At the same time as the chemical age began, there were promising experiments with biological control of pests. All living things have natural predators. There are birds that eat insects. There are insects or animals that feed on specific plants. What scientists began to realize in the 20th Century is that the rise of unwanted plants or insects often occurs when one species is transported from one part of the globe to another where that species’ natural predators aren’t present.
That is what happened with the Klamath-weed in California. Controlling this “weed” became one of the first successful experiments in biological control. Ironically, what was once a weed is now a medicinal herb with $45 million dollars in sales in the U.S. alone.
The weed was known in the 1940s as Klamath weed or goatweed. The plant had been brought from Europe, first appearing in 1793 near Lancaster, Pennsylvania. By 1900, it had reached California by the Klamath River, from which it derived its common name.
The Klamath weed has a woody stem, small yellow flowers and an extensive tap root system. It can take over rangelands, crowding out the native grasses or sagebrush. More importantly, the leaves produce a chemical that causes animals that eat it, like cattle, to become sensitive to light. Cattle breeders found their animals developing blisters, rashes, sore mouths and a super sensitivity to light. Some animals died.
Some regions tried to spray herbicides to kill that Klamath weed. But, the chemicals killed other plants as well. So, scientists began to look at the area that the weed came from.
In Europe, Klamath weed is also known as St. Johnswort, and it is kept under control by specific predators. So in 1944, researchers imported two species of beetles from southern France. These pea-sized, metallic-colored beetles were so adapted to the Klamath weed that they feed and reproduce only on it. They were introduced to the rangeland around the Klamath River.
By 1948, the two species of beetles were so well adapted that researchers stopped importing more beetles. By 1959, a survey showed that the infestation of the weed had been reduced to one percent of its former range. This was the first large-scale successful trial of biological control of weeds.
Ironically, now 50 years later, the Klamath weed is more commonly known by it original European name, St. Johnswort. The dried leaves and flowers of the plant are known as the herbal medicine St. John’s wort. The herb is thought to be an effective natural remedy for mild to moderate symptoms of depression, and some estimates put U.S. sales of the herb at over $45 million a year.