Has herbicide resistance in ryegrass in Western Australia plateaued?

“The nice part about being a pessimist is that you are constantly being either proven right or pleasantly surprised,” George Will, American journalist, author and Pulitzer Prize-winner.

 

We are not pessimists at Australian Herbicide Resistance Initiative (AHRI), but let’s face it, we rarely have good news when it comes to reporting on the level of resistance progression on Australian farms. We are normally proven right that herbicide resistance levels are continually increasing.

 

The latest results from the AHRI random ryegrass resistance survey of WA led by Dr Mechelle Owen isn’t necessarily good news, but it’s about as good as we could have hoped.  

 

We know that herbicide resistance levels almost never decrease through time, so the very best that we can hope for is that resistance levels plateau, which is what Mechelle found for a number of herbicides.

 

Every five years, Mechelle, one of our dedicated AHRI researchers, undertakes the massive task of visiting 500 fields in Western Australia just before harvest to sample seeds of surviving weeds for resistance testing with GRDC support.

 

She found that the percentage of paddocks with resistant ryegrass has only risen slightly since the last survey in 2010. Mechelle is reporting on all levels of resistance, with more than 1% survival to a herbicide.

 

It’s no surprise that resistance to the sulfonylurea (SU), and Fop (Diclofop) herbicides didn’t worsen from 2010 to 2015, as these herbicides were already totally shot. What was surprising, was that resistance to clethodim (Dim) and trifluralin and glyphosate was roughly the same in 2015 as it was in 2010. This was a very pleasant surprise.