Fungus Guarantees Rubbervine Will Not Bounce Back

BRISBANE, Australia, April 23, 2002 (ENS) - The alien invasive Rubbervine weed has been stopped in its relentless march across Queensland. The introduction of a fungus in combination with fire has worked when a hundred years of other efforts were unsuccessful, an international team of scientists said last week.

The rust fungus from Madagascar has proven to be a successful weapon in the eradication of Rubbervine weed (Cryptostegia grandiflora), an invasive vine that has choked more than 25,000 square miles of land in Australia, Hawaii, and Florida, reports CABI Bioscience weed pathology expert, Dr. Harry Evans.

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Rubbervine weed (Photo courtesy U.S. Dept. of Agriculture)
Since the middle of the 19th century, land owners have fought the voracious climbing plant with everything from backbreaking work to serial fires in an effort to stop its persistent growth.

Now, after a seven year trial, 95 percent of the rubbervine has been eradicated or is in retreat. Landowners are able to burn the intruding plant after the rust fungus has debilitated it enough for fire to succeed.

Rubbervine was brought to Australiaís early mining towns by settlers who longed for a touch of green amidst the harsh conditions surrounding the mines. Originally from Madagascar, the plant adapted to the wide open spaces of northern Australia. Rubbervines found easy routes up the native eucalyptus trees, and when the vines reached the canopy, they smothered the trees.

Robbed of vegetation, the sparsely located eucalypts died off in record numbers. Within a few years, the rubbervines encircled and choked off all the native trees and bushes. The denuded upper branches left most animal species without shelter, and they too began to die off at a record rate.

Since the plant is poisonous to animals and humans, it found no natural enemies. When the vine is dry, a fine powdery dust emerges which causes violent coughing, swelling of the nose and blistering of the eyelids in some people. Dried trimmings of the plant give off a dust that is irritating to the eyes, nose and throat. The acrid sticky milky sap is a skin irritant.

A single rubbervine produces as many as 8,000 other vines in a single season. Through seeds propagated by the wind, the plants leapt across the Australian outback.

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Rubbervines overgrowing a stand of eucalypts in Queensland (Photo courtesy CABI)
Rubbervine begins its infestations around waterways, where it blocks access to animals and then covers all the surrounding areas with a dense, choking foliage. The plants grow to such great heights and density that cattle and wild animals have found themselves trapped within the woody vines.

Rubbervine sap can be made into latex, but this useful characteristic was dwarfed by the negative impact the species was having upon the entire northern half of the Australian bush country.

Fire seemed the only answer, but land owners could not burn the vines fast enough to halt their spread.

In the late 1980s, the Queensland government declared the plant a menace to the state and charged landowners with eradication. But the cost to landowners to eradicate the aggressive vine made it out of the question for individuals.

Moving in to take charge of the situation, the Australian government tried aerial spraying of herbicides, to little avail. Meanwhile, the rubbervine was spreading toward the Australian National Parks. Aerial spraying was not only ineffective, but also environmentally undesirable.

The plant seemed beyond containment, and the situation hopeless until CABI Bioscience, a nonprofit organization based in the United Kingdom, offered to assist in eradicating the plant using a new rust producing fungus that attacks the underside of the plants' leaves.

CABI Bioscience is the scientific division of CAB International, a global, nonprofit organization that applies practical solutions to agricultural problems through sustainable applied life sciences.

Established by a treaty level Agreement among its Member Countries, CABI works with a range of stakeholders, including corporations, NGOs, institutes, governments, agricultural extension centers and farmers.

Exploratory surveys by CABI scientists in western Madagascar revealed the rust fungus (Maravalia cryptostegiae) to be a promising biocontrol agent. Extensive trials were carried out in quarantine in the UK to check the rust's virulence and purity.

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Rust on rubbervine leaf (Photo courtesy CABI)
Following mass production in Brisbane, Australia, the rust was released during the wet season of 1995 at 29 sites across Queensland, using manual and aerial spraying, and the deployment of rust infected plants and foliage.

"The rust is now present throughout the area of Queensland affected by the weed, which is estimated at over 40,000 square kilometers," said Dr. Evans.

The rust fungus has caused widespread defoliation and a marked reduction in the fecundity and biomass of the rubber vine weed. In some areas it has caused widespread plant death.

With the plants dying off, land owners have begun to set fires that may now eliminate the woody vine, enabling native plants and grasses to grow back. A series of controlled burns following introduction of the fungus has proven to be 99 percent effective in eradication of the rubbervine.

"The presence of the rust disease appears to have contributed to the success of the fire, and the amount of rubbervine killed," said project leader Dr. Faiz Bebawi. "Rust reduces the vigor of the plants, making the plants more susceptible to fire as well as enabling more pasture growth and therefore an increased fuel load."

"The trials have shown the follow up burn is essential. If a follow up isn't done, the 20 per cent of the weed that is not killed will regenerate from the base," Dr. Faiz said.

Wrotham Park manager Henry Burke agrees that the results of the trials were outstanding. "Fire is proving to be the most successful and economical way of controlling rubbervine," he said. "From this experience, we'll continue to use this strategy to control the rubbervine."

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Rubbervines infected with rust fungus die back and become burnable. (Photo courtesy CABI)
In Hawaii, the United States Geological Service lists 130 invasive plants, including rubbervine, as severe threats to the native plants.

Experts estimate that one new species was established in the Hawaiian Islands about every 35,000 years before humans arrived. Now, between 20 and 30 species a year become established on the islands, approximately a million-fold rate of increase.

Rubbervine has also been seen as an invader throughout the Pacific Islands chain, on all of the Virgin Islands and, most recently, in Florida.

Experiments carried out at the Northern Crop Science Laboratory (NCSL) in Fargo, North Dakota, have shown rubbervine to be a possible candidate for use as an industrial crop to meet demand for fuels, chemicals, and raw materials.

The plant appears to be an attractive possibility for fuel since it contains a high percentage of easily burnable biomass that produces more heat than equal amounts of coal. It requires minimal agronomic management, can survive extreme environmental conditions, and is suitable for annual harvesting.

The high oil content of rubbervine indicates that the species has the potential to produce raw industrial materials as an alternate source to petroleum.

Another attractive attribute is that the species has the potential to flourish in marginal arid lands where it would not compete with conventional agricultural crops.

But the NCSL study makes no mention of the plantís designation as an invasive species or its voracious propagating habits.