Garlic mustard was introduced to the United States from Europe and has become a problem because it is an opportunistic plant with no natural enemies here.
Garlic mustard looks far less fearsome in Europe, where numerous insects eat it, so a primary hope for controlling it here is to purposely introduce one or more of those natural enemies — specifically, a weevil, said Adam Davis with the U.S. Department of Agriculture’s Agricultural Research Service in Urbana, Ill.
This biological control plan has its own hazards: Scientists have to make sure the new pest eats only garlic mustard and that it won’t run amok, creating a new problem.
Major research is going on at Michigan State University, East Lansing; Cornell University, Ithaca, N.Y.; the University of Illinois, Champaign-Urbana, and the Centre for Agricultural Biosciences International in Switzerland. The latter was chosen because experiments can be done outside of quarantine since the weevil is already there, Davis said.
“The field experiments look hopeful,” he said. “In its home range, where it has to deal with the weevil, garlic mustard looks scruffy. It’s on the ropes.”
He hopes the weevil can be released within five years. “I’m sorry I can’t say it will be this year, but we need to err on the side of caution,” he said.
As for how this weevil would get disseminated over the millions of acres where garlic mustard is a problem, Davis sees hope in citizen-scientist involvement — that is, regular people helping to rear the weevils and getting them to woodlands.
A similar tactic has been used in Michigan, where elementary school students have reared beetles used to control purple loosestrife, an invasive plant now in wetlands. “That model has a lot going for it,” Davis said.
There is hope on another front, too, albeit in the future.
A major problem with garlic mustard is not just that it crowds out native plants but that it also secretes allelo-chemicals into the soil that actually suppress the growth of natives.
A concern is that, over time, the oak and hickory forests as we know them would disappear because tree seedlings and wildflowers would not grow.
But now there are indications that these allelochemicals become weaker over time.