Environment: Weed Wars

In the fight against invasive plants, conservationists are bringing out the small guns.

Hawaii’s extreme landscapes—steep cliffs, remote valleys—don’t make it easy for natural resource managers to tackle Miconia calvescens, a species that’s earned a reputation as an invasive and potentially damaging plant. But conservationists aren’t waving the white flag just yet. Enter Hawaii’s newest weed-fighting weapon: the paintball gun. (Yes, the same, off-the-shelf version with which you bombard your best friend.)

Since early last year, a new method called Herbicide Ballistic Technology (HBT) has been used in East Maui and in Wailua on Kauai to combat miconia. Here’s how it works: A pilot, a spotter, and an applicator fly over miconia-inhabited areas in a helicopter, searching for culprits. When a plant is located, the pilot skillfully maneuvers the chopper within 100 feet. Herbicide-filled capsules are then fired at its branches. Soon, it’s lights out for the weed.

“One of the greatest problems in controlling miconia is that the species likes to grow in areas that are hard to reach,” says James Leary, research specialist with the College of Tropical Agriculture and Human Resources at the University of Hawaii. He came up with the concept about six years ago, though paintball was never a personal hobby. “With HBT, we can now effectively treat about 100 plants in an hour, with very small amounts of herbicide,” he says. “That’s a lot of miconia in a little amount of time, with a small footprint on the landscape.” The federal and state registration process for HBT took two years. The technology isn’t being used anywhere else in the world. 

Miconia was introduced to Hawaii as an ornamental plant in the early ’60s and, today, has infested forested watersheds on all islands, except Lanai and Molokai.

A typical mature tree can produce a few million seeds, two to three times per year. Worse, the seeds—the size of sand grains—need little light to germinate and can survive 20 or more years. Once grown, its large leaves shade native understory plants, leaving sparse ground cover that can lead to soil erosion.

Before HBT existed, another herbicide-based technology, dubbed the spray ball, had been used for more than 20 years to treat miconia. Controlled by a helicopter pilot, the tool delivers herbicide to a plant from an 80-foot cable connected to the belly of a helicopter. The technology was derived from the US Drug Enforcement Agency, who used the tool to eradicate marijuana. The only problem is that the device has to be able to hover over a target. That’s where HBT comes in. A shooter can hit miconia even if it’s growing under a tree canopy, or sideways on a steep cliff. “We just changed the game in being able to treat all targets,” says Leary.

He notes, however, that the spray ball is still effective for areas with a large amount of miconia, since it can treat multiple plants faster. “It’s essential to have diverse tools for different situations,” adds Teya Penniman, manager of the Maui Invasive Species Committee (MISC), a partner in the HBT project.

The next phase for HBT includes miconia treatments in Manoa. Future stages could include targeting other invasives, such as kahili ginger, Australian tree fern and strawberry guava.

Did you know? In Tahiti, miconia has affected more than 70 percent of the island's native forests, a warning to Hawaii conservationists.