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Searching native Australian plants for natural herbicides - a case study

Min An1,2 and Jim Pratley2

1 Environmental and Analytical Laboratories, Charles Sturt University, Wagga Wagga, NSW 2678, Email man@csu.edu.au
2
EH Graham Centre for Agricultural Innovation, Charles Sturt University, Wagga Wagga, NSW 2678

Abstract

In searching for alternatives for reducing reliance on synthetic herbicides, reducing environmental damage and health hazards from chemical inputs and for counteracting herbicide resistance, natural compounds offer excellent prospect as herbicides. Natural compounds can be either used directly as herbicides or used as leads for new chemical families of herbicides. The interest in natural products as sources of herbicide chemistry has increased.

Due to its large size and geological isolation, Australia holds a vast number of native plants that are unique to this continent and are rich sources for natural compounds. For thousands of years Australian native people, i.e. aboriginals, have been using native plants for medicinal purposes. Recently a new broad-spectrum maize weed herbicide, Callisto, has been developed from an Australian native Bottlebrush (Callistemon citrinus), a species that was introduced to Britain in 1789. Callisto has been released into the market (Syngenta 2005). Callisto has more effective weed control than existing herbicides, with excellent crop safety and a good environmental profile (Syngenta 2005).

In our case study a native tree, Gidgee, from the genus Acacia has caused our attention. The genus Acacia belongs to the family Mimosaceae. There are some 1350 species of Acacia found throughout the world and close to 1000 of these are to be found in Australia. Commonly known as Wattle, Acacia is the largest genus of vascular plants in Australia. Australia's national floral emblem is Acacia pycnantha, the Golden Wattle.

Within Australia Acacia occupies vast areas of the continent and is to be found in a wide range of differing habitats from coastal to sub-alpine regions and from high rainfall to arid inland areas. They are particularly prevalent in the arid, semi-arid and the dry sub-tropical regions of the country.

Gidgee or Gidyea (Acacia cambagei) is a small greagarious tree and is characteristic in the north west district of Queensland and central Australia. It is commonly observed that where Gidgee grows little else grows. It gives off a very distinctive and unpleasant odour during rain and humid weather. Gidgee is also called stinking wattle.

Preliminary studies demonstrated that gidgee shows strong herbicidal potential in suppression of annual ryegrass (Lolium rigidum Gaud.), an important weed in Australia. It was found that the aqueous extracts of gidgee foliage caused up to 90% inhibition of ryegrass seedling growth. Chemical analysis identified several natural chemicals, which are known to possess strong allelopathic activities. Comprehensive investigations on its full herbicidal capabilities are currently under way.

Media summary

Native Australian plants are rich sources for developing natural herbicides combating herbicide resistance and reducing reliance on synthetic herbicides.

Key Words

Allelopathy, allelochemicals, gidgee, Acacia cambagei, annual ryegrass, Lolium rigidum

Reference

Syngenta (2005). www.syngenta.com. Press releases – New natural herbicide controls maize weeds.

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