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Pyrethrum insecticide

Pyrethrum – A Very Incomplete History……or how the Dalmatian Daisy helped build the Panama Canal

By Beet 2022 06 June

Dalmatian Daisy – Chrysanthemum cinerarifolium

Gardeners are all familiar with one of the oldest insecticides still in frequent use, the extract of the dried flower heads of Chrysanthemum cinerariifolium or a powder produced from the dried flowers. The plant has had other names such as the common one, “dalmatian daisy,” and the scientific names Tanacetum cinerariifolium or Pyrethrum cinerariifolium.

What has that daisy got to do with such a heroic construction project as the Panama Canal? In the right hands, it could keep the construction workers alive! The right hands in this case were those of military sanitation officer William Gorgas. He was transferred to the Panama Canal Zone from Cuba, where he had cleared the island of yellow fever and malaria during the Spanish-American War. With the then-new knowledge that mosquitos were the carriers of those diseases,  he started a systematic program of killing mosquitos with pyrethrum, sulfur, and the elimination of standing water.

The United States had acquired control of a 10-mile-wide strip across Panama through gunboat diplomacy in 1903, while also buying the remnants of a failed French attempt to construct a canal. 

Work on the Panama Canal started in 1904 with sanitation officer Gorgas present until the canal’s completion in 1914. With about 4,100 sanitation workers, he made war on the mosquito. The workers’ housing was improved with screens on windows, a city drinking water plant, and apparently with sulfur fumigation. There were quinine dispensaries along the construction zone for treatment of malaria. The pyrethrum was mixed with kerosine oil to make it stickier and it was applied liberally to mosquito habitat. Workers ceaselessly drained any standing water as much as was possible. Within 2 years, yellow fever had completely disappeared and malaria cases had fallen by 90%. Less than 10% of the workforce died through disease or accident during construction, compared to a 25% death rate during the French attempt, which was only 40% completed. 

Pyrethrum is still the first insecticide I think of when needed in the garden, as it is comparatively less toxic to humans than alternatives and breaks down quickly from sun, air, and water. If you use it, read the label and use precisely according to instructions. It still is a poison, after all.