How to kill weeds

Chemicals

In this website we confine our advice to two commonly-sourced (and relatively inexpensive) herbicides – Roundup 360 (or equivalent) (Glyphosate 360g/L) and Brush Off (600 g/kg Metsulfuron-methyl).

In general terms, Roundup will kill everything it comes into contact with, whereas Brush Off will act only on woody plants. Use the chemicals in the ratios suggested in the accompanying instructions, however, we do suggest some ratios for specific uses for our nine problem weeds.

We also suggest that you add some harmless dye to your chemical mixtures so you can see your progress. Against some particularly resistant weeds, we also suggest adding a wetting agent or surfactant (a small amount of dishwashing liquid will act the same way) helping to stick the chemical to the plant, make the plant draw in the chemical in and to displace any moisture on the leaves you are spraying.

As a general rule, the more you attack the weeds physically, the less chemical you will need to use. We suggest brush-cutting an area of concentrated weed infestation and dealing with the residual plants to lessen the amount of chemical required.

Cut and paint

Cut and paint is a cost-effective technique used to cut a weed low to the ground (below the leaf area) and quickly (within 15-20 seconds) apply a concentrated dose of chemical to the exposed stem. If done correctly, you can kill the root system using this technique and prevent the plant from re-growing. The chemical needs to be applied quickly before the plant naturally forms a “scab” and protects itself from your efforts.

Dealing with cuttings

If you are pulling plants out roots and all, cutting branches or cutting plants at the base, you should not leave the cuttings on the ground. Most of our problem weeds can, and will, grow again if left in contact with the ground. And, because they are generally full of seed, moving them to a pile somewhere else will only spread the infestation to the new area.

We suggest laying down builders plastic before making a pile and then either burning them when they are sufficiently dry (obviously not during the fire restriction period) or covering them with plastic and neutralising them over the next six to 12 months via a process called solarisation. Once solarised, the organic matter can be used as compost or mulch.

Timing

Timing is important when spraying herbicides. The best time to attack a weed is when it is growing quickly and happily absorbing liquids through its leaves. Spring is a good time to get active as you will be able to more easily identify a plant that is in flower and the weeds are beginning to grow in response to the warmer weather. Check the weather forecast before you start because rain can undo all your good work.

Fire

Fire is an effective weapon in the battle against weeds but it can be a double-edged sword. With some weeds species (in particular gorse and broom) fire will germinate the lingering seed in the ground so you need to plan an effective follow-up in the following seasons.

Follow up

The war against weeds will not be won overnight. Where a weed has been allowed to grow and drop seed, it is likely to keep coming back for many years, if not decades. The resulting seedlings are vulnerable and can be dealt with easily if you remain vigilant.

Help

Members of Blackwood and Barry’s Reef Landcare Group are happy to help identify problem weeds on your property and advise about their eradication. We are also seeking new members to assist our work. For further details, email admin@blackwoodlandcare.org.au.