HUNTINGTON, Vt. — Last year, when the sap stopped running from some of Bruce Curavoo's maple trees, it kept running in others. He got enough to make about 300 more gallons of syrup from his crop.

His secret: A tiny adaptor that, when plugged into tap holes, helps reduce the amount of sap flowing back into trees from the vacuum tubing used to carry it to sugarhouses for boiling into maple syrup.

"They work," says Curavoo, 36, of Starksboro, who used the device on half his 5,000 trees last year and will use it on all of them this year. "The longer you keep the sap running, the more (syrup) you make."

Last year, he used the check valve adaptors on half of his trees. This year, he's got them on almost all the trees as he awaits the start of the season, which typically begins in mid-March.

The adaptors were developed by maple researchers at the University of Vermont to extend the six-week sugaring season. By reducing backflow, the gadget limits the amount of naturally-occurring pseudomonas bacteria, microorganisms that can end sap flow if they get back into the tree, causing it to reflexively wall off the tap hole as a defense.

Made of hard nylon, it's about an inch tall, sells for 35 cents per unit retail and looks like a tiny rocket ship. But developers say it has big possibilities — the potential to sharply boost sap yield.

Typically, when a vacuum system is shut off or a line is punctured or ripped out by a falling tree, the tapped tree reflexively begins to suck sap back in from tubing, sometimes carrying bacteria. Once the tree detects that, it begins to wall off the tap hole, stopping sap production.

Last year, maple production nationally dropped by nearly 20 percent, according to the U.S. Department of Agriculture, the result of warm weather that started sap runs early — before some trees were even tapped — and ended them in early April.

Vermont, the nation's leading producer, made 890,000 gallons of maple syrup, down slightly from the year before because of a string of early April days with temperatures in the 70s and 80s.

Sugar makers in Maine, New Hampshire, and New York tried the device for the first time in 2010, though no one knows exactly how many, or how they affected production overall.

It takes about 40 gallons of sap to make a gallon of maple syrup, and the sap starts running from trees when temperatures rise into the 40s by day and drop back into the 20s by night.

"The ones that have used them are using them again, they feel there's promise in them," said Peter Purinton, a maple sugar producer who used the devices on his trees last year and distributes them for supplier Leader Evaporator Co.

Timothy Perkins, director of the University of Vermont's Proctor Maple Research Center, who helped develop it, said almost all those surveyed by UVM after last year's season said they would try it again this year.

At 35 cents a tap, what's to lose?

Still, not everyone was impressed. Tim Taft, 38, a sugar maker who lives near Purinton, used 90 of the adaptors in his 5,000-tree sugarbush last year.

"We saw no difference," said Taft. "They didn't run any longer than the other spouts." But he's trying again this year, saying that even if he gets longer sap runs once every five years, the adaptors will have been worth the investment.

Perkins says research by UVM and Cornell found the device did improve sap yields last year.

UVM, which owns the rights and has a patent application pending, licensed the device to maple equipment supplier Leader Evaporator, in Swanton, which sells it. Perkins gets 45 percent of the University's licensing revenue from the deal.

According to Perkins, the fluctuating nature of year-to-year maple syrup production and the fact that not all producers are using the device make it unlikely that it would result in a glut of syrup on store shelves — or a price decrease.