Noxious Weeds

It is time to start thinking Noxious Weeds
Weeds thrive on disturbance. As well as taking action to remove weeds, you need to look at what has contributed to the infestation, and treat the causes, as well as the symptom (the weeds). Reliance on simply spraying weeds as they appear is an expensive spiral of increasing disturbance and increasing infestation. Healthy, vigorous native vegetation or pasture is relatively weed-resistant. Nevertheless, timing is the crucial factor in weed control. Remove weeds before they produce seed. If you are too late, collect the seed and burn it, bury it deeply, or place it in plastic bags in the sun to rot. However, the rotting process requires moisture so make sure you include some moist, green material. Plastic bags are easily broken, so DON’T take weeds carrying light wind blown seed to landfill, whether in bags or not. Remember; removing a weed may simply result in its replacement by another rapidly growing coloniser of empty space, usually another weed. Look at the whole picture, and decide what you want to achieve before starting a weed control program.

Herbicides are very useful in the battle against weeds, but need to be used carefully. The use of non-selective herbicides (which kill every plant they contact) creates bare ground, This encourages further weed invasion. It is always best to spray with the appropriate selective herbicide to minimise damage to non-target plants.

Always read the instructions on the label before use. Be aware that there are restrictions on using herbicides near waterways. Use them only on the plants for which their use is registered. For many non-agricultural weeds not listed on product labels, there may be an off-label permit which covers them. If in doubt, contact NSW Agriculture, the National Registration Authority, Council weeds officers, or the product manufacturers. Note that under the Pesticides Act 1999 it is an offence to use a herbicide in a manner that could cause injury to a person, damage to another’s property or harm to a non-target plant.

When to use herbicides

  • When no other effective and efficient method is available,
  • Only after you have read the label.
  • When the plant is actively growing. This may be in winter for some species (such as bridal creeper).
  • Do not use when the plants are drought stressed, in extremely hot or cold conditions, or when plants are diseased.
  • Don’t spray if it looks like rain or is windy.
  • For many plants the best time to treat is between flowering and fruit set.
  • Spray deciduous plants in late spring through to early autumn, when in full leaf. If leaf colour has begun to turn it is too late.

Methods of herbicide application
Spraying should not be done in windy conditions. If plants are tall, slash first then spray when there is vigorous regrowth. If old grass tussocks do not contain many actively growing leaves, they may also be better slashed first to promote new growth which will take the chemical up more readily. Avoid spraying non-target plants, especially when spraying vines whose foliage may be entangled with that of the supporting plant. Use a selective herbicide if possible. Mix it to the right concentration for the target species (found on the label) and spray to thoroughly wet foliage, but no more. If the plant you are treating has waxy leaves, you may need to add a penetrant to improve take-up of the herbicide. Adding dye makes it much easier to see where you have sprayed. Marking your control areas with stakes and coloured tape or painted stakes makes it easier to manage longer term weed control on properties by giving you an easily identifiable reference point.

Weed wipers can be used to apply herbicides to foliage in a more controlled manner. There are a range of possibilities here, from wiping herbicide onto individual plants with a sponge in a gloved hand (useful for bulb foliage), to hand-held wick wipers, to larger wipers towed behind a tractor or quad bike. This method can be useful for removing taller weeds without affecting the pasture beneath them. Generally wiping with two passes at 90º to each other is needed to ensure sufficient coverage. Check whether the chemical you plan to use is registered for this method of application.

Cut and paint is suitable for woody weeds. The plant is cut off close to ground level with a horizontal cut, and undiluted herbicide (usually glyphosate) applied immediately to the cut surface. If you are too slow air is sucked into the sap vessels, preventing take-up of the herbicide. In some plants, such as willows, it may be necessary to apply herbicide to both the stump and the cut end of the rest of the tree. This ensures that the top part of the plant dies, rather than taking root again if it is left lying on moist soil. For a larger stump, only the outer edge, just inside the bark needs to be treated, not the whole surface. Wear rubber gloves, and avoid moving around carrying an open container of herbicide. This method and the two below are best done as a two person job.

Scrape and paint is used for large vines and scrambling plants with a woody stem. Scrape 20 to 100cm of the stem with a knife, to expose the sapwood just below the bark. Within 20 seconds, apply undiluted herbicide to the scraped section. Don’t scrape right around the stem, do only a third of the diameter. Stems over 1cm in diameter can be scraped on two sides. If killing vines with herbicide, leave them to die in place. Pulling them down can damage the plants they are growing over.

Stem injection is used on woody weeds where you want them to die in place, rather than cutting them down. There are purpose-built stem injection devices, but the job can also be done with a hammer and chisel or a cordless drill. You need to make an angled cut or hole down into the sapwood, just below the bark, and apply undiluted herbicide into the cut immediately. Don’t drill too deeply, or you will get into the heartwood, which does not take up the herbicide.

Basal bark treatment is used on young woody weeds and root suckers. Diluted herbicide (check label for rates) is painted or sprayed onto the bark at the base, from ground level to 30cm high.

If you have any questions or need assistance in planning a weed control strategy for your property, contact your local Shire Noxious Weeds Inspector at 02 6941 2547.  Council is there to help.  Although the regulatory aspects of weeds control fall to council to enforce, it is always the preference to work with landholders and assist in developing effective and manageable strategies for weed control rather than strongarm enforcement.

Two excellent management guides are “Noxious and Environmental Weed Control Handbook fourth edition” and “Weed Control in Lucerne and Pastures 2010”. Both of these publications are available from your Council Weeds Inspector or from the Department of Industry and Investment.

Click the link to view Noxious Weeds Data Sheets