Just received the official Quick-test® results on the paraquat resistant ryegrass from the southern WA vineyard and low and behold, we also have moderate glyphosate resistance.

The virtual loss of the two main knockdown herbicide modes of action begs the question about longer term weed management in all vineyards. The owners have recently used a robust rate of Fusilade® to kill the ryegrass. I have suggested however that while this solves a short term problem Group A herbicides should not be used by themselves in the longer term.

This situation is an excellent example of how rotating herbicide modes of action only delays the development of resistance while creating multiple resistance in the longer term.

What must be used is a series of tactics (herbicide and mechanical) within a season that ensures that potentially resistance survivors of the previous tactic are prevented from setting seed. This is the ONLY way you manage herbicide resistance. Ensure you always use the higher end of the herbicide label rate with the best possible application methods and under the best possible conditions.

A Great Southern (WA) vigneron, who was worried about his under-vine weed control, contacted me in early September. Sally Peltzer, DAFWA, and I paid him a visit to discuss the potential problem and to collect samples for testing.

For the past 20 years the vigneron had regularly used paraquat (L) under the vines rotated with glyphosate (M) and the occasional Basta® (N) application. As can be seen in the image the paraquat applied two weeks earlier has had little effect on the annual ryegrass.

Live samples were sent to Plant Science Consulting in South Australia to conduct Quicktests® to determine herbicide resistance status before the grass had set seed.

The results are back and yes the annual ryegrass is resistant to paraquat with a low level of glyphosate resistance in some plants. Seed will be harvested from test survivors for more detailed testing in 2014.

I am now discussing best management strategies now and the future with the vigneron.

This highlights the fact that rotating herbicide modes-of-action delays resistance and doesn’t prevent it. To prevent/manage herbicide resistance multiple tactics must be used in the ONE season to PREVENT SEED SET of any survivors.

Those vineyard managers and broadacre farmers rotating modes-of-action need to have a rethink of their weed management strategies.

Following a wine tasting foray to Denmark, Western Australia last weekend I thought it timely to flag the issue of glyphosate resistance in vineyards.

While Sally and I were sampling the delectable products of this prize-winning winery I turned my attention out the window to the vineyard.  Yes, old habits die hard. What caught my eye were the beautiful healthy annual ryegrass plants scattered along the under-vine strip that is normally kept weed free (See image below).

Glyphosate resistant annual ryegrass getting a root-hold in the vineyardThis is typical of the early stages of the development of glyphosate resistance where an over-reliance on glyphosate for weed control allows naturally resistant individual plants to multiply and eventually dominate if management isn’t changed.

Currently twenty two separate populations of glyphosate resistant ryegrass have been confirmed in South Australian and Western Australian in vineyards (http://www.glyphosateresistance.org.au/register_summary.html).

This is likely to be the ‘tip-of-the-iceberg’ and vineyard managers need to take action immediately to prevent these glyphosate resistant plants from producing fertile seed. A range of post emergent herbicides with different modes-of-action are registered for use in vineyards and can be used NOW to kill the existing plants. These herbicides include amitrole (Group Q), Alliance® (Groups Q + L), glufosinate (Group N), paraquat (Group L), Spray.Seed® (Group L) and Fusilade® (Group A).

An integrated weed management program then needs to be developed for the management of herbicide resistance in our fantastic vineyards.