Grand County Weed Control supervisor Tim Higgs said the method involves the use of tiny insects called gall midges, which weaken the knapweed plant during its early growth stages.
“It reduces the amount of seeds produced and controls the spread of the plant, even though it probably won’t kill the plants themselves,” Higgs said.
He added that herbicides and other control methods will still likely be needed.
“It’s part of an integrated approach,” he said.
Russian knapweed (Acroptilon repens) is a noxious perennial with purplish colored flowers. The plant was accidentally introduced from Asia to North America in the late 19th century. Russian knapweed has since become a problem throughout 45 states and several Canadian provinces. The invasive plant tends to crowd out other vegetation and can be toxic to horses and other livestock, Higgs said, adding that the weed can be found throughout Grand County in riparian areas along the Colorado River, in meadows and fields, and even in the mountains.
Higgs said recent tests conducted in a mesh 6-by-12 foot tent set up on private property near Cisco, about 30 miles northeast of Moab, have shown that the midge gall does damage the knapweed plants without harming beneficial plants. The midge also has been found to be effective in controlling perennial pepperweed, another noxious plant, he noted.
“There were a couple of earlier attempts that didn’t take, but this one seems to be doing well,” Higgs said. “We’re trying to get it established so we can send it to other parts of the state.”
The county’s plan is to eventually introduce the gall midges to a 20-acre site along the Colorado River, to see if they will help control knapweed there, he said.
The weed control project is one of several ongoing efforts that are being conducted with the approval of the Grand County Council, in conjunction with the Animal and Plant Health Inspection Service (APHIS) and other agencies, as part of the Utah Partners for Conservation and Development’s (UPCD) Watershed Restoration Initiative.
Other methods of bio-control have seen success in the Grand County area, Higgs said. The most notable example of successful bio-control is the tamarisk beetle, first introduced to the area in 2004 to combat the spread of tamarisk, or salt cedar trees.
“We’ve seen an 80 percent decrease in tamarisk in some areas, with numerous trees now dying and falling over,” Higgs said.
Although not as widespread as they once were several years ago, the tamarisk beetles’ effect on the salt cedar trees can still be seen, with browning tamarisk foliage still being observed along many sections of the Colorado River, he said.
In addition, a certain species of mite has been shown to be effective in curbing the spread of bindweed, Higgs said, noting that experimental testing with that bio-control agent is now being done at a site in Castle Valley.