Control gamba grass

Before you spray

You should consider the following when you are planning to spray your property:

• spray only when leaves are green and at least 40cm long - glyphosate can be absorbed only by growing leaves and stems
• spray early in the wet season, before it reaches full height - this gives better results for less herbicide and effort
• before spraying, consider removing tall, dry grass stems and encouraging new growth of mature gamba grass - controlled burning or slashing may help with this
• allow time for slashed, mown, grazed or burnt gamba grass to grow new leaves before spraying
• always spray before seeding
• gamba grass is still susceptible to herbicide when flowering.

Where to prioritise

You should prioritise fire risk areas.

All gamba grass within 15m of roads, tracks, property boundaries, houses, sheds and other infrastructure must be controlled.

Control all gamba grass in fire access trails. This also prevents spread to adjoining properties.

Eradicate isolated plants and outbreaks to prevent establishment in new areas.

Control plants which are likely to cause further gamba grass spread, such as on the edge of tracks.

Ensure your control efforts do not contribute to unintended seed spread.

Under the law, you must follow instructions on the herbicide label.

Read the safety data sheet of any herbicide you use for information including:

• potential health effects
• first aid
• personal protective equipment
• spill and disposal procedures.

Follow these guidelines for safe herbicide use:

• don't spray plants other than declared weeds as glyphosate can kill plants other than gamba grass if it comes into contact with them
• don't spray in windy conditions as spray drift can damage plants you are not targeting
• don't contaminate dams, waterways or sewers with glyphosate.

For more advice on using herbicides, go to page 8 of the NT Weed Management Handbook PDF (1.3 MB).

Watch a gamba grass mixing herbicide demonstration below.

You must dilute the glyphosate before you apply it to gamba grass.

When you dilute glyphosate, you must use only the described ratio of water to herbicide.

For glyphosate 360g/L , mix 1 litre of concentrate with 100 litre of clean water for a 1% ratio.

Ratios that are:

• too strong can burn leaves and may not kill the whole plant.
• too weak may not kill the plant.

You must do all of the following:

• mix herbicide with rainwater, tap water or good quality bore water
• not use creek or dam water that may contain clay or organic matter
• consider adding a wetting agent to help the glyphosate get through the hairy surface of gamba grass leaves
• consider using a marker dye to show if you missed any weeds.

Watch a gamba grass spraying demonstration below.

The following is a checklist for how and when to spray:

• Adjust your nozzle to produce medium to heavy size droplets so you can get full coverage of the plant while reducing spray drift.
• Coat the entire plant - each stem of a gamba grass tussock is an individual plant, if any stems are missed the plant can recover.
• Spray until herbicide drips from the leaves to make sure it gets through the fur on the leaves.
• Don't spray in windy conditions to avoid damage to non-weed plants nearby.
• Use only aquatic approved glyphosate near watercourses to avoid harming plants and animals in the water.
• You should spray in the mornings, and at least an hour before rain as it takes an hour for plants to absorb the herbicide.

For best results, you should spray:

• every part of the plant
• when actively growing and young (when leaves are at least 40cm long)
• before they reach full height - this 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.

If plants have not wilted and yellowed within 4 to 7 days, you will need to spray again.

Check all treated areas for missed plants, regenerating plants and new seedlings.

You may need 3 or 4 rounds of spraying for good results in the first year of control.

Follow-up control in subsequent years will also be necessary.

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.

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
• provide improved access to control by other means.

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.

You should treat plants with herbicide before 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.

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 4 to 5 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.