Weed control methods
IntroductionAdvice on weed control methods and practical tips for spraying.
The key principle is to choose the 'Method Of Least Disturbance' (or MOLD). Apply this principle for each weed control option. Control options are often used in combinations, such as chemical control of mature plants, followed by hand pulling of seedlings.
Letting native plants take their course. Succession can result in the natural replacement of weeds by native plants e.g. in some situations, gorse can act as a nursery for native plants. This is a long-term solution and is a great option if you have the patience.
Options for physical control include shading, hand weeding, ring barking, grubbing, felling and mulching. These methods are labour intensive but have the advantage of targeting the weed in question. Apply the MOLD principle to help decide which control option to use. For example, felling trees may damage native seedlings.
There are often several herbicides available to control a particular weed. Always read and follow the label instructions regarding safety and dose rates. To find out what chemical to use for a particular weed, go to the Weedbusters website.
Check with your regional council to see if there are any biological control options available for that weed. Biological control is a longer-term option and does not eradicate the weeds. It is designed to tilt the balance in favour of native plants, helping them to compete with the weeds.
- Spraying e.g. with the use of knapsacks.
- Injecting herbicides into trees e.g. drill and fill methods and cut and stump treat – these work well for softwood trees e.g. wattle and woolly nightshade.
- Swabbing stumps with a herbicide e.g. with a paintbrush or using a herbicide gel, such as Vigilant gel.
Selecting a herbicide - issues to consider
- A common mistake is avoiding herbicide usage. Some weeds are difficult to control without using some herbicide. Using a small amount of herbicide early can avoid having to use a much larger amount later.
- Where will the herbicide enter the plant e.g. leaves/stem (usually applied by sprayer or wiper) or root/soil (usually applied by granules or sprayer)?
- Selectivity. Some herbicides are very selective and the herbicide will only kill targeted groups of plants e.g. Gallant kills grass weeds while Versatill kills legumes and daisies.
- Persistence (the length of time the herbicide remains in the soil). Some chemicals will stay in the soil for a long time and nothing may grow there.
Residual herbicides don’t break down in the soil, while non-residual herbicides break down on contact with the soil e.g. Escort is residual while Glysophate is non-residual.
You don't want to kill the wrong plant by mistake. Reduce spray drift by:
- Do not spray when it is windy.
- Spray early in the morning or late in the afternoon. In the middle of the day warm air rises.
- Increase the particle size by manipulating the trigger to get a stream rather than a mist – this will reduce spray drift.
- Do not spray in wet conditions.
- When spraying around native plants use a shield such as half a bucket.
Safe disposal of weeds
The safe dispoal of weeds is critical when removing weeds from an area. Many plants can grow from the bits you remove. Check for the best way to dispose of weeds.
Methods for disposal include deep burying, mulching or putting the weeds in a plastic bag and leaving in bright sunlight until they are dead.
Some plants should not be composted, such as those that can easily re-sprout from their roots or stems. This includes:
Do not compost seed heads and bulbs unless you know they won't re-grow.
Never dump garden waste in a green belt area as this will spread bad weeds.
Reducing regrowth of weeds
Open sites can be readily colonised by a new weed species, so the planting of native trees, shrubs and grasses, as well as mulching the weeded area, will make a big difference in reducing weed regrowth.
In coastal areas, you may find it worthwhile to protect native plants from wind and salt spray while they become established. You can also encourage your native plants to grow more quickly by weeding around your plantings to reduce the competition from weeds. Be careful not to dig deeply around desirable plants so you don't damage their roots.
Weeds can be reduced or suppressed by adding a layer of mulch around each plant. Most rotted organic matter such as leaf mould, compost, straw, lawn clippings or silage can be used for mulching. Old wool carpet or underlay provides a degradable weed mat.
Remember, a new plant needs water – it is not enough to just plant it.