Miconia calvescens, commonly known as "miconia," originally hails from South and Central America, and was introduced to Maui in the 1960s and '70s as an ornamental plant. One mature plant, which is able to self-fertilize, can produce more than a million seeds in a matter of months. And new shoots grow quickly, which means the plant reaches maturity in three to four years. As well, miconia's shallow roots affect the forest's integrity, and modify the ecosystem by crowding out other vegetation. In large enough numbers, this purple plague can suck parts of the watershed dry.

From its initial introduction, miconia has spread to approximately 80 square kilometers of Maui's eastern slope.

Leary, originally from Michigan, first came up with his novel plan to fight Hawai'i's miconia around a decade ago. The green-draped jungle of Maui's eastern slope is extremely rugged and mostly uninhabited. The clouds forced up by the steep sides of the Haleakalā volcano make the area one of the wettest on the planet. Reaching parts of this area on foot would mean climbing cliffs and passing over waterfalls. Putting boots on the ground carries some risk, both to the scientists and the ecosystem.

"Every time we go into these pristine areas by foot, we are imposing impact," Leary says.

As it happens, miconia often grows at the edges of cliffs where Leary suspects perching birds drop seeds.

The team needed a way to kill the plants from afar, and herbicide-filled paintballs seemed the perfect answer. Leary contacted chemical and paintball companies, and eventually brought them together to make a product that could be tested for use in the field. Each paintball delivers about the same amount of active ingredient as an aspirin tablet, he says, and this small quantity is by design. A "high precision, high accuracy, and surgical mentality" allows the team to target the miconia from a distance of up to 30 meters, while minimizing splash damage to the surrounding vegetation.

"You're literally shooting plants. It's like a weed safari," Leary says of the technique, dubbed "Herbicide Ballistic Technology."