1991 April: Wagait and Daly River Reserves. Weed Control: Tebuthiuron

Just For Once, Nature Needs Chemicals

Sydney Morning Herald Tuesday April 30, 1991 CHIPS MACKINOLTY

WHILE conservationists around the world would be expected to oppose the use of herbicides, the Australian Conservation Foundation (ACF) is poised to support the use of chemical defoliants to rid Australia of an introduced weed that endangers tropical wetlands stretching from Bundaberg in Queensland to Broome in Western Australia.

It has not been an easy decision, according to the ACF’s Mike Krockenberger, but one that is necessary in the face of Mimosa pigra – an exotic Central American shrub that has established itself as the major threat to native fauna and flora across millions of hectares of Australia’s northern coastline. “We don’t endorse the use of these chemicals elsewhere, but we feel that – with strict controls and monitoring – its use is justified.”

But it is not just green sensibilities that are at stake. It is an issue that fundamentally affects thousands of Aboriginal people. Mimosa has forced the Aboriginal-controlled Northern Land Council to plead for urgent assistance to stem the tide of a biological enemy that poses a threat to the lifestyle of thousands of their own people, as well as tourism and other developments in the region.

Not only can mimosa wipe out world renowned heritage areas such as Kakadu National Park, it has the potential to choke virtually every river system in northern Australia. With some 800 square kilometres of the Northern Territory already covered, it is suggested that mimosa-affected land can potentially double in size every year.

At this stage, most infestations are on Aboriginal land, but, according to the director of the Northern Land Council, Mike Dodson, mimosa is a danger to the entire North.

An introduced plant, mimosa has no natural predators in Australia, and has proved a ruthless competitor as it has established a monoculture that has destroyed all native fauna and flora in its path. The strength of its conquests may be seen by the fact that it can produce up to 12,000 seeds per square metre compared with only 100 seeds per square metre in its native Mexico, where it normally faces hundreds of natural predators.

Mimosa was first introduced to northern Australia in the late 1800s as a stock feed, and caused little problem until it was first noticed in the Adelaide River region of the Top End in the ’50s. Even now, infestations mostly affect only Aboriginal land in Arnhem Land, Wagait and Daly River reserves.

Mimosa forms dense, impenetrable thickets that choke out virtually all other plants and thereby in turn deprive native birds and animals of their food and natural environment. From only 100 hectares in the Oenpelli region on Aboriginal land east of Kakadu in the early ’80s, the infestation had reached 7,000 hectares within six years.

The Northern Land Council, which has been involved with the Northern Territory and Commonwealth governments in small-scale mimosa eradication measures in the Oenpelli region since 1987, has proposed an extensive use of Tebuthiuron and other chemicals over a five-year program to limit the spread and, it hopes, limit the range of mimosa infestation until such time as biological agents can be introduced to control the weed.

The environmental projects officer for the Northern Land Council, Mr Andrew Jackson, says that chemical control is the only practicable method available in the short term. “Mechanical techniques don’t work – bulldozers can’t cope because of the way the plants grow: they just run over them without killing. Hand removal only works in small isolated pockets and large-scale removal such as the use of napalm is entirely inappropriate.

“To contain, let alone remove, Mimosa we are forced to propose chemical eradication methods. Biological methods are at least five years away, despite active research.”

Tebuthiuron, marketed as Graslan, is the principal chemical proposed, and would be applied in a pellet form by fixed-wing aircraft as well as helicopters.

According to an environment report prepared for the council and released publicly a fortnight ago, it is highly unlikely to spread to watercourses, although it is expected that there will be some “sacrifices” among native trees, including eucalypts common across areas where the mimosa will be targeted.

The council says that such losses would be outweighed by environmental benefits derived from the eradication of the weed. The choice, according to Aboriginal interests, is the spending of money on chemical defoliants now rather than reaping the harvest of a biological disaster in years to come.