Herbicide application methods for weeds (invasive plants)

There are various application methods for treating weeds (called invasive plants in the Biosecurity Act 2014) with herbicides. It's important to choose the right method for your particular problem and the types of herbicides you are using.

Foliar spray

In foliar spraying, the herbicide is diluted with water or diesel at a specific rate, and sprayed over the foliage to point of run-off (until every leaf is wetted, but not dripping).

This method is most suited to shrubs, grasses and dense vines less than 6m tall. Advantages include quickness and economy. Disadvantages include the potential for spray drift and off-target damage.

Foliar spraying can be done a number of ways, including:

  • blanket spraying using a boom spray from a tractor
  • a hose and handgun spraying solution from a herbicide tank
  • a backpack spray unit
  • with splatter guns (larger droplets at higher concentrations) for regrowth.

Basal barking

This method involves mixing an oil-soluble herbicide in diesel and spraying the full circumference of the trunk or stem of the weed.

Basal bark spraying is suitable for:

  • thin-barked woody plants
  • undesirable trees
  • saplings, regrowth, and multi-stemmed shrubs and trees.

Basal barking will usually destroy weeds as long as the bark is not wet or too thick for the diesel to penetrate.

The following video demonstrates the basal barking method.

Transcript of video

Stem injection

The stem injection method involves drilling or cutting through bark into the sapwood tissue of woody plants and trees to transport the herbicide throughout the plant.

It is essential to apply the herbicide immediately (within 15 seconds of drilling or cutting), as stem injection relies on the active uptake and growth of the weed to move the herbicide through its tissue.

Drill and fill method

The drill and fill method is used for trees and woody plants with stems or trunks greater than 5cm in circumference, and is also referred to as tree injection.

This method uses a battery-powered drill to drill downward-angled holes into the sapwood approximately 5cm apart. Using a backpack reservoir and syringe can deliver measured doses of herbicide solution.

Only trees and shrubs that can be safely left to die and rot should be treated this way. If the tree or shrub is to be felled, allow it to die completely before felling.

Axe cut method

The axe cut method can be used for trees and woody plants with stems or trunks greater than 5cm in circumference. It involves cutting through the bark into the sapwood tissue in the trunk, and immediately placing herbicide into the cut. The aim is to reach the tissue layer just under the bark, which will transport the herbicide throughout the plant.

Using an axe or tomahawk, horizontal cuts are made into the sapwood around the circumference of the trunk at waist height. The axe is then leaned out to make a downward angled pocket to allow herbicide to pool. It's important not to entirely ringbark the trunk, as this will decrease the uptake of herbicide.

Cut stump

The cut stump method involves cutting off the weed completely at its base (no higher than 15cm from the ground) using a chainsaw, axe, brushcutter or machete. A herbicide solution is then sprayed or painted onto the exposed surface of the cut stump, with the objective of destroying the stump and the root system.

It is essential that the herbicide solution is applied as soon as the trunk or stem is cut. A delay of more than 15 seconds for water-based herbicides and 1 minute for diesel-soluble herbicides will give poor results.

The following video demonstrates the cut stump method.

Transcript of video

Cut and swab

This method is similar to the cut stump method, but is suited to vines and multi-stemmed shrubs. Here, the weed stems are cut through completely, close to the ground. Herbicide is then applied immediately to the cut surface emerging from the ground, via spray or brush application.

The following video demonstrates the cut and swab method.

Transcript of video

Stem scraper

Stem scraping is used for weeds and vines with aerial tubers. A sharp knife is used to scrape a very thin layer of bark from a 10cm section of stem. Herbicide is then immediately applied to the exposed, underlying green tissue.

Wick applicators

This method consists of a wick or rope soaked in herbicide from a reservoir attached to a handle, or assisted with 12-volt pump equipment. The wetted wick is used to wipe or brush herbicide over the plant.

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