Turning a non-native weevil loose to feed on the invasive weed yellow starthistle likely won’t harm native plants or cause other environmental damage, the USDA said Tuesday.
The USDA announced in the Federal Register that it will permit Ceratapion basicorne, an insect native to Europe and western Asian, to be used to control a weed that poisons horses and harms grazing lands.
Yellow starthistle infests 16 million to 20 million acres, mostly in California but also in Idaho, Oregon and Washington, according to the USDA. Ranchers are most affected by the infestations, the agency said.
The USDA noted that biological controls often don’t work and said it was difficult to predict how effective the weevil will be on yellow starthistle.
The weevils won’t kill plants, but they will reduce seed production. “The weevil is not expected to cause extinction of yellow starthistle, but it is expected to continue impacting the weed year after year,” according to USDA’s environmental assessment.
The announcement came more than 10 years after the USDA released a report on enlisting Ceratapion basicorne in the war on yellow starthistle. Since then, research has shown the weevil isn’t likely to spread to other plants, including safflower, according to the USDA.
Initially, weevils will be released at several sites in California. In the future, the USDA anticipates releases in Idaho, Oregon, Washington, Nevada and possibly other states.
The weevils will be descendants of ones collected in Turkey in 2001. The USDA has raised them in a laboratory in Albany, Calif.
Yellow starthistle was introduced to the U.S. in contaminated alfalfa seeds shipped from the Mediterranean to California during the gold rush.
Land managers have tried to control the weed with herbicides, and by mowing and tilling. Other biological controls — beetles, flies and a pathogen — have been tried, too.
Some value yellow starthistle, the USDA notes. The plant provides late-season forage for bees.
It’s toxic to horses, however. Continued feeding causes a fatal syndrome known as “chewing disease.”
The weed is not poisonous to other animals, but the flowers have inch-long spines that can damage eyes, according to the USDA. Cattle that subsist on yellow starthistle will lose weight, the agency said.
The USDA said there was a “slight possibility” the weevil would attack other plants.
“If other plants were to be attacked by C. basicorne, the resulting effects could be environmental impacts that may not be easily reversed,” the USDA stated.