Title: Weed 'time bomb’ warning as paraquat loses potency
[Weekly Times 27 Oct 2010, p. 102 By Peter Hemphill] -- AUSTRALIAN scientists have found annual ryegrass -- the biggest weed problem in cropping regions -- has developed resistance to paraquat herbicides. The discovery means annual ryegrass has now developed resistance to the two knockdown herbicides used to control the weed -- glyphosate and paraquat -- and sets the stage for a "time bomb" to explode in coming years unless new modes of control are developed.
University of Adelaide weed experts Chris Preston and Peter Boutsalis discovered resistance to paraquat in ryegrass samples taken from two separate properties at Naracoorte, in South Australia, where the plant was being grown for the seed industry.
"Annual ryegrass is the single most important weed affecting Australian cropping and this discovery has major implications for Australian farmers," Dr Preston said.
Paraquat is best known by its trade name. Gramoxone, although it is also present as a mix with diquat in another chemical, Spray.Seed, used to control both broadleaf weeds and grasses at the same time.
Dr Preston said it was important for farmers to rotate glyphosate and paraquat as knockdown herbicides in alternate years plus use other weed management practices, such as chaff carts and haymaking, to extend the efficacy of the chemicals.
He said the industry ideally needed a chemical with a new mode of action on annual ryegrass.
"But we don’t have one now to take over from these chemicals (paraquat and glyphosate)," Dr Preston said.
Article: WeedsNews1243 (permalink) Date: 27 October 2010; 11:39:21 AM AEDT