[July 2021]
Weeds? Pain in the proverbial. We all know that herbicides will eventually lose efficacy due to herbicide resistance, and the rate of new modes of action are few and far between, combine that knowledge with Metabolic resistance and we could be stranded relatively quickly, but what is a realistic answer to this problem?
“At the end of the day we have precious resources, water, sunlight, nutrients - they should go into growing food, fibre and energy. Going into weeds that don't need to exist in the first place is a waste, spending resources on getting rid of them is wasteful and spraying anything other than weeds is again, a waste. There is a lot of innovation still to be had in this space but there is so much out there already that can be adopted today” - Dr Nick Berry
Throw everything at them
Weeds are excellent at surviving, adapting and evolving to whatever we throw at them, which is why we need to mix up our weed control strategies. David Brunton from The University of Adelaide's Weed Science Research Group is researching strategies to prolong the effectiveness of these herbicides by incorporating diverse and sustainable crop production practices “we’ve spent the past 20-30 years using herbicides to control weeds, think of what you will do in 5-10 years if we continue to rely on herbicides and are no longer able to control problematic weeds using herbicides due to resistance?” he says.
Annual ryegrass is one of these problematic weed species, which has developed resistance to a number of pre and post-emergent herbicides, across multiple herbicide groups (modes of action). The current story of herbicide rotation has clearly been demonstrated as a non-sustainable long-term tactic. Incorporating non-herbicidal methods of weed control in combination with strategic herbicide use is fundamentally the way forward.
So what are some of the options?
- Harvest Weed Seed Control (HWSC) – includes chaff carts, narrow windrow burning, chaff tramlining / chaff lining and mill technology e.g. the Seed Terminator. Not all weed seeds are captured at harvest, but why spread next years weeds up and down the paddock?
- Crop competition – works well with HWSC and improves herbicide efficacy as well as being stand-alone weed control in its own right
- Mouldboard ploughing – 98% suppression of weeds in the seed bank and significant yield response in year 1 with a long term benefit to follow
- Strip and Disc farming – this is an in depth topic; in short helping and hindering different weeds but it does change the weed seed bank dynamics
- See and Spray technology – still a herbicide but can reduce herbicide use by 95%+ in some situations and can make higher rates or more expensive chemicals more feasible
- Healthy soil – if the crop grows better, naturally there is higher suppression of weeds (eg. mouldboard ploughing and lime application)
- Double break crops – still talking herbicides here but get the benefit of a disease break eg legume, canola
- Companion planting – sowing a range of species then either harvesting them all or terminating some and harvesting the cereal that remains.
Why Harvest Weed Seed Control?
“It seems crazy that we spend a lot of time and money killing weeds all year only to reward the survivors at harvest and spread them out so we have something to spray next year”
- Peter Newman, Planfarm Extension Agronomist
The weeds present at harvest are the fittest, they are the ones who have escaped in season control. We know that each surviving weed can produce a huge number of seeds to spread back onto the paddock to be the following years weed problem and worse yet, we wonder why the weeds missed the in-season control, was there a spray issue? Have the weeds evolved dormancy? Or worse, are the surviving weeds herbicide resistant?
Dr Nick Berry states "you couldn't design a better weed seed spreader than a combine harvester. It separates the grain out, then the weeds go round and round the tailings, distributing them nicely across the paddock." There are three aims with HWSC
1 | Stop the spread of weeds
2 | Drive the weed population down
3 | Target Herbicide Resistant weeds
You can see from the graphic below at harvest we have a real opportunity to target the fittest weed seeds with Harvest weed seed control measures.
Using the Seed Terminator weed and volunteer seeds are captured and pulverised, preventing them from being spread back onto the paddock to grow next year. By adding weed control at harvest farmers are able to specifically target any potential herbicide resistant weeds while reducing the weed seedbank each season without any additional passes and controlling the green bridge. This can result in maintaining the longevity of herbicides in general but also allow farmers to be more selective with choices around herbicides and allowing them to lower production costs.