Weeds in fields are killed by “herbicides.” “Insecticides” kill insects, and both are known as “pesticides.”

In the 1930s, farmers were still using primitive chemicals they had been using for up to 100 years to attempt to control weeds.

For instance, copper sulfate was first used for weed control in 1821. It was known by the colorful name blue vitriol. In the early 20th Century, scientists in Europe started using the salts of heavy metals to control weeds, but when the experiments were attempted in the U.S. the low humidity in the western states prevented the chemicals from being absorbed by the weeds.

Other chemicals were tried, but many had drawbacks. For instance, carbon bisulfide was used to control thistles and bindweeds. But it smelled like rotten eggs and was – perhaps understandably – unpopular. Sulfuric acid was effective against weeds, but it would corrode equipment and can harm people who got it on their skin.

The first synthetic organic chemical for selective weed control to come out of the labs was introduced in 1932. Its chemical name was 2-methyl-4, 6-dinitrophenol, and it could control some broadleaf weeds and grasses in large seeded crops like beans.

But, in the middle of the Depression, few farmers could afford to buy the new chemicals. The stage was set for developments in the succeeding decades.

Written by Claudia Reinhardt and Bill Ganzel, the Ganzel Group. First written and published in 2003.

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