MISSION AND GAMBA GRASS

Introduction

   Mission Grass        Gamba Grass

 The Northern Territory Fire and Rescue Service (NTFRS) recognises a potential increase in fire danger across the Top End of the Northern Territory. The introduction and rapid spread of mission and gamba grass has greatly increased fuel loading (tonnes per hectare of flammable material) of the wooded savanna ecosystem common throughout the region.  This substantial increase in fuel loading combined with the later curing time has the potential for a major change in the fire regime across the entire Top End.

Mission grass (Pennisetum polystachion) and gamba grass (Andropogan gayanus) were introduced to the Northern Territory as experimental pasture for the cattle industry. They share many similarities, including their African origin, prolific seed production and ability to colonise non pastoral land.  Both grasses have thrived in the tropical environment of Northern Australia.

Distribution....

Particular concern is expressed toward gamba grass introduced by Commonwealth Scientific and Industrial Research Organisation (CSIRO) into the Katherine Research Station in 1946.  Seeds were then taken to Berrimah Experimental Farm in the 1950s.  A large infestation of gamba grass  in the Hidden Valley area originates from the experimental plots at Berrimah farm.

Gamba and mission grass are both prolific seeders, usually in May during the height of fire hazard abatement in the rural area.  Contractors involved in slashing or hay making and transportation are though to be a major contributor to the spread of seed along our roadways.  Recent wet season flooding has deposited seeds and encouraged growth throughout the rural areas.

Comparative Fuel Load....

Considerable evidence shows that intense late dry season fires have a devastating effect on the wooded savanna common to the Top End.  Experiments at Kapalga in Kakadu National Park found a 14.3% mortality rate occurred in native trees and shrubs subjected to intense late season fires [Lonsdale and Braithwaite, 1991].

Fuel loads for the savanna in the Darwin rural area are on average low.  Total fuel loading estimated of savanna in the Top End vary between 2.6 tonnes per hectare. and 5.6 tonnes per hectare. [Mott and Andrew, 1985 and Panton, 1993].  Fuel loading comparisons [Peris Barrow, 1995] within areas densely infested with gamba grass showed on average a fuel loading twice as high as an adjacent area free of gamba grass.  Three test sites were used, Hidden Valley, Wildman River and the intersection of Stuart and Arnhem Highways.

Particular interest for the NTFRS is the fuel loading for Hidden Valley at 17 tonnes per hectare. and Stuart and Arnhem Highway intersection at 20 tonnes per hectare.  The figure shows the site at Stuart Highway also has a greater volume of other vegetation due to the presence of weeds such as mission grass.

NTFRS Approach....

To approach the problem of a changing fir regime, the NTFRS initiated a "gathering of experts" to establish the level of research and possible solutions for this increased threat to public safety.  This meeting was held at the Litchfield Shire offices on 12 May 1997.  (Participants can be found under acknowledgments.)

Participants confirmed that the major threat to both the public and the environment from the uncontrolled spread of mission and gamba grass, was from hotter and seasonally later fires.  NTFRS firefighters have experienced great difficulty on controlling and extinguishing fires in heavy infestations of mission and gamba grass.  In the past St John Ambulance has given medical air to firefighters overcome by the intense heat and huge volume of smoke from burning gamba grass.

The areas most likely to be affected by this change in fire regime are the large undeveloped private and government owned parcels of land.   Fires on these large blocks generally develop very quickly and firefighters are often forced to combat these fires on the boundaries.  Attempting to back burn off narrow fire breaks between four meter high hedges of dry grass would be a very dangerous practice.

The NTFRS is assisting the Department of Primary Industry and Fisheries in the mapping of mission and gamba grass in the Darwin Fire District.  The information gathered will identify high priority areas suitable for the upcoming wet season control program.

Slashing Mission and Gamba Grasses

Cost to the Community....

Cost to the community may occur from an increase in property loss.  Large uncontrollable wild fires may also inflict loss on the local horticultural industry.  The greatest loss however, will be felt by the environment, as much of the Top End native flora and fauna will not survive the change in the fire regime.

The grass fire fighting units used by the NTFRS have proved to be insufficient in water capacity and pump pressure for quick control of fire in gamba and mission grass.  Additional funding may be required to replace the light weight grass fire units with larger capacity appliances capable of foam application.

Management....

Gamba grass is fire resistant  - experiments have shown that regrowth was generally greater in burnt blocks than that in unburnt areas.   Late dry season burns did achieve suppression of regrowth, however, the resulting high mortality of native vegetation makes this option unsuitable.

Ploughing followed by harrowing had some success, however, this option would only be suitable for open paddocks where alternative pasture can be planted to prevent invasion of other weeds.  Hand grubbing and removal of individual plants was very effective in the eradication of gamba from Kakadu National Park however, this is a very labour intensive method.

Slashing does not kill mature plants, however if slashed at least three times a year seed production may be reduced [Misha and Chaterjee, 1968].  The interaction of slashing and herbicides has also shown to have little effect.  The reduced leaf area simply led to less absorption of herbicide.

The greatest effect of trailed herbicides has come from Glyphosate.  This is absorbed through the leaf and distributed through the plant finally killing the root system.  Glyphosate is relatively cheap, readily available and does not generally kill woody plants unless contacted with the leaf.  Experiments have shown that spraying with Glyphosate and wetting agents during the plants maximum growth period, mid wet season, is the most successful method of control.

Although gamba grass has been recognised as a problem outside the boundaries of the pastoralists it is still not classified as a weed.   Until this occurs weed control legislation is not an option to restrict the spread of gamba seeds.  The NTFRS and the BFCNT do have legislation to issue fire hazard reduction notices to property owners where fuel loading has reached dangerous levels.

Conclusion....

The "gathering of experts" at the Litchfield Shire Chambers on 12 May 1997 supplied the Fire and Rescue Service with much valuable research data and management advice.  Common advice given by researchers is the warning of change to our present fir regime.  Concern was expressed that the very high fuel   loading and late curing of gamba grass will lead to intense, destructive, late dry season fires.

It is clear that the most effective and efficient option for control of gamba grass is by the application of herbicide.  Application of herbicides by spraying has, in the past, created some public outcry.  Further trials should be conducted to test the suitability of wick applicators which brush on the herbicide to possibly reduce the amount of spraying along road sides.

The participants also recommended a substantial education program to inform the public of the fire hazard of mission and gamba grass and also encourage private land owners to control the plants of their properties.  Public education to the potential dangers of uncontrolled spread of mission and gamba grass may reduce the public outcry usually associated with the use of herbicides.

The success of any control program will be determined primarily by the level of funding.  If the spread of mission and gamba grass is not stemmed there will be a significant change to the fire regime within the Top End and as a result a significant change will occur within out environment.

Media release

Acknowledgments....

The NTFRS thanks the following participants who answered the call of assistance to better understanding the problem we face with the invasion of mission and gamba grasses:

Grant Flannigan - Department of Primary Industry and Fisheries
John Pitt - Department of Primary Industry and Fisheries
Graeme Shultz - Department of Primary Industry and Fisheries
Gary Cook - Commonwealth Scientific and Industrial Research Organisation
Sabylla Brautigan - Department of Transport and Works
Hannah Feneley - Department of Transport and Works
John Brock - Litchfield Shire Council
Gerry Wood - Litchfield Shire Council
Libby Benson - Department Lands Planning and Environment
Bill Panton - Parks and Wildlife Commission of the NT
Piers Barrow - Kakadu National Park
Mike Clark - Greening Australia NT Incorporated
Simon Goodhand - Greening Australia NT Incorporated
Russell Anderson - Bush Fire Council of the NT
Jeremy Russell-Smith - Bush Fire Council of the NT

A special thanks must go to John Brock, Litchfield Shire Vegetation Officer, who gathered the experts and set the scene of co-operation between the various participants.  Much of the information in this brief is credited to Piers Barrow, who compiled an extraordinary amount of information on gamba grass in his final report to the Australian Nature Conservation Agency, The Ecology and Management of Gamba Grass (Andropogan gayanus Kunth, 1995).