Gamba grass

Gamba grass is a declared Class A and Class C weed except in areas where it is classified as Class B and Class C

It is also a Weed of National Significance.

Go to the Weeds of National Significance website for more information.

Go to the gamba grass declaration zone map (729.1 kb).

Gamba grass also has a statutory weed management plan (1.6 mb) which outlines the legal requirements for control, and a weed management guide (8.5 mb) with more information.

Another name for this plant is Andropogon gayanus.

Find out about free help to control gamba grass.

Gamba grass - infestation 

Identification

You should use this as a guide. There may be other plants or weeds that look similar.

If you are unsure, contact the Weed Management Branch.

Habit

These features describe the habit of this plant:

  • tussocks up to 4m tall
  • up to 70cm in diameter.

Gamba grass - habit

Stems and branches

These features can identify the stems and branches:

  • robust
  • covered in soft, white hair
  • shallow root system up to 1m diameter
  • stems dry off after seeding and may appear dead.

Gamba grass - stems and branches

Leaves

These features can identify the leaves:

  • up to 1m long and 3cm wide
  • distinctive white midrib
  • stay green after native annual grasses have died off
  • covered in fine soft hairs.

Gamba grass - leaves

Seed heads

These features can identify the seed heads:

  • flower heads are on tall stems above the leaves
  • seed heads are v-shaped
  • seed head consists of up to six groups of branches.

Gamba grass - seed heads

Seeds

These features can identify the seeds:

  • fluffy
  • contained within a v-shaped seed head.

Gamba grass - seeds

Similar looking plants

While it is very important to control gamba grass on your property, it is also important to avoid accidentally removing certain beneficial native grasses that will compete with the invasive weeds and help the native bush to regenerate. The following plant species look similar to gamba grass:

Itch grass (Rottboellia cochinchinensis) is a native perennial grass that also has a distinctive white midrib, however stems and leaves are smooth, flexible and lack furry white hairs. There is little harm in confusing the two grasses and many people choose to control itch grass as well.

Itch grass 

Giant spear grass (Heteropogon triticeus) is a native perennial grass that grows up to 1.8m tall with smooth stems and hairless nodes.

Giant spear grass (Heteropogon triticeus) 

Northern cane grass (Mnesithea rottboellioides) is a native perennial grass that grows up to 2.5m tall with smooth, hairless, branching stems and sharp spiky rhizomes.

Northern cane grass / Mnesithea rottboellioides 

Impact

Gamba grass is tolerant of drought, fire and low nutrient soils found in north Australian savannas. 

It produces up to 250,000 seeds per season that can establish in both disturbed and undisturbed areas. It grows rapidly to form tussocks which are bigger, taller and denser than native grasses. 

Gamba grass can have all of the following impacts:

  • creates high fuel loads which cause late and intense fires
  • fires dramatically alter the structure of native plant communities
  • severely decreases biodiversity
  • replaces woodlands with tall grasslands
  • alters water cycles.

Habitat and distribution

Gamba grass is originally from Africa. It was introduced to the Northern Territory (NT) as a pasture species in the 1930s. Research and trials resulted in wide plantings in pastoral and agricultural areas of the Top End.

It currently affects up to 15,000 square kilometres of the NT, but has the potential to affect 380,000sqkm of the NT. Most infestations are north of Katherine.

Gamba grass is suited to most Top End soil types, except for heavy clays. 

It needs at least 600mm of rain each year. Gamba grass generally flowers in April, with seed production and fall from May to August. A second seeding may occur in November in response to an early Wet Season.

Spread prevention

Gamba grass seed can be spread via wind, water, livestock, feral animals and on contaminated machinery. It can also be spread accidentally in landfill, gravel or bailed hay containing seeds.

You can prevent the spread of gamba grass by doing all of the following:

  • map infestations to help develop a management plan
  • control minor infestations, isolated outbreaks or seedlings first
  • design and implement a seed spread prevention program
  • designate wash down areas and actively work to prevent contamination of clean areas
  • schedule control works prior to seed maturation
  • in areas where gamba grass can be legitimately used for pasture, graze it with enough stock to keep grass height below 90cm, in order to reduce seed production
  • spray/destroy any tussocks that establish on fence lines, fire breaks and roadsides or outside paddocks
  • ensure any gravel, sand, livestock, hay or any other product is free of gamba grass seeds
  • monitor areas that you have treated and watch for re-infestations
  • where possible integrate weed management into a broader natural resource management program.

Gamba grass - spread

Control

Chemical control

The best time to treat gamba grass is from December to March. Below is a list of treatment methods that can be used.

Chemical and concentration Rate Situation, method and notes
Glyphosate 360 g/L
Various trade names and formulations
10mL / 1L Seedling or adult (individuals or infestation):
Foliar spray - apply when actively growing (Dec-Mar)
Use surfactant

Effective chemical control of gamba grass relies on spraying the entire plant. 

For optimal uptake of the herbicide and high mortality rates gamba grass should be sprayed when actively growing and young (leaves should be at least 40cm long). 

Spraying plants prior to reaching full height will reduce time and herbicide requirements. 

Gamba grass is still sensitive to herbicide when flowering. Once gamba grass is seeding and the leaves are drying out herbicide will not work.

Non-chemical control

Hand pulling and grubbing

Weeds, including their roots, are physically pulled out of the ground by hand or using hand tools. 

This is an effective method of control for individual weeds and recent outbreaks that haven’t released seeds yet, but it requires a lot of labour.

Slashing

A brush-cutter, slasher or mower are used to cut weeds off above the ground level. 

This can be effective in suppressing flower and seed development.

Slashing will not eradicate gamba grass, but it can reduce the biomass, prevent seeding, create an opportunity for more desirable species to establish and provide improved access to control by other means.

Fire

Fire as a management technique is most effective when it is used together with other methods. 

It is useful for mass seedling control if there is a sufficient fuel load.

Burning will not kill gamba grass, but low intensity fires, undertaken in the wet season, can remove rank growth improving access for slashing or spraying. 

Plants may need to be treated with herbicide prior to burning to create enough dry matter to carry a fire. Fire may have the ability to carry seed in hot air currents, therefore avoid using fire as a control method while plants are seeding.

Grazing

In areas within the Class B declaration zone gamba grass may continue to be used in established pasture areas, however there is a requirement to disallow any further spread. 

Gamba being used as a pasture should be grazed with enough stock to keep grass height below 90cm. 

Above this height tussocks may be avoided by stock and allowed to produce vast quantities of seed. 

After lightly grazing pasture in the early wet season, a stocking density of four to five head per hectare is required to control growth for the remainder of the wet season. 

Increase grazing pressure if the grass nears 90cm. Gamba grass is not recommended for cattle production on smaller properties as it requires high stocking densities to keep it low and palatable.

Last updated: 27 June 2017