Download Understand how herbicide resistance works

Weed management
Cropping
Understand how herbicide resistance works
Enzymes carry out work in plant cells
essential to normal plant growth and
development. When the chosen herbicide is
applied, it binds to the targeted enzyme in the
plant cell. The weed dies as the enzyme is
unable to do its work.
by Annabel Bowcher,
CO-OPERATIVE RESEARCH CENTRE
FOR AUSTRALIAN WEED
U
nderstanding the mechanisms behind
herbicide resistance can help growers
fight this serious problem.
Figures 1–4 show the relationship between
plant enzymes, target sites, herbicide
attachment, natural weed gene mutations and
herbicide resistance.
If there is no herbicide resistance, all
herbicide options are available (represented by
herbicides 1 , 2 and 3 ).
There are many ways to manage herbicide
resistance and to slow its onset. Planning
Figure 1
Apply
1
1
1
3
2
Herbicide 1 binds to
target site. Enzyme cannot
do its work and the weed dies.
Herbicide options.
• A range of strategies.
• Flexibility.
• Regular review and revision.
Investigate the various weed management
options available, determine which herbicide
groups are the most appropriate and rotate crop
and pasture phases.
Only spray small weed numbers.
It is important to ‘confuse’ the weeds to stop
them adapting. For example, change tillage
practices, crops, seeding dates and herbicide
groups.
FIGURE 1 All herbicide options could be available
Enzyme target sites on
an enzyme inside a
weed cell.
is essential. A simple cropping system may be
easy for farmers but it is also easy for weeds.
Create a weed management plan that has:
By adopting this approach, farmers can
integrate the many ways of managing weeds in
a planned but flexible strategy.
FIGURE 4 Cross-resistance*
Figure 4
Target sites for
herbicides 1 and 3
are very close together.
All herbicide options available.
Source: CRC for Australian Weed Management.
FIGURE 2 Herbicide resistance is detected but other options are available
Figure 2
Known herbicide resistance to
herbicide 1
Natural gene mutation
changes shape of
herbicide 1 target sites.
Apply
1
Herbicide 1
cannot bind to
target site and
weed survives.
Apply
2
1
2
Herbicide 2 binds to target
site. Enzyme cannot do its
work and the weed dies.
Natural gene mutation
changes shape of
herbicide 1 target sites.
Herbicide 1
cannot bind to
target site and
weed survives.
Herbicide resistance may be detected to one herbicide but other herbicide options are still available.
1
Apply 3
Source: CRC for Australian Weed Management.
FIGURE
Figure 33 Example of multiple resistance: known resistance to*
Natural gene mutation
changes shape of
herbicide 3 target sites.
Apply
3
3
Use
non-chemical
options
Herbicide 3
cannot bind. Weed
survives. Now resistant
to all herbicide options.
As no chemical options are
available, other selected
integrated weed
management strategies are
required to kill the weed.
* herbicides 1 and 2.
Sometimes multiple resistance to herbicides occurs and few herbicide options remain to eliminate the
weeds (when no herbicide options are available, other management strategies are required).
Source: CRC for Australian Weed Management.
FA R M I N G A H E A D
No. 125
May 2002
Interference to herbicide 3
target site has occured
due to its close
proximity to target site 1
3
Herbicide 3
cannot bind to
target site.
Weed survives so
need to use other
strategies to kill it.
* example.
Cases can arise when a weed develops cross
herbicide resistance. This occurs when a
single resistance mechanism confers
resistance to several herbicides. The diagram
shows how this could occur in a plant cell.
Source: CRC for Australian Weed Management.
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