Controlling weeds successfully is not that hard once you know how. This page explains some of the techniques referenced in the control methods.
For recommendations on control for individual species use our weed search.
As well as knowing the techniques, successful weed control in the long term requires a good ‘plan of attack’. This involves deciding what to tackle first, ensuring you do not try to do too much at once and can complete the follow up work, and knowing the end ground cover you are aiming for (to suppress germination and infestation by other weeds – Weeds love bare ground!).
Manual control vs. techniques using herbicide
Manual removal is usually best for the environment, but it is not always feasible, depending on the species and the scale of the infestation. Herbicides, when used correctly, are an excellent tool. Opt for low herbicide use methods first, and wide use of herbicide only where necessary. Treat weeds as a resource for your soil and mulch and compost on site where possible.
When using any herbicide or pesticide PLEASE READ THE LABEL THOROUGHLY to ensure that all instructions and safety requirements are followed.
Weed Action recommends being trained in the safe handling and use of agrichemicals. Even if you have used chemicals for years there is still much that you can learn from these courses. Check out http://www.growsafe.co.nz for more information or contact Weed Action at firstname.lastname@example.org
Weed Control Techniques
Drill and fill
- Great for large trees and some hard to kill species, as plants continue translocating herbicide to roots for longer period resulting in more herbicide uptake.
- Uses less herbicide than most other methods and minimal amounts of water. Very targeted herbicide application.
- Can generally be used all year round.
- Aim is to access cambium layer (under bark) so deep holes not necessary.
- Only suitable for use in areas where eventual tree fall will not pose a risk to people or property
- Using a large drill bit (10 – 14mm), drill downward sloping holes at the recommended interval around base of the trunk (often 10 -20cm intervals). Holes can be angled slightly across the trunk, rather than straight into the middle as most of the vascular tissues are concentrated below the bark. On multi stemmed trunks, if you can’t get below the branch point, drill around each trunk.
- Fill each hole (usually about 10-15ml in each) with the recommended herbicide using a trigger sprayer (on jet not spray) or drench gun and pack. It is usually advisable to wait till the first amount of herbicide is absorbed and then fill again.
Cut stump application
- Good for smaller trees, saplings and shrubs, for species where cut material resprouting is not an issue
- Uses minimal herbicide, reasonably targeted application
- Cut low to the ground, and level to create a good platform for herbicide application. For hardwood species and big trees, peeling back the bark around the cut edge is also advised. This exposes more of the cambium layer resulting in more herbicide uptake when treated.
- Treat as soon after cutting as possible, as the cut vascular tissue starts to seal relatively rapidly. The cut edge of the cambium layer (the slippery zone under the bark) must be coated, as this is where most growth sprouts from.
- Herbicide can be applied to the cut stump using a gel formulation in a squeeze bottle, a trigger spray, a paint brush, drench gun, or knapsack.
Frill and fill
- Can be quicker to do then cutting or drilling for some larger trunks, or for species with soft trunks.
- Kills plants standing which can make future access easier,
- Killing standing also means plants continue translocating herbicide to roots for longer period resulting in more herbicide uptake.
- Goal is to create cuts/notches around the base of the trunk but not to ring bark, to ensure translocation continues. This method is sometimes referred to as feathering, or ‘partial frilling’ where frilling is being used to refer to complete ring-barking.
- Using a saw or hatchet, cut a notch that will crete a catchment for herbicde application, into the sapwood at regular intervals around the trunk. Immediately apply the reccommended herbicde. A gel formulation in a squeeze bottle, a trigger spray, or a drench gun can be used to apply the herbicide.
- A chisel and mallet can also be used to create notches, using the chisel to lever them open for herbicide application.
- Uses a hockey stick type wiper to apply herbicide to leave/stems by direct contact
- Useful as alternative to foliar spraying for species where cut/drill/frill applications are impractical, such as grasses, rushes and soft herbs,
- More targeted foliar application then foliar spraying
- Look for a weed wiper that has a narrow or controlled release reservoir.