Friday, December 08, 2023

Weevil nursery planted near Libby

| September 3, 2004 12:00 AM

By Roger Morris, Western News Publisher

The weevils are back.

County weed program director Dan Williams is spreading knapweed root weevils around the county and hoping to establish a ³nursery² near Libby.

The knapweed root weevil attacks the root of the spotter knapweed plant.

The distinctive gray, black and white weevils are easy to spot, especially on a sunny, warm day.

³The weevils climb to the top of the knapweed plant and rest on the flower waiting for a mate,² Williams said. ³We were out yesterday (Tuesday) looking for them.²

The weevil was initially released in a drainage in the Yaak in 1997 by the U.S. Forest Service. Williams said there is a dramatic difference in that drainage seven years later.

³It generally takes about two to three years for the bugs to make a difference,² he said.

The knapweed root weevil crawls down the plant and eats its way into the crown of the root where it lays its eggs. Larvae hatch in 10-12 days and begin to tunnel into the plant root. They overwinter in the root of the plant.

In the spring the adults chew their way out of the root and emerge in mid-July to early September. They spend most of their 10-week life on the root crown.

Williams purchased 375 weevils from a Bozeman company, Biological Control of Weeds Inc. He released weevils in the Troy, Eureka and Libby areas and used 150 bugs to establish a ³nursery² on the knap-weed laden clay banks across Libby Creek from the old mill site.

³I¹m trying to create a nursery where we can gather the weevils and spread them all over the county,² he said.

He expects to be able to harvest weevils in 3-5 years. Williams picked that location because the clay banks are an area that can¹t be disturbed, making it the perfect location.

³I should be able to gather some in three years from over there,² he said.

In addition to the weevil, past efforts have released a seedhead fly that consumes the knapweed seeds, Williams noted.

³By using both we¹re eliminating the seed source and the plant,² he said.

And Williams advocates using herbicides on an annual basis to kill knapweed.

³You have to use the biological and the herbicide to control this or we¹re not ever going to get control over it,² he said. ³We can¹t spray herbicide over the whole county, it¹s too large.²

And the herbicide doesn¹t harm the bugs.

He also warns area residents that knapweed seeds lay on the soil surface, which shouldn¹t be disturbed. It¹s estimated that a plant produces a 15-year supply of seeds.

³As you walk on them, drive on them, till the soil or build a road, you¹re planting all these seeds,² he said.

For more information about knapweed, the knapweed root weevil or other weeds in the county, call Williams at the Lincoln County Weed District, 293-7781 ext. 260. Or visit Biological Control of Weed¹s website at