What's the problem with weeds?

What’s the problem with weeds?

Weeds are plants that grow where we do not want them. They take up water and food from the soil so that the plants we want to grow have to compete for nutrients and water.

Weeds can also be noxious to animals that eat the weeds or the insects that are beneficial to our crops.

To get rid of weeds in a small garden is easy – we can pull them out or dig them in. If the weeds are growing in a path we can use a herbicide, a chemical designed to kill plants or inhibit their growth. There are selective herbicides that only affect particular types of plants.

Getting rid of weeds in crops is not easy, as they usually grow intermingled with the crop plants. Most farmers have to remove weeds mechanically but this is not always desirable because mechanical weeding, called tilling, can degrade soils.

A more convenient method, and less physically damaging to the soil, is to spray weeds with a herbicide before the crop begins to grow. Spraying continues after the crop has grown to control weeds that grow at the same time. Usually the spraying is carried out using an aircraft or a boom sprayer pulled by a tractor. Although spraying is carefully regulated, there are problems:

If the wind conditions are not right it can be hard to control where the herbicide falls.
The herbicide can drift onto houses, other valuable plants and into dams, creeks and rivers. This may lead to concerns about the health of people, plants and animals living close to the sprayed areas. High levels of pesticide use have been linked to severe skin and eye irritation, and to breathing difficulties in people living in affected areas.
It is often difficult to get the right weather conditions for spraying at exactly the right stage in the growth of the weeds and crops.
The herbicide must kill the weeds but not harm the crop species.
A single herbicide may not kill all species of weeds and a mixture of chemicals may be required.
Generally a few individual weeds are not killed by a herbicide because they may be naturally resistant to the herbicide. These individuals may produce offspring that are also naturally resistant. This means that the number of weeds resistant to the herbicide used may increase from year to year.

Alternative approaches to the use of herbicides in the control of weeds are being investigated. One such approach is the idea of biological control; an organism is introduced into the environment that consumes the weed but does not harm other plant species including the crop plant.

Read about several biological control projects happening at CSIRO Entomology: http://www.ento.csiro.au/research/plant_protection.html

For more information on weeds, their impact and the methods farmers use to tackle them, go to the Cooperative Research Centre for Weed Management: http://www.weeds.crc.org.au/projects/project_2_1_1.html

A problem with weeds - work sheet [PDF 47kb | 2 pages]

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What is biotechnology? Human uses Environment Food and agriculture Feed Me A problem with weeds - the canola story Why do we grow canola? What's the problem with weeds? Using herbicides to kill weeds A biotechnology solution to weeds Concerns about herbicide tolerance Concerns about GM herbicide tolerance Is GM canola good or bad? A problem with insects - the cotton story Other reasons to modify crops - soybeans The international scene Genetically modified food labelling Regulation of research in Australia Ethics for Food and Agriculture research Careers	What’s the problem with weeds? Weeds are plants that grow where we do not want them. They take up water and food from the soil so that the plants we want to grow have to compete for nutrients and water. Weeds can also be noxious to animals that eat the weeds or the insects that are beneficial to our crops. To get rid of weeds in a small garden is easy – we can pull them out or dig them in. If the weeds are growing in a path we can use a herbicide, a chemical designed to kill plants or inhibit their growth. There are selective herbicides that only affect particular types of plants. Getting rid of weeds in crops is not easy, as they usually grow intermingled with the crop plants. Most farmers have to remove weeds mechanically but this is not always desirable because mechanical weeding, called tilling, can degrade soils. A more convenient method, and less physically damaging to the soil, is to spray weeds with a herbicide before the crop begins to grow. Spraying continues after the crop has grown to control weeds that grow at the same time. Usually the spraying is carried out using an aircraft or a boom sprayer pulled by a tractor. Although spraying is carefully regulated, there are problems: If the wind conditions are not right it can be hard to control where the herbicide falls. The herbicide can drift onto houses, other valuable plants and into dams, creeks and rivers. This may lead to concerns about the health of people, plants and animals living close to the sprayed areas. High levels of pesticide use have been linked to severe skin and eye irritation, and to breathing difficulties in people living in affected areas. It is often difficult to get the right weather conditions for spraying at exactly the right stage in the growth of the weeds and crops. The herbicide must kill the weeds but not harm the crop species. A single herbicide may not kill all species of weeds and a mixture of chemicals may be required. Generally a few individual weeds are not killed by a herbicide because they may be naturally resistant to the herbicide. These individuals may produce offspring that are also naturally resistant. This means that the number of weeds resistant to the herbicide used may increase from year to year. Alternative approaches to the use of herbicides in the control of weeds are being investigated. One such approach is the idea of biological control; an organism is introduced into the environment that consumes the weed but does not harm other plant species including the crop plant. Read about several biological control projects happening at CSIRO Entomology: http://www.ento.csiro.au/research/plant_protection.html For more information on weeds, their impact and the methods farmers use to tackle them, go to the Cooperative Research Centre for Weed Management: http://www.weeds.crc.org.au/projects/project_2_1_1.html A problem with weeds - work sheet [PDF 47kb \| 2 pages]
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What’s the problem with weeds?