Grains Research and Development

Integrated Weed Management Hub

Using this resource

Rapid expansion of herbicide resistance and the lack of new modes of action (MOA), require that non-herbicide tactics must be a significant component of any farming system and weed management strategy.  Inclusion of non-herbicide tactics is critical to prolong the effective life of remaining herbicides, as well as for new products and modes of action that have not yet been released or indeed invented.  Effective herbicides are key components of profitable cropping systems.  Protecting their efficacy directly contributes to the future sustainability and profitability of cropping systems. 

We need to look after what we have.  It is a shock to some that the last significant new herbicide mode of action released in Australia was Group H chemistry, first launched in Australia in 2001. Prior to that, the most recent other new mode of action was Group B chemistry, when chlorsulfuron was commercialised in Australia in 1982.  Integrated weed management manual cover page

This manual is an on-line resource to assist Australian grain growers and advisers to quickly locate useful web based information on weed management in Australian broadacre cropping systems. 

This manual is a road map to information.  It summarises the role, use and benefits of different weed management tactics.  The many links embedded in these web pages provide access to a myriad of more detailed on-line multi media resources.  These links provide access to the detailed information that readers will need on the topics being researched for on-farm adoption. 

It is intended that this manual will continue to evolve with links added and updated on a regular basis as new material comes to hand.  

One of the key resources that is linked to extensively in the IWM Hub is the Integrated Weed Management Manual. This manual, Updated in 2014 is a key reference in the management of weeds.


Section 1 - Herbicide resistance Section 2 - Agronomy to enhance weed management Section 3 - Managing weed seedbank Section 4 - Managing weed seedlings Section 5 - Stopping weed seed set Section 6 - Managing weeds at harvest Section 7 - Managing farm hygiene Section 8 - Profiles of common weeds of cropping Section 9 - Case studies Integrated Weed Management Manual

Introduction to Integrated Weed Management

Successful weed management requires a field by field approach. Knowledge of weeds and weedbank status, soil types as relevant to herbicide use as well as cropping and pasture plans are all critical parts of the picture. Knowledge of paddock history and how much summer and winter weeds have been subjected to selection to resistance (and to which herbicide modes of action) can also assist. 

When resistance has been identified, knowledge of which herbicides still work becomes critically valuable information.

The following 5 point plan will assist in developing a management plan in each and every paddock. 

  1. Review past actions and history
  2. Assess current weed status
  3. Identify weed management opportunities
  4. Match opportunities and weeds with suitably effective management tactics
  5. Combine ideas into a management plan. Use of a rotational plan can assist

Review past actions

Knowing the historical level of selection pressure can be valuable information to give managers a ‘heads up’ as to which weed/ MOA groups are at greatest risk of breaking.  Such knowledge can prompt more intensive monitoring for weed escapes when a situation of higher risk exists.  Picking up newly developing resistance issues while patches are still small and before they spread can mean a big difference in the cost of management over time. 

From all available paddock records, calculate or estimate the number of years in which different herbicide MOA’s have been used.  The number of years in which a herbicide MOA has been used is of far greater relevance than the number of applications in total.  For most weeds, using a herbicide MOA in two consecutive years presents a far greater selection pressure for resistance than two applications of the same herbicide MOA in the one year.  If the entire paddock history is unavailable to you, state what is known and estimate the rest.  Collate separate data on MOA use for summer and winter weed spectrums.  Further sub divide these into broadleaved and grass weeds. 

Account for double knocks.  Where survivors of one tactic would have been controlled in large part by the use of another tactic, reduce the number of MOA uses accordingly.  An example might be: Trifluralin has been used 20 times, but there have been 6 years when in-crop Group A selectives were used and several more years where in-crop group B products that targeted the same weed as the trifluralin were used.  These in-crop herbicides effectively double knocked the trifluralin, thus reducing the effective selection pressure for resistance to trifluralin somewhat. 

Review the data you have collected and identify which weed / MOA groups have been selected for at a frequency likely to lead to resistance in the absence of a double knock.  Trifluralin typically takes about 10-15 years of selection for resistance to occur.  Thus in the above example, a ‘watching brief’ would be in place for trifluralin and other Group D MOA herbicides.

Paddock history can also be useful information when evaluating the likely reasons for herbicide spray failures, in prioritising strategies for future use and deciding which paddocks receive extra time for scouting to find potential patches of weed escapes. 

Information on MOA use history should be added to paddock records.

Table 1. Typical number of years of use to develop resistance MOA groups

Herbicide Group

Typical years of application

Resistance risk

A (fops/dims/dens)

6-8

High

B (SU’s, IMI's)

4

High

C (triazines, subst. ureas)

10-15

Medium

D (trifluralin, Stomp)

10-15

Medium

F (diflufenican)

10

Medium

I (phenoxies)

>15

Medium

L (paraquat/diquat)

>15

Medium

M (glyphosate)

>12

Medium

RIM

RIM (Ryegrass Integrated Management), provides insights into the long-term management of annual ryegrass in dryland broadacre crops facing development of herbicide resistance. RIM enables alternative strategies and tactics for ryegrass management  to be compared for profit over time and impact on weed numbers. The software’s underlying model integrates biological, agronomic and economic considerations in a dynamic and user-friendly framework, at paddock scale and over the short and long-term.

The tool tracks the changes through time on a 10 year crop cycle for ryegrass seed germination, seed production and competition with the crop. Financial returns are also estimated annually and as a 10 year average return.

A free download is available from: http://www.ahri.uwa.edu.au/RIM

Assess the current weed status

Record the key broadleafed and grass weed species for summer and winter and include an assessment of weed density, with notes on weed distribution across the paddock.  Include GPS locations or reference to spatial location of any key weed patches or areas tested for resistance. 

Include any data, observations or information relating to the known or suspected herbicide resistance status of weeds in this paddock. 

Add this information to paddock records. 

Identify weed management opportunities within the cropping system

Identify what different herbicide and non-herbicide tactics could be cost effectively added to the system and where  in the crop sequence these can be added. For information on the different integrated weed management tactics please, see this section in the IWM manual.

Fine tune your list of options

Which are your preferred options to add to current weed management tactics to add diversity and help drive down the weed seed bank?

Weed Seed Wizard

The Weed Seed Wizard helps growers understand and manage weed seedbanks on farms across Australia’s grain growing regions.

It is a computer simulation tool that uses paddock management information to predict weed emergence and crop losses. Different weed management scenarios can be compared to show how different crop rotations, weed control techniques, irrigation, grazing and harvest management tactics can affect weed numbers, the weed seedbank and crop yields.

The ‘Wizard’ uses farm specific information and users enter their own farm management records, their paddock soil type, local weather and one or more weed species. The ‘Wizard’ has numerous weed species to choose from including annual ryegrass, barley grass, wild radish, wild oat, brome grass and silver grass in the southern states and liverseed grass, barnyard grass, paradoxa grass, feather-top Rhodes grass, bladder ketmia, fleabane, sowthistle, sweet summer grass, cowvine, and bellvine in the north.

A free download is available from: https://www.agric.wa.gov.au/weed-seed-wizard-0

Combine and test ideas

Computer simulation tools can be useful to run a number of ‘what-if’ scenarios to investigate potential changes in management and the likely effect of weed numbers and crop yield. Two simulation tools being used are the “Weed Seed Wizard” and RIM – Ryegrass Integrated Management.

Combine ideas using a rotational planner, or test them in using decision support software such as RIM &/ or Weed Seed Wizard.

Useful links

Throughout these pages you will find a number of useful links to papers, videos and other information on weeds. There are a few major resources that deserve a link up the front.

Integrated Weed Management Manual

NSW DPI weed management in winter crops

NSW DPI weed management in summer crops

Update papers

Biology and management of summer weeds (2015)

Hardseeded annual legumes (2015)

Herbicides for control of clethodin-resistant annual ryegrass (2015)

Hitting the right target - what are our most costly weeds? (2015)

Impact of crop residues on summer fallow weeds (2015)

New technology for improved herbicide use efficiency (2015)

NGA chickpea herbicide trials (2015)

Seeding systems and pre-emergence herbicides (2015)

Summer weeds reduce moisture and nitrogen (2015)

Using crop competition for weed control in barley and wheat (2015)

Why the obsession with the ryegrass seed bank? (2015)