What are pesticides and how do they work?
Plants, insects, bacteria, fungi and other organisms are a natural part of the environment. Some can benefit people, while others can be pests that you may need or want to control. You can choose from many different methods to control a pest. One method is to use a pesticide.
A pesticide is any substance or mixture of substances used to destroy, suppress or alter the life cycle of any pest. A pesticide can be a naturally derived or synthetically produced substance. A pesticide can also be an organism, for example, the bacterium Bacillus thuringiensis which is used to control a number of insect pests, or even a genetically modified crop (see Bollgard II cotton). The legal definition of a pesticide in NSW covers a wide range of substances.
Pesticides include bactericides, baits, fungicides, herbicides, insecticides, lures, rodenticides and repellents. They are used in commercial, domestic, urban and rural environments.
There are currently thousands of pesticide products registered for use in NSW by the Australian Pesticides and Veterinary Medicines Authority (APVMA).
Some families or groups of chemical products which are considered pesticides under current NSW legislation are:
Bactericides - These destroy, suppress or prevent the spread of bacteria. Examples are swimming pool chemicals containing chlorine, and products used to control black spot (bacterial blight) on garden plants or in orchards. Household disinfectants and some industrial disinfectants are excluded and not considered pesticides.
Baits - These may be 'ready to use' products or products which need to be mixed with a food to control a pest. This category includes baits prepared for the control of large animals, such as foxes, wild dogs and rabbits, and baits for insects (such as cockroaches and ants) and molluscs (snail and slug pellets).
Fungicides - These control, destroy, make harmless or regulate the effect of a fungus. Examples include chemicals used to treat Grey mould on grape vines and fruit trees, or Downy Mildew on cucumbers.
Genetically Modified Organisms (GMOs) - Agricultural crops can be genetically modified to make them more resistant to pests and diseases, or tolerant to certain herbicides. For example, a gene from the bacterium Bacillus thuringiensis can be incorporated into cotton to provide protection against the larval stages of the cotton bollworm and native bollworm.
GMOs are regulated by the Commonwealth Government through the Office of the Gene Technology Regulator (OGTR) under the provisions of the Gene Technology Act 2000. Where a genetically modified product is determined to be a pesticide, it is subject to an assessment and registration process in accordance with APVMA requirements.
Herbicides - These destroy, suppress or prevent the spread of a weed or other unwanted vegetation, for example, the herbicide glyphosate is used to control a range of weeds in home gardens, bushland and agricultural situations.
Insecticides - These destroy, suppress, stupefy, inhibit the feeding of, or prevent infestations or attacks by, an insect. Insecticides are used to control a wide variety of insect pests, including thrips, aphids, moths, fruit flies and locusts. In NSW, pesticides include products such as flea powders and liquids used externally on animals. Injections or other medicines administered internally to treat animals are veterinary medicines and are regulated by the NSW Department of Primary Industries under the Stock Medicines Act 1989.
Lures - These are chemicals that attract a pest to a pesticide for the purpose of its destruction. Solely food-based lures, for example cheese in a mousetrap, are excluded and are not considered pesticides.
Rodenticides - These are chemicals used specifically for controlling rodents such as mice and rats.
Repellents - These repel rather than destroy a pest. Included in this category are personal insect repellents used to repel biting insects.
A number of living organisms that can control pests have also been registered as pesticides. Rabbit Haemorrhagic Disease, for example, has been used to control rabbit numbers; and bacteria that act as biological insecticides have been used to control various insect larvae, such as moths and mosquitoes.
Many natural substances can be used as pesticides, such as extracts of pyrethrum, garlic, tea-tree oil and eucalyptus oil. When these natural chemicals are used as pesticides they become subject to the same controls as pesticides produced synthetically.
The term pesticide covers a wide range of substances that are used for the control of pest species.
A common misunderstanding is that the Pesticides Act 1999, which controls the use of pesticides in NSW, does not apply to the use of herbicides. This misunderstanding arises because the term pesticide is sometimes wrongly used to describe insecticides only. The legal definition of a pesticide (below) under the Pesticides Act does, in fact, cover herbicides, insecticides, fungicides, rodenticides and many other types of substances.
Under the NSW Pesticides Act 1999, a pesticide is an 'agricultural chemical product' as defined in the Agricultural and Veterinary Chemicals Code Act 1994 (Cwlth), namely:
'a substance or mixture of substances that is represented, imported, manufactured, supplied or used as a means of directly or indirectly:
- destroying, stupefying, repelling, inhibiting the feeding of, or preventing infestation by or attacks of, any pest in relation to a plant, a place or a thing; or
- destroying a plant; or
- modifying the physiology of a plant or pest so as to alter its natural development, productivity, quality or reproductive capacity; or
- modifying an effect of another agricultural chemical product; or
- attracting a pest for the purpose of destroying it.'
Under the NSW Pesticide Act 1999, some external parasite treatments are also considered to be pesticides if the product requires dilution or mixing in water before use and is not prescribed under the Stock Medicines Act 1989 as a low-risk veterinary chemical product.
Another common misconception is that pesticides made from natural substances or 'home brews' are intrinsically safer in all respects than synthetically produced or commercial pesticides. Sodium fluoroacetate (1080) occurs naturally in a number of Australian plants; however, it is a highly toxic substance that is used to kill pest animals such as rabbits, feral pigs, wild dogs and foxes. All substances whether they are synthetic or naturally derived involve some degree of risk when they are used to control pests.
It is important that pesticides are used only where they are absolutely justified. It is essential that you carefully identify the pest you wish to control and then fully consider all the control options. If you choose to use a pesticide, then it is your legal responsibility to ensure that it is used correctly by following all the instructions on the pesticide product label or on a permit issued by the Australian Pesticides and Veterinary Medicines Authority (APVMA).
Pesticides control pest organisms by physically, chemically or biologically interfering with their metabolism or normal behaviour.
Most pesticides are lethal to target pests when applied at the rate specified on the pesticide label.
Some pesticides are non-lethal to the target pest. These include repellents or attractants (such as personal insect repellents), sterilising agents (which interfere with the reproductive ability of a pest), some defoliants (that cause leaf drop without killing the plant) and some pesticide products that boost the action of another pesticide without being particularly toxic themselves (such as piperonyl butoxide which may form part of pyrethrum-based insecticides).
The route that brings a pesticide in contact with the target pest depends on the nature of the pesticide, how it is applied and the type of environment in which the pesticide is placed. Common application methods include spraying, fumigating and baiting.
Many pesticides are 'contact' pesticides. This means to be effective they must be absorbed through the external body surface or the exposed plant tissue; for example, tetramethrin used in household fly sprays, and bipyridillium herbicides such as paraquat.
Contact pesticides have to reach their target directly to be effective.
Other pesticides are systemic in action. Systemic pesticides can be moved (translocated) from the site of application to another site within the plant or animal where they become effective; for example, insecticides that are absorbed by foliage and translocated throughout the plant where they kill chewing or sucking insects; or nematicides that are applied to the leaves of plants and are transferred to the roots of the plant to kill worms or caterpillars that are attacking the plant's roots.
Similarly, blood anticoagulant rodenticides in baits take effect once they have been transferred from the digestive system to the bloodstream of rats or mice.
Systemic pesticides move from where they are applied to other parts of the plant to reach their target.
Some pesticides are residual in action and continue to be effective for days, weeks or months after their application. Examples are the triazine herbicides that persist in the soil and kill emerging weeds over the lifetime of a crop and some insecticides that remain active in the soil for several years when used as a chemical barrier to termites entering buildings.
Many modern pesticides do not persist for long in the environment. They act quickly and are then degraded to non-toxic substances by environmental or microbial processes. This helps prevent their build-up in crops or non-target organisms. How quickly a pesticide breaks down depends on its chemical properties, how much is applied and how it is distributed, as well as environmental factors such as temperature, moisture, soil pH and the availability of micro-organisms.
The label on the pesticide container is an essential and important source of information about how the pesticide can be legally used. You must read the label, or have it read to you, before using a pesticide so that you can determine what precautions need to be taken when using the pesticide and what constraints there are on use. If the product does not include information on the label about the pest and situation in which you want to use the product then you must find a product that is registered for that purpose. The APVMA has a database (PUBCRIS) which can be used to find a pesticide that can be legally used to control the pest species you want to control. Also manufacturers of pesticides or pesticide resellers can give you advice on what pesticide can be used to control the pest you are needing to control.
In addition to the label on the pesticide container all pesticide products are required to have a Material Safety Data Sheet (MSDS) which contains additional information. The MSDS is available from the pesticide manufacturer or supplier at no additional cost. If you use pesticides in your workplace then you need to obtain MSDSs for the products that you use. For more information contact NSW WorkCover.
When using a pesticide you must always follow label directions or APVMA permit instructions. A material safety data sheet (MSDS) must be readily accessible to anyone using pesticides in the workplace.
Page last updated: 04 December 2012