Stop weed seed set

You can listen to the article being read above!

We all know that old saying – ‘one year seeding, seven years weeding’ or some variant of it, and know it is true. But it is easy to overlook just how important weed seedbank management is, until herbicide resistance begins to reduce the efficacy of previously reliable tools.
For a few decades herbicides really took the focus away from seedbank management because the chemical options were so effective at killing weeds that they appeared to be a complete solution to weed management.
But all along, growers, agronomists and researchers have known it was too good to last. The WeedSmart Big 6 strategy has struck a chord because it is a useful check list that can be used to prompt growers to consider using a selection of the many available weed control tools.

No one tool will do the job – just as herbicides alone have failed, so too will harvest weed seed control or crop competition if they are not part of a planned and multi-pronged assault on the weed seedbank. This is the underlying principle for integrated weed management.
In economic simulations conducted using the RIM and WeedRisk models in 2006, agricultural economists Randall Jones and Marta Monjardino showed that although many things impact on the economic assessment of weed management practices, there is strong evidence that when seasonal risk is taken into account, and the economic assessment is for a period of 20 years, integrated weed management consistently out-performs herbicide-only systems, regardless of the weed in question.
Herbicides provide high level control and are considered an essential component of broadacre cropping systems, however, other tactics that specifically target weeds that have escaped herbicide control are what make IWM systems more profitable in the long-run (see Table 1).
For weeds like wild radish, which produce large quantities of seed that can remain viable in the soil for many years, taking a non-integrated approach of using post-emergent herbicide only has the potential to ‘crash the system’, from an economic point of view.
It will always be a numbers game and IWM consistently wins, usually by a considerable margin, primarily due to lower weed seedbank numbers and conservation of the highly effective herbicide resource for tactical use over time in integrated weed management systems.
TABLE 1 The economic impact ($/ha) of different crop and IWM systems on meana annualised discounted returns for wild oats, wild radish and annual ryegrass in a southern New South Wales cropping system (4-year crop phase followed by 3-year perennial pasture phase).

Economic return ($/ha)a

Wild oats

Wild radish

Annual ryegrass

Continuous cropping
 
 
 

No IWM

268 (± 35)

-9 (± 27)

284 (± 34)

IWM

332 (± 38)

315 (± 37)

335 (± 38)

Crop + pasture rotation

No IWM

288 (± 29)

157 (± 25)

284 (± 28)

IWM

319 (± 32)

300 (± 30)

320 (± 31)

a The shown in brackets following ± are the standard deviation.
Source: Jones R, Monjardino M and Asaduzzaman Md (contributors) (2019). Section 1: Economic Benefits of Integrated Weed Management, in: A.L. Preston (Ed) 2019. Integrated weed management in Australian cropping systems. Grains Research and Development Corporation.
Use the WeedSmart Big 6 to prepare an IWM plan for your farm
To develop an integrated weed management plan (IWM), it is useful to collate some historical information about past weed control activities, test weeds for herbicide resistance and use the WeedSmart Big 6 to match opportunities and weeds with suitable and effective control tactics, remembering that there are many weed control tools at your disposal.
With your agronomist’s assistance, aim to create a plan that maps out when each tactic will be applied. Ideally, try to include three or more of the Big 6 tactics in each crop, fallow or pasture phase.
Diversity is key. Some people prefer to have a set cropping sequence while others choose the crops in response to seasonal or market conditions, but either way it is important to look for ways to add as much diversity to your farming system as possible and to keep downward pressure on weed numbers at every opportunity.
While preventing weed seed production completely is unrealistic in the real world, a focus on the weed seedbank will pay dividends in the long run.

Development Officer at Merredin Research Station Glen Riethmuller gives some useful insights into harvesting low, crop lifters and also discusses crop topping. We also hear from Meckering farmer Darren Morrell. He recently received resistance test results which showed one of the farms he is leasing has 80% trifluralin resistance. Darren talks about what tactics he’ll be using to get on top of the weed problem he is now facing.
Listen to the podcast below.

Glen Riethmuller at Merredin Research Station 

In the podcast this week, we focus on crop topping and the relatively new herbicide, Sharpen. In our last podcast, Andrew Messina talked to us about Case IH harvester set-up. This week farmer Lance Turner gives us the rundown on John Deere gear.
AHRI and WeedSmart Agronomist Greg Condon talks to us about the benefits of crop topping and what to do if you suspect you’ve got herbicide resistance.
We also hear from BASF Technical Services Manager, Phil Hoult, about the herbicide Sharpen. It’s now registered as a harvest aid in winter pulses, for winter cleaning of Lucerne and for wild radish seed-set control in winter cereals, so we’ll find out in more detail about its applications for broadacre croppers.

Join your hosts Jessica Strauss and Peter Newman in the first podcast for March! Spraying weeds and choosing seeds are the hot topics this podcast. We chat with Nufarm Australia Spray Application Specialist Bill Gordon, who gives some great tips and insights on correct set-up. Rohan Brill also joins us for insight on choosing canola seeds and the benefits of crop competition!
Our webinar series is also kicking off for 2017 next week! If you’d like to register for the March 7 webinar with Rohan Brill, who will be going into more detail on crop competition, click here!