Texas Parks & Wildlife Magazine   


Mean Green Aliens

In the battle against invasive plants, scientists try everything from airborne herbicides to ravenous bugs to sterile fish.

By John H. Ostdick

When a federal government program in 1823 began introducing the pink-flowered, gangly saltcedar (Tamarix spp.) into the western United States to stem the rate of soil and bank erosion in arid riparian systems, administrators overlooked how the trees might react when removed from their natural predators.

The long-term results had far-reaching consequences: The saltcedar spread and multiplied at voluminous rates, choking off native grasses, cottonwoods and willows. Today, saltcedars occupy more than 800,000 hectares ( 1.977 million acres) of highly valuable land along streams and lakeshores from the central Great Plains to the Pacific, and from Montana into northern Mexico. In 1999, the NASA-sponsored Texas Synergy Project identified 12,500 acres of likely saltcedar stands in the state, data that the Texas Department of Agriculture is using to prioritize control efforts.

Saltcedars and other invasive species are wreaking havoc on a number of the state’s lakes and rivers, crowding out more beneficial vegetation while putting down water-sucking roots along shorelines, in some instances clogging rivers and power plants, damaging wildlife habitats and, in the most severe instances, killing out other aquatic life in lakes.

The economic impact of terrestrial and aquatic invasives is staggering — yet difficult to estimate with any precision. According to the Washington-based Union of Concerned Scientists, an independent nonprofit alliance of more than 100,000 scientists and concerned citizens, the nationwide economic impact of invasive plants is $13 billion a year. Certainly, water-related invasives pose a significant threat to the state’s water quality and supply, wildlife habitats, its tourism and the more-than-$6-billion sportfishing industry.

In February 2003, UCS published the results of a three-state study (Texas, Alaska and West Virginia) that provided the first comprehensive tally of invasive species. In Texas, it identified 122 non-native species — from the saltcedar to beaver-like rodents called nutria — that are “wreaking havoc on Texas’s crop lands, native plants and animals, and the state’s resource-based economy,” reports Phyllis Windle, a UCS senior scientist and invasive species project manager.

Invasive species are legally defined as alien species whose introduction does, or is likely to, cause economic or environmental injury or harm to human health. Any species not native to an ecosystem is considered an alien species; the introduction can come in many forms, both intentional, as in the case of the saltcedar, and accidental.

“Basically, saltcedar is in every river west of Interstate 35, with the possible exceptions of maybe the Nueces and the Frio,” says Danny Allen, an Austin-based analyst with the Wildlife Habitat Assessment Program at the Texas Parks and Wildlife Department.

Hydrilla (Hydrilla verticillata), first introduced into North America in the mid- to late-1950s by the aquarium trade, is one of the state’s worst aquatic invaders. Today it covers about 100,000 surface acres and is growing in nearly all of Texas’ 100 reservoirs, according to Earl Chilton, Aquatic Habitat Enhancement Program Director for Aquatic Vegetation Programs at TPWD in Austin.

Dense mats of hydrilla alter water quality by raising pH, decreasing oxygen levels under the mats and increasing water temperature. Stagnant water created by hydrilla mats also provides good breeding grounds for mosquitoes. Hydrilla growing from the bottom of the water body increases the roughness of the bottom, slowing the conveyance of water.

Giant salvinia (Salvinia molesta) is a floating, rootless water fern native to South Africa. Predators control its population within its natural habitat, but outside their reach it spreads astronomically, doubling its population every two to eight days. It can grow to 2 feet thick, and kill off an entire body of water, says TPWD’s Chilton. In Texas, the fern was first noted in a small pond in 1998; it now has been documented in 10 public waterways and many more private bodies. The floating invasive is particularly insidious: A single leaf transported into a new water source on boat trailers or propellers can launch a new population.

Water hyacinth (Eichhornia crassipes), a free-floating plant native to South America, can vary in size from a few inches tall to more than 3 feet and produces a showy purple or lavender flower, which makes it a popular ornamental. However, massive weed colonies can grow when introduced into areas that are conducive to their proliferation — posing a significant challenge in East Texas in Caddo Lake, Toledo Bend, Lake Houston, Lake Livingston and Lake Texana. Texana is a Molotov cocktail of invasives, with hydrilla, giant salvinia and water hyacinth all present.

In most cases, eradication of these invasives is extremely problematic because of both cost and logistical factors, especially in larger bodies of water and in rivers that pass through large tracts of privately held property. Biologists and agency officials are searching for the best methods to restrict new introduction and a combination of chemical and biological agents to control their existing populations and limit the damage they can cause in Texas waters.

Sitting in his Temple office amid boxes of research and correspondence that have put down almost as many roots as the nearest stand of saltcedars some 300 miles away, Jack DeLoach believes he has a viable biological control for the invasive species.

“Many people have never heard of biological countermeasures, although the practice began in 1863,” says Deloach, an entomologist with the Grassland Soil and Water Research Laboratory at the U.S. Agriculture Department’s Agriculture Research Service. “There have been 1,100 cases of insects being released in more than 25 countries since.”

DeLoach, who started working on the saltcedar problem in March 1986, is a member of the Saltcedar Biological Control Consortium, a coalition of about 35 federal and state agencies, universities, and private and environmental groups organized in 1997 to research biological control alternatives to saltcedar infestations (about one-third of the participating organizations are in Texas).

“When saltcedar first invaded the Colorado River, it spread at the rate of 50 to 60 miles a year,” says DeLoach, whose longish, slightly askew gray hair, large glasses, dark blue work shirt with pocket protector, and blue jeans embody how a New Yorker cartoonist might sketch an entomologist. “They have tiny seeds that ride on the wind or are carried on the water. Talk of saltcedar eradication is nonsense. What you try to do is keep the population controlled, below the threshold of damage.”

In five overseas trips from 1992 to 1998, DeLoach and consortium colleagues helped identify more than 20 types of insects that were tested against all related plants in the saltcedar-affected areas. After research indicated it would not harm other organisms in the regions involved, DeLoach gained approval to use a leaf beetle from Fukang, China, and Chilik, Kazakhstan, for sample testing release.

DeLoach was ready to do the first release in 1995 when federal concerns about a possible threat to the willow flycatcher, an endangered species that had started nesting in some isolated saltcedars in New Mexico, delayed the project while DeLoach conducted follow-up impact studies. In May 1999, his group received approvals for open field tests at eight of 10 approved sites, including West Texas. Under an agreement with the U.S. Fish and Wildlife Service, researchers will not release the beetles within 200 miles of a flycatcher nesting in saltcedar.

Although DeLoach could have done some cage tests at that point, Texas open field tests were delayed another two years because the original beetles proved ineffectual in the state due to climate differences from their native land. “We had to find more beetles in the Mediterranean area (Diorhabda from Crete) and test them,” he notes.

The worst concentration of saltcedar in the country is along the Rio Grande, from Presidio to almost El Paso. “It’s called the ‘Forgotten River,’ because water from the El Paso area is absorbed by the saltcedar and doesn’t make it to Presidio,” DeLoach explains.

Although early estimates of the water saltcedars actually draw per day were highly overestimated, where the saltcedars grow and how they impact habitats make them formidable threats to water resources and wildlife habitats. The saltcedar not only chokes water supplies, it also degrades existing water and soil quality by secreting salt from its leaves.

Cottonwood and willows are far more valuable from a wildlife habitat perspective, DeLoach notes. “Further, cottonwood and willows can only live in areas where there are shallow water tables,” he says. “Saltcedar can live in both shallow and deeper water tables, so it can grow much farther back from the river, using water over the whole river valley. That’s why they use a lot more water overall.”

The Texas Parks and Wildlife Department, the Texas Department of Agriculture and the Texas A&M Extension Service are involved in various ways with other entities on the saltcedar project, wildlife habitat analyst Allen says.

“For example, the Texas A&M Extension Service has been doing a project on the Pecos River, in cooperation with the Pecos River Water Authority, spraying the river with a herbicide carrying the trade label Arsenal, from Red Bluff Dam all the way to the confluence with the Rio Grande,” he says. “The river authority considered it an important water-yield project, calculating that for every dollar it spends on the treatment of saltcedar it can get so much value in water return. In many places, for saltcedar control the money is the problem — it costs about $180 an acre to spray.”

Because spraying with herbicides like Arsenal results in about a 90 percent kill immediately, many local entities see it as the best option. “But Arsenal will kill all the vegetation there [it’s not toxic to wildlife because it specifically works on a photosynthesis pathway],” Allen says. “When we’ve still got a mix of some cottonwoods in there, some willows or some native herbaceous vegetation mixed in, and you’ve got a sprinkling of saltcedar, it becomes more of an issue.”

Control efforts are adopting “almost a two-pronged approach,” Allen says. “There are immediate needs that we’re spraying, and hopefully we can use biological control to get into the spots that we can’t reach and to use as a long-term to control regrowth.”

The phone rattles loudly in DeLoach’s Temple office.

Consortium partner Ray Caruthers, of the Exotic Invasive & Weeds Research Group of the USDA-ARS in California, is touching base before traveling to a laboratory just outside of Buenos Aires to do further saltcedar research.

“I owe my life in the program to Ray Caruthers,” DeLoach says. “He got a $3 million grant that all of us involved in this project shared for four years. We’re out of money, and we’re just getting started on our work. We need about $800,000 over a three- to four-year period, shared between members of the research project, and then we can get this well on the way.”

The project has had its greatest success with 1,400 beetles released in Lovelock, Nevada, in May 2001. In September, local researchers reported that 65,000 acres of saltcedar have been defoliated, 100 miles up and down a river system. In areas where there is other vegetation, the saltcedars are defoliated but the other plants are untouched, DeLoach says.

In the rosiest of scenarios, DeLoach thinks the Crete beetle can do the same in Texas — they are actually only established at Big Spring and Artesia in the open field — and other southwestern states. “Three years from now, these beetles could control all of the saltcedar along these release areas and no additional controls will ever be needed,” he says.

DeLoach and technician Tom Robbins, who has been working on the project for more than 20 years himself, walk toward a cluster of meshed beetle testing tents at the research center.

“This is as close to natural conditions as we can get and still keep them confined,” DeLoach says. The researchers bag branches with larvae on them so they can study them and how much they grow, including an over-wintering program to see how the beetles survive the Texas winter and how soon they emerge in the spring.

On a blustery early-spring day, inside the tents the saltcedars’ pinkish flowers, which emerge before their wiry green foliage, are just popping out. A smattering of tiny green beetles works up and down the gangly trees. “It doesn’t matter how small the beetles are if there are enough of them,” DeLoach says. “Eventually, we’ll have field days here, and landowners will be able to come pick up beetles from the lab and release them on their own property. The only cost will be gasoline that they use in coming to get them. We’re about ready for that in several places.”

Finding further research funds is the greatest obstacle DeLoach faces. He has modest expectations for a March meeting, which drew “representation from all aspects of society, federal and state agencies from both Texas and New Mexico,” seeking to build a broader consortium for the project.

Federal and state agencies are battling aquatic invasives in the state with a combination of harvesting, chemical and biological measures as well.

In giant salvinia’s native habitat, a hyperactive small weevil — Cyrtobagous salviniae — controls the spread of salvinia. They were used as a highly effective countermeasure in Australia and New Guinea, and are being tested in the United States.

“About the best we can hope for is to keep it (salvinia) under control," says Chilton of TPWD’s Aquatic Habitat Enhancement Program. “While herbicides can prove effective at eliminating salvinia from small bodies of water, cost and impact considerations make large-scale eradication efforts impossible on large reservoirs or river systems.”

From 1998 to 2003, a three-part cocktail of mechanical harvesting, herbicides and the introduction of sterile carp (a controlled introduction of sterile fish shouldn’t have a long-term impact on the native fish populations) helped water managers get the upper hand on the hydrilla problems along the Rio Grande south of McAllen, Allen notes. Significant problems remain upstream between McAllen and the International Falcon Reservoir.

UCS senior scientist Windle, cites the importance of the National Aquatic Invasive Species Act, which would reauthorize 1996 legislation that expired in 2002. Windle worries that the legislation’s complicated reach will continue to stall it in Congressional subcommittees.

“It was first introduced in 2002, when the ’96 act expired,” Windle says. “There is increasing pressure to break the legislation apart and just pass its first section, which deals with ballast water issues. I’m increasingly worried that would take us back to the piecemeal approach to the whole invasive species issue that has failed us in the past.”

On April 13, 2005, nine senators co-sponsored a reintroduction of a bipartisan National Aquatic Invasive Species Act to “reauthorize and strengthen the National Invasive Species Act of 1996.” As introduced, it would “regulate ballast discharge from commercial vessels; prevent invasive species introductions from other pathways; support state management plans; screen live aquatic organisms entering the United States for the first time commercially; authorize rapid response funds; create education and outreach programs; conduct research on invasion pathways, and prevention and control technologies; authorize funds for state and regional grants; and strengthen specific prevention efforts in the Great Lakes.” Five representatives also introduced complementary legislation consisting of two bills, one research-oriented and the other geared toward preventive measures for the future.

“The lack of funds is certainly an issue for Texas,” Windle says. “This legislation also addresses for the first time what we call screening of intentionally introduced organisms for invasiveness before they could be introduced. That is a pioneering step we really need.”

In the last year, Congress passed four separate laws on invasive species, but all were very narrow and often addressed a single species or particular issue. Windle concludes, “This problem cannot be addressed on a species-by-species basis.”

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