. Cyclopedia of farm crops. Farm produce; Agriculture. CHEMICAL WEED-KILLERS OR HERBICIDES 115 CHEMICAL WEED-KILLERS OR HERBICIDES By L. R. Jones The use of chemicals as herbicides offers no spe- cific cure-all against weeds. Cultivation, short rotations, watchfulness against the introduction and scattering of weed seeds, are all of more fun- damental importance than chemicals in combating weeds. There are, however, various cases in which chemicals intelligently used are more expeditious and economical than any other means for weed- killing. A practical difficulty is so to use the her- bicide
. Cyclopedia of farm crops. Farm produce; Agriculture. CHEMICAL WEED-KILLERS OR HERBICIDES 115 CHEMICAL WEED-KILLERS OR HERBICIDES By L. R. Jones The use of chemicals as herbicides offers no spe- cific cure-all against weeds. Cultivation, short rotations, watchfulness against the introduction and scattering of weed seeds, are all of more fun- damental importance than chemicals in combating weeds. There are, however, various cases in which chemicals intelligently used are more expeditious and economical than any other means for weed- killing. A practical difficulty is so to use the her- bicide as to kill the obnoxious plants without working permanent injury to the soil or to neighboring cultivated plants. This difficulty limits the chief usefulness of chemicals as weed-killers to the following cases: (1) When an especially obnoxious weed, as poison ivy, occurs in a limited locality and is to be destroyed regardless of consequences to soil or neighboring plants. (2) When the aim is to render the soil permanently sterile, as in roadways, tennis courts, and the like. (3) When the weed plant, as orange hawk- weed and mustard, is much more sensitive than the associated useful plants to the action of some herbicide. Chemicals useful as herbicides. Any soluble chemical, even including the various commercial fertilizers, if used in sufficient amount, will kill plants. Some act directly and quickly as poisons, e. g., arsenic and carbolic acid; others, such as salt, have little or no direct poisonous effect but kill the plants primarily by drawing the water from the tender foliage, or by holding the moisture of the soil so that it cannot be absorbed by the roots. It is important in this connection to note that in either case the herbicide is most effective on young plants that are in active growth. Effectiveness in one or the other of these ways, together with cheapness and convenience of application, are the things to determine choice among the various compounds available. Wi
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