In other areas, they’re targeting white-footed mice, a major source of blood for deer ticks. They soak cotton balls with insecticide, place the balls in PVC pipes and leave the pipes in the forest. Mice use the cotton balls to make nests, and when ticks get on the mice the insecticide kills them.

“It’s a bit like treating your dog with Frontline,” Paskewitz said.

In some plots, the researchers do both activities. In others, they do neither, so they can compare the effect.

Monthly, from May to August, they trap mice and chipmunks, and drag white sheets across parts of each area, to count ticks and test them for Lyme.

Last year, in the sites where buckthorn was removed and/or cotton balls were used, about 4 percent of immature ticks tested were infected with Lyme. In the untouched areas, it was 12 percent.

Overall, the figure was 8 percent. Statewide, it ranged from 5 percent in the northeast to 32 percent in the northwest.

The Arboretum plots where both activities were done also had about half the number of immature ticks last year as the areas that were left alone, Paskewitz said.

“It looks like we have reduced the risk of encountering an infected tick significantly,” she said.