VERMONT AGRICULTURAL REPORT. ig 



CHEMICAI^ WEED KILLERS OR HERBICIDES. 



L. R. J0NE;S, botanical department^ VERMONT EXPERIMENT 



STATION. 



It should be emphasized at the outset that the use of chem- 

 icals as herbicides offers no specific cure-all against weediness. 

 Cultivation, short rotations, watchfulness against the introduc- 

 tion and scattering of weed seeds are all of more fundamental 

 importance than chemicals in combating weeds. There are 

 however, various cases where chemicals intelligently used are 

 more expeditious and economical than any other means for 

 weed killing. A practical difficulty is so to use the herbicide 

 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. Where an especially obnoxious weed, like poison ivy, 

 occurs in a limited locality and is to be destroyed regardless of 

 consequences to soil or neighboring plants. 



2. Where the aim is to render the soil permanently sterile 

 as in roadways, tennis courts, etc. 



3. Where the weed plant, as orange hawkweed, is much 

 more sensitive than the associated useful plants to the action of 

 some herbicide. 



CHEMICALS USEEUL AS HERBICIDES. 



Any soluble chemical, even including the various commer- 

 cial fertilizers, if used in sufficient amount, will kill plants. 

 Some act directly and quickly as poisons, e. g., arsenic and car- 

 bolic acid; others, such as salt, have little or no directly poison- 

 ous effect but kill the plants primarily by drawing the water 

 from the tender foliage, or by so holding the moisture of the 

 soir 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. Effective- 

 ness in one or the other of these ways, together with cheapness 



