Multiple resistant ryegrass confirmed in southern WA

Multiple resistant ryegrass has recently been confirmed in a southern West Australian vineyard, prompting a local herbicide expert to issue a warning to Australian vineyard managers.

Andrew Storrie, Executive Officer for the Australian Glyphosate Sustainability Working Group, says the finding of both paraquat- and glyphosate-resistant ryegrass by the official Quick-test® in September 2013 should act as a wakeup call to the grapegrowing industry.

‘The loss of two main knockdown herbicide modes of action (Groups M and L) raises the question about our general approach to weed management in vineyards’, he said.

Officially, there are 22 confirmed cases of glyphosate resistant annual ryegrass from South Australian and West Australian vineyards.1

‘This is “the tip of the iceberg” regarding herbicide resistant weeds in Australian vineyards’, Mr Storrie said.

‘A recent visit to another southern WA vineyard showed healthy ryegrass in the vine row despite multiple applications of glyphosate.

According to Storrie, ‘when confronted with herbicide resistance, vineyard managers should not just opt for another herbicide from a different mode of action’.

‘This vineyard is an excellent example of how rotating herbicide modes of action only delays the development of resistance and creates multiple resistance in the longer term. The alternating of glyphosate and paraquat had been conducted for around 20 years in this case.

‘The vineyard manager has since killed the errant ryegrass with a robust dose of Fusilade® (Group A), however this is a short term fix due to Group A herbicides being prone to developing resistant weeds’, he said.

Storrie urges vineyard managers to use a series of tactics within a season to ensure that potentially resistance survivors of the previous tactic are prevented from setting seed.

‘This is the only way you can manage herbicide resistance’, Mr Storrie said.

‘Effective application of herbicides is also critical to ensure the higher end of the herbicide label rate is used with the best possible application methods and under the best possible conditions.

‘Beginning the weed control in early winter to treat small weeds will also increase control levels and help store soil water for spring’, he said.

1. http://www.glyphosateresistance.org.au/register_summary.html

Paraquat&glyphosate_resistant ryegrass