The European import had arrived on this country's shores sometime in the mid-1920s. By the late 1960s, the plant was already crowding out native grasses and taking over large portions of the Montana landscape.
“Back then, knapweed was everywhere,” Story said. “Every piece of unmanaged pasture was completely covered with knapweed, especially here in the Bitterroot Valley.”
“The economic return on rangelands was simply not enough to justify the cost of applying herbicide over that large of an area,” Story said. “Everyone realized that conventional control methods weren't going to do the job this time around.”
Story was among the first group of researchers who began looking at the potential of controlling the weed using its own natural enemies.
He traveled to Europe and on hands and knees sought out the flies, weevils and other bugs that depended on knapweed for food and reproduction. He helped develop the tests that ensured the insects wouldn't harm beneficial plants once they were released into Montana's wild. And then he found ways to raise them and then spread them about.
Now, more than 30 years later, Story is one of the lucky few who know that his life's work has made a difference.
“There's no question that anybody who's been here in the Bitterroot Valley will certainly recognize that there's less knapweed here now than what there was,” Story said. “There's been a significant change.”
The chief culprit for that change is a root weevil not much bigger than a fingernail. Brought here from the eastern European countries of Romania and Bulgaria, the bug's voracious appetite for knapweed root dramatically weakens the plants over the course of a couple of years.
The weevil was first released onto Montana knapweed fields in 1988.
It took some time for the bug's numbers to reach a critical mass large enough to affect knapweed populations, but Story's seen it happen over and over again.
“The last couple of years I've received phone calls from farmers wondering what this bug is that's crawling all over their fence posts,” he said. “I've seen solid stands of knapweed reduced to the point it's hard to find a plant.”
The weevil wasn't the first bug that researchers imported into this country.
That honor went to a tiny fly whose larvae had an appetite for knapweed seed. Since the mid-1970s, researchers have received the USDA's green light to release a dozen varieties of knapweed-eating bugs.
The different bugs attack the plant from both above and below ground.
That combination - plus perhaps some help from Montana's long-term drought - has proved effective in reducing knapweed, Story said.
It hasn't happened overnight.
“One of the problems we've faced is that it takes a long time to establish a population of insects,” Story said. “Spotted knapweed isn't a plentiful plant in eastern Europe. There aren't many bugs to collect.”
Over the years, Story and others have perfected methods to reproduce and grow large numbers of the insects at the agricultural center and other locations.
“There was a time lag before the insect populations were large enough to actually start making an impact,” he said. “It's now some 30 years later and we're seeing the impact.”
There are now five different insects flying around Montana that feast that on knapweed seeds.
“They're now very well established,” Story said. “We're seeing a measurable reduction in the number of seeds produced by knapweed plants in the range of 50 to 75 percent.”
There have been some unexpected ecological shifts along the way.
Ecologists have documented that deer mice populations grew after that species learned to key on the larvae eating knapweed seed. And now, researchers have noted that another invasive weed, cheatgrass, often replaces the dying knapweed.
Cheatgrass has its own issues.
The weed can outcompete other native plants because it takes advantage of early spring moisture and is often finished growing before other plants even get started. Cheatgrass also cures early in the season and makes a fine fuel for wildfire.
“It can create a whole new set of problems,” Story said.
There are no guarantees when it comes to tinkering with nature. The spread of knapweed and other invasive weeds change the landscape and the way flora and fauna relate to it.
“We're not God,” Story said. “We can't predict everything that's going to happen. We try to do this as safely as possible, but there are no guarantees that we can return everything back to the way it was.”
Montana still has about 4 million acres infested with knapweed.
“We've got a long way to go before we see all of that controlled,” Story said.
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