Weed Control Techniques

 

Once you have correctly identified invasive species on your property, you need to know what control techniques to apply. Remember that weed control requires persistence and an integrated approach conducted over time using different control techniques at different stages of a species lifecycle. Off target damage of indigenous species needs to be considered for both chemical and non-chemical techniques. Methods should aim to minimise the weed seed in the soil seed bank while promoting native seed.

Manual (non-chemical) control

Hand removal

Weeds can be pulled out by hand if it is easy to do so and if plant material will not be left behind (e.g. seeds, roots, rhizomes, and tubers). This method is most effective for seedlings and small infestations of grasses.

Care should be taken to ensure there is minimum soil disturbance, replacing it where necessary to minimise the opportunity for more weeds to become established. This method is often easier (and causes less disturbance) after rain. All fertile material must be bagged and disposed of carefully.

A knife is excellent for teasing weeds from in between desirable vegetation and helps to minimise soil disturbance. Other useful tools include use of a chisel, trowel, or daisy puller. A tree popper can be used to remove larger woody weeds.

Slashing

Slashing is useful for controlling or reducing biomass of annual and perennial weed grasses and shrubs. It is usually done using a mower, brush cutter or hedging shears. Care should be taken to minimise damage to indigenous plants and if herbaceous indigenous ground covers are present the slashed material should be removed.

Slash annual grasses high (10 cm above ground) and before seed heads start to develop, typically in late winter. This may require follow-up slashing after 4-6 weeks. As these are annuals, preventing the production of seed will ensure their seedbank will diminish over time. Perennial grasses can be slashed at any time of year, however best results will be obtained during winter and spring.

Solarisation

Solarisation is an effective chemical free weed control method for dense infestations of invasive grasses and herbaceous (non-woody) weeds using the heat from the sun. Cover the area with black plastic sheeting for at least a 4-6 week period before removing the plastic.

Although chemical free, consideration should still be given to off-target damage and loss of the ‘good’ soil seed bank, as indigenous species may be inadvertently removed.

Chemical control

Under Victorian legislation, there are controls on the use of chemicals. It is the responsibility of the herbicide user to be familiar with this legislation. You can find more information about the use of chemicals on the Agriculture Victoria website. Always follow the manufacturer’s guidelines when using herbicide chemicals to control weeds.

Cut and Paint

The cut and paint technique is often used for small to medium sized woody weeds or when the soil too dry for hand pulling.

Cut the stem close to the ground then apply systemic herbicide (neat or 90% diluted with 10% water) to the exposed stump.

 

The herbicide needs to be applied (usually using a dabber bottle) within 10- 20 seconds, as many weeds begin quickly sealing wounds, which reduces the absorption and effectiveness of the herbicide.

Drill and Fill

The drill and fill technique is very useful for larger woody weeds with a base 4 cm in diameter or larger. A drill is used to make 45-degree holes into the plant’s moist cambium layer (the thin, actively growing tissue between the bark and the wood of a tree).

The hole is then immediately filled with a systemic herbicide and left to die in situ.

The plant will drop its leaves within 6 weeks and die within a few months. It will be necessary to monitor the plant and if it resprouts, the process will need to be repeated.

Do not use this technique where there is a risk of the dying tree falling on roads, paths, dwellings or areas frequented by children such as playgrounds.

The soil beneath large woody weeds usually contains huge numbers of seeds from the parent plant. It is essential that follow-up control of seedlings or regrowth is undertaken in subsequent years.

There are benefits of leaving the plant to remain in situ to die, including retaining its habitat value, preventing the establishment of other weeds and minimising soil disturbance or erosion,

Frill and Fill

Instead of using a drill, a small hatchet or a chisel with a mallet can be applied to the trunk at a 45-degree angle to frill, or chip, the outer layers of the trunk, exposing the cambium layer.

These cuts must circle the entire trunk, at 5 cm intervals, however ensure that the plant is not ringbarked as herbicide will not be transported into the plant. Systemic herbicide then should be immediately applied to the exposed cambium layer.

Stem scraping

Mainly used on vines and small shrubs, a knife is used to scrape away a section of the outside bark before the inner tissue is painted with a systemic herbicide.

Wiping

Wiping foliage using a weedbrush or tongs is useful on large infestations of plants with bulbs, tubers or corms, especially those that are difficult to remove completely through hand removal. The brush or tongs are wiped onto the foliage of individual weeds. For plants with waxy leaves, it may be necessary to add a surfactant to allow the herbicide to be absorbed into the plant.

Spraying

Spraying should only be conducted where there little to no risk to indigenous vegetation. Take care that the herbicide does not drift onto native species, avoiding spraying in hot or windy conditions.

Should your specific situation require you to spray, engage a suitably qualified bushland regenerator or undertake training in the safe use of chemicals.