Herbicide resistance now a matter of can-do management
“Successful people manage herbicide resistance.” Weed management specialist Andrew Storrie says growers need to hear this message, not scare tactics
Andrew Storrie from Agronomo spends a lot of time talking to growers about herbicide resistance and he has observed one particular aspect time and again. Growers do not want bad news, but bad news is what they have been getting, Mr Storrie says.
He believes it is time to change the focus from alarm to a discussion about how to manage herbicide resistance. And central to the management of the issue is testing.
“Herbicide resistance is a reality,” Mr Storrie says. “So as it becomes more common we need to stop talking about how to eradicate it and instead talk about how to manage it.
“We need to know which herbicides still work. This makes testing one of the best management tools we can use.”
He points out that spray failure is not necessarily a sign of herbicide resistance “Sometimes failure is due to plant stress, poor application technique or multiple tank mixes reducing the efficacy of some components,” he says.
Mr Storrie says many growers and agronomists indicated at a recent Grains Research Update in Bendigo, Victoria, that they were surprised to find that mixing certain pesticides could render the tank mix less effective.
While data from Charles Sturt University senior technical officer John Broster showed that the number of samples submitted for glyphosate-resistance testing has markedly increased since 2005 (Figure 1), the vast majority of these samples are coming from resellers (Figure 2).
“The resellers are making a difference to the numbers,” Mr Storrie says. “They are often submitting samples on behalf of their grower clients. Currently, less than five per cent of samples are coming from individual growers and this needs to change.”
Mr Storrie acknowledges that testing is time-consuming and takes place at a busy time – harvest. He suggests that advisers, who are often less time-constrained during this period, could be recruited to assist.
“Without being able to quantify the levels of resistance on a property, it is difficult to formulate the optimum strategy to address it,” he says. “If you are giving herbicide advice and you don’t know what resistance is in the paddock, you obviously like to gamble.”
Mr Storrie is encouraged by the success of some growers he has worked with in the way they have addressed herbicide resistance on their own properties.
Through a mix of integrated weed management (IWM) tactics – including resistance testing – Chris Reichstein, Murray Scholz and Mic Fels are three growers he points to as having turned the tide on herbicide resistance in their operations.
"You don't have to be clever to manage glyphosate resistance, just vigilant."
Western Australian grower Chris Reichstein knew he was taking on a substantial herbicide-resistance problem when he purchased his property ‘Warekila’, north of Esperance in 2008.
Mr Reichstein’s response has been to implement a program of resistance testing and he regularly sends away samples.
“My motto is: ‘If you can’t measure it, you can’t manage it.’ You don’t have to be clever to manage glyphosate resistance, just vigilant,” he says.
In his first season applying a summer glyphosate knockdown on his sandy soils, he noticed some annual ryegrass survivors. He did a Quicktest® for glyphosate resistance, which came back positive.
He also left one hectare unsprayed and ran some in-crop selective herbicides over it. This hectare showed developing resistance to clethodim and full resistance to the Group A mode of action fops subgroup. He then tested each paddock, which also had some wild radish, and found Logran® herbicide was 85 per cent effective, Brodal® herbicide 65 per cent effective, but Spinnaker® herbicide only 45 per cent effective.
Because Mr Reichstein could accurately quantify the herbicide-resistance levels on his property, he was able to design a chemical rotation strategy to protect the chemistries remaining to him.
For example, in the lupin and field pea phases he could use Factor® herbicide (butroxydim 250 grams/kilogram) rather than clethodim, and save clethodim for the canola phase. Such awareness of his resistance status meant he could better manage it.
Mr Reichstein uses non-conventional crop rotations as part of his suite of IWM tactics.
By having two broadleaf crops in a row, he can change the herbicide modes of action and optimise the effectiveness of remaining Group A herbicides, while giving him the opportunity to crop-top in either the lupins or the field peas. This strategy has significantly driven down the annual ryegrass population on his property.
Harvest weed-seed management is also integral to the management of herbicide resistance. Initially, Mr Reichstein used narrow windrow burning and crop-topping to prevent weed seed-set and reduce weed numbers quickly.
Chaff carts were bought for the 2013 harvest to continue control of weed seed-set at harvest, while retaining as much organic matter and soil cover as possible.
He has also incorporated some other simple practices. These include paired-row sowing with high sowing rates to increase in-crop competition, a light autumn tickle to stimulate weeds prior to sowing and delayed sowing to reduce reliance on in-crop herbicides.
He narrow windrow burns his canola, barley and wheat stubble, swathes his canola and is very particular about machinery hygiene.
His success with the tactics he has used on his ‘problem property’ has seen him extend these strategies to his other properties.
For more about Chris see: Peer-to-peer learning pushes success in extension
"We have to farm as if there will never be another new herbicide."
New South Wales growers Murray and Emma Scholz run a mixed farm at Culcairn where they grow wheat, canola, lupins and barley.
Mr Scholz is now a WeedSmart champion, but back in 2000 his herbicide-resistance problem was so severe it culminated in the total failure of a lupin crop.
That same paddock is now free of resistant weeds after focusing on the prevention of weed seed-set. Getting to this point, however, was not without sacrifice.
“We had to take that paddock out of production for two years straight and that was very expensive. However, by doing that, we have totally beaten resistance,” Mr Scholz says.
Across his farm he has adopted a range of other IWM practices, such as windrow burning.
“We condense all the residue that comes out the back of the harvester in our canola and lupin crops and then slow burn it in narrow rows.
“Our aim is to get that windrow to burn at 400°C for a minimum of 10 seconds. That length of time and heat makes most weed seeds unviable. For every seed I destroy, that’s one plant I don’t have to worry about spraying with herbicides.
“We’re not destroying every seed that goes through the harvester, but if we’re removing 80 per cent or 90 per cent, that’s a big help, and it’s been a very low-cost and effective method,” he says.
Other methods Mr Scholz employs are increased crop competition, making hay and silage, and strategic fertiliser application.
“We use variable-rate pH mapping so we can get the right rate of lime applied over the whole paddock,” he says.
“By lifting that soil pH the crop is better able to compete with weeds, because annual ryegrass appears to be a lot more acid tolerant than wheat. The really low-pH soils were often also where the bad ryegrass patches were.”
While he concedes IWM is much harder than just using herbicides, Mr Scholz is convinced it is the only option left.
“We have to farm as if there will never be another new herbicide.
“Strategies I recommend are finding ways to reduce that seedbank. Whatever it is, just bite the bullet and do it. And when you find a problem, act. Don’t let it get away from you.”
Mic FelsManaging annual ryegrass dominates most of the decisions Mic Fels makes on his property at Esperance, WA.
In 2003, just two years after purchasing his property, large parts of the farm were overrun with the weed.
Mr Fels cut and baled the worst areas but there were other areas that received no seed-set control. Then in 2007, when he was applying a knockdown spray prior to sowing, he noticed ryegrass germinating 23 centimetres apart.
“I hadn’t used 23cm row spacings since 2003, as I converted to 30cm spacings in 2004,” Mr Fels says. “It made me realise I needed at least two consecutive clean years to reduce the seedbank. The traditional one-year break was not enough.”
He says the increased crop competition achieved with narrow row spacings is his most effective tactic against ryegrass.
He changed to 19cm spacings in 2011 after designing his own disc seeder. This system has worked so well that this year he has set up a new 18-metre machine with 19cm spacings.
“Trial after trial showed huge yield benefits with narrow rows. We were previously doing all these great IWM things but were still on 30cm spacings. I felt like I was giving the ryegrass a ‘free kick’.”
Mr Fels also uses a hybrid of two conventional weed-management tactics: dropping weed seed on tramlines and narrow windrowing.
Chutes on the back of the headers drop chaff into the middle of the header pass, rather than on the tramlines, and spread the remaining straw onto the paddock.
This has several benefits: it is cost-effective, at about $200 for the chute, and it creates one chaff row instead of two.
Mr Fels also double knocks every paddock if there is time, using paraquat at 1.5 to 2 litres/ha as the second knock.
To prevent glyphosate resistance developing in his RoundUp Ready® canola, he uses only paraquat as a knockdown in this crop.
This allows him to use two applications of glyphosate during the season.
| Weed species
|| Year first documented
|| Number of confirmed populations in September 2014
| Annual ryegrass (Lolium rigidum)
|Barnyard grass (Echinochloa colona)
| Liverseed grass (Urochloa panicoides)
|Fleabane (Conyza bonariensis)
|Windmill grass (Chloris truncata)
|Great brome (Bromus diandrus)
|Wild radish (Raphanus raphanistrum)
|Sowthistle (Sonchus oleraceus)
|Red brome (Bromus rubens)
| Sweet summer grass (Brachiaria eruciformis)
SOURCE: Christopher Preston, Australian Glyphosate Sustainability Working Group
| Seed test
|| Resistance In-Season Quick (RISQ) test
||All||All||Ryegrassm phalaris, wild oats
|Mode of action
||A, B & M
|What is collected?
||Seedlings – grasses before growth stage 30; broadleaves before bolting
||Seedlings up to three-leaf (growth stage 13)
|How are they tested?
||Germinated, seedlings sprayed
Plants trimmed and potted.
Sprayed when regrown
|Seedlings planted in medium containing herbicide
||April to June 2015
||4 to 6 weeks
14 days – A & B modes of action
More information:Andrew Storrie,
08 9842 3598,
A fact sheet on Cropping with herbicide resistance is available at: www.grdc.com.au/GRDC-FS-HerbicideResistance
Region South, West, North