Herbicides--Use of chemicals to control weeds dates back to 1895 to 1909. During 
that period copper sulfate, common salt, iron sulfate, sulfuric acid, carbolic acid, form- 
aldehyde, sodium arsenite, and sodium arsenate were studiedin this country and in Europe 
for control of weeds. In the 1930's the selective herbicidal actions of certain dinitro com- 
pounds were discovered by workers in France. Some of these early explorations dem- 
onstrated the feasibility of chemical control of weeds and provided stimulus for continuing 
search for chemicals for selective killing of weeds among crop plants. Early use of 
chemicals for weed control was limited, because they lacked high potency and adequate 
selectivity. 
Discovery of selective herbicidal action of phenoxyacetic acids in 1943-1944 is the 
major breakthrough with far-reaching effects on weed control. Since this discovery a 
new science of weed control has rapidly evolved. 
Nematocides--Although plant parasitic nematodes have been studied for more thana 
century in Europe the discovery and development of nematocides have been slow because 
of the small number of workers concerned with nematodes and their control. Although 
carbon bisulfide was used in Germany in 1881 to kill sugar beet nematodes without 
notable success, as late as 1911 it was still considered the most efficient chemical for 
the control of nematodes in the field. Even though effective it has never been used ex- 
tensively (6). 
Of the nematocides used today, chloropicrin was studied first in Great Britain in 
1919. Subsequently it was evaluated on a field basis in this country and later in Hawaii. 
By 1935, chloropicrin was used rather extensively for nematode control in pineapple 
ue ont cee it was sold as a nematocide, largely for use in greenhouses and seed- 
beds (7). 
The successful use of methyl bromide for controlling soil nematodes in 1940-41 (8) 
provided the first real stimulus for synthesis and development of additional chemicals 
for controlling nematodes in soils in the field. 
Today more than 10 nematocides are produced commercially and their retail sales 
are estimated as more than $16 million. Since few growers use soil nematocides except 
where returns from the crops are at least four times the cost of the nematocides, 
farmers presumably profited to the extent of more than $64 million last year through the 
use of nematocides. Nematocide application has become astandard practice for producing 
pineapples in Hawaii and tobacco in many parts of the Southeastern States. 
Growth Regulators--The present availability of selective organic chemicals that regu- 
late plant growth and control weeds incrops can be traced to investigations of Darwin who 
published a book called ‘‘The Power of Movement in Plants,’’ in 1880. Work on the nat- 
urally occurring plant auxins a and b and the discovery of 3-indoleacetic acid asa plant- 
growth regulator stimulated attempts to isolate the chemically pure compounds from 
plants and to synthesize compounds that would influence the growth of plants. 
Among the synthetic organic compounds evaluated as growth regulators was 2,4- 
dichlorophenoxyacetic acid (2,4-D). When tested as a herbicidal agent 2,4-D was found 
to have extremely high potency in killing broadleaved weeds and strangely did not 
noticeably harm grass plants. After this discovery of the selective control of weeds with 
highly potent organic chemicals, many industrial and public agencies took rapid steps 
to synthesize and evaluate additional organic compounds as growth regulators and se- 
lective herbicides. 
RECENT PROGRESS 
The number of noninsecticidal pesticides produced and used in the United States 
reflects the progress in the development ofthese materials for agricultural uses (table 1). 
18 
