Using the WeedSmart Big 6 to tackle weeds and herbicide resistance

Following the WeedSmart Big 6 integrated weed management program, agronomists and growers use several chemical and non-chemical tactics to place downward pressure on the weed seed bank and reduce herbicide resistance risk. 

1. Rotate crops and pastures 

Jim Finlay, Agronomist at Nutrien Ag Solutions in Campbell Town, TAS: 

“Across the Central Midlands of Tasmania, our main crops are cereals and canola, but irrigation water allows us to also grow a wide variety of crops in rotation which helps us manage weeds – particularly annual ryegrass – in crops. 

Using crop rotation is a popular weed management technique, and one example of this is where a client has over sown Italian ryegrass into a paddock that was previously a clover seed crop. It might sound counterintuitive, but the competitive ability of the Italian ryegrass, in combination with maturity difference in the ryegrass – the weedy ryegrass is early heading – means we can use tactics like grazing and silage strategically in combination with crop competition to ensure the weedy ryegrass doesn’t set seed.” 

2. Increase crop competition 

Gus van Tilborg, Agronomist at Nutrien Ag Solutions in Cobram, VIC: 

“Across Northern Vic and Southern NSW, it’s important that we increase crop competition in our fight against herbicide resistance. We often take advantage of an early break to double knock ryegrass and get crops established early in the season to compete with later germinating weeds. 

A large portion of our canola grown here is hybrid canola which has greater early vigour that we feed with nitrogen early, to promote biomass growth and competition against weeds before it gets too cold in winter.” 

3. Mix and rotate herbicides 

Claire Tucker, Agronomist at Nutrien Ag Solutions in Minlaton, SA: 

“It’s important to rotate the herbicide modes of action you use in each crop and mix different modes of action within the same herbicide mix or in consecutive applications. In our system this looks like adding 2-3 modes of action in the one tank mix to broaden the weed spectrum and hit the target weeds in different ways. Double knocking with glyphosate and a Group 14 knockdown spike followed by paraquat is another way we try to mix up consecutive herbicide applications pre-sowing. 

Now we have a few new pre-emergent herbicides available to us in cereals, canola and pulses, it’s important to use them and rotate each year so we can keep the older chemistry working for longer. 

Rotating buys you time, mixing buys you more shots. 

It’s also really important to get out there post seeding and look for weeds that have escaped the knockdown or pre-emergent herbicide, like large, clumpy ryegrass plants. Take samples and test these surviving weeds for resistance so you can make a plan for future herbicides and crop rotations.” 

4. Optimise spray efficacy 

Angus Dalgliesh, Agronomist at Nutrien Ag Solutions in Dalby, QLD: 

“In my region, it’s important to pick the right herbicides for the job, and double knock if required. We also want to ensure we target the right weed size for the herbicide being used; and make sure we have the right nozzles and water rate for the job at hand. Examples of this are high water rates for Group 1, Group 22 and Group 14 herbicides. Nozzle selection, boom height and ground speed also help reduce drift.” 

5. Stop weed set 

Alex Tier, Agronomist at Nutrien Ag Solutions in Lockhart, NSW: 

“In Southern NSW growers are using several tools to ensure we stop seed set at all costs! Not all tools are applicable to every enterprise, however each of my growers are implementing at least one tool into their system.  

After our run of wet years strategic tillage has been used prior to sowing, in conjunction with double knocks, to make sure we are removing all weeds. At the back end of the season crop topping or pre harvest sprays have also been a great way to manage late germinating weeds, along with the option to cut weedy paddocks for silage or hay and export the weed seed off the paddock.  

I also have growers utilising header mills but we have agreed it is not a guaranteed method of 100% reduction in weed seeds, nor is any other tool, and must be used in conjunction with other Weedsmart Big 6 strategies.” 

6. Implement harvest weed seed control  

Andy Regan, Agronomist at Nutrien Ag Solutions in Wongan Hills, WA: 

“Across the Central West and Central Wheatbelt of WA, there are a variety of practices employed at harvest which aim to implement harvest weed seed control. This is particularly important as the final opportunity to destroy weed seeds before they are returned to the weed seed bank.   

Techniques that growers are using include: seed impact mills installed in headers, narrow windrow burning, chaff lining and chaff carts. 

No matter what control method is being used, optimal harvest set up is required to make sure that the maximum amount of weed seeds are entering the header and that these captured weeds are destroyed.” 

About WeedSmart 

WeedSmart Week brings together a wealth of knowledge and experience from local and interstate growers, agronomists, and technology experts – putting the spotlight on herbicide resistance and weed control. Designed to engage growers and advisors on the WeedSmart Big 6 messages, WeedSmart Week offers a unique opportunity for growers and industry stakeholders to hear first-hand about innovative and practical weed solutions. 

Nutrien Ag Solutions has recently signed up as a silver partner of the WeedSmart herbicide stewardship program to spread the WeedSmart Big 6 message amongst growers and advisors to tackle herbicide resistance in Australia.   

For more information about sponsorship opportunities and implementing the WeedSmart Big 6, please visit the website: www.weedsmart.org.au