Avoiding and managing herbicide resistance
Key points on resistance
- Weed numbers - the higher the numbers the greater the risk of resistant weeds being present.
- Each herbicide application will increase the proportion of resistant individuals in the population.
- Resistance is generally not reversible (particularly for Group A and B herbicides).
- The proportion of resistance in subsequent populations is not increased after the use of a herbicide if seed set is prevented.
- Resistance occurs quickest where there is repeated use of only a limited number of weed control methods.
Management tactics
Tactic |
Management |
Practical issues |
---|---|---|
Deplete weed seed bank in the soil |
Burn residues |
Increase erosion risk on some soils |
Invert seed bank by ploughing |
Only practical in deep soils |
|
Autumn tickle |
Useful to increase weed germination |
|
Delay sowing |
Only practical in years with an early break |
|
No till seeding |
Keeps seed on surface from germinating |
|
Control seedling weeds in the target area |
Fallow and cultivate pre-sowing |
Can increase germination of dormant weed seeds |
Herbicides |
||
Knockdown herbicides |
Glyphosate or paraquat plus spike for difficult to control weeds |
|
Double knockdown |
Glyphosate followed by paraquat three to four days later |
|
Pre-emergent herbicides |
Trifluralin (Group D) + Dual® Gold (Group K) or Avadex® (Group E) mix |
|
Selective post-emergent herbicides |
Group A herbicides applied when weeds small and actively growing Clearfield™ system Atrazine and simazine application to triazine tolerant varieties |
|
Non-selective post-emergent herbicides |
Glyphosate application to Roundup Ready® varieties Glufosinate application to InVigour® varieties |
|
Crop competition |
Sow early using narrow row spacing Ensure correct sowing depth and good seed soil contact for rapid and even emergence |
|
Stop weed seed set |
In crop weed management |
|
Cut for hay |
This may be the best longer term option where there are high numbers of resistant weeds |
|
Windrowing |
Will reduce seed set |
|
Spraying with non-selective herbicides |
Apply glyphosate during the windrowing operation to kill surviving plants/stop seed set |
|
Prevent viable weed seeds being added to seed bank |
Weed seed collection at harvest |
May be impractical; slowing harvest, demand on header power, disposal of weed seeds |
Weed seed destruction at harvest |
Not yet available; greater power requirement; degree of effectiveness |
|
Narrow header rows |
Enables header rows to be burnt |
|
Prevent introduction of viable weed seed |
Sow weed-free seed |
|
Clean farm machinery and vehicles |
||
Prevent introduction in hay and grain |