

 formula, which the writer has used, it must be 

 combined with sal soda, which is somewhat both- 

 ersome. (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. For this reason they are the 

 most useful herbicides to use on roadways and 

 other plain surfaces, as explained below. 



More specific directions for use. 



Any of the above chemicals will kill any plant 

 if applied directly to it in sufficient amount. In 

 addition to the more general advice included in the 

 above account, the following specific directions are 

 adapted to special cases. 



Gravel roadways, gutters, tennis courts and like 

 surfaces can be kept free from weedy growths by 

 the application of any of the above. If salt is 

 used it should be scattered freely in the dry form. 

 Caution is necessary where it is liable to be 

 washed on to lawns, lest it damage the grass bor- 

 ders. Carbolic acid or arsenical poisons are pref- 

 erable, being- both less liable to wash and more 

 enduring in their action. One quart of crude car- 

 bolic acid in 8 gallons of water, or one pound of 

 either arsenical compound mentioned above in a 

 like amount of water, will suffice to cover a square 

 rod or more of surface; and one, or, at most, two 

 applications per year, will be sufficient. 



Charlock, known also as kale or wild mustard 

 (Brassiea arvensis, Pig. 143), is easily destroyed 

 in oat-, wheat-, or other grain-fields by spray- 

 ing with a solution of 1 pound of copper sul- 

 fate in 4 to 6 gallons of water (2 to 3 per cent 

 solution). A force pump should be used, supplied 

 with fine nozzles. The treatment is most effec- 

 tively made when the grain is 3 to 6 inches tall, 



Fig. 169. Common poison ivy (Ehus Toxicodendron). 

 Climbing or trailing, 



since at this stage the large charlock leaves 

 spreading above the grain are easily covered by 

 the spray. One barrel or less of the solution (30 

 to 50 gallons) suffices to cover an acre and destroy 



