Learn to identify and effectively control weeds

You learn about both chemical and non-chemical control methods (e.g. mulching, burning, slashing), the use of spray equipment, and safety procedures which should be followed. This course is appropriate to anyone who needs a better understanding of weeds, including:

  • Land owners
  • Farmers
  • Land Managers (Park managers, Golf Course superintendents, foremen, etc)
  • Environmental Officers
  • Farm contractors
  • Farm suppliers
  • Landscape contractors


Study Weed Control for improved Farm Productivity



The course is divided into 8 lessons as follows:

 1.  Weed Identification: review of the system of plant identification, general characteristics of the weeds, further information, contacts, etc.

 2.  Weed Control Methods: practical research on management of weeds, understanding terminology and the use of mulches

3.  Chemical Weed Control: review of commercial and domestic herbicides, determining what differentiates them, their availability and use.

4.  Weed Control In Specific Situations: understanding weed control strategies for particular situations, accessing first hand information about weed control from industry leaders and determining a weed control program for five different sites.

5.  Safe Chemical Application: reviewing what types of chemicals and application methods are used in the industry and the required safety procedures for the handling and administrating chemical herbicides.

6.  Non-Chemical Weed Control: determining any detrimental effects chemical herbicides have on the environment, reviewing non-chemical applications and their effectiveness.

7.  Dealing With Specific Weed Control Problems: looking at current industry practices for weed control and the effects on the environment, in relation to specific weed control problems.

8.  Developing A Major Weed Control Program: a practical lesson where the student can fully demonstrate their understanding of weed control by devising a weed management plan for a designated area.


Duration: 100 hours



  • To distinguish between different types of weeds, and identify common weed species, growing in your locality.
  • To understand the characteristics of different weed control methods.
  • To be able to explain the use of chemical herbicides to control weeds.
  • To be able to specify appropriate weed control methods, for different types of situations.
  • To determine appropriate techniques for the safe application of chemical herbicide in a specific situation.
  • To be able to explain different non-chemical weed control methods.
  • To be able to devise appropriate methods for control of weeds, for specific problems, in both the horticultural and agricultural industries
  • To be able to determine a detailed weed control program for a significant weed problem.



  • Observe and consider over 100 different varieties of weeds and prepare plant review sheets with descriptions and illustrations for different weed plants.
  • Make up a list of information resources.
  • Plant, grow and observe different varieties of weeds.
  • Make drawings of young seedlings of at least fifteen different weeds.
  • Speak/interview people who have to deal with weed control in their daily life.
  • Visit a retailer or supplier that sells herbicides to the public.
  • Visit at least one supplier of herbicides for industrial and agricultural use.
  • Contact larger chemical companies for leaflets on different herbicides.
  • Investigate at least two workplaces where weed control programs are regularly carried out.
  • Visit and inspect different sites where weeds are a problem.
  • Photograph different places that have been treated with weedicides.
  • Contact your local Department of Agriculture or Lands Department for researching purposes.
  • Visit several farmers who raise different types of livestock.
  • Develop a 12 month guideline for an integrated weed control program for a particular site


1. Suffocation

A popular weed control method is to suffocate the weed (block out light) &/or put a physical barrier over it which it can't grow through. This is more commonly known as mulching. Mulching kills weeds by simply smothering them. The weeds are deprived of light and in order for them to grow, they have to break through the barrier formed by the mulch. A mulch can take the form of almost anything, but the more popular ones in use are:

  • Wood shavings and chips
  • Pine Bark, Ecomulch.
  • Hay or Straw.
  • Grass Clippings.
  • Leaves.
  • Newspaper.
  • Carpet underfelt
  • Cardboard
  • Seaweed
  • Woodchips, sawdust, leaves, etc.

The depth of the mulch will be determined by the weeds that you are trying to control. Vigorous weeds will need a greater depth of mulch than perhaps small annual weeds. Most weeds seedlings will require a depth of mulch of 8‑10 centimetres over the top of them.

Mulch Mats ‑ these are also known as weed mats. They are usually made of a closely woven fabric, that have holes large enough to allow water to penetrate through, but they are small enough to prevent most weeds from growing through.

NB. Since mulching can be a very effective method of weed control, it will be discussed in greater detail later in this lesson.


2. Shading

Some trees & plants with dense foliage or foliage right to the ground will shade out weeds. Such trees include: Ash, Maple, Citrus, Salix, Casuarina, Pines.

Shrubs which shade out weeds include Diosma, Grevillea, Conifers, Coprosma repens, Echium fastuosum.

Other plants and trees drop many leaves, which create their own mulch.

Examples of these are:

  • Conifers‑pine needles deter weed growth
  • Eucalypts ‑oils in leaves deter weed growth
  • Melaleucas and Leptospermums ‑oils in leaves deter weed growth
  • Acacias ‑tannins are washed off the leaves by rain in some species.

A border of weed suppressing plants can be grown around a vegetable patch to prevent entry of spreading weeds, such as couch and kikuyu grass. Comfrey or lemon grass may be used for this.


3. Burning/Heat

Weeds can be burnt using a spot flame device, or with heat created by covering, temporarily, the weed (or weed seed) infested area with a plastic sheet (this is known as solarisation).


Weeds can be burnt either using a flame thrower (if weeds are green or dry), or by lighting a "controlled" fire (if vegetation is dry enough to burn). When burning the weeds it is essential to follow fire prevention regulations for your area. Contact the local fire brigade for details. Burning will always leave a residue of charcoal, which is dirty, but will disappear with time. Flame throwers are portable burners fuelled by Paraffin or Propane Gas. They can usually be hired from a hire shop for a reasonable price. Care should be taken with them as the heat generated from them can be quite considerable, and can also damage other plants, as well as causing nasty burns to the operator. Flame throwers are useful along fence lines, roadways or paths, or any other area where the flame won't cause unwanted damage.

Burning off can be an excellent method of controlling large areas of weed growth, on vacant or rural land, or to control large clumps of problem weeds such as blackberry.

It can be dangerous though if not done properly and under the right weather conditions.

Never use fire on windy or very hot days. Never burn more than you can control easily with manpower and water available. Mow fire breaks before commencing a large burn to confine the operation to a series of small burns. Wear full clothing (eg. firm boots, overalls and a hat); and have a first aid kit on hand. Above all, check with the local fire brigade before burning.

Plastic Sheet:

This method is also known as solarisation. Large sheets of clear plastic are spread over the surface of the ground in warm weather. The sun's rays will cause the ground under the plastic to heat up enough to kill many types of weeds and soil diseases. After a week or so the plastic can be removed and the area planted. Solarisation is an ideal method of ground clearing prior to planting a vegetable garden, or annuals in a border, and is relatively cheap.


4. Cultivation

Cultivation, or the digging of the soil with either a spade or a hoe, will often kill weeds, especially annual weeds. Weeds can be controlled by physically burying them in the soil, and regular hoeing of the soil surface may deter some types of weed seeds from germinating. Weeds that do germinate will be easily chopped off with a hoe. Regular hoeing of the soil surface will also assist in water penetration of the soil.

In some cases where weeds have a vigorous root system, cultivation alone may not be enough, and the weeds may well have to be physically removed by hand. It is advisable not to water the soil directly after cultivating, as hot sunlight can kill exposed weed roots. Some weeds are almost impossible to control by hand, for example, couch, kikuyu and wandering jew, or weeds with bulbs or corms (e.g. oxalis, watsonia).

In some cases cultivating can worsen a weed problem by chopping up and spreading underground parts such as roots, rhizomes or bulbs. Many weeds are adapted to invade cultivated or otherwise disturbed ground. Some weed seeds require light to germinate, and cultivation can bring these to the surface so mulching may be required as well.

  • Soil which is cultivated often is easier to cultivate so don't put the job off.
  • Young weeds are damaged more by cultivation than established weeds
  • Do not water after cultivation. (The hot sun kills exposed roots).
  • Some weeds will die quickly when you cut the top from the roots (others will regrow from the smallest piece of stem or root lying in the soil)
  • There will always be some hard to kill weeds which need removing by hand.
  • Moist (but not wet) soil is easier to cultivate. Wet soils should not be cultivated, however, as this destroys soil structure.


5. Grazing

One of the best animals to affect weed control by grazing would without doubt have to be the goat. They will eat virtually anything, including ropes that act as a tether for them. They also have a great deal of strength and will easily break down weak barriers that are designed to keep them in. With this in mind then it is important to only allow the goat access to the weeds and not the desired plants. In a small back garden it may be difficult to keep the goat under control, but in a large area this will not be so much of a problem. Probably the ideal use for a goat would be in cleaning up an area, before you make a new garden there.

Here are a few hints if you're considering a goat:

  • You're better to borrow one than buy one. Otherwise when you run out of weeds, feeding it can become a problem.
  • Goats are best used to keep a wild area under control on a large property, or to clean up an area prior to making a new garden there.
  • Goats are very strong. They can break small gauge chains, eat through ropes and pull stakes out of the ground. Use a heavy chain and tie them up to something very solid such as a fence post or large tree.
  • Goats will stand on their back legs to reach plants, they will eat all types of plants and even strip the bark off trees.
  • The goat makes a tempting target for roaming dogs, unless it is well protected (good fencing).

Sheep can also be used for grazing, but can be a little more choosy in what they are prepared to eat. Chickens, ducks and geese will also eat a variety of weeds, and cultivate the soil by scratching. Wire netting is sometimes placed on the ground in a poultry run to stop hens digging up the soil too much. Penned pigs will also cultivate the soil with their digging. Even pet rabbits, or guinea pigs can be caged and allowed to graze weeds.


6. Mowing/Slashing

This involves cutting the tops off the weeds on a regular basis, ideally before any seed heads develop. Any cut foliage should be allowed to fall back on the beds and this will help to return nutrients to the soil. If the weeds are long in growth when cut, then they may well act as a mulch, preventing other weeds from germinating and growing. The weeds should be cut close to the ground to effectively control them, and an ideal machine to use would be a brushcutter or whipper snipper.


7. Flooding

Flooding of an area will kill a wide range of weeds but not all. This method is sometimes used on flat sites prior to planting.


8. Changing pH

By raising soil pH you can discourage growth of some weeds, such as Sorrel (Rumex sp.). Adding organic matter to the soil will also gradually cause sorrel growth to slow down.


9. Biological Control

This involves introducing natural predators into an area to attack weeds.

It is a method which has been used occasionally with dramatic results, but which can "backfire" if the full implications of introducing something new into an environment are not understood.

Prickly Pear   Prickly Pear (a cacti which was a severe problem in many regions) was brought under control by introducing a parasitic moth which has a grub that attacks the plant.

Blackberries   A rust (fungal) disease has been utilised in some regions in an attempt to control blackberry weeds. Though this has had some affect, to this stage it has only been a mild deterrent.

Water Hyacinth    Insects have been used to control the spread of water hyacinth in the United States and Australia.


10. Chemicals

There are a wide variety of herbicides used to control weeds, however, it is very important to note that weedicides that are available in one region or country may be banned in another region. Before using chemicals to control weeds, one should become familiar with the regulatory agencies in your region and keep yourself up to date on what products are legal and certified for use in weed control. This is a very dynamic subject, with the list of banned and approved products being altered frequently. Many chemicals require an appropriate government certification in order to apply them. Others are available over-the-counter and are for general use. Even when using approved herbicides, extreme caution should be taken and all safety measures adhered to.





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