A hardy invasive grass that has grown out of control on Kaua'i and the Big Island has taken root on O'ahu, threatening one of the island's most pristine valleys and an urban Windward neighborhood.

Bush Beardgrass (Schizachryium condensatum) is a drought-tolerant grass that grows in dense clumps, displaces native plants and increases the risk of brushfires.

State authorities feel they can thwart the plants' growth on O'ahu, but first they have to get the help of Island residents — something they've been struggling with since the eradication started three years ago.

A team from the O'ahu Invasive Species Committee has been working to control the growth of the grass in Halawa Valley. Although the plant is nearly eradicated in a residential area next to the Valley of the Temples Memorial Park in 'Ahuimanu, total success eludes the group because it is unable to get access to a couple of sites where the noxious plant grows.

"It's not something where we don't have the manpower," said Josh Fisher, field supervisor. "We have the manpower to go in every month."

Fisher said one resident who has the grass growing in her yard refuses access and another resident hasn't been home to grant access. The seeds from plants in those yards are spreading across the entire neighborhood, which has about 200 homes, he said. He also said the committee has no power to force cooperation and is considering asking for legislation that would place the plant on a noxious weed list, thereby giving the state Department of Agriculture the power to act.

The team recently visited the 'Ahuimanu neighborhood, leaving flyers and approaching residents to ask permission to remove or kill the invasive pest. The committee has been working in 'Ahuimanu for about two years, making monthly visits and pulling the grass from homes in the upper reaches of Hui Kelu Street and the roads that spike from it, including Hui Ulili Street and Heno Place, Fisher said.

The beardgrass grows along roads or in areas where the soil has been disturbed. A vacant lot in 'Ahuimanu was home to hundreds of plants until a house was built on the property, he said, adding that when the control program in 'Ahuimanu began two years ago the team removed a thousand plants a month. Now, only six or seven are found on the monthly trips, he said.

Each plant produces large, tufted heads, each with millions of seeds that are spread by the wind, animals, vehicles and people. In 'Ahuimanu, the team is monitoring about 40 homes that can become a breeding ground for the pest.

The Invasive Species Committee wants to prevent the grass from spreading to the drier areas of the island, said Christine Meyers, a team member. The committee, a partnership of government, organizations, landowners and communities, targets 10 invasive species — and two of them are grasses.

Meyers said the team was out on patrol in Halawa Valley yesterday, scouting a three-mile stretch of the H-3 maintenance road where the plant is concentrated about midway up the valley. The road runs parallel to the freeway, sometimes crossing under the freeway and over the stream.

Invasive species line the road where soil is disturbed, a perfect environment. The committee believes the seeds were brought to O'ahu via construction vehicles from the Big Island, which were used for the H-3 project, Meyers said.

Above the road, forests of 'ohi'a, kukui and hau cover the hillsides along with ferns.

"We don't want it to spread any further up in the valley because it's so native and pristine," she said.

Wildlife authorities say the grass is beyond control on Kaua'i and the Big Island.

On the Big Island, "It's pretty abundant from 2,000 to 4,000 feet (above sea level)," said a staffer at the Hawai'i Volcanoes National Park.

Kaua'i rancher and agricultural extension agent Lincoln Ching said ranchers from the north to the southern parts of the island are looking for ways to control it, because their animals won't eat it.

"For us, it's a problem because it's a fire-promoting species," he said. "No animals graze on it. Goats have been tried, cattle don't eat it, and horses don't touch it."

The grass established itself on Kaua'i after Hurricane Iwa in 1982 and spread dramatically during Hurricane Iniki in 1992, said Ching and forester Galen Kawakami of the state Division of Forestry and Wildlife.

"It started on the North Shore, but it's now in Hanalei, along the western ridges, the Na Pali cliffs, around Halfway Bridge, it's in the (Alaka'i) Swamp and you find it on the south side," Kawakami said. "The seeds are so light that they will go airborne in two shakes."

To eradicate, the team cuts off the grass's distinctive flowering heads, bags them and takes them to the city's incinerator, Meyers said. The team has no trouble finding the 3-foot tall plants, but if residents continually cut them, they will flower just inches off the ground, making them difficult to see, Meyers said. Plants are usually pulled to get the roots and on occasion chemicals are used in stubborn established sites, said Meyers, adding that they prefer to pull the pest.

"We try to veer away from using chemicals because of the watershed," she said.