Will weevils help? There are cases where weevils have controlled milfoil in N. Michigan

Jeff Broddle | Cadillac News Milfoil damaged by weevils is displayed by EnviroScience Project Manager Cortney Marquette, who was recently stocking weevils in Lake Cadillac. Although it is too early to say for sure, Marquette said it is possible weevils could be used to control milfoil in the future Ñ without the help of chemicals.

It is a problem that can quickly get unmanageable if not taken care of.

It can slow down engine propellers on boats, grab swimmers and make it impossible to go fishing.

The culprit is milfoil.

“There are a number of reasons why milfoil is a nuisance, mainly because it is so aggressive,” said Howard Wandell of the MSU Department of Fisheries and Wildlife. “It tends to negatively affect native species because it forms a canopy. It is bad for recreation and can quickly get out of hand.”

Although there is no way to completely get rid of the plant, there are three known methods to control the weed — including harvesting and herbicides.

Using chemical herbicides can be very costly, and harvesting can cost quite a bit of money, too. But for those lakes with an abundance of weevils, milfoil can be controlled for virtually no expense.

CADILLAC — It is the same story every year.

After wintering in the brush along the shoreline, weevils awake from their hibernation at the first scent of milfoil — yes, they can smell it — like a freshly brewed pot of coffee in the morning.

The tiny bugs, the size of a sesame seed, make their way to the milfoil beds through flight. They then eat to their heart’s content, but making sure they don’t eat up all of their food source.

Once fall comes along, the tiny bugs use their weak wings to make the journey back to shore, where they collapse and hibernate until the next spring.

That is the plight of a milfoil weevil, although one weevil doesn’t make that journey since it has a lifespan of about 30 days.

Every year, more than tens of thousands of weevils make that journey in Paradise Lake in northern Michigan. The weevils have been maintaining milfoil to levels acceptable to boaters and others who use Paradise Lake for water recreation. Paradise Lake Association President Marilyn Smith doesn’t see that changing anytime soon.

“This is our 10th year using weevils,” said Smith. “We put in 12,000 weevils that year in three spots, and haven’t had any problems. Those and the weevils that were here naturally have really helped.”

In 1996, the city called Carp Lake had an aquatic plant study done that identified 17 percent of the lake as having dense surfaced milfoil. After looking at all the options — including harvesting, chemicals and cutting paths through the milfoil — the lake association decided to use weevils.

“We were one of the first lakes to go this route and it has worked for us,” Smith said.

It worked so well, in fact, that the city holds an annual festival honoring the weevil.

There is no known way to totally eradicate milfoil from a lake, except killing all the vegetation and fish. Therefore, milfoil isn’t totally out of sight.

“Every other year you see a little resurge of weeds, but it has never come back nearly as bad as the beginning,” Smith said. “We had three major beds at that time — one disappeared and never came back. We still have less than 10 percent of the total volume with milfoil.”

As for Lake Cadillac, there is a natural population of weevils, according to Cortney Marquette of the Lake Management Division. Last year was the first year more weevils were added to the lake.“It seemed to have worked really well,” she said. “But chemicals were used, too, away from where the weevils were stocked.”

Although the chemical won’t hurt the weevil, it does take away its food source. Since weevils aren’t good swimmers or flyers, they usually try to find milfoil as close to shore as possible.

“With a large lake, like Cadillac or Mitchell, it might be difficult for them to get a half mile or mile from land,” said Howard Wandell of the Michigan State University Department of Fisheries and Wildlife. “To survive the winter, weevils need something more than just lawn to survive. They need a good area with vegetation.”

Another obstacle for weevils is predators. Those lakes with an abundant supply of blue gills may not be a good place to stock weevils.

“Blue gill love to eat weevils — they chow down on them,” Wandell said.

A large benefit for using only weevils in Paradise Lake, besides it being chemically free, is the cost factor. After the initial cost for 12,000 weevils — with it costing about $1 per bug — there has been no cost since.

But it still remains to be seen if local lakes could survive on weevils alone.

“It is different for every lake, and it is hard to determine whether Lake Cadillac could use just weevils after one year of stocking,” said Marquette. “But depending on what else they are treating, it is possible weevils could control milfoil long-term. The habitat for weevils seems suitable.”

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Ways to control milfoil

What can be done to control milfoil?

Milfoil can be controlled using natural killers such as weevil, aquatically approved herbicides or by mechanical means, such as a harvester or cutter. The DNR Aquatic Plant Management Program regulates the control of aquatic plants. In most cases a permit from the DNR is required to control aquatic plants, including milfoil.

What can I do?