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County Attacks Die-Hard Grass At Cockroach Bay

Tribune photo by ROBERT BURKE

Hillsborough County is treating large areas of Guinea grass with herbicides to rid the exotic vegetation that grows rapidly and crowds out native plants.

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By SUSAN M. GREEN

The Tampa Tribune

Published: June 11, 2008

RUSKIN - It's the Bruce Willis of botanical bullies.

You can cut it, burn it, poison it. It just keeps coming back.

And it comes back big.

"It's so thick and so bunchy," said Brandt Henningsen, an environmental scientist involved in coastal restoration projects along Tampa Bay. "We're talking about a grass that's 6, 7, 8 feet tall. You can't walk through that."

The species: Guinea grass, native of Africa.

Its arrival: First spotted on Tampa Bay coastal sites eight or nine years ago.

Its departure: Scientists wish they knew.

Henningsen said he first noticed the towering green blades in 1999 or 2000, when he was working on a habitat restoration project for the Southwest Florida Water Management District at Cockroach Bay.

"Before that, it was cogon grass, cogon grass, cogon grass," Henningsen said, referring to another nemesis to native Florida foliage that's tough to kill. "This Guinea grass puts cogon grass to shame because it grows so big."

Like other vegetative villains, including Australian pine and Brazilian pepper, unchecked Guinea grass chokes out environmentally friendly flora and eventually creates a habitat that won't support the birds and wildlife that need native landscapes to survive.

"Biodiversity will be out the door," said Richard Sullivan, a Hillsborough County environmental scientist who manages the Cockroach Bay Aquatic Preserve.

"It grows until it becomes a monoculture, and then there will be nothing else."

Sullivan said Guinea grass is among the worst invasive species to threaten preservation tracts in Hillsborough County. The only two he considers bigger threats are Old World climbing fern and Japanese climbing fern, which infest trees and kill them by blocking sunlight.

At Cockroach Bay last week, environmental technicians sprayed a herbicide on hip-high clusters of Guinea grass that sprang back after a mid-April fire prescribed for land management. The verdant blades grew amid palmettos and pine trees that still sported charred trunks and withered brown foliage from the burn.

Last year, Patricia Ollen, an intern with the water management district, conducted experiments and identified chemicals that seemed to knock down the invasive species for the longest time.

Then Sullivan discovered another potentially effective treatment by accident as he was preparing the preserve's observation mound, nicknamed Mount Cockroach, for an outdoor reception.

He said he sprayed herbicide on huge clumps of the unwanted grass, then burned it.

"That was in October, and it still hasn't come back," Sullivan said.

He said he plans to continue experimenting with chemicals and combinations of eradication techniques this summer to try to rid the preserve of the unwanted grass.

Henningsen said he has noticed that Guinea grass is more prevalent on tracts that have been cleared or plowed and then left fallow for long periods. It has been seen at Rock Pond, the newest habitat restoration project being undertaken by the water management district on the south side of Cockroach Bay.

When native plants are re-introduced and become established in habitat restoration projects, they seem to keep the grass from running amok, Henningsen said.

Sullivan said he is optimistic that Guinea grass treatment at Cockroach Bay will pioneer eradication techniques for other county-owned preservation tracts.

"We'll get rid of it," he said. "We'll do it here at Cockroach Bay because we have some open areas."

Down the road, however, another pest plant may be lurking. Native to India, it is commonly known as giant reed and wild cane, and Sullivan said he saw patches of it in a ditch in Manatee County, just south of Cockroach Bay.

So far, he said, he has not seen it on Hillsborough County preservation land.

GUINEA GRASS

SCIENTIFIC NAMES: Panicum maximum, Urochloa maxima

DESCRIPTION: A fast-growing grass that reaches up to 9 feet tall and sends out long roots. It resists drought and fire but does not like wet areas.

ORIGIN: Southern Africa; introduced to the United States as livestock fodder

STATUS: Listed on the Florida Exotic Pest Plant Council's 2007 invasive species list, www.fleppc.org

WHAT MAKES A PLANT INVASIVE?

Scientists consider invasive plants to be nonnative species that escaped cultivation and spread, causing environmental or economic harm. The state and local governments spend tens of millions of dollars annually to keep invasive vegetation in check.

Sources: Center for Aquatic and Invasive Plants, University of Florida, and Florida Department of Environmental Protection

Reporter Susan M. Green can be reached at (813) 865-1566 or sgreen@tampatrib.com.

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