A large Russian thistle plant is shown growing along a fenceline. The USDA proposes to biologically control Russian thistle with a mite. (Courtesy Forest and Kim Starr/Star Environmental)

The USDA proposes to turn loose tiny mites from Eurasia to gnaw on that symbol and scourge of the West — Russian thistle, also known as tumbleweeds, which also originated in Eurasia.

Tumbleweeds clog irrigation canals, harbor crop-eating pests, fuel wildfires, tumble into traffic and pile up against fences and homes. Tumbleweeds are tough to root out and are becoming resistant to herbicides, according to the USDA’s Animal and Plant Health Inspection Service.

The microscopic mite, Aceria salsolae, might help, according to an APHIS assessment published June 27. The mites have been collected in Turkey, Uzbekistan and Greece and have been found only on Russian thistle.

Because the mites are host specific, it’s unlikely they will feed on native plants, according to the assessment.  “The mite is not expected to directly harm any plants outside the targeted Russian thistle,” APHIS states.

Tumbling tumbleweeds are not native to the United States. Russian thistle was accidentally introduced in 1873 in flax seed planted in South Dakota, according to APHIS. The thistle spread to a dozen states over the next 20 years and now infests 100 million acres in the West, the equivalent of 45 Yellowstone parks.

APHIS describes using the mites as classical biological control — recruit from the Old World the ancient natural enemy of an exotic plant making trouble in America. Worldwide, biological weed control programs have been successful 33% of the time, according to APHIS.

APHIS assessed using the mites in 2009, but decided against issuing permits. A USDA entomologist pointed to research showing the mites could survive for several weeks on three plants native to California.

A later field experiment confirmed the mites could survive for weeks on at least one of the plants, but in low densities and with no signs of reproduction.

Once released on a tumbleweed, the mites could go anywhere. When a mite finishes feeding on a thistle, it moves to the top of the plant, stands on its head and waits for a gust of wind to blow it away, according to APHIS’ assessment.

“Dispersing mites have little control over how long they are blown and where they land,” the assessment states.

If the mites work, farmers will save money, according to APHIS.

Crop pests such as beet leafhopper, Say’s stinkbug and lygus bug depend on Russian thistle to get through dry months. Without the thistle, more insect populations would die out each summer, according to APHIS.

Cattle will graze on young Russian thistle before the plants become prickly. Grazing apparently has not slowed down tumbleweeds much, however, according to APHIS.

The USDA will take public comments until July 28 on issuing permits to release the mites.