THE most recent data available on herbicide resistance in Western Australia was presented to agronomists and industry professionals at a Crop Protection Forum, hosted by the Australian Herbicide Resistance Initiative (AHRI) at The University of Western Australia (UWA) on Tuesday of last week.
AHRI has detailed information on herbicide resistance in the State dating back to 1998, with the most recent statistics from 2015 showing that ryegrass was present in 86 per cent of paddocks and wild radish was in 27pc.
Speaking at the forum, WeedSmart western extension agronomist Peter Newman presented the research which had been conducted by AHRI senior research officer Mechelle Owen.
"Over the years ryegrass infestation has held level and are looking similar to 2015, while wild radish infestation had dropped," Mr Newman said
"In the previous survey in 2010 wild radish was present in about 40pc of paddocks, by 2015 that had dropped to 27pc and currently radish is being found in around the same percentage of paddocks."
When it comes to ryegrass, there is multiple resistance all over WA, with blowouts to diclofop and sulfometuron that started more than 20 years ago still present now.
Mr Newman said it was a different story for clethodim, with an enormous jump in resistance to the herbicide from 2003 to 2010, but only a slight increase since then.
"From the 2010 to 2015 survey, there was not a big increase in resistance and currently 68pc of the populations have resistance to clethodim," he said.
"In 2003 there was lots of susceptibility and in 2015 there was resistance, however it's possible to say there is about 90pc resistance to clethodim in the high and medium rainfall zone and lower resistance in the low rainfall zone."
Across 2018 and 2019, AHRI research fellow Roberto Busi conducted research on 140 populations of ryegrass collected from agronomists from around WA.
He found 37pc of the fields with some resistance to a 500 millilitre rate of clethodim, 30pc with resistance to a 180g rate of butroxydim, but only a 9pc resistance when the two were put together.
In terms of other chemicals, trifluralin has been going through a small increase in resistance since testing was introduced in 2003 and in 2015 there wasn't a huge blow out.
"Atrazine was a herbicide that in the US was one of the first big problems for resistance and it was thought that WA's heavy reliance on them would have caused a blow out a long time ago, but in the resistance testing it is still effective on ryegrass," Mr Newman said.
"For wild radish, chlorsulfuron resistance was developed a long time ago, there are big problems with diflufenican with 65pc resistance and 2,4-D has high levels of resistance with 61pc.
"Fortunately though there are some other herbicides, such as Velocity, atrazine and glyphosate, that are still working for most growers."
The results presented by Mr Newman were a snapshot of herbicide resistance five years ago and sampling is taking place of new specimens from 750 paddocks in WA and testing will start next winter, with the results being available towards the end of 2021.