Fighting weeds naturally
From the October 2006 edition of Agriculture Today.
Natural plant defence mechanisms are being investigated for their potential in the fight against weeds.
NSW Department of Primary Industries (DPI) weeds agronomist Dr Hanwen Wu said researchers at the E H Graham Centre for Agricultural Innovation, an alliance between NSW DPI and Charles Sturt University, are looking to nature for effective solutions to the nation’s costly weeds problem.
He said during millions of years of evolution, plants had evolved naturally, with an array of defensive chemical armoury to secure their territory and protect themselves from possible invaders, such as weeds, insects and diseases.
“One of the natural defence mechanisms is called allelopathy,” he said.
“This is the ability of plants to produce defensive chemicals and excrete them into the surrounding soil, to cause either direct or indirect harm to weeds, by negatively affecting their germination, growth, or development.“
Dr Wu said allelopathy offered a number of alternative ways to manage weeds, such as allelopathic cover crops and rotational crops, toxic extracts from allelopathic plants, mulch or incorporation of crop residues, natural herbicides and breeding allelopathic crops.
He said many field crops had been evaluated for their allelopathic potential in weed suppression, such as cucumber, sunflower, sorghum, rice, oats, barley and wheat.
He said some wheat genotypes were very effective on annual ryegrass, including a ryegrass biotype resistant to glyphosate, as well as other herbicides with different modes of action.
“Genetic markers associated with allelopathic activities of wheat and rice have also been identified, allowing the incorporation of allelopathic traits in future breeding programs.”
A current project with the E H Graham Centre, funded by Meat and Livestock Australia, is investigating the allelopathic activity of eucalyptus species on silverleaf nightshade and prairie ground cherry.
Natural compounds with herbicidal activity will be identified to effectively reduce the infestations of these troublesome perennial summer weeds.
“Although allelopathy alone will not completely kill weeds, the long exposure of weeds to sublethal natural compounds exuded by crop plants during the entire growing season and post harvest, will have a positive long-term effect on reducing weed populations,” Dr Wu said.
Contact Dr Hanwen Wu, Wagga Wagga, (02) 6938 1602, hanwen.wu@dpi.nsw.gov.au
