Annual ryegrass is the world champion of herbicide resistance. It has developed
resistance to more herbicides faster than any other weed on the planet.
Every five years or so AHRI with GRDC investment conducts a statewide random survey
Mechelle Owen one of our AHRI researchers leads that survey now, her last survey
was in 2015, sampled in 2015. The survey shows that
for some of our older herbicides they had very high levels of resistance years
ago and that's still the case, so our SUs and our FOPS in the high 90s
for resistance so even though it plateaued, it plateaued at almost 100 per cent resistance, so
that's not big news. What was interesting was clethodim was around about that
40 per cent resistance level in the 2010 survey and is about 44
per cent of our populations in Western Australia have Clethodim resistance to
the high rate of clethodim. In a couple of the other important herbicides
trifluralin was at around about 27-28 per cent
resistance in 2010, now about 30 per cent of our populations in Western Australia
have trifluralin resistance. So that, even though it plateaued a little bit,
that's big news, that's a big problem coming from Western Australian grain
growers. With a random survey, it can be hard to find resistance with these
surveys, with a random survey roughly a one in three chance that you've got trifluralin
resistance. That's a big threat and glyphosate resistance while it's only at
about eight per cent in ryegrass in a random survey, if we do a more targeted survey we find
much higher levels of glyphosate resistance. The good news is there's
still a lot of herbicides that work, we've had a suite of new herbicides come out
of our pre-ems - Sakura, Boxer Gold® propyzamide - those sorts of herbicides
we don't have resistance in those yet. We didn't find any paraquat resistance so
we still have an effective knockdown herbicide. So we do still have a suite of
herbicides that are available to our grain growers. We used to talk a lot
about rotating herbicides, so if we used one herbicide last year don't use it
next year. Now we more talk about mixes, mix two
herbicides this year and mix another two herbicides next year, so the mix and
rotate message. So rotating is still a good idea but mixing two herbicides
together is even better and it doesn't even have to be in the same tank. It can
be a good pre-em with a good post-em herbicide, but it's all about double
knocks, can we get two hits at the same weed with multiple herbicides. We can end
up with lots of trifluralin, so we could end up with say trifluralin,
Sakura one year, trifluralin, propyzamide the next, trifluralin, Boxer Gold®
the year after that. It sounds bad having trifluralin in all of those years, it all
in one rotation, whereas in the past we used to say if you used that last year
don't use it this year. Whereas we're more comfortable now saying that's okay
to overuse say perhaps a product like trifluralin, if it's effective
on your farm as long as it's mixed with another
effective herbicide and/or has those second knocks in the system. And those
second knocks can come in the way of an effective post emergent herbicide; and
good crop competition; and stopping seedset; and harvest weed seed control.
Our WeedSmart Big 6, in a nutshell, is to rotate crops and pastures, it's to double
knock to preserve glyphosate, mix and rotate our herbicides, grow competitive
crops, stop seed set wherever we can and use harvest weed seed control. That's a
lot to take in in one mouthful but that is the WeedSmart Big 6 and you
can find more information on that on the WeedSmart website.
We've seen huge success in growers that have used all the tactics but also used
harvest weed seed control. They've got their weed numbers down and they're
keeping them down for a long period of time and these growers are continuous
cropping and confident about the future of continuous crop because their seed banks are just
so low. What's going on with this cross resistance even though there's some
different groups of herbicide in there, we are finding that there is metabolic
resistance likely due to P450 enzymes that can give resistance across a range
of herbicides. And so what do we do with that? Well that is probably worst case
scenario and so what we need to do is we to use that information and then develop
the best mix and rotate herbicide messages that we can with with all of
that in mind.