Biological weed control: blessing or curse? |

Biological weed control: blessing or curse?

Amy Hadden Marsh
Ag Talk

When I first heard about the Palisade Insectary, I imagined creepy scientists in white coats, creating giant Franken-bugs. You know, like the grasshopper that ate Grand Junction or some entomological version of a jackalope — probably because I have a very active imagination from watching too many sci-fi B-movies as a kid. But last fall I was working on some stories about weed control, and I had to go to the insectary, which is home to the Colorado Department of Agriculture’s biological weed control program. And, surprise, none of the scientists wore white coats and none of them were creepy, unless you think a fascination with bugs is creepy.

I toured the insectary’s maze of labs, offices and greenhouses just east of Grand Junction. And, yes, there were lots of bugs, which gave me the heebie-jeebies at first. But most of them are too small to really see and they’re all harmless to humans, and 99 percent of them are contained. In other words, no one handed me a net to wear over my face or a protective suit when I walked in, and I left unscathed.

Meanwhile, I learned a lot about biological weed control, starting with entomologist Dan Bean, director of the state’s biological control program and insectary manager. “Bio-control is the use of living organisms in pest management,” he explained. For example, the insectary got its start in the 1940s when a non-native pest called the Oriental fruit moth threatened to wipe out the local peach crop. Local farmers didn’t have chemicals to control the moth so they decided to try a tiny, parasitic wasp that attacks the moth and kills it. The plan worked, and the insectary still raises millions of the wasps every year.

Most of the bugs at the insectary are used to control invasive plants. Bean said the target list of plants is based on which ones are causing the most problems around the state, and it’s a moving target. “We gain targets as we get biological controls for them and as they become more serious pests,” he said. Russian knapweed fits that bill. So do Canada thistle, field bindweed, leafy spurge — which is the focus of Garfield County’s Purge the Spurge program this month — and others.

The insectary releases and monitors about 20 species of bio-control agents for both weed and insect pests — either for study or to private citizens who want to get rid of weeds without using chemicals. The bindweed mite is a common agent that feeds on field bindweed and eventually kills the plant. The Russian knapweed gall midge forms galls around the flowering head of the plant and keeps it from spreading seeds. The tamarisk beetle defoliates and slowly kills its eponymous plant.

Insectary scientists say that the bugs they work with are naturally occurring and are not genetically altered or specially bred to do their work — no Franken-bugs. And it’s effective. I’ve seen it in a rancher’s field south of Silt where the bindweed mite is slowly but surely killing off the bindweed, and in a study area near Rifle where the Russian knapweed gall midge is taking hold.

Biological weed control seems like a simple way to manage invasive species. You introduce the plant’s natural predator, and it gradually kills off the plant. But its success is limited. It takes a long time. It doesn’t work every time. And there’s the question of what happens to the bugs when their host plant is all gone. Do the bugs go after other plants?

Dr. Svata Louda, of the University of Nebraska, says sometimes they do. Her research in 1999 and 2000 proved that a weevil released in the early 1990s in the western U.S. to kill off the non-native Canada thistle also killed native thistles. She believes that bio-control is not as environmentally benign as it seems.

“The real constraint on bio-control is trying to predict the behavior, dispersal, reproduction and population growth of an exotic species in a new ecosystem,” she explained. “Once you release a self-reproducing, self-dispersing bio-entity into an environment, you can’t stop it even if you’ve decided it’s a mistake.” She said scientists must monitor bio-control agents already released before moving on to new ones.

Personally, I think bio-control is a good idea, but it’s also a symptom of a larger problem: over-managing local ecosystems. Humans brought the Asian tamarisk, for example, to the U.S. in the 1800s to control erosion. Now, it’s considered an invasive species, notorious for consuming lots of water and turning native ecosystems into monocultures. So what do we do? We introduce a bug to help take out the plant. So far, the tamarisk beetle has remained true to its host plant, but the beetle is one more human-introduced tool to manage a human-induced problem. It’s like taking medication to relieve the side effects of taking medication.

Bean admits that some agents haven’t worked well, but other than the Canada thistle, the agents he and his colleagues work on do not jump plant families. He sees a positive future for bio-control to reduce the use of pesticides.

Bean believes that applied research, such as what’s done at the Palisade Insectary, is necessary. “It’s up to us as bio-control practitioners to make the bio-control agents we currently have work as best as we possibly can,” he said. “It’s a challenge. It’s not just a matter of tossing them out the window. We have to know the agents very well and know how they work on a [target] plant or insect.”

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