Hey farmer, farmer

Put away that DDT now

Give me spots on my apples

But leave me the birds and the bees

Please!

“Big Yellow Taxi,� by Joni Mitchell

It’s possible that Joni Mitchell’s 1970 lyrics owe a debt to Rachel Carson’s (1962) book Silent Spring. Why not? The book was a major influence on the environmental movement, inspiring Earth Day, the Environmental Protection Agency (EPA), and the US ban on DDT, besides. Less often mentioned, the book also touched off integrated pest management (IPM).

For all that, Carson makes few mentions of farmers in her book. Many of the cases she meticulously described are of the US and Canadian governments arrogantly dropping insecticide from airplanes, blanketing forest, field, stream, pasture, and even suburban communities.

DDT and other noxious organophosphate insecticides were applied in each case to kill some specific pest: The Japanese beetle, the spruce budworm, and the fire ant, for example.

In every case, the results were disastrous. Dead livestock, and cancer in humans, but the birds were decimated. The bald eagle, national bird of the USA, was nearly exterminated by DDT. The bald eagle has since made a comeback, but many other bird species are on the decline.

The chemical companies that sold these pesticides to the government had the audacity (or the stupidity) to claim that insects would not be able to evolve resistance to the toxins. The pests would be eradicated!

But they weren’t. The bugs won the war. In every single case, the target pest species was more numerous a few years after the spraying started.

To explain this, Carson coined the analogy of the pesticide treadmill. Before a pesticide is used, an insect’s population is controlled by its natural enemies, such as spiders, wasps, ants, and birds. Insecticide kills the pest, and its natural enemies, too. The pest evolves resistance to the pesticide, much quicker than do its natural enemies (which often reproduce more slowly and absorb more of the poison). Once freed from its natural enemies, the pest population explodes. Now it has to be managed by pesticides.

In 1962, Carson mused that Darwin would have been pleased to see how well his theories were proven, as insect pests had quickly evolved resistance to pesticides. If Carson were here today, she might not be so happy to see how the chemical companies have also evolved. They have engineered maize and soy varieties that can withstand herbicides, so fields can be sprayed with glyphosate that kills all the plants, except for the ones with designer genes. The corporations that sell the seed conveniently sell the herbicide as well. Companies like Monsanto once claimed that the weeds would not be able to evolve resistance to the genetically modified crops.

But they did. At least 38 species of weeds are now resistant to glyphosate.

As Carson said nearly 60 years ago (and it’s still true), farms and forests are biological systems. Their pest problems have to be solved with biology, not with chemistry. In Rachel Carson’s day, only 2% of economic entomologists were working on biological pest control. Most of the other 98% were studying chemicals. Funding for chemicals breeds contempt for biological alternatives.

Biological pest control uses natural enemies to control pests. Carson cites the famous case of the cottony cushion scale, a citrus pest in California. The pest was controlled in 1872, long before DDT was available, by importing a lady bird beetle from Australia that ate the scale insects. The scale insects then became rare in California orchards until the 1940s, when insecticides killed the lady bird beetles and the pests exploded.

A recent book by Biovision and IPES Food suggests that many big donors still fund conventional research in pesticides. Perhaps it’s time to invest in scientists who can pick up Rachel Carson’s challenge, and solve biological problems with biology.

Further reading

Carson, Rachel 1962 (1987 edition). Silent Spring. Boston: Houghton Mifflin.

Heap, Ian, and Stephen O. Duke 2018 “Overview of glyphosateâ€�resistant weeds worldwide.” Pest Management Science 4(5): 1040-1049.

On chemical companies denying that weeds would develop resistance to their herbicides see chapter 5 in:

Philpott, Tom 2020 Perilous Bounty: The Looming Collapse of American Farming and How we can Prevent It. New York: Bloomsbury Publishing. 246 pp. (See also a review of this book in Our threatened farmers).

Biovision Foundation for Ecological Development & IPES-Food. 2020. Money Flows: What Is Holding Back Investment in Agroecological Research for Africa? Biovision Foundation for Ecological Development & International Panel of Experts on Sustainable Food Systems

Videos on natural, biological pest control

The wasp that protects our crops

Killing fall armyworms naturally

Weaver ants against fruit flies