The weeds are evolving | annual ryegrass & wild radish

Findings from one of Australia’s longest running paddock surveys have been an integral component in revealing some fascinating insight on weed survival in intensive cropping systems. And it’s got implications for the entire grain belt of Australia. Through the careful analysis of more than 18years of paddock data, the study is one of the first to determine that cropping weeds constantly evolve to evade all forms of weed control, including non- herbicide strategies. So this project has been able to identify, not only that weeds are able to adapt to herbicides which we’ve always known, and that growers have really understood well. But they are also able to adapt to nearly every component of weed control.

Whether that be the timing, 00:54 - whether that be a harvest cutting height, whether that be the level of competition that we apply. The study reveals capacity for weeds to adapt and evolve as an evolutionary consequence of a prescriptive approach. The same approach taken at the same time every year results in weeds effectively predicting what’s coming next and building resistance. Ryegrass - It’s the absolute bane of all grain growers in the southern grain belts of Australia. It’s become resistant to every herbicide we have and now it’s becoming resistant to the non-herbicide weed control tactics as well. It’s adapting so growers need to adapt as well.

01:36 - Mike says the research shows that annual ryegrass is germinating later to evade glyphosate knockdowns as well as pre-emergent herbicides. Our ryegrass is actually becoming slightly more vigorous, right? To compete with competitive crops. And it’s flowering earlier in order to be able to set an awful lot of seed in this highly competitive environment. For wild radish, the intensive research found that in-crop populations lower the height of their pods to avoid harvest weed seed control. What we’re actually finding is that radish is flowering dramatically earlier.

It’s becoming more dormant than its original population. And because of that early flowering as well, it’s actually setting its pods far lower. Wild radish was actually setting its pods 12 centimetres lower than the original population. And quite a lot of those pods were actually below the 10 centimetre harvest cutting height. So as a result, wild radish was becoming less susceptible to harvest weed seed control, basically reducing the effectiveness of it.

02:39 - We came across wild radish populations that were shedding nearly all of their pods before harvest, and that is a real concern to the effectiveness of harvest weed seed control. But ongoing trials at the site are revealing other strategies that can work against the evolutionary tactics of weeds. At this site, GRDC is heavily invested into agronomy research, into improving the crop competition of crops against this species, being wild radish. And what we’re finding is that increasing your seed size, increasing your seeding rate, maximising the number of plants you have per square metre really do an awful lot towards reducing the seed production of this terrible weed. Mike is adamant growers need to maintain investment in harvest weed seed control, but he encourages, for example, incorporating different timings such as early sowing to outcompete annual ryegrass. Focus on the seed bank, not the weeds. The evolution of resistance is a numbers game.

03:42 - Keep those numbers really, really low and do that by continually utilising harvest weed seed control and all of the excellent tools that we have. While the research still being unpacked, Mike describes success as achieving long-term sustainability of the small number of control tools we have left by using them a little differently each time. For instance, if we have our best field and we always sow that one first, our weeds are going to naturally become more dormant in that field. Okay, so how would a grower respond to that? Rotate the timing of sowing, for instance. Sow our best paddock last every so often in order to be able to control those late emerging populations.

04:24 - Also crop rotation, because crop rotation actually allows us to put different tools in place. So why do we always need to go to continuous cropping phase? How about a pasture phase? How about a phase, like a serradella phase where we can actually utilise tools in different timings in order to be able to control these time and lifecycle amended populations. Mike says the research strongly supports constantly and increasingly diversifying weed management strategies to position growers a step ahead of the evolutionary process. And that includes tools and timings to outwit with the weeds, keep farming tactics on their toes and to remove predictability from weed control strategies. It’s always a hard thing to sell and to tell growers that they need to continue to adapt.

However, I am sure that growers are going to be thinking about this. They are world leaders when it comes to understanding herbicide resistance and when it comes to phenotypic resistance or lifecycle adaptations. I think they’ll be onto it really fast as well. Think about your paddock planning. Think about what you’ve been doing, the history of that field and continue to change it up. Okay, because farming is always going to be about change. .